Document 6523584

Outline of today’s lecture
• Part I
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Why YOU should care about hormones?
Definition--What is a hormone?
Introduction to behavioral endocrinology (4 levels of analysis)
Common techniques in behavioral endocrinology (50% of today)
• Part II
– The endocrine system (other 50%)
• major hormones: hypothalamic, pituitary, thyroid, GI, pancreatic,
steroid, monoamines
– Regulation
– Revisiting question #1 and comparison with fMRI
Why should social-personality psychologists study hormones?
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Conservative estimate--the human brain is riddled with billions
and billions of endocrine receptors?
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Prima facie evidence of hormonal influence on behavior, thought,
mood, emotion, personality?
Ignorance of the hormone-behavior link could have dire
consequences
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Corticotropin-releasing hormone (CRH) is a key
neuroendocrine factor implementing endocrine, immune and
behavioral responses to stress. The expression of CRH
receptors was analyzed for the first time in pituitaries of suicide
victims by in situ hybridization (2001--Molec. Psych). There
was a shift in the ratio of the two major CRH receptors (R1 and
R2) in the pituitaries of suicide victims, relative to those who
died of natural causes. Causality unclear.
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Today’s lecture does NOT focus on the hormone-behavior link.
That stuff you can pick up from journal articles, with new and
exciting research coming out each week! Today we need to
cover the bedrock, the core, the basics, the stuff that you need
to function effectively and intelligently in this world.
And just to keep you from drifting off during the biological
onslaught that is about to hit, let’s take a peek at the final slide
next.
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What is a hormone?
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Hormones coordinate the physiology and behavior of an animal by
regulating, integrating, and controlling its bodily functions.
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Example: The same hormone (e.g., Luteinzing Hormone--LH) that
causes egg or sperm maturation also stimulates mating behavior in
many species.
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This dual function ensures that mating occurs ONLY when animals
have mature gametes (eggs or sperm) available for fertilization.
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Hormones are similar to neurotransmitters, but can operate over a
greater distance and over a much greater temporal range than
neurotransmitters.
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Differences between hormones and neurotransmitters:
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Testosterone plays a crucial role in neuronal function, but
elevated concentrations may have deleterious effects. Here it is
shown that supraphysiological levels of testosterone
(micromolar range) initiate the apoptotic cascade. Short
periods of elevated testosterone levels (six to 12 hours), such
as those resulting from the use of muscle-building steroids,may
lead to "cell death" and may have long term effects on brain
function.
The dual effect of LH:
LH stimulates gonads to
produce gametes, and
stimulates gonads to
produce testosterone
Neural messages can only travel along existing nerve tracts;
hormonal messages can travel in the circulatory system; thus any
cell receiving blood is potentially able to receive a message.
Neural messages are digital, all-or-none events that have rapid
onset and offset; neural signals can take place in milliseconds;
plus, electrical signal can travel along myelinated axons at speeds
up to 100 meters per sec! Hormonal messages are analog,
graded events that can take seconds, minutes or hours to occur
(more detail to follow).
How does a hormone exert its influence?
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Only cells with receptors for that hormone can be influenced
Called target cells
Interaction of a hormone with its receptor leads to a genomic
response whereby the hormone activates genes that regulate
protein synthesis (e.g., up-regulation: synthesis of a receptor for
that hormone).
Some hormone effects are nongenomic.The monoamines.
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Nongenomic (transcription-independent) effects are
principally characterized by their insensitivity to inhibitors of
transcription and protein synthesis. The most obvious
experimental evidence suggesting their existence is rapid
onset of action (within seconds to minutes). These rapid
effects are likely not be mediated through intracellular
receptors.
Action potentials propagate faster in axons of larger diameter, other things being
equal. They typically travel from 10-100 m/s.
Hormonal Effects
Androgen receptor (computer image, left;
electron micrograph, right)
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Sufficient number of receptors must be available for hormonal effects to occur.
Popular belief that individual differences in behavior reflects differences in hormone
concentrations. For example, it is assumed that roosters that crow frequently have more
testosterone than roosters that seldom crow (or that aggressive men have higher T).
Not necessarily true!
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Hormones rarely change the function of a cell; rather, they alter the rate of
normal cellular function.
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Individual differences in behavior can reflect hormone concentrations,pattern of hormone release,
numbers and location of hormone receptors, and the efficiency of those receptors in affecting gene
transcription.
Thus, hormones affect cell morphology and size (including development of muscle and neuronal
cells), and affect cell death (apoptosis) throughout the nervous system.
Although hormones obviously affect behavior, it is also true that behavior can
influence hormonal levels and hormonal effects.
How might behavior affect hormones
(most research does not look at this)
little Dutch football fan
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Behavior can and often does affect hormone levels which in turn can influence subsequent behavior.
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World Cup Soccer Fans were assayed for testosterone before and after the Brazil-Italy final. Brazil won on
penalty kicks. 11/12 Brazil fans showed an increase in testosterone, whereas 9 of 9 Italian fans showed a
decrease.
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Testosterone concentrations were measured in four heterosexual couples over a total of 22 evenings. On
11 evenings, saliva samples were obtained before and after sex; on the remaining 11 evening, two samples
were obtained, but there was no sex. Having sex caused an increase in testosterone in both men and
women. No changes were seen in the no-sex nights. The early evening samples revealed no difference in
testosterone concentrations between sex and no-sex evenings, suggesting that sex increases testosterone
more than testosterone (concentrations) cause sex. Alternatively, physical exercise may have caused the
increase (it increases CORT, which can correlate positively with T).
How does one go about answering a research question in the field of
behavioral endocrinology?
Example: What causes the Zebra Finch to sing?
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(What causes Zebra Finches to Sing?)
Four correct answers, based on Levels of Analysis
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Immediate causation: mechanisms mediated by the nervous and endocrine
systems
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Example: Singing in male zebra finches (In contrast to mammals in which structural
differences in neural tissues have not been directly linked to behavior, structural
differences in avian brains have been directly linked to a sexually dimorphic behavior:
bird song).
Female zebra finches never sing, even after testosterone treatment in adulthood.
Other species (wrens, canaries) show no or a diminished sex difference
The size of nuclei in two major brain circuits (HVc, RA, & Area X) implicated in learning
and production of bird song parallel sex differences in singing behavior (e.g., large
dimorphisms in zebra finches,undetectable dimorphisms in wrens in which no singing
difference is observed).
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But why the sex difference in the zebra finch?
If female finches are treated with androgen soon after hatching, and then treated with
androgen when adults, they don’t sing, but they showed a small increase in the number
of neurons in the song production region.
If female finches are treated with estrogen soon after hatching, then as adults, they
show a marked increase in the number and size of neurons in this region, but still no
singing.
However, if treating with estrogen soon after hatching and then treated with androgen as
adults, they show the same size and number of neurons as their male conspecifics, and
they SING. Conclusion: Estrogens are necessary to organize the neural machinery
underlying the song system, and androgens activate it. Bird testes produce circulating
androgens which enter neurons containing aromatse, an enzyme which converts
androgens to estrogen. These neurons are generally found in the hypothalamus, as
well as in the structures constituting the neural circuit controlling bird song.
Development
Behavioral responses change through the lifespan as a result of gene X environment
interaction.
The mating dance of columba chippendalia is
virtually unique in the animal kingdom
Levels of Analysis (Zebra Finch song)
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Evolution
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This approach involves many generations of animals and addresses the ways that specific behaviors change
during the course of natural selection.
Biologists study the evolutionary bases of behavior in order to learn why behavior varies between closely related
species as well as to understand the specific behavioral changes that occur during the evolution of a new species.
Behaviors rarely leave interpretable traces in the fossil record, so this approach relies upon comparing existing
species that vary in relatedness (e.g., old v. new world monkeys).
Someone at this level might say that zebra finches sing because they are finches, and that all finches sing because
they have evolved from a common ancestral species that sang.
Adaptive Function
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Hormonal events affecting the fetal and neonate can have profound consequences later in life.
Most research has focused on how early events influence adult behavior; however, the decay of behavioral
patterns during aging is also a new and expanding area to those pursuing developmental questions.
Possibly, zebra finches sing because they have undergone puberty or because they learned songs from their
fathers.
Synonymous with adaptive significance; role that behavior plays in the adaptation of animals to their environment
and with the selective forces that currently maintain behavior.
Could be argued that male zebra finches sing because it will increase the likelihood of reproduction by attracting
females to their territories and dissuading competing males from entering.
So, if we want to study HOW, then focus on questions of immediate causation and development.
If WHY, then questions of evolution and function.
How might hormones affect behavior
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The study of the hormone-behavior relationship is organized around the idea that animals are composed of
three interacting components:
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Input systems (sensory)
Integrators (CNS)
Output systems (e.g., muscles)
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Example: Removing the testes of the male zebra finch stops it from singing. Reinplant the testes, or
provide the primary testicular hormone, testosterone, and singing resumes. Obviously, testosterone is
involved in singing, but how?
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Input: Examine the sensory system. Does testosterone alter the birds’ sensory capabilities, making the
environmental cues that elicit singing more salient? If this were the case, females or intruders might be
seen or heard more easily.
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CNS: Testosterone could change the Neural Architecture or speed of neural processing. Higher processes
(e.g., motivation, attention) might be influenced.
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Effectors: Testosterone concentrations might affect the muscles of the syrinx (the avian vocal organ).
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This 3-part framework can aid in the design of hypothesis and experiments to help understand how
hormones affect behavior.
Classes of evidence for determining
hormone-behavior interactions
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1st: A hormonally-dependent behavior should disappear when the hormonal source is removed or actions of
the hormone are blocked. Example--ADT.
2nd: After the behavior stops, restoration of the missing source or its hormone should reinstate the absent
behavior. Again, ADT.
3rd: Hormone concentrations and the behavior should covary; in practice, the behavior should be
observed when concentrations are relatively high and never or rarely observed when
concentrations are low.
This 3rd class of evidence is difficult to obtain because many hormones have a long latency of action
(why? up-regulation.) and/or a long offset latency (why? down-regulation) and are released in a
pulsatile manner. For example, a pulse may be released into the blood and then no more released for an
hour or more, so a single sample will not provide an accurate picture of the endocrine status of the animal.
Another problem is that biologically effective amounts of hormones are TINY and thus difficult to measure
accurately. Effective concentrations are measured in micrograms, nanograms, or picograms (10 to the
negative 6th, 9th, or 12th, respectively).
Unfortunately, the 1st two classes of evidence are thus considered more reliable, but research on humans
is typically limited to the 3rd (with exceptions--ADT, for example).
Common techniques in behavioral
endocrinology
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Ablation & replacement
Bioassays
Immunoassays
Immunocytochemistry (ICC)
Autoradiography
Blot tests
In situ hybridization
Pharmacological Techniques
Genetic Techniques (transgenics and knockouts)
Common techniques in behavioral
endocrinology
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Ablation and replacement
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1. A gland that is suspected to the the source of the hormone affecting behavior is surgically removed
2. Effects on behavior are observed
3. Hormone is replaced, by reinplantation, injection of an extract from the gland or injecting a purified
hormone
4. Determination is made whether the observed consequences of ablation are reversed by
replacement therapy.
5. Is the surgically removed gland the hormonal source?
Common techniques in behavioral endocrinology
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Bioassays
Once the existence of a hormone has been established, the next step is to
identify the chemical processes involved in its actions.
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Typically, this involved a test of its effects on a living animal (which can
serve as a reliable, quantifiable response system on which to test
hormonal extracts and chemical fractions).
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A bioassay need not be conducted on the same species from which the
hormone was obtained.
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Example: THE RABBIT TEST (or Friedman test).
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Developed by Maurice Friedman in 1929 (used until the late 1950s).
Used to test for the presence of human chorionic gonadotropic (hCG--a
hormone released from the implantation site of a blastocyst. hCG
prevents menstruation). hCG found in women’s urine.
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BTW, hCG produced by the rudimentary placenta that forms immediately
after blastocyst formation (hCG maintains corpus luteal function during
pregnancy--thus, progesterone secretion--and inhibits ovulation).
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Urine injected into a rabbit, and if hCG present, rabbit’s ovaries would
form corpora lutea, or “yellow bodies” (temporary ovarian endocrine
structures formed following ovulation within 48 hours and produce
progestins--horomones that support pregnancy).
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It is a common misconception that the injected rabbit would die only if the
woman was pregnant. This led to the phrase "the rabbit died" being used
as a euphemism for a positive pregnancy test. In fact, all rabbits used for
the test died, because they had to be surgically opened in order to
examine the ovaries. While it was possible to do this without killing the
rabbit, it was generally deemed not worth the trouble and expense.
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The rabbit test was better than the earlier mouse test (developed in 1928)
which required 6 or more mice and 96 hours to complete.
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However, if the rabbit was stressed, spontaneous corpora lutea formation
occurs (in the absence of hCG), so there was a significant false positive
rate.
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In the frog test for pregnancy, a woman’s urine is injected into a male
frog or toad. In 2-4 hours, the animal would begin to produce sperm if
the woman’s urine contained hCG. However, there were seasonal
variations in frogs--in the summer, they had a greater tendency to
produce false negatives.
corpus luteum
Common techniques in behavioral
endocrinology
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Immunoassays
Bioassays require a great deal of time, labor, and the sacrifice of many animals for every assay.
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The development of the radioimmunoassay (RIA) reduced these problems and increase the precision with which hormone
concentrations could be measured.
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Based on competitive binding of an antibody to its antigen. An antibody produced in response to any antigen (defn: any
molecule that stimulates an immune response) has a binding site THAT IS SPECIFIC FOR THAT ANTIGEN.
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Antigen molecules can be labeled with radioactivity, and an antibody cannot discriminate between an antigen that has
been radiolabeled (or “hot”) and one that is normal (or “cold”). A given amount of antibody possesses a given number of
binding sites for its antigen.
STEPS INVOLVED IN RIA:
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1. First, inject the hormone of interest (e.g., T) into an animal to raise antibody (anti-T)
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2. Then, collect antibody from blood, and purify.
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3. Develop a standard curve
• Set up 5 or 6 reaction tubes, each containing the same amount of antibody, the same amount of radiolabeled
hormone, and different amounts of cold purified hormone of known concentrations (from low to high concentration)
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(The radiolabeled and cold hormone compete for binding sites on the antibody, so the more cold hormone present, the less hot
hormone will bind to the antibody)
4. The quantity of hot hormone that was bound can be determined by precipitating the antibody and measuring its
radioactivity.
5. The concentration of hormone in an UNKNOWN sample can then be determined by subjecting it to the same procedure
(substituting unknown sample for cold hormone in STEP 3) and comparing the results with the standard curve
The enzymoimmunoassay (EIA) works on the principle of competitive binding of an antibody to its antigen. The major
difference is that EIAs do not require radioactive tags. Rather, the antibody is tagged with a compound that changes
optical density (color) in response to binding with the antigen.
Example: The home pregnancy test.
However, most EIAs provided quantitative information, and thus a standard curve is generated, so that different amounts
of the hormone in question provide a color gradient that is read on a spectromoter. A similar technique is called enzymelinked immunosorbent assay (ELISA).
Anatomy of an ELISA test
• Animation of an HIV ELISA test (both
positive and negative test--notice that you
can test for presence of antigen (e.g., a
hormone assay) or its complement antibody
(viral assay).
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http://www.biology.arizona.edu/IMMUNOLOGY/activities/elisa/technique.html
Common techniques in behavioral
endocrinology
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Immunocytochemistry (ICC)
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ICC techniques use antibodies to determine the location
of a hormone in the body.
Antibody molecules linked to marker molecules (usually
a fluorescent dye) are introduced into dissected tissue
from an animal, where they bind with the hormone or
neurotransmitter of interest.
Tissue is examined under a fluorescent microscope, and
concentrated spots of fluorescence will appear,
indicating where the protein hormone is located.
Commonly used marker is the enzyme horseradish
peroxidase.
human sputum cells
Common techniques in behavioral endocrinology
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Autoradiography
– Typically used to determine
hormonal uptake and indicate
receptor location.
– An animal can be injected with
a radiolabeled hormone, or the
study can be conducted in vitro.
– Top picture: Human NMDA
receptor (NDMA is a receptor
for the amino acid glutamate,
which is the most abundant
neurotransmitter in the
mammalian nervous system).
– Bottom indicates transport in a
young tomato plant: The
distribution of elements (e.g.
micronutrients, pollutants) are
visualized by autoradiographic
techniques.
Other techniques in behavioral endocrinology
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Blot tests (uses a technique called gel
electrophoresis to separate proteins
based on their length and weight (in kDa)
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Used to determine presence of a particular
protein or nucleic acid in a specific tissue.
Southern blot used to assay DNA
Northern blot used to assay RNA
Western blot used to assay proteins
In Situ Hybridization
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Previous techniques can determine
only whether or not a particular
substance is present in a specific
tissue, but in situ hybridization can be
used to determine if the substance is
produced in a specific tissue.
Used at the cellular level to examine gene
expression.
More specifically, used to identify cells that
are producing mRNA for a specific protein
(e.g., a hormone or neurotransmitter).
Called hybridization because a
radiolabeled cDNA probe (cDNA, or
complementary DNA is synthesized from
mature mRNA by the enzyme reverse
transriptase) is introduced into the tissue.
If the mRNA of interest is present, the
cDNA will form a tight association (i.e.,
hybridize) with it.
These are
chromosomes from
the canola seed
showing the location
of various
retrotransposons,
which are genetic
elements that can
amplify themselves
within a genome.
Other techniques in behavioral endocrinology
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Pharmacological Techniques
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Use of synthetic agonists (mimics) and
antagonists (blockers) to determine
endocrine functioning.
Some agents act to stimulate or inhibit
endocrine functioning by affecting the
release of hormones; they are called
general agonists/antagonists.
Others act directly on receptors,
enhancing or negating the effects of the
focal hormone; these are receptor
agonists/antagonists.
Example: CPA is a powerful anti-androgen
used clinically to treat male sex offenders
(about 20% of patient don’t show the
expected behavioral response). CPA
binds to androgen receptors but doesn’t
activate them, thereby blocking effects of
androgen.
Other techniques in behavioral endocrinology
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Common genetic manipulations in behavioral endocrinology are the
insertion (transgenic) or removal (knockout) of the genetic
instructions encoding a hormone or hormone receptor.
Briefly: The genetic instructions for each individual are contained in
the DNA, located in the nucleus of nearly every cell.
Each gene (composed of a specific order of four nucleotides: adenine,
thymine, cytosine, and guanine) is determined by the sequence of
nucleotides along the “rails” of the double helix.
To inactivate (knockout) a gene, you scramble the order of the
nucleotides that make up the gene. The identification of the genome
has been most successful in the mouse; thus mice are most
commonly used in knockout studies.
Knocking out a gene is more difficult than it sounds:
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gene of interest must be identified, targeted, and marked precisely.
A mutated form of the gene is then created (e.g., mutating the marker gene
via genetic engineering).
Embryonic stem cells are harvested and cultured, and the mutated gene is
introduced into the cultured cells by microinjection.
A small number of the altered genes are incorporated into the DNA of the
stem cells via recombination.
The mutated embryonic stem cells are inserted into normal embryos
(blastocycts), which are then implanted into surrogate mothers.
That’s it!!!!
All of the cells from the mutated stem cells will have the altered gene; the
descendents of the normal embryonic cells will have normal genes.
Thus, the offspring will have a mixture of cells--some containing the mutated
gene and some containing the normal (wild-type) gene.
This animal is called a chimera
The chimeras are then bred (interbred or bred with wild-type animals) to
produce wild-type (+/+), heterozygous (+/-), and homozygous (-/-) animals
with respect to that gene. Behavioral performance can then be compared.
n.b In Greek mythology, a Chimera is a monster, depicted as an animal with the head of a lion, the
body of a she-goat, and the tail of a dragon
Chimeras
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Chimeric animals:
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Pictured on the right is a baby “geep”, made by
combining a goat and sheep embryo. Notice the
chimerism evident in the skin - big patches of skin
on front and rear legs are covered with wool,
representing the sheep contribution of the animal,
while a majority of the remainder of the body is
covered with hair, being derived from goat cells.
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There is also some potential that this technique
can be applied to problems such as rescue of
endangered species. It is possible, for example to
construct a goat-sheep chimera such that a goat
fetus is "encased" in a sheep placenta. This
enables a sheep to carry a goat to term, which will
not occur if you simply transfer goat embryos into
sheep (the sheep will immunologically reject the
goat placenta and fetus). It may be possible to
extend this procedure to allow embryos from
severely endangered species to be carried by
recipient mothers from another species.
Fat mice--Using all of the techniques discussed previously to understand obesity
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Effects of Leptin
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Recently leptin (derived from Greek leptos, meaning
thin) discovered as a hormone released from fat cells.
It is known that a specific mutation in mice on the ob
gene can cause extreme obesity (in mice homozygous
for defective ob).
Thus, these naturally-occuring mutants can be
considered “natural knockouts” for the ob gene.
ob/ob mice have a pair of defective ob genes, overeat,
are obese, and are sterile.
The ob gene normally codes for leptin, which is released
into the bloodstream and travels to specific receptors in
the CNS and elsewhere to regulate feeding and energy
balance.
Although it has been known for a long time that the
ob/ob mutation affects body weight in mice, only recently
has the ob gene been cloned, inserted into a bacterial
system, and thus purified leptin made available to
researchers.
Replacement studies could now be done in which leptin
was provided to ob/ob mice to determine if leptin
replacement would ameliorate obesity.
It did (see mouse on the right (25g--average mouse is
15g; one on the left is w/out replacement at 35g).
•Availability of purified leptin allowed for the development of antibodies used to develop assays to determine blood concentrations.
•RIA determined that there was no connection between plasma leptin concentrations and obesity/diatetes IN HUMANS.
•A leptin ELISA was developed for rats, which determined that fasting or exposure to low temperatures caused leptin to fall.
•Immunocytochemistry determined that leptin was present in both white (energy utilization) and brown (generation of body heat) adipose tissue.
•Autoradiography determined that tagged leptin was found in a brain area located in the front of the third ventricle.
•This tissue was then used to clone a leptin receptor
•In situ hybridization found that the mRNA for the leptin receptor was expressed in the hypothalamus.
•Efforts to “cure” obesity involved transgenics--treating ob/ob mice with a recombinant virus expressing mouse leptin cDNA, resulting in leptin
production. A dramatic reduction in food intake and body mass resulted.
•This treatment also reverses the sterility found in ob/ob mice.
•However, only two (out of thousands) of obese humans displayed a ob mutation. Sadly, the effects of leptin on humans have been disappointing,
dashing the Nobel dreams of more than a handful of psychologists.
The Endocrine System
• Where do hormones come from?
– They are produced by glands, and are secreted into the
bloodstream.
• Where do hormones go?
– They travel to target tissues containing hormone-specific
receptors.
• What do hormones do?
– By interacting with their receptors, they initiate biochemical
events that activate genes to induce certain biological
responses (e.g., protein synthesis). In some cases,
hormone-receptor interactions result in nongenomic effects
on cellular function (these are fast, and are just now being
studied in their role in mediating behavior).
Types of chemical communication
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Intracrine mediation
– regulation of intracellular events
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Autocrine mediation
– autocrine substances feedback
to influence the same cells that
secreted them.
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Paracrine mediation
– paracrine cells secrete
substances that affect adjacent
cells (e.g., nerve cells).
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Endocrine mediation
– endocrine cells secrete
chemicals into the bloodstream
where they may travel to distant
target cells.
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Ectocrine mediation
– Ectocrine substances, such as
pheromones, are released into
the environment to
communicate with others.
General Features of the Endocrine System
• Endocrine glands are ductless
• Endocrine glands have a rich blood supply.
• Product of endocrine glands (hormones) are secreted into the
blood stream
• Hormones can travel to virtually any cell in the body (cells in the
lenses of the eye are an exception--no blood supply)
• Hormone receptors are specific binding sites, embedded in the
cell membrane (in the case of peptide hormones) or in the
cytoplasm (in the case of steroid hormones) that interact with a
hormone or class of hormones
• Exocrine glands have ducts or tubes (e.g., salivary, sweat,
mammary). Some glands have both endo- and exo- structures
(e.g., pancreas)
The Endocrine Glands
In touch with his feminine side
Four classes of hormones
Protein & peptide hormones
Steroid hormones
Monoamines
Lipid-based hormones
(prostaglandins)
Cellular and molecular mechanisms of hormone action-Protein Hormones (the majority of hormones)
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Protein hormones require a second messenger (i.e., a molecular
middleman--typically, an enzyme or another protein) to
transduce (conversion of one type of signal into another) the
hormonal signal
In really simple terms, the hormone binds to the receptor which is
coupled to a protein called G. When this mess is formed, a
messenger called cAMP is created. cAMP combines with an
enzyme that activates another enzyme which acts on the target
substance (e.g., in the case of glucagon, this final enzyme
converts glycogen into glucose).
Receptors are coupled to special proteins (G) that mediate
intracellular events (all G proteins have 3 different subunits). The
G protein receptor family includes glucagon, oxytocin, and
vasopressin receptors.
When the hormone-receptor complex binds to G, G in turn
activates adenylate cyclase, which in turn stimulates that
formation of cyclic adenosine monophosphate, or cAMP.
When formed in response to a hormone-receptor bind, cAMP is
referred to as the 2nd messenger (the hormone is the 1st
messenger)
Once formed, cAMP can combine with an enzyme called protein
kinase A (PKA), an enzyme that in turn activates (phosphorylates)
another enzyme called phosphorylase kinase in a variety of
cells.
For example, phosphorylase kinase A breaks down glycogen into
glucose to provide intracellular energy.
glycogen
Cellular and molecular mechanisms of hormone action-Steroid Hormones
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Steroid hormones are fat soluble and move easily through cell membranes (as
a result, these hormones are never stored but leave the cells in which they are
produced almost immediately--nomadic).
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In the blood, steroid hormones must bind to water-soluble carrier proteins to
increase their solubility and the ability of the blood to carry them to their target
tissues.
Upon arrival, they dissociate from their carrier proteins and diffuse through the
cell membrane into the cytoplasm of the target cell, where they bind to
cytoplasmic receptors.
The steroid-receptor complex is transported into the cell nucleus, where it
binds to DNA sequences called hormone response elements and then either
stimulates or inhibits the transcription of specific mRNA.
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The precursor to all vertebrate steroid hormones is cholesterol (made from
acetate in the liver).
The precise mechanism through which binding to the hormone response
elements occurs is unknown.
The transcribed mRNA migrates to the cytoplasmic rough endoplasmic
reticulum, where it is translated into specific proteins or enzymes that
produce the physiological response (much more on this later).
Note: changes in the types of proteins a cell makes (aka, the gene products)
can be observed within 30 minutes of hormone stimulation.
cholesterol
The major vertebrate hormones
•
Protein & peptide hormones:
–
–
–
–
–
–
Make up the majority of hormones
Protein hormones that are only a few amino acids in length are called
peptide hormones (larger ones called protein or polypeptide hormones)
Include: insulin, the glucagons, the neurohormones of the hypothalamus
(monoamines), the hormones of the anterior pituitary, inhibin, calcitonin,
parathyroid hormone, the GI hormones, leptin, and the posterior
pituitary hormones
These hormones are blood-soluble (they don’t need a carrier protein to
travel to their target cells, as do steroid hormones). However, they may
bind with other blood plasma proteins
The metabolism of a hormone is reported in terms of its half-life, which
is the amount of time required to remove half of the (radioactively
tagged) hormone from the blood
Generally, larger protein hormones have longer half-lives (e.g., growth
hormone with 200 amino acids has a half life of 20-30 mins, whereas
thyroid releasing hormone has 3 amino acids and a half life of fewer
than 5 minutes).
Insulin (not Europe)
Human growth hormone
Too much human growth hormone
(tumor on the anterior pituitary)
Hypothalamic hormones
•
•
The peptide hormones secreted by the hypothalamus are best thought of as a
special class of neurotransmitters that act on a variety of cells in the anterior
pituitary.
Five releasing hormones and one inhibiting hormone have been isolated.
–
–
–
–
–
–
•
TRH--thyrotropin-releasing hormone
GHRH--growth hormone-releasing hormone
GnRH--gonadotropin-releasing hormone
MSH--melanotropin-releasing hormone
CRH--corticotropin-releasing hormone
Somatostatin--growth hormone-inhibiting hormone
Peptide and protein hormones vary in amino acid sequence (and vary by
species--e.g., GnRH possesses a different sequence in frogs than in horses;
horse GnRH will not affect a frog’s reproductive function (although salmon
calcitonin is used in humans to promote bone mineralization). Hormones differ
in species specificity.
Notice inter-species discrepancies in the 2nd position (glycine), 8th position (methionine),10th, 11th,
and many others moving forward. Calcitonin is a thyroid hormone. It lowers blood levels of calcium
by inhibiting calcium release from bone. Interestingly, it is regulated by blood calcium levels, not by
pituitary hormones.
Anterior Pituitary hormones
•
•
All protein hormones, all, ranging in length from 39 to 220 amino acids.
Anterior pituitary is composed of three types of cells:
–
–
–
Acidophils (these cells stain readily with acidic stains)
Basophils (stain readily with basic stains)
Chromatophils (do not take up either acidic or basic stains)
Basophil-secreted:
•
Lutenizing hormone (LH), follicule-stimulating hormone (FSH), and thyroid-stimulating
hormone (TSH) are secreted by basophils.
•
LH and FSH and controlled by hypothalamic GnRH. TSH is controlled by hypothalamic
TRH.
•
All consist of 200-220 amino acids and have molecular weights of 25-35K daltons.
–
Note: LH and FSH are known as gonadotropins because in response to GnRH, they
stimulate the production of steroids in the gonads.
Acidophil-secreted:
•
Growth hormone (GH) and prolactin (PRL)
•
TRH stimulates PRL secretion; hypothalamic dopamine inhibits. GHRH and
Somatostatin control GH.
•
190-220 amino acids in length.
•
GH shows fair amount of species specificity.
•
GH stimulates body growth INDIRECTLY (does not induce skeletal growth).
–
•
•
•
Stimulates production of growth-regulating substances--somatostedins--by the liver and
kidneys. Somatostedins cause bone to take up sulfates leading to growth.
GH also stimulates protein synthesis, fat mobilization,and hyperglycemia (because of
its anti-insulin properties).
Prolactin (PRL) best known for promoting lactation in female mammals, but in fact PRL
has hundreds of physiological functions. Was originally called luteotropic hormone
because its 1st known function was to promote corpus luteum function in rat ovary.
PRL functions can be broken down into 5 basic classes:
–
Reproduction
–
Growth and development
–
Water and electrolyte balance
•
•
•
–
Salt marsh killfish
e.g., corpora lutea formation/maintenance
e.g., second metamorphosis of salamanders from terrestrial to aquatic adult
e.g., certain minnows can migrate between seawater and fresh water. They are
euryhaline.
Maintenance of integumentary system (external body covering)
•
e.g., pigeons and doves feed their young crop milk, which is secreted by the PRL-developed
crop sac.
–
Actions on steroid-dependent target tissues or synergisms with steroids to affect target
tissues.
–
Note: Elevated PRL levels appear to mediate paternal behavior in the California mouse
and marmoset (reductions in testosterone have the same effects in the marmoset).
Humans?
•
e.g., PRL necessary to maintain LH receptors in the testes of mammals
crop sac
actual crop milk
Anterior Pituitary hormones
(cont.)
chromatophil secreted
•
•
•
ACTH (Adrenocorticotropic hormone) secreted by
the chromatophils.
39 amino acids; 4500 daltons in weight
ACTH released in response to CRH from the
hypothalamus; stimulates the adrenal cortex to
secrete mineralocorticoids and glucocorticoids
(including cortisol, the primary glucocorticoid,
which may feed back to control ACTH release. This
conclusion is based on an increase in ACTH
secretion after adrenalectomy.)
Relationship between CRH, ACTH, and adrenals
Posterior Pituitary hormones
•
Two peptides, oxytocin and vasopressin, are released from the
posterior lobe of the pituitary in mammals.
•
Oxytocin regulated by electrical activity of the oxytocin cells in the
hypothalamus. Vasopressin secreted in response to increased
osmotic pressure in the heart, veins, and carotid arteries.
Oxytocin (Greek: “quick birth”) influences reproductive function
–
–
–
•
Important in birth:
Causes uterine contractions (synthetic oxytoxin--Pitocin--used to
induce labor)
Causes the letdown reflex (in response to sensory stimulation of the
nipples, oxytocin is released, travels to the mammary glands, which
contract upon exposure, causing milk letdown--and because of prior
associations--cry of a hungry baby, or the sound of a milking
machine (in cows) produces the same mechanism.
Behaviorally:
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–
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oxytocin injected into the cerebrospinal fluid causes spontaneous
erections in rats
In the Prairie Vole, oxytocin released into the brain of the female
during sexual activity is important for forming a monogamous pair
bond with her sexual partner
Sheep and rat females given oxytocin antagonists after giving birth
do not exhibit typical maternal behavior. By contrast, virgin female
sheep show maternal behavior towards foreign lambs upon
cerebrospinal fluid infusion of oxytocin
Crossing the placenta, maternal oxytocin reaches the fetal brain and
induces a switch in the action of neurotransmitter GABA from
excitatory to inhibitory on fetal cortical neurons. This silences the
fetal brain for the period of delivery and reduces its vulnerability to
hypoxic damage
Vasopressin (aka antidiuretic hormone--ADH--or arginine vasopressin-AVP--acts to retain water in four-footed vertebrates.
•
Rate of filtration in the kidneys slows in response to ADH, resulting in
water retention.
•
ADH has hypertensive effects during serious blood loss--blood
vessels constrict in response to severe hemorhage, slowing blood
flow.
•
Behaviorally, vasopressin seems to induce the male to become
aggressive towards other males.
Review
• Hypothalamic hormones
–
–
–
–
–
–
GHRH
GnRH
MSH
TRH
CRH
Somatostatin
• Pituitary Hormones
– Anterior
•
•
•
•
GH (GHRH)
FSH, LH (GnRH)
TSH, PRL (TRH)
ACTH (CRH)
– Posterior
• Oxytocin (hypothalamic
oxytocin cells)
• Vasopressin (aka, ADH,
AVP--increases in osmotic
pressure).
Some other protein hormones
The Thyroid hormones
•
•
•
Thyroid gland releases its hormones in response to
TSH stimulation from the anterior pituitary
There are two biologically active thyroid hormones,
both derived from a molecule called thyroglobulin
T3, also known as tri-iodothyronine and T4,
thyroxine have three general effects:
–
–
Increases metabolism--generally, thyroid activity is
greater in the winter.
Growth and differentiation--closely related to actions of
GH; in fact, effects probably represent permissive
actions on GH target cells
•
–
permissive effects occur when one hormone
induces receptor production for a second hormone.
These effects are common.
Behavioral effects--insufficient production can affect
CNS development, causing cretinism; insufficient
production can also delay sexual maturation
Endemic cretinism in the Democratic Republic of Congo. Four inhabitants aged 1520 years : a normal male and three females with severe longstanding
hypothyroidism with dwarfism, retarded sexual development, puffy features, dry
skin and hair and severe mental retardation
The GI hormones
•
Three major gastrointestinal hormones:
–
Secretin
•
–
Gastrin
•
–
Released by the duodenum (1st segment of small
intestine). Stimulates pancreas to produce water and
bicarbonate, which aid in digestion. Also stimulates
liver to produce bile.
Released by the stomach. Stimulates insulin release,
smooth muscle contractions of gut, gallbladder, and
uterus.
Cholecystokinin (CCK)
•
Released by duodenum. Causes pancreas to
secrete digestive enzymes; causes gallbladder to
contract and release bile
The Pancreatic hormones
•
Insulin
–
•
Only known hormone in the animal kingdom that
can lower blood sugar (many hormones act to raise
blood glucose levels). All cells (except for CNS cells)
have insulin receptors. When an insulin receptor is
activated, glucose is taken up into the cell, used, or
stored as glycogen in muscle or fat cells.
Glucagon
–
Travels to the liver, where it breaks down stored
glycogen (glycogenolysis), serving to increase blood
levels of glucose. It acts in opposition to insulin.
Other peptide hormones
•
Enkephalins
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•
Inhibin
–
•
Blocks secretion of FSH and aromatase (an enzyme
that converts estrogens from androgens); released by
the gonads (testes and ovaries). See figure at right.
Activin
–
•
Possibly involved in the stress response; released by
the adrenal medulla
Directly stimulates aromatase activity in the gonads
(opposite of inhibin?); released by the gonads
Relaxin
–
Softens pelvic ligaments during pregnancy to allow the
large head of the fetus clear passage through the
vaginal canal during birth; released by the ovaries
Female mouse on top left is a transgenic mouse used to explore the
potential effects of excess inhibin on the reproductive axis. The inhibin
subunit protein was overexpressed in transgenic mice. The
transgene is expressed in numerous tissues and levels of inhibin are
highly elevated compared to control mice, leading to a decrease in
serum FSH, and an increase in testosterone and serum LH. Activin
levels are also somewhat depressed. The female mice are subfertile
and have very small litters. This is a consequence of decreased
ovulation, probably secondary to alterations in FSH and LH. Most
interestingly, female mice that carry this transgene develop several
unique ovarian pathologies, including distension of the bursal sac, the
presence of large fluid-filled cysts, and the presence of atypical follicles
that contain multiple oocytes (Figure 3).
The Steroid hormones
•
•
•
•
•
All steroids have a common chemical structure-three six-carbon rings plus one conjugated five
carbon ring
The precursor to all steroid hormones is
cholesterol (produce from acetate in the liver)
Recall that steroid hormones are fat-soluble and
move easily through cell membranes (slide 25)
Further recall that in circulation, they must bind to
water-soluble carrier proteins (slide 25)
Three major classes of steroid hormones:
–
–
–
Progestins/Corticoids
Androgens
Estrogens
cholesterol
The C21 steroids: Progestin & Corticoids
Two types of C21 hormones--progestins and corticoids
•
In response to anterior pituitary signals, cholesterol
is converted into various steroid hormones in the
adrenals
•
P450-linked side chain cleaving enzyme, or
desmolase cuts cholesterol down into
pregnenolone, which is a progestin and is the
precursor to all other steroid hormones
•
Pregnenolone is a prohormone.
–
•
A prohormone is a substance that can act as a
hormone and can be converted into another
hormone with different endocrine properties
Progestins are named for their pregnancymaintaining effects. Progesterone is important in
maintaining pregnancy and in the initiation and
cessation of mating behaviors (also, perhaps
attachment)
Two types of corticoids: glucocorticoids and
mineralocorticoids
•
The glucocorticoids are involved in carbohydrate
metabolism and are released under stress; the two
primary are corticosterone and cortisol. All
reptiles and birds, as well as rats and mice secrete
corticosterone; the primary glucocorticoid in
primates is cortisol
•
Aldosterone is the most important
mineralocorticoid. Primarily responsible for
retaining sodium and excreting potassium
The C19 steroids: The Androgens
Progestins are precursors to all androgens.
Enyzmes found in the gonads convert pregnenolone to
several different androgens (from Greek andros for
man).
•
Most biologically important are testosterone,
androstendione, and dihydrotestosterone (DHT)
•
Produced in the Leydig cells of the testes; Sertoli
cells are source of the androgen-binding proteins
that carry androgens through the blood
–
Another androgen, DHEA (and DHEA-S) are
produced in the adrenal cortex.
•
•
•
•
Physiological functions of androgens
–
–
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•
Spermatogenosis
Maintenance of the genital tract
Maintenance of the accessory sex organs
(prostate et al.)
Secondary sex characteristics (body hair in
humans, comb size in roosters, antler growth in
deer)
Behavioral functions
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–
•
Relatively weak
Physio functions unknown
DHEA replacement may ameliorate certain
aging effects (increased muscle mass,
decreased fat mass)
Courtship
Copulation
Aggression
Dominance
Many other social behaviors (just beginning to be
discovered)
Metabolic functions
–
–
–
–
Increase in muscle mass due to protein
metabolism
Increase in respiration
At supraphysiologic levels, hypertrophy of organ
systems due to widespread androgen receptor
density (e.g., liver, heart, kidneys). Thus, chronic
exposure to supraphysio levels can lead to a
reduction in function
Reproductive function often compromised at
supraphysio (along with testicular shrinkage due
to downregulation of Leydig and Sertoli tissues)
The C18 steroids: The Estrogens
Androgens are the precursors of all estrogens just as progestins are the
precursors of all androgens
Estrogen means “producing” (coined 1927)
•
Enzymes in the ovaries convert testosterone and androstendione to
estrogen by a process called aromatization (because removal of the
19th carbon results in an aromatic compound).
•
Biologically significant estrogens are estradiol, estrone, and estriol.
•
Note that the ovaries produce androgens, which are then aromatized
into estrogens.
•
Sometimes excess androgens are produced or insufficient enzymes
are present and the female is masculinized.
•
Conversely, if high levels of enzymes that convert androgens to
estrogens are present in the testes, then estrogens will be secreted
into the blood and the male will be feminized. DHT cannot be
aromatized (why is this important?)
•
Physiolgical functions
–
–
–
•
Metabolic functions
–
–
•
Initiate corpora lutea formation
Uterine mass density (estrogen levels positively correlated with . . .)
Development of secondary sex characteristics
Water retention
Calcium metabolism (bone mass increases in the presence of
estrogen)
Behavioral functions
–
–
Very important in maternal aggression and sexual behavior (e.g., in
combination with progesterone, prolactin, oxytocin, estradiol induces
rats to behave maternally in the presence of pups).
Progesterone is primary in maternal aggression, but estrogens may
play a role. Maternal aggression in women has not been studied.
Many other social behaviors (just beginning to be discovered)
Androgens & Estrogens are not sex-linked
•
•
•
All males produce estrogens and progestins
All females produce androgens
The sex difference in circulating hormone
levels is due to levels of gonadal enzymes.
–
–
•
Testes have more enzymes for making androgens
and less aromatase than do ovaries
Ovaries produce high concentrations of androgens
but these are easily aromatized into estrogens in
the ovaries. These can be converted back into
androgens, but this is an energetically expensive
reaction
Recall that the adrenals produce sex hormones
–
Gene mutation(s) can lead to enzyme deficiencies
which in turn can lead to an ovary or adrenal gland
producing large quantities of androgens. See
example at right
Congenital andrenal hyperplasia (lacking the enzyme to
metabolize cortisol and aldosterone, and as a result,
produce too much androgen. This is a female with an
extremely virilized clitoris.
Review
FYI, no such medically recognized condition as adrenal fatigue.
The monoamines
•
•
Derived from a single amino acid
Two classes
–
–
Catecholamines
Indole amines
Adrenal medulla monoamines
–
–
–
•
•
•
epinephrine
norepinephrine
dopamine
All derived from Tryosine
Released in response to sympathetic neural signals
(evoked by stress, exercise, low temp, anxiety,
emotionality, and hemorrhage). In humans, norepi and epi
are released at a ratio of 1:4
Actions:
–
–
–
–
–
Increase heart rate
Vasoconstriction of deep arteries and veins
Dilation of skeletal and liver blood vessels
Increased glycolysis
Increased blood glucagon concentrations and decreased
insulin secretion
Pineal gland indole amines
–
–
•
•
•
•
Derived from tryptophan
5-HT levels high in the pineal during the day, but low at
night as 5-HT is converted into melatonin
Actions:
The success of the SSRIs (e.g., prozac) work in
depressives who lack the normal sensitivity to serotonin
and thus benefit from the delay in reuptake that the SSRI
provides. In essence, the serotonin has multiple chances
to be recognized by the malfunctioning serotonin receptors
due to lack of reuptake.
–
•
•
Serotonin (5-HT)
Melatonin
Low levels of 5-HT associated with aggression in many
mammalian species
Melatonin involved in regulation of puberty onset and
seasonal organization of breeding
Also, implicated in maintenance of biological rhythms
(circadian, diurnal, seasonal)
The brains of baby rhesus monkeys who endured high
rates of maternal rejection and mild abuse in their first
month of life produced less serotonin. Low levels of
serotonin are linked to anxiety and depression and
impulsive aggression in both humans and monkeys.
Regulation
•
Negative feedback
–
–
–
–
–
•
Example:
GnRH is released from hypothalamus
Gonadotropins are released from anterior pituitary
Steroid and gamete production in gonads is stimulated
Resulting steroid hormones turn off GnRH production in the hypothalamus, which shuts
down gonadotropin release
Up-regulation
–
Increase in PRL stimulates production of more PRL receptors
•
•
•
Back to point raised on Slide #11 (many hormones have a long latency of action ). Up-regulation is the
result of protein synthesis, and can take weeks for the necessary quantity of receptors to
accommodate to the higher hormone levels (case in point--action of certain anti-depressives
require a substantial increase in # of receptors to show effects; must wait on receptor
synthesis).
This point also explains the failure of short-term hormone experiments (insufficient receptors to
accommodate the sudden supra-physio hormone load).
Down-regulation
–
High insulin concentrations reduce the number of insulin receptors
So, WHY should social-personality psychologists study hormones?
•
Tiny handful of folks doing this stuff
•
•
Upside potential is unlimited
Grant $$ is untapped
–
•
•
•
Prostate cancer example
Opportunities for collaborations are great
Behavioral endocrinology is an interdisciplinary approach
fMRI?
–
–
Powerful tool to correlate cortical location, and it should be seen as one tool in the
toolbox, just as self-reports should be seen as one tool among many. Other tools are
critical if personality and social behavior are to be understood
So, what about the stuff that doesn’t or cannot get scanned--the limbic system, the
amygdala, the hippocampus, the midbrain, the thalamus, the hypothalamus, the
pituitary, and of course, the medulla oblongata