Unformatted text preview: Reproductive behavior • Sexual Differentiation
• Genetic Sex
• Phenotypic Sex • Reproductive Behaviors
• Hormonal Control
• Neural Control • Sexual Orientation
• Gender differences Classes of hormones 1. Protein hormones:
composed of long chains of amino acids (e.g. insulin)
2. Peptide hormones:
smaller than protein hormones, are composed of fewer
amino acids (e.g. vasopressin, oxytocin)
Both protein and peptide hormones activate second
messenger systems within the cell, similarly to a
3. Steroid hormones: Steroid hormones
•Derived from cholesterol
•Contain four carbon rings Mechanism:
1. Binding to membrane
2. Entering cells and activate
certain kinds of proteins in
3. Binding to chromosomes
where they activate or
inactivate certain genes. Steroids hormones include:
1. Cortisol (humans)/ corticosterone (rodents)
• Released by adrenal gland in response to stress
• Induce breakdown of fats and proteins into
chemicals the body can use for energy including
1. Sex hormones
• Released by gonads
• Androgens (e.g. testosterone/ DHT)
DHT (Dihydrotestosterone) Steroid hormones are essential for sexual differentiation… Sexual Determination Occurs at Various Levels:
Chromosomal Gonadal sex Hormonal sex Morphological sex Behavioral sex Levels of Sexual Determination:
Chromosomal sex Sexual Development: Genetic Sex
Your genetic sex is determined by your biological father’s
•Sperm and ova contain only ONE of
each of the 23 pairs of chromosomes.
•22 of the 23 chromosomes will
determine your physical characteristics,
independent of gender.
•The last pair differentiate genetic males
•If Y then SRY (sex determining region of Y)
•If SRY then TDF (testis determining factor)
If Sexual Differentiation: Sex Organs
testes & ovaries • Internal Sex Organs
Wolffian & Mullerian ducts • External Genitals Differentiation of gonads and internal sex organs
Y --> SRY --> TDF -->
gonads become testes and begin testosterone (T)
and anti-Mullerian hormone (AMH) production. T --> stimulates development of Wolffian system.
AMH --> inhibits development of Mullerian system. Differentiation of gonads
begins 4-6 weeks after
fertilization Sexual Development: Gonadal Sex
AMH & Androgens
Wolffian develops Sexual Development: External Genitalia
Embryonic Development : Urogenital sinus differentiates into male or
- Genital tubercle --> clitoris/penis
- Genital folds --> labia/scrotum
Genital DHT (Dihydrotestosterone)
essential for the development of the
male external genitalia.
5-alpha-reductase converts T to
DHT. No androgens --> Female external
genitalia What if something abnormal occurs during these
Rosenzweig M.R. et al., Biological Psychology (2002) Androgen insensitivity syndrome
– XY males
– Insensitive to androgens.
– Caused by genetic mutation that prevents
formation of functioning AR.
– Testes develop normally and secrete AMH
– Uterus and Fallopian tubes do not develop.
– External genitalia is female and at puberty
they develop a woman’s body.
– Without uterus or ovaries, they can’t
reproduce. 5 alpha-reductase deficiency
Results in incomplete masculinization of
At birth, they are often assigned as
At puberty, though there is no DHT,
high levels of other androgens
induce male-typical changes in the
external genitalia. congenital adrenal hyperplasia (CAH)
In females, endogenous androgens come
from either the ovaries or adrenal glands.
Adrenal glands produce too much
androgens, instead of cortisol.
Exposure to high levels of T conversion to
DHT occurs --> male genitalia develops
Surgery at birth corrects the genitalia, and
lifelong hormone treatments are needed. Hormonal Control of Sexual Differentiation • Organizational
•permanent • Activational
•after organ differentiation
•temporary Sexual Differentiation of the Nervous System
Y (sry) Undifferentiated
gonads No sry
No testes Testes Antimullerian
T will bind androgen
binds DNA Female Brain?
Male Brain? Sexual Differentiation of the Nervous System
•Differentiation occurs during early-developmental critical period.
•One area that is readily differentiated during development is the POA
•Large lesions of POA impair male sex
•The POA is sexually dimorphic in size •Treating females with T just before and after birth --> POA more
•Castrating males at birth results in the POA being more femalelike.
•It is not T itself that masculinizes the POA, but rather a metabolite
of testosterone, estrogen.
of Aromatization Hypothesis
•Aromatase, which is abundant in hypothalamus, converts T to E
•E binds E-receptors to induce masculine MPOA.
•It is the E that masculinizes the brain!
•Naturally occurring cell death drives differentiation of the MPOA
•There are more dying cells in the MPOA of females than in males Why doesn’t estrogen have the same effect in females?
alpha-fetoprotein •Females have an abundance of alpha-fetoprotein.
•A protein that binds to estrogen during neonatal period.
•Alpha-fetoprotein soaks up all the estrogen in the female, so
no estrogen is available to act on the brain.
no Secondary Sexual Differentiation: Puberty Gonadal trophin releasing hormone Activational Effects Lutenizing hormone
Follicle stimulating hormone
Fisk, C.L. & Foster, D.L., Nature Neurosci, 7(10), 2004, 1040-1047. Reproductive Behaviors
•Propagate parental genes
•Maximize survival of offspring ♀ •Few gametes
•Large energy cost
•Selective ♂ •Many gametes
•Small energy cost
•Not Rosenzweig M.R. et al., Biological Psychology (2002)
picky Female sexual behavior and Hormones
• The periovulatory period is the time of maximum
fertility and high estrogen levels when ovulation
• Studies suggest that women become more sexually
responsive during this time when estrogen levels are
– Show increased attention to sex-related stimuli.
– show increased mate preference towards men
who act and look more masculine. Reproductive Behaviors: Hormonal Control Lordosis Rosenzweig M.R. et al., Biological Psychology (2002) Male sexual behavior and hormones
Castration Impairs Male Sex Measured nocturnal erections in
hypogonads, treated, and controls The MPOA Is Important for Male Sexual Behavior Damage to the medial preoptic
area (MPOA) impairs male
sexual behavior. Liu, et al. (1997) J. Neurosci. Stimulation of the MPOA
enhances male sexual behavior. Rodriguez-Manzo, et al. (2000) Behav. Neurosci. DA in the MPOA Facilitates Male Sexual Behavior Dopamine (DA) agonists
microinjected into the MPOA
enhanced male sexual behavior.
3 * 3 Number of Ejaculations Ejaculation Frequency 2 .5 2 1 .5 1 0 .5 0 Microinjections of DA
antagonists impair copulation Veh
Hull, et al. (1986) Brain Res. Apo 2 .5 2 * 1 .5 * 1 0 .5 0 VEH 20 T
FLU 10 C
FLU Warner, et al. (1991) Brain Res. 15 C
FLU 20 C
FLU Sexually Dimorphic Nucleus (SDN) Rosenzweig M.R. et al., Biological Psychology (2002) Maternal behavior and mPOA Maternal behavior and Hormones
• Stimulates contraction of the uterus during delivery of
• Stimulates the mammary gland to release milk
• Released during orgasm and triggers a state of
• Facilitates formation of pair bonds between mating
partners and mother and infant Sexual orientation and brain He-M Ho-M •Interstitial Nucleus of the Anterior Hypothalamus (INAH): human SDN
Larger in He-M than Ho-M and He-F •Anterior Commissure
Larger in He-F and Ho-M than He-M •Pheromonal Effects
Activates brains of He-F and Ho-M, but not He-M
Rosenzweig M.R. et al., Biological Psychology (2002) Sexual Orientation Ho-F and exposure to fetal androgens? Organizational or activational Effects?
Genetic/physiological or environmental? Rosenzweig M.R. et al., Biological Psychology (2002) Do hormones play a role in shaping boys and girls to
behave in different ways?
Or is gender-sensitive behavior a result of strictly our
upbringing? Evidence from studies of women with CAH Girls with CAH
Were more likely to initiate fighting and aggressive play
Play more with boy typical toys
More likely to be generally aggressive
Show less interests in interacting with infants than their sisters Boys:
-Tend to draw mobile objects and
-Use dark colors.
-Use bird’s-eye-view composition
when they draw.
-Tend to draw human motifs
(especially girls and women)
-Flowers and butterflies with light
and warm colors
-Tend to arrange motifs in a row on
the ground. Drawings of CAH girls Results:
1. The feminine index for the
pictures of CAH girls was
significantly lower than that for
2. The masculine index for CAH
girls was significantly higher than
that for unaffected girls. 3. The masculine index for CAH
girls was not significantly
different from that of unaffected
boys. Non-human animals display sex-specific behaviors, which
allow for easier study of possible endocrine effects.
allow e.g.) Male rhesus monkeys are more likely to fight, be more
aggressive, and express more rough and tumble patterns
Give perinatal androgens to female offsprings -->
external genitalia is masculinized and more likely to
express play patterns similar to males.
express Female vervet monkeys prefer
“girl-typical toys” (dolls/cooking
pots), whereas males prefer
“boy-typical toys” (cars/balls): What is responsible for these differences? What predicts hormone regulated gender
differences in behavior?
Organizational stage --> brain differences (size) --> differences in
Larger size in hypothalamus of:
Males: SDN-POA, BNST
Females: SCN, AVPv
Larger size in structures associated with language:
Females: temporal planum, dorsolateral prefrontal cortex, superior
Structures connecting hemispheres:
Females: Corpus callosum, anterior commisure, intermediate thalamus
1. whole brain mass/ size larger in males
2. women have more folds in the frontal cortices Caveat interpreting these differences:
Do the differences in size cause difference in behavior or did the
difference in behavior cause the anatomical differences?
It’s not always this simple. Organizational Activational Behavior Hormones Organizational Activational Hormones Behavior Do effects of hormones produce gender differences beyond
sexual preference and physical characteristics?
Sensation and perception.
Women have higher sensory acuity
in all senses except visual.
• Women are 1000 times more sensitive to musk-like odors
• Increased sensitivity to musk for women begins at puberty
and is likely estrogen dependent
and • Periovulatory and women in early pregnancy display greater
olfactory sensitivity (result from prog and E).
• This decreases during menstruation and late pregnancy
• Generally, hormonal signals affect olfactory sensitivity in women.
• Women with irregular menstrual cycles showed reduced
olfactory women Women had 8X greater response
to olfactory stimulation than men.
to men Taste
•Women are better at discriminating tastes than
men, especially bitter tastes
•Differences appear after puberty and increase
during pregnancy and during the follicular phase,
and are diminished after menopause.
•Studies show that during increased estrogen
women also have a higher preference for sweet
Click-evoked otoacoustic emissions (EOAEs)
•echolike noises produced by all our cochlea in the
•brief clicks into ear--> record response
•Women have louder EOAEs than men, from birth
(suggesting organization by hormones).
(suggesting •Women w/ twin brothers have more male-like EOAEs
•Homosexual or bisexual women also produce lower
EOAEs McFadden and Pasanen 1998 PNAS Vision
•Men have better acuity than women
•Women have higher tolerance for strong light intensity
•Women undergo light adaptation more quickly than men
•May result from protective role of
androgens during development
(androgen inhibit cell death)
•Male rats have 20% more cells in
the primary visual cortex than
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- Spring '08
- Psychology, Sex organ, external genitalia, Sexual differentiation, Rosenzweig M.R.