reproductive behavior_S12

reproductive behavior_S12 - Reproductive behavior •...

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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 metabotropic receptor. 3. Steroid hormones: Steroid hormones •Derived from cholesterol •Contain four carbon rings Mechanism: 1. Binding to membrane receptors like Neurotransmitters. 2. Entering cells and activate certain kinds of proteins in the cytoplasm. 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 glucose. 1. Sex hormones • Released by gonads • Estrogens • Progesterones • Androgens (e.g. testosterone/ DHT) DHT (Dihydrotestosterone) Steroid hormones are essential for sexual differentiation… Sexual Determination Occurs at Various Levels: Chromosomal sex Chromosomal Gonadal sex Hormonal sex Morphological sex Behavioral sex Levels of Sexual Determination: Levels Chromosomal sex Sexual Development: Genetic Sex Your genetic sex is determined by your biological father’s Your genetic sperm. sperm •Sperm and ova contain only ONE of Sperm ONE each of the 23 pairs of chromosomes. each •22 of the 23 chromosomes will 22 determine your physical characteristics, independent of gender. independent •The last pair differentiate genetic males The genetic from females. from Why? •If Y then SRY (sex determining region of Y) (sex If •If SRY then TDF (testis determining factor) (testis If Sexual Differentiation: Sex Organs • Gonads testes & ovaries • Internal Sex Organs Wolffian & Mullerian ducts • External Genitals Differentiation of gonads and internal sex organs Differentiation Y --> SRY --> TDF --> --> gonads become testes and begin testosterone (T) gonads 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 fertilization Sexual Development: Gonadal Sex Sexual Y SRY TDF Testes AMH & Androgens Mullerian withers Wolffian develops Sexual Development: External Genitalia Embryonic Development : Urogenital sinus differentiates into male or Urogenital female genitalia. - Genital tubercle --> clitoris/penis Genital - Genital folds --> labia/scrotum Genital DHT (Dihydrotestosterone) essential for the development of the male external genitalia. male 5-alpha-reductase converts T to DHT. No androgens --> Female external No genitalia genitalia What if something abnormal occurs during these steps? 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 and androgens. – 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 XY males Results in incomplete masculinization of external genitalia. At birth, they are often assigned as females. 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 •prenatal •permanent • Activational •after organ differentiation •temporary Sexual Differentiation of the Nervous System Sexual Y (sry) Undifferentiated gonads No sry No TDF No testes Testes Antimullerian hormone and testosterone Inhibits female system and promotes male differentiation T will bind androgen receptors, this steroid receptor 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 Treating male-like. male-like. •Castrating males at birth results in the POA being more femalelike. •It is not T itself that masculinizes the POA, but rather a metabolite It 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? Why 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 Alpha-fetoprotein 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 occurs. • Studies suggest that women become more sexually responsive during this time when estrogen levels are high. – 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 • Oxytocin • Stimulates contraction of the uterus during delivery of a baby • Stimulates the mammary gland to release milk • Released during orgasm and triggers a state of complete relaxation. • 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? behave Or is gender-sensitive behavior a result of strictly our Or upbringing? 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 mechanical objects -Use dark colors. -Use bird’s-eye-view composition when they draw. Girls: Girls: -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 unaffected girls. 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 e.g.) aggressive, and express more rough and tumble patterns than females: than Give perinatal androgens to female offsprings --> Give 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? differences Organizational stage --> brain differences (size) --> differences in behavior? 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 temporal gyrus Structures connecting hemispheres: Females: Corpus callosum, anterior commisure, intermediate thalamus Other differences: 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? sexual Sensation and perception. Women have higher sensory acuity Women in all senses except visual. in Olfaction • Women are 1000 times more sensitive to musk-like odors Women • 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). olfactory • This decreases during menstruation and late pregnancy This • Generally, hormonal signals affect olfactory sensitivity in women. Generally, • Women with irregular menstrual cycles showed reduced olfactory sensitivity olfactory women Women had 8X greater response Women to olfactory stimulation than men. to men Taste Taste •Women are better at discriminating tastes than Women men, especially bitter tastes men, •Differences appear after puberty and increase Differences during pregnancy and during the follicular phase, and are diminished after menopause. and •Studies show that during increased estrogen Studies women also have a higher preference for sweet tastes. tastes. Audition Click-evoked otoacoustic emissions (EOAEs) Click-evoked •echolike noises produced by all our cochlea in the echolike inner ear. inner •brief clicks into ear--> record response •Women have louder EOAEs than men, from birth Women (suggesting organization by hormones). (suggesting •Women w/ twin brothers have more male-like EOAEs •Homosexual or bisexual women also produce lower Homosexual EOAEs EOAEs McFadden and Pasanen 1998 PNAS Vision 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 May androgens during development (androgen inhibit cell death) (androgen •Male rats have 20% more cells in Male the primary visual cortex than females. females. ...
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