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Hormones, Sexual Development, & Sexual Behavior Lecture 11 Sexual Dimorphism Two forms male and female What determines your sex? Genetic determinants XX or XY XO ? Turner’s syndrome no ovaries default = FEMALE MALE Override genetic program Genotypic vs Phenotypic Sex Genotype complete genetic makeup Phenotype expression of genes Olympics & Sex Gene tests Stella Walsh XY Disqualify her? Sexual Differentiation of Body Chromosomal sex - XX or XY single gene Sex-Determining Chromosome SRY Region on the Y SRY Turns on switch testes development XX + SRY? male XY - SRY female Monozygotic nonidentical twins? Development of Reproductive Organs Primordial Gonad Indifferent gonad Potential for both sexes Medulla testes Cortex ovaries Differentiation at 6 weeks SRY medulla ----> testes No SRY cortex ----> ovaries Internal Reproductive Ducts < 6 weeks 2 sets Mullerian system = female upper vagina uterus fallopian tubes Wolffian system = male seminal vesicles vas deferens 3d month development 1 set withers SRY ---> testes testosterone Mullerian Inhibiting Hormone - MIH Mullerian Inhibiting Hormone Testes ---> scrotum Mullerian degenerates Testosterone stimulates wolffian Testosterone to female get both systems No MIH Critical periods No MIH ---> Mullerian External Genitalia Dihydrotestosterone (DHT) critical period testosterone ------------------------> DHT 5-alpha-reductase M & F - same tissue Sexual Differentiation of the Brain Masculinization Gonadotropin release patterns Female natural pattern Brain masculinized by... testosterone? Structural differences? Hypothalamus Sexually Dimorphic Nucleus - SDN Spinal Nucleus of the Bulbocavernosus Masculinization of the Brain testosterone -------------------> estradiol aromatase Aromatase present in neonates inject estradiol into neonate female brain masculinized What protects females? Rats - alpha-fetoprotein Primates - placenta? Secondary sex characteristics Puberty Increased M/F sex hormone activity Secondary characteristics maturation of genitals breasts body shape Pubic & axillary hair females- androstenedione from adrenal cortex African Spotted Hyena vicious predators Females dominate bigger, stronger, more aggressive than males Why? ovaries ---> androstendione during pregnancy converted to T rather than E low aromatase levels Masculinizes offspring highly aggressive Siblicide Sexual Development Syndromes Adrenogenital Syndrome Congenital adrenal hyperplasia prenatal adrenal cortex hyperactivity high levels of androgens partially masculinized external genitalia Androgen Insensitivity Syndrome What sex? Phenotype? Genotype? Androgen Insensitivity Syndrome Genetically XY No androgen receptors Genetic mutation - X chromosome gene Born with vagina, raised as female Undescended testes become functional at puberty. NOW WHAT HAPPENS? 5-alpha Reductase Syndrome Genetically XY Fetal 5-alpha reductase deficiency T not converted to DHT Born with vagina - raised as female At puberty Undescended testes become functional at puberty NOW WHAT HAPPENS? Hormones & Sexual Behavior Female behavior: rats Proceptive ear wiggling darting hopping Receptive - lordosis head down haunches up Male behavior: rats Mounts no testosterone ---> no mounting Intromits several times Ejaculates 4-5 times 5 min refractory period Organizational Effects of Hormones SDN & SNB Critical periods Humans - prenatal Rats - Perinatal easily manipulated Hormones: Sexual Behavior Castrate XY males at birth Later... testosterone ---> no male behavior estrogen? lordosis Brain not masculinized Ovariectomize female at birth give testosterone Later... estrogens ---> no female behavior testosterone ---> male behavior Brain masculinized Human Sexual Behavior No stereotypical M & F behaviors Men are like rats T plays a activational role Castration decline in sexual behaviors variable rate Role of oxytocin? probably not knockout mice Hormones - Women Estrogen & Progesterone no activational effects Ovariectomy has no effect Some fx on willingness to copulate increased during ovulation E & P are high Testosterone levels correlated with frequency of intercourse Oxytocin uterine and vaginal contractions sensations associated with orgasm Brain Mechanisms: Rats Male - Medial preoptic area lesion SDN ---> no sexual behavior NOT sexual motivation barpress for female Female - Ventromedial nucleus lesion- no sexual behavior Masculinizes by preventing cell death Homosexuality Sex hormones role? rats - yes Humans? NOT SURE Learning experiences? or biologically determined? Biological Factors Levels of circulating sex hormones? No Differences in brain structure? Perhaps - Where? Homosexuality Simon LeVay Brains of male AIDS victims Anterior Hypothalamus Anterior commissure SDN (rats) Humans: 3rd interstitial nucleus 3d interstitial nucleus .15 Volume mm3 .10 .05 F H-M M Anterior commissure larger in females Similar relationship Homosexuality 2 Hypotheses 1. Androgen levels low in XY fetuses that---> gay high in XX fetuses ---> lesbian Homosexuality 2 Hypotheses 2. Genetic differences in fetal brains response to androgens Xq28 - tip of the X chromosome shared by large % of gay brothers gene influences M sexual orientation?