1. Hormones, Sexual Development, & Sexual Behavior Lecture 11

2. Sexual Dimorphism n Two forms male and female n What determines your sex?

3. Genetic determinants n XX or XY n XO ? Turner’s syndrome no ovaries n default = FEMALE n MALE Override genetic program

4. n Genotype complete genetic makeup n Phenotype expression of genes Genotypic vs Phenotypic Sex

5. Olympics & Sex n Gene tests n Stella Walsh l XY n Disqualify her?

6. Sexual Differentiation of Body n Chromosomal sex - XX or XY n single gene n S ex-Determining R egion on the Y Chromosome l SRY

7. SRY n Turns on switch testes development n XX + SRY? male n XY - SRY female n Monozygotic nonidentical twins?

8. Development of Reproductive Organs

9. Primordial Gonad n Indifferent gonad Potential for both sexes n Medulla testes n Cortex ovaries

10. Differentiation n at 6 weeks n SRY medulla ----> testes n No SRY cortex ----> ovaries

11. Internal Reproductive Ducts n < 6 weeks 2 sets n Mullerian system = female upper vagina uterus fallopian tubes

12. n Wolffian system = male seminal vesicles vas deferens n 3d month development 1 set withers n SRY ---> testes testosterone Mullerian Inhibiting Hormone - MIH

13. Mullerian Inhibiting Hormone n Testes ---> scrotum n Mullerian degenerates Testosterone stimulates wolffian n Testosterone to female get both systems No MIH n Critical periods No MIH ---> Mullerian

14. External Genitalia n Dihydrotestosterone (DHT) critical period testosterone ------------------------> DHT 5-alpha-reductase n M & F - same tissue

15. Sexual Differentiation of the Brain

16. Masculinization n Gonadotropin release patterns Female natural pattern n Brain masculinized by... testosterone? n Structural differences? l Hypothalamus l Sexually Dimorphic Nucleus - SDN l Spinal Nucleus of the Bulbocavernosus

17. testosterone -------------------> estradiol aromatase n Aromatase present in neonates n inject estradiol into neonate female brain masculinized n What protects females? n Rats - alpha-fetoprotein n Primates - placenta? Masculinization of the Brain

18. Secondary sex characteristics n Puberty n Increased M/F sex hormone activity Secondary characteristics maturation of genitals breasts body shape n Pubic & axillary hair females- androstenedione from adrenal cortex

19. African Spotted Hyena n vicious predators n Females dominate - bigger, stronger, more aggressive than males

20. Why? n ovaries ---> androstendione during pregnancy n converted to T rather than E low aromatase levels n Masculinizes offspring highly aggressive n Siblicide -

21. Sexual Development Syndromes

22. Adrenogenital Syndrome n Congenital adrenal hyperplasia n prenatal adrenal cortex hyperactivity n high levels of androgens n partially masculinized external genitalia

23. Androgen Insensitivity Syndrome n What sex? n Phenotype? n Genotype?

24. Androgen Insensitivity Syndrome n Genetically XY - No androgen receptors n Genetic mutation - X chromosome gene n Born with vagina, raised as female n Undescended testes become functional at puberty. n NOW WHAT HAPPENS?

25. 5-alpha Reductase Syndrome n Genetically XY n Fetal 5-alpha reductase deficiency n T not converted to DHT n Born with vagina - raised as female

26. At puberty n Undescended testes become functional at puberty n NOW WHAT HAPPENS?

27. Hormones & Sexual Behavior

28. Female behavior: rats n Proceptive ear wiggling darting hopping n Receptive - lordosis head down haunches up

29. Male behavior: rats n Mounts no testosterone ---> no mounting n Intromits several times n Ejaculates 4-5 times 5 min refractory period

30. Organizational Effects of Hormones n SDN & SNB n Critical periods Humans - prenatal Rats - Perinatal easily manipulated

31. Hormones: Sexual Behavior n Castrate XY males at birth n Later... testosterone ---> no male behavior estrogen? lordosis n Brain not masculinized

32. n Ovariectomize female at birth give testosterone n Later... estrogens ---> no female behavior testosterone ---> male behavior n Brain masculinized

33. Human Sexual Behavior n No stereotypical M & F behaviors n Men are like rats T plays a activational role n Castration - decline in sexual behaviors variable rate n Role of oxytocin? probably not knockout mice

34. Hormones - Women n Estrogen & Progesterone no activational effects Ovariectomy has no effect n Some fx on willingness to copulate increased during ovulation E & P are high

35. n Testosterone levels correlated with frequency of intercourse n Oxytocin uterine and vaginal contractions - sensations associated with orgasm

36. Brain Mechanisms: Rats n Male - Medial preoptic area lesion SDN ---> no sexual behavior NOT sexual motivation barpress for female n Female - Ventromedial nucleus lesion- no sexual behavior Masculinizes by preventing cell death

37. Homosexuality n Sex hormones role? rats - yes Humans? NOT SURE n Learning experiences? n or biologically determined?

38. Biological Factors n Levels of circulating sex hormones? No n Differences in brain structure? Perhaps - Where?

39. Homosexuality n Simon LeVay Brains of male AIDS victims Anterior Hypothalamus Anterior commissure n SDN (rats) Humans: 3rd interstitial nucleus

40. 3d interstitial nucleus Volume mm 3.15.10.05 n Anterior commissure larger in females n Similar relationship F H-M M

41. Homosexuality 2 Hypotheses n 1. Androgen levels low in XY fetuses that---> gay high in XX fetuses ---> lesbian

42. 2. Genetic differences in fetal brains response to androgens Xq28 - tip of the X chromosome n shared by large % of gay brothers - n gene influences M sexual orientation? Homosexuality 2 Hypotheses