Topics

2. Topics

3. Developmental and Activational Effects of Sex Hormones • Developmental (or “organizational”) – influencing the development of anatomical, physiological, and behavioral characteristics that differentiate the sexes • Activational – triggering reproduction-related behavior in mature individuals • Adolescent surges have both developmental and activational effects

4. Exocrine – release chemicals into ducts which carry them to their targets Sweat glands, for example Endocrine – ductless; release hormones directly into the circulatory system Only organs whose primary function is hormone release are referred to as endocrine glands Neuroendocrine System: Glands

5. Neuroendocrine System: Glands FIGURE 13.1: The endocrine glands

6. Neuroendocrine System: Glands Male testes produce sperm cells Female ovaries produce ova Sperm and ova each have 23 chromosomes Fertilization Sperm cell + ovum = zygote 23 pairs of chromosomes X and Y – sex chromosomes XX = female, XY = male

7. Classes of Hormones Amino acid derivatives Epinephrine, for example (adrenal medulla) Peptides and proteins Short and long chains of amino acids Steroids Synthesized from cholesterol (fat) Fat-soluble – able to enter cells and bind to receptors in cytoplasm or nucleus

8. Sex Steroids Released by gonads Androgens - e.g., testosterone Estrogens - e.g., estradiol Adult testes release more androgens and ovaries more estrogens Progestins – also present in both sexes Progesterone prepares uterus and breasts for pregnancy Adrenal cortex – also releases sex steroids

9. Hormones of the Pituitary “Master gland” Tropic hormones influence the release of hormones by other glands Posterior pituitary – hormones synthesized in the hypothalamus Anterior pituitary – tropic hormones

10. Hormones of the Pituitary FIGURE 13.2: A midline view of the posterior and anterior pituitary and surrounding structures

11. Cyclic vs. Steady Gonadal Hormone Levels • Female hormones go through a 28-day cycle, the menstrual cycle • Male hormone levels areconstant • Anterior pituitary activity is controlled by the hypothalamus • The hypothalamus determines whether hormone levels cycle

12. Neural Control of the Pituitary Bird research was first to implicate the control over pituitary function by the nervous system Light/dark cycling and breeding changed hormone release Lesion and stimulation experiments established the hypothalamus as the regulator of the anterior pituitary Did not explain how the signal was mediated as the anterior pituitary is not “connected” to the hypothalamus by neurons The human brain

13. Control of the Pituitary by the Hypothalamus • Posterior pituitary – neural input from hypothalamus • Vasopressin – antidiuretic hormone • Oxytocin – labor and lactation • Synthesized in hypothalamic paraventricular and supraoptic nuclei • These nuclei have terminals in the posterior pituitary • Anterior pituitary – hypothalamopituitary portal system carries hormones from the hypothalamus to the anterior pituitary

14. Control of the Pituitary by the Hypothalamus FIGURE 13.4: Control of the anterior and posterior pituitary by the hypothalamus

15. Discovery of Hypothalamic Releasing Hormones Thyrotropin-releasing hormone first isolated from the hypothalamus of sheep and then pigs Triggers the release of thyrotropin from the anterior pituitary Thyrotropin then stimulates release of hormones from the thyroid gland

16. Regulation of Hormone Levels Neural All endocrine glands (except the anterior pituitary) receive neural signals From cerebral or autonomic neurons Hormonal Tropic hormones, negative feedback Nonhormonal chemicals Glucose, Ca2+, Na+

17. Summary Model of Gonadal Endocrine Regulation FIGURE 13.5: A summary model of the regulation of gonadal hormones

18. Hormones and Sexual Development of the Body Humans are dimorphic – exist in two forms Genetic information on the sex chromosomes normally determines male or female development

19. Fetal Hormones and Development of Reproductive Organs: Gonads • Initially there is a primordial gonad • Cortex – Potential to be an ovary • Medulla – potential to be a testis • If XY, the Sry gene on the Y chromosome triggers the synthesis of Sry protein • If no Sry protein present, cortex develops into ovary

20. Fetal Hormones and Development of Reproductive Organs: Gonads FIGURE 13.6: The development of an ovary and a testis from the cortex and the medulla, respectively, of the primordial gonadal structure that is present 6 weeks after conception.

21. Fetal Hormones and Development of Reproductive Organs: Internal Reproductive Ducts • Both sexes begin with two sets of reproductive ducts • Wolffian system – male – seminal vessicles, vas deferens • Mullerian system – female – uterus, vagina, fallopian tubes • Third prenatal month: differentiation of ducts • Testes produce testosterone and Mullerian-inhibiting substance • Wolffian system develops, Mullerian degenerates, testes descend • No testes – no testicular hormones • Mullerian system develops, Wolffian degenerates

22. Internal Reproductive Ducts FIGURE 13.7: The development of the internal ducts of the male and female reproductive systems from the Wolffian and Müllerian systems, respectively

23. External Reproductive Organs • External reproductive structures – genitalia – develop from one bipotential precursor • Differentiation occurs in second month • Testosterone produces male structures • Without testosterone, female structures develop

24. Puberty Body language Personal space Explicit acts • Fertility achieved • Secondary sex characteristics develop • Features unrelated to reproduction that distinguish sexually mature men and women • Increase in release of anterior pituitary hormones • Growth hormone – acts on bone and muscle • Gonadotropic hormone • Adrenocorticotropic hormone

25. Sex Differences in the Brain • Pfeiffer first discovered a sex difference in mammalian brain function • Pfeiffer (1936) gonadectomized and implanted gonads in neonatal rats: • Transplant of testes to males or females causes steady (male) gonadotropin release pattern • Perinatal androgens lead to male pattern • Gonadectomy causes cyclic (female) gonadotropin release pattern

26. Aromatization Hypothesis Sex steroids are all derived from cholesterol and are readily converted from one to the other Aromatized testosterone becomes estradiol Evidence suggests that estradiol masculinizes the brain, at least in rodents

27. Evidence that Estradiol Masculinizes the Neonatal Brain • Neonatal injections of estradiol masculinize • Dihydrotestosterone can’t be converted to estradiol – doesn’t masculinize • Alpha fetoprotein deactivates circulating estradiol but does not cross the blood-brain-barrier • Blocking aromatization or estradiol receptors interferes with masculinizing effectsof testosterone

28. Mother’s Estradiol Doesn’t Masculinize Female Brains In female rodents, Alpha fetoprotein in blood during perinatal period … Protects the female brain from estradiol Binds to circulating estradiol, so none gets to the brain In male rodents, testosterone enters the brain and then is converted to estradiol In humans, aromatization is apparently not necessary for testosterone to masculinize brain

29. Modern Perspectives on Sexual Differentiation of the Mammalian Brain • No single mechanism can account for the development of sexual dimorphisms of mammalian brains: • Aromatase is only required for testosterone effects on masculinization in some areas of the brain • Female brain development may not automatically occur in absence of estrogens • Various dimorphisms emerge at different stages under different influences • Sex chromosomes influence brain development independent of their effect on hormones • Studies with gene knockout mice indicate that estradiol plays an active role in the female program of brain development

30. Perinatal Hormones and Behavioral Development • Masculinize – promoting male behavior (i.e., mounting) • Defeminize – preventing female behavior (i.e., lordosis) • Perinatal testosterone masculinizes and defeminizes • Neonatal castration of male rats – feminizes and demasculinizes

31. Subject: Anne S. The Case of the Woman Who Wasn’t Anne is chromosomally male, XY • Internalized testes, but no ovaries • Hormone levels are those of a man Androgenic insensitivity syndrome • Normal male androgen levels, but no response to them • She does respond to estrogens, so she effectively has more estrogens than androgens – leading to the development of female secondary sex characteristics

32. Subject: Elaine The Case of the Little Girl Who Grew into a Boy Born with somewhat ambiguous genitals but raised as a girl Developed male secondary sex characteristics in puberty Eventually diagnosed with adrenogenital syndrome

33. Subject: John/Joan The Case of the Twin Who Lost His Penis A surgeon’s error led one of a pair of male twins to be raised as a girl Artificial vagina created Estrogen administered at puberty John/Joan never felt or acted like a girl – indicates that the key to one’s gender is in the brain John/Joan chose to become John later in life, but never recovered from the ordeal David Reimer (“John”) took his life in May, 2004

34. Male Reproduction-Related Behavior and Testosterone • Effects of orichidectomy (Bremer, 1959) • Reduced sexual interest and behavior • Rate and degree of loss varies • Still have adrenal testosterone • Level of male sexuality is NOT correlated with testosterone levels in healthy men • Increasing male testosterone levels does NOT increase sex drive

35. Female Reproduction-Related Behavior and Gonadal Hormones • Rats and guineas pigs – surges of estrogen and progesterone initiate estrus, a period of fertility and receptivity • Women – sexual motivation and behavior not tied to cycle • Sex drive may be under androgenic control

36. Human Female Sexuality and Androgens Testosterone increases the proceptivity of ovariectomized and adrenalectomized female rhesus monkeys Correlations seen between sexual motivation and testosterone Testosterone found to rekindle sexual motivation in ovariectomized and adrenalectomized women

37. Anabolic Steroid Abuse • Anabolic – growth-promoting • No firm scientific evidence that muscularity and strength are increased • Sex-related side effects • High circulating hormones cause a reduction of natural release (negative feedback loop) • Men – testicular atrophy, sterility, gynecomastia (breast enlargement) • Women – amenorrhea (cessation of menstruation), sterility, hirsutism (excessive growth of body hair)

38. Neuroprotective Effects of Estradiol • Reduces brain damage if given just before or after inducing cerebral hypoxia • Reduces inflammation, encourages axonal regeneration, promotes synaptogenesis • Increases adult neurogenesis • May account for sex difference in longevity and some diseases • Possible salutary cognitive effects

39. Neural Mechanisms of Sexual Behavior Sexually dimorphic nucleus (SDN) Medial preoptic area of rat hypothalamus Larger in males, due to estradiol shortly after birth Size of male SDN correlated with testosterone levels and aspects of sexual activity Nuclei in preoptic, suprachiasmatic, and anterior regions of the hypothalamus are larger in men than in women The human brain

40. Medial Preoptic Area of the Hypothalamus Contains the SDN Destruction abolishes male sexual behavior of mammalian males and females studied, but does not affect female sexual behaviors in females Stimulation elicits copulatory behaviors Evidence favors a motivational role for male sexual behavior

41. Ventromedial Nucleus (VMN) of the Hypothalamus Contains circuits critical for female rat sexual behavior Lesion eliminates lordosis Microinjections of estrogen and progesterone induce estrus Lesions of periaqueductal gray (PAG) or the tracts to it eliminate lordosis

42. Sexual Orientation and Sexual Identity Heterosexual – sexually attracted to members of the opposite sex Homosexual – sexually attracted to members of the same sex Bisexual – sexually attracted to members of both sexes

43. Sexual Orientation and Genes • 48% homosexual concordance rate for monozygotic twins; 16% for dizygotic twins • Limited evidence for a particular gene related to homosexuality Source: Bouchard & McGue, 1981

44. Sexual Orientation and Early Hormones • Orchidectomy reduces sexual behavior of males, but does not redirect it • Non-human studies indicate that perinatal hormones can influence sexual “orientation” • Human research is less conclusive • No differences in adult hormone levels • Prenatal exposure to artificial estrogen has weak correlation with homo- or bisexuality in women • Fraternal birth order effect: younger brothers are increasingly more likely to be homosexual

45. Independence of Sexual Orientation and Sexual Identity Sexual attraction, sexual identity, and body type are sometimes unrelated Points to many possible differences in brain development, organization, and function between individuals

46. Listen: Psychology in the News: Sexuality and Gender Watch: Adolescence: Identity and RoleDevelopment and Sexual Orientation Note: To view the MyPsychLab assets, please make sure you are connected to the internet and have a browser opened and logged into www.mypsychlab.com.

47. Acknowledgments

48. Acknowledgments