Hormonal Influences on Sex Sexuality Hormones Sex Gender

Hormonal Influences on Sex & Sexuality

Hormones, Sex, & Gender n Dr. discovers young married woman is male! n Adolescent girl grows penis! n Baby boy undergoes sex change!

Hormones Chemical messengers n Organizational l development l critical periods n Activational l control behavior & physiological processes ~ n

Sex Hormones Steroids l derived from cholesterol n Estrogens l estradiol n Androgens l testosterone l dihydrotestosterone (DHT) ~ n

5 - a- reductase Dihydrotestosterone aromatase Estradiol Testosterone

Sexual Differentiation Sexually dimorphic n Genotypic sex l sex genes n Phenotypic sex l expression of genes ~ n

Sexual Differentiation Single gene n Sex-Determining Region on the Y n n Chromosome l SRY Testis Determining Factor (TDF) ~

Development of Reproductive Organs

Primordial Gonad Indifferent gonad l first 6 weeks n No TDF --> ovaries l cortex n TDF --> testes l medulla ~ n

Internal Reproductive Ducts Mullerian system l female n Wolffian system n l male ~

Internal Reproductive Ducts 3 d month l 1 set withers n TDF ---> testes l testosterone l Mullerian Inhibiting Hormone - MIH ~ n

External Genitalia Dihydrotestosterone n M/F same primordial tissue ~ n

Sexual Differentiation of the Brain

Sexual Differentiation of the Brain Rats n Hypothalamus l Sexually Dimorphic Nucleus (SDN) n Spinal Cord l Spinal Nucleus of the Bulbocavernosus (SNB) ~ n

Masculinization Gonadotropin release patterns l Female: cyclical l Male: steady n Brain masculinized by. . . l testosterone? n NO!--->ESTRADIOL ~

Sexually Dimorphic Nucleus male female androgenized female

Spinal Nucleus of the Bulbocavernosus M F M-A F+A

Secondary sex characteristics Puberty l Increased M/F sex hormone activity n Secondary characteristics l maturation of genitals l breasts l body shape n Pubic & axillary hair l females- androstenedione ~ n

Sexual Development Syndromes

Congenital Adrenal Hyperplasia n Prenatal adrenal cortex hyperactivity l high levels of androgens l partially masculinized external genitalia ~

Congenital Adrenal Hyperplasia

Androgen Insensitivity Syndrome Genetically XY l No androgen receptors l Genetic mutation X chromosome n Female body, brain, & gender identity l functional testes ~ n

5 - a - Reductase Syndrome Genetically XY n Fetal 5 - a - reductase deficiency l no dihydrotestosterone l genitalia not masculinized ~ n

At puberty n Undescended testes functional l Functioning penis develops l Normal male development ~

Hormones & Sexual Behavior

Sexual Behavior: Rats Controlled by sex hormones n Female l Proceptive n ear wiggling, darting, hopping Receptive - lordosis n Male l mounts l copulates ~ l

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

Hormones: Sexual Behavior Gonadectomy l at birth n Adult males l testosterone ---> no male behavior l estrogen ---> lordosis n Adult females l estrogens ---> no female behavior l testosterone ---> male behavior ~ n

Human Sexual Behavior No stereotypical M & F behaviors n Men are like rats l Testosterone: activational role n Women l Estrogens no activational effects l Testosterone levels correlated with frequency of intercourse ~ n

Homosexuality n Sex hormones role? l rats - yes l Humans? no difference in circulating hormones Learning experiences? n or biologically determined? n

Homosexuality Simon Le. Vay l Brains of male AIDS victims l Anterior Hypothalamus l Anterior Commissure n SDN (rats) l Humans: 3 rd interstitial nucleus of the Anterior Hypothalamus l INAH-3 ~ n

INAH-3 Male SDN Female

INAH-3

INAH-3 n Anterior Commissure similar relationship

Suprachiasmatic Nucleus Swaab & Hoffman (1990)

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

Homosexuality 2 Hypotheses 2. Inherited Genes n MZ twin concordance approx. 50% l DZ twins approx. 20% n Xq 28 - tip of the X chromosome l 33 of 40 pairs of gay brothers l fetal brain response to androgens ~

Nature vs. Nurture John/Joan l penis destroyed during circumcision n 1960 s - Gender deemed neutral at birth l constructed female genitalia l hormone treatment l 12 yrs old: positive results reported ~ n

Nature vs. Nurture By 14 yrs old: living as male l reconstructive surgery l male hormone treatment l married by 25 n Reassessment in 1996 l rejected female role much earlier n Pendulum swings back toward nature l sex/gender not so malleable ~ n