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Topic 18 Sex and the Brain Lange

Topic 18 Sex and the Brain Lange. Biology 463 - Neurobiology. Introduction. Influence of brain on sex hormones…. and the influence of the sex hormones back on the brain. Sexual and reproductive behaviors Male and female brains. Sex and Gender.

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Topic 18 Sex and the Brain Lange

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  1. Topic 18 Sex and the Brain Lange Biology 463 - Neurobiology

  2. Introduction Influence of brain on sex hormones…. and the influence of the sex hormones back on the brain. • Sexual and reproductive behaviors • Male and female brains

  3. Sex and Gender • Concepts of Gender are very much inter-realated, but will involve specifics of: • Biological characteristics of gender associated with architecture: • Morphology • Organization of the brain • Gender features associated with psychology and perception: • Self-assessment • Societal expectations • Gender-identity • Perception of gender • Gender features associated with biochemistry: • Genetics • Hormones

  4. 44 + XY 44 + XX Parents 22 + X 22 + XY 22 + Y Ova Sperm 44 + XY 44 + XX Zygotes (offspring) (a) The X-Y system 22 + XX 22 + X (b) The X-0 system 76 + ZW 76 + ZZ (c) The Z-W system 16 (Haploid) 32 (Diploid) (d) The haplo-diploid system Some chromosomal systems of sex determination Female = default sex Male = default sex Male = default sex Male = default sex

  5. Sex and Gender The Genetics of Sexual Determination • Y Chromosome encodes testis-determining factor (Tdf) • Tdf is produced from the SRY gene on Y chromosome • Guides development of testes and production of testicular hormones • Promotes fetal development as male

  6. Sex and Gender Differentiation of fetus and development of gonads

  7. Hormones regulate physiological processes Sex hormones: Steroidal hormones Endocrine glands: Gonads release sex hormones Pituitary gland: Regulates endocrine glands (LH & FSH) Small structural differences affects function of hormone Primary “male” hormones: androgens (testosterones) Primary “female” hormones: estradiols and progestins The Hormonal Control of Sex

  8. The Hormonal Control of Sex The Principle Male and Female Hormones in adulthood • Men: High concentration of androgens • Women: High concentration of estrogens & progestins Aromatization Process for Steroid Hormones: Testosterone (androgen) + aromatase  estradiol (estrogen)

  9. The Hormonal Control of Sex Concentration of estradiol receptors in sagittal section of rat brain

  10. The Hormonal Control of Sex • Males: Testes- release androgens • Androgens (testosterones) – increase at puberty leads to development of secondary sex characteristics • Females: Ovaries- secrete estradiol (estrogens) and progesterone (progestins) For both sexes, blood concentrations of sex hormones vary: • Males- levels fluctuate mildly during a 24 hour cycle • Females- levels fluctuate more extensively but on a 28-day cycle

  11. The Hormonal Control of Sex Pituitary and Hypothalamus Control of Sex Hormones • Gonadotropins: LH and FSH • Males- LH stimulates testosterone; FSH aids sperm maturation • Females- LH, FSH cause estrogen secretion

  12. The Neural Basis of Sexual Behaviors Mammalian Mating Strategies: • Polygyny • Male mates with many females • Polyandry • Female mates with many males • Monogamy • One mate

  13. The Neural Basis of Sexual Behaviors • The Neurochemistry of Reproductive Behavior • Prairie voles: Solidly monogamous • Meadow voles: Asocial and promiscuous • Affected by oxytocin and vasopressin… Prairie voles exhibit higher levels of vasopressin and oxytocin…. Suggesting a role in the brain

  14. The Neural Basis of Sexual Behaviors Role of oxytocin and vasopressin receptors in reproductive behavior • Prairie voles display more oxytocin receptors in females and more vasopressin receptors in males • Meadow voles, fewer receptors in both sexes

  15. Why and How Male and Female Brains Differ Sexual Dimorphisms of the CNS • Sexually dimorphic nucleus (SDN) • INAH in humans analogous to rat SDN

  16. Why and How Male and Female Brains Differ • Organizational effect of hormones • Tend to be irreversible • Activational effect of hormones • Tend to be temporary

  17. Why and How Male and Female Brains Differ An example of the activational effects of hormones… in the somatosensory cortex, the plasticity of the ventral surface for the nipples increases by ~100% to encourage lacation . This increase in sensation is associated also with increases in prolactin, oxytocin, and a variety of birthing, parental care, and reproductive behaviors.

  18. Why and How Male and Female Brains Differ Sexual Orientation • INAH-3 - twice as large in heterosexual males compared to heterosexual females: Sexually dimorphic • INAH-3 in homosexual males: Similar in size to that in heterosexual females • INAH – 3 in homosexual females does not appear to differ from heterosexual females • See Levay, 1991.

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