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Lecture Outline

Lecture Outline . Early Sexual Development Hormonal Control of Sexual Behavior Neural Control of Sexual Behavior. Markers of Sex. Genetic: XX or XY (23rd chromosome pair) Gonadal: testes or ovaries Hormonal: Estrogen/androgen Internal reproductive: presence of

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Lecture Outline

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  1. Lecture Outline • Early Sexual Development • Hormonal Control of Sexual Behavior • Neural Control of Sexual Behavior

  2. Markers of Sex • Genetic: XX or XY (23rd chromosome pair) • Gonadal: testes or ovaries • Hormonal: Estrogen/androgen • Internal reproductive: presence of • Müllerian system or Wolffian system • External reproductive

  3. Sexual Development • “Nature’s Impulse is to create a female” • In the absence of androgen, female pattern develops: • Müllerian system • External genitalia • Brain

  4. Male Sexual Development • Sry gene on Y chromosome induces development of testis (H-Y antigen) • Testes secrete: • Anti-Müllerian hormone (defeminizing effect) • Androgens: stimulate Wolffian system development • External male reproductive structures require dihydrotestosterone (androgen)

  5. Androgen insensitivity XY-females Adrenogenital syndrome Deficit in adrenal cortisol release Adrenal hyperactivity Excess adrenal androgens Turner’s syndrome- XO, apparent female no ovaries Sex reassignments-1975 twin’s case. Other species- e.g. Hyena Increasingly earlier onset of puberty in humans No real external hermaphrodites Alterations in Development

  6. Female Hyena Pup & Mom

  7. Male Intromission Pelvic thrusting Ejaculation Female Lordosis response Receptivity Proceptivity Attractiveness Adult Sexual Behaviors (Rodent)

  8. Adult Sexual Behavior: Females and Hormones • Organizational: Lack of exposure to androgens results in feminization • In humans: • Menstrual cycle • Other influences-male initiation • Androgens- sex drive • Rodent Adult sexual behavior depends on • Estrogen followed by progesterone: facilitates: • Receptivity, proceptivity, and attractiveness • Oxytocin: contributes to orgasm

  9. Adult Sexual Behavior: Males and Hormones • Early androgen exposure promotes: • Behavioral defeminization as an adult • Behavioral masculinization • Due to estrogen derived from testosterone • Activational effects: • Male sexual behavior requires testosterone, estrogen • Oxytocin may contribute to orgasm • Vasopressin may mediate male sexual refractory period • Contrary to popular belief: • Levels of sexuality (macho) are not correlated with levels of testosterone. • Sex drive is not increased with increases in testosterone

  10. Anabolic Steroid Abuse • Males- • increases musculature, athletic performance. • Used cosmetically. • Causes tissue damage, emotional changes, testicular atrophy, breast development ,oral-liver damage. • Females- • Causes masculinization –many symptoms.

  11. Sexual Orientation • Most work on males • Genetic factors • twin studies • Hormones • Early exposure to synthetic estrogens cause high rates of female bisexuality • Congenital adrenal hyperplasis-increases homosexuality in females (ca. 48%), normal males. • Brain differences- • size, lateralization, anatomy (SCN, ant. commisure, INAH-3). • Identity-(BNST)

  12. Pheromones • Rodents and most mammals: • Vomeronasal organ- accessory olfactory bulb • Lee-Boot– estrous ceases in grouped females • Whitten - male urine reinitiates estrous • Vandenberg - male urine speeds onset of puberty. • Bruce- new male urine aborts pregnancy. • In human females: olfactory stimuli • Synchronized menstrual cycles • Androstenol- increased social interaction • Little evidence for sex attractants

  13. Neural Control of Male Sexual Behavior • Adult sexual behavior depends on sufficient plasma testosterone • Hormone effects activity of • Sensory neurons on sex organs • Spinal cord neurons that participate in sexual reflexes (e.g. bulbocavernous nuc.) • Neurons within medial preoptic area (MPA)

  14. Medial Preoptic Area • MPA involvement in male sexual behavior: • MPA contains testosterone receptors • Infusions of testosterone into MPA restore copulation in castrated rats • MPA neurons are active during copulation • Both firing rate and c-fos studies • Electrical stimulation of MPA induces copulation • Lesions of the MPA disrupt copulation

  15. Neurotransmitters and Male Sexual Behavior • Oxytocin: increases likelihood of penile erections, speeds latency to ejaculation • Vasopressin: may facilitate male sexual behavior • Dopamine: may facilitate male sexual behavior • Sexual activity increases dopamine release within the MPA • Intra-MPA infusion of DA antagonist impairs male copulation

  16. Female Sexual Behavior: Ventromedial Hypothalamus • VMH may play a critical role in modulating female sexual behavior in rats: • VMH lesions block lordosis in female rats after estrogen/progesterone • Electrical stimulation of VMH facilitates lordosis • Copulation is associated with fos production in the VMH (and amygdala) • Connections of VMH with amygdala and PAG

  17. Hormonal Effects Via the VMH • Female sexual behavior is influenced by: • Estrogen/progesterone: • VMH infusions restores sexual activity in ovariectomized rats • Oxytocin • Receptors are found within the VMH • Oxytocin receptors depend on earlier estrogen/progesterone treatments • Oxytocin infusions into VMH facilitate female sexual behavior • VMH infusions of oxytocin antagonist decrease female sexual behavior

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