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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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lecture outline
Lecture Outline
  • Early Sexual Development
  • Hormonal Control of Sexual Behavior
  • Neural Control of Sexual Behavior
markers of sex
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
sexual development
Sexual Development
  • “Nature’s Impulse is to create a female”
  • In the absence of androgen, female pattern develops:
      • Müllerian system
      • External genitalia
      • Brain
male sexual development
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)
alterations in development
Androgen insensitivity


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
adult sexual behaviors rodent


Pelvic thrusting



Lordosis response




Adult Sexual Behaviors (Rodent)
adult sexual behavior females and hormones
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
adult sexual behavior males and hormones
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
anabolic steroid abuse
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.
sexual orientation
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)
  • 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
neural control of male sexual behavior
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)
medial preoptic area
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
neurotransmitters and male sexual behavior
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
female sexual behavior ventromedial hypothalamus
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
hormonal effects via the vmh
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