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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

  • Early Sexual Development

  • Hormonal Control of Sexual Behavior

  • Neural Control of Sexual Behavior

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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

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Sexual Development

  • “Nature’s Impulse is to create a female”

  • In the absence of androgen, female pattern develops:

    • Müllerian system

    • External genitalia

    • Brain

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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)

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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

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Female Hyena Pup & Mom

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Pelvic thrusting



Lordosis response




Adult Sexual Behaviors (Rodent)

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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

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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

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    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.

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    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)

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    • 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

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    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)

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    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

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    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

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    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

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    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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