Chapter 9: Reproductive Behaviors
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
Mullerian system or Wolffian system
External reproductive
Sexual Development
"Nature’s Impulse is to create a female"
In the absence of androgen, female pattern develops:
Mullerian system
External genitalia
Brain
Male Sexual Development
SRY gene on XY chromosome induces development of testis
Testes secrete:
Anti-Mullerian hormone (defeminizing effect)
Androgens: stimulate Wolfiian system development
External male reproductive structures require dihyrotestosterone (androgen)
Adult Sexual Behaviors (Rodent)
Male
Intromission
Pelvic thrusting
Ejaculation
Female
Lordosis response
Receptivity
Proceptivity
Attractiveness
Adult Sexual Behavior: Male
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
Adult Sexual Behavior: Female
Organizational: Lack of exposure to androgens results in feminization
Adult sexual behavior depends on
Estrogen followed by progesterone: facilitates:
Receptivity, proceptivity, and attractiveness
Oxytocin: contributes to orgasm
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
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
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
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
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