Hormonal Control of Sexual Behavior - Psychology Notes PDF

HORMONAL CONTROL PUBERTY hypothalamus kisspeptin pituitary follicle-stimulating hormone (FSH) luteinizing hormone (LH) kisspeptin HORMONAL CONTROL OF FEMALE REPRODUCTIVE CYCLES human and great apes have menstrual Both menstrual and estrous cycles are controlled by the two ovarian hormones es...

HORMONAL CONTROL PUBERTY hypothalamus kisspeptin pituitary follicle-stimulating hormone (FSH) luteinizing hormone (LH) kisspeptin HORMONAL CONTROL OF FEMALE REPRODUCTIVE CYCLES human and great apes have menstrual Both menstrual and estrous cycles are controlled by the two ovarian hormones estradiol and progesterone Menstrual cycle • Female reproductive cycle of most primates, including humans Estrous cycle • Female reproductive cycle of most mammals (other than most primates) • Characterized by menstruation (if pregnancy does not occur), concealed ovulation, and the absence of a mating season. • Females that have estrous cycles do not menstruate; they reabsorb their endometrium. They also display clear outward signs of ovulation and fertility. • Sexual arousal is somewhat influenced by ovarian hormones, but ability to mate is not. Animals with a menstrual cycle exhibit sexual activity throughout the cycle. • They are typically only sexually active during the estrous phase of their cycle, which is referred to as being “in heat”. This change in physiology and behavior alters the behavior of nearby males. HUMAN FEMALE SEXUAL BEHAVIOR Relative to the estrous cycle, menstrual cycles are associated with only very small fluctuations in sexual behaviour and sexual desire. no fluctuattion in sexual behaviour following the cycle Mean scores of care-giving, care-receiving, in-pair sexual desire, and extra-pair sexual desire as a function of menstrual cycle phase in adult women. HORMONAL CONTROL OF SEXUAL BEHAVIOR • The organizational effects of hormones on the body (i.e. sex organs) is largely over by birth. However, the organizational effects of hormones on the brain continues for a few weeks after birth, at least in rodents. • One consequence of this is that we can masculinize or feminize the brain of rodents by altering hormone signaling immediately after birth, after the anatomical development of their sex organs is complete. • For example, when male rodents are castrated at birth (which stops further androgen signaling), they develop some female-typical behaviours. If they are injected with female sex hormones in adulthood (estradiol and progesterone), they will try to get other males to have sex with them (i.e., they will assume lordosis in the presence of other males). • Injections of female sex hormones in non-castrated male rats (or males castrated in adulthood) have relatively small behavioural consequences, at least following single injections. RODENT FEMALE SEXUAL BEHAVIOR This chart shows how female rats respond in adulthood when given injections of male or female sex hormones, depending on whether or not they were given testosterone injections immediately after birth. HORMONAL CONTROL OF SEXUAL BEHAVIOR • Similar phenomena are seen in humans. Human adrenal glands, which are present in men and women, typically secrete a small amount of androgens. However, some people’s adrenal glands secrete abnormally large amounts of androgens, which can start either before or after birth. • In males, excess androgen signaling from adrenal glands has minimal effect, since their testes already secrete tons of androgens. However, in females, excess androgen signaling can cause some degree of masculinization of either the body or brain or both. If the condition is present at birth, it is congenital adrenal hyperplasia (CAH). • Depending on the amount of androgen signaling during development, sex organs can become slightly masculinized (e.g., enlarged clitoris, partially fused labia). Brain anatomy and function can also be masculinized. Females with CAH have a higher likelihood of identifying as a man and being sexual attracted to women in comparison to other females. • The implications of this research are that sexual orientation and gender identity might be determined by the timing and effectiveness of androgen signaling in the brain during early development. FEMALE SEXUAL BEHAVIOR NEURAL CIRCUITRY By injecting transneuronal retrograde tracer in muscles responsible for lordosis response in female rats, researchers identified the important neural pathways: VMH → PAG → nPGi → motor neurons in spinal cord FEMALE SEXUAL BEHAVIOR NEURAL CIRCUITRY Ventromedial nucleus of hypothalamus (VMH) Large nucleus in the hypothalamus that plays essential role in female sexual behavior. In rodents… • Electrical stimulation of VMH facilitates female sexual behavior. • Injections of estradiol and progesterone directly into VMH also stimulates sexual behavior, even in females whose ovaries have been removed. • Female with bilateral lesions of VMH will not display lordosis, even if she is treated with estradiol and progesterone MALE SEXUAL BEHAVIOR NEURAL CIRCUITRY The important neural pathways for male sexual behavior include: mPOA → PAG → nPGi → motor neurons in spinal cord MALE SEXUAL BEHAVIOR NEURAL CIRCUITRY Medial Preoptic Area (mPOA) Nucleus in the anterior hypothalamus that plays essential role in male sexual behavior. • Electrical stimulation of mPOA in rodents elicits male copulatory behavior. • Within the mPOA, there is an area called the sexually dimorphic nucleus (SDN) of preoptic area. This nucleus is much larger in males than in females. • Lesioning the mPOA of female rats does not affect their sexual behavior, but it does cause them to ignore their offspring. This figure shows the preoptic area of a rat brain in (a) a typical male, (b) a typical female, and (c) an androgenized female that was given testosterone immediately after birth. SDN = sexually dimorphic nucleus of the preoptic area; OC = optic chiasm; V = third ventricle; SCN = suprachiasmatic nucleus; AC = anterior commissure.