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Lecture 13

Lecture 13 - Feb 28.pdf

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Department
Psychology
Course
PSYC 211
Professor
Yogita Chudasama
Semester
Winter

Description
- A castrated male rat will cease sexual activity which can be reinstated with a injection of testosterone. !  Sexual behaviour in female rats depends on estradiol and progesterone released by ovaries. - Ovariectomised rats are not sexually receptive but it can be produced by administering estradiol followed by progesterone. Reproductive Cycles: Reproductive cycle of female mammals is called the estrous cycle (menstrual cycle in primates) • • A female rat in estrous behaves differently which goads the male rat to behave differently as well The sexual behaviour of mammals is linked with ovulation (in primates, females can mate anytime • during their menstrual cycle) • Menstrual and estrous cycles are controlled by hormonal secretions of the pituitary gland and ovaries Hormonal Control of Sexual Behaviour in Laboratory Animals: • Sexual behaviour in male rats depends on testosterone released by testes Se•uA castrated male rat will cease sexual activity which can be reinstated with an injection of !  Whentestosteroneptive, the female rat arches her back which elevates • Sexual behaviour in female rats depends on estradiol and progesterone released by the ovaries • Ovariectomized rats are not sexually receptive but it can be produced by administering estradiol !  Althfollowed by progesteronent, she is active in initiating copulation; she may entice him by sniffing and nuzzling the males genitals and Sexual make quick, short hopping movements with rapid ear wiggles. • When she is receptive, the female rat arches her back which elevates her hindquarters (lordosis) !  Male rats are most responsive to a female rat on ‘heat.’ • Although a passive participant, she is active in initiating copulation; she may entice him by sniffing an nuzzling the male genitals and make quick, short hopping movements with rapid ear wiggles !  Males will ignore females whose ovaries have been removed but • injections of estradiol and progesterone will increase her • attractiveness.re females whose ovaries have been removed but injections of estradiol and progesterone will increase her attractiveness Presenting and Lordosis and earwiggle approach Genital Investigation Mounting intromission Sexual Behaviour In Male Laboratory Animals: • Intermission (entry of penis into female vagina), pelvic thrusting (rhythmic movement of the hindquarters) and ejaculation (semen discharge) are characteristics of all male mammals • When a male rat encounters a receptive female, he will spend more time sniffing, nuzzling and licking her genitals, as well as mount her and engage in pelvic thrusting 2 • He will mount her several times and intromit on most occasions but will ejaculate only after about 8-15 intromissions • After a refractory period, the male will return to copulate again • If the male is exhausted by repeated copulation with the same female, he will respond more quickly if presented with a new female • Successive introductions with new females keeps up his performance for long periods of time Behavioural Defeminization: • Androgens are male sex steroid hormones which stimulate the development of the male sex organs • Androgens have a defeminizing effect; they inhibit the later development of anatomical or behavioural female characteristics birth, behavioural defeminization will suppress the neural circuits controlling female sexual behaviour, and behavioural masculinization will allow the rat to engage in male sexual behaviour as an adult. !  If a female rat is ovariectomised at birth and then treated with testosterone as an adult, she will attempt to mount an• copulate with a receptive female. i.e. it acts as if itical time during development (shortly after were a male. birth), and treated with estradiol and progesterone as an adult, the rat will engage in female sexual behaviour • If a male rat is castrated after birth and given injections of estradiol and progesterone as an adult, it will respond to the presence of another male by assuming lordosis, i.e. It acts as if it were a female Behavioural Masculinization: • If a rodent brain IS exposed to androgens shortly after birth, behavioural defeminization will suppress the neural circuits controlling female sexual behaviour, and behavioural masculinization will allow the rat to engage in male sexual behaviour as an adult • If a female rat is ovariectomized at birth and then treated with testosterone as an adult, she will attempt to mount and copulate with a receptive female. i.e. It acts as if it were a male Behavioural Defeminization and Masculinization: Pheromones: Pheromones are chemicals that carry messages from one animal to another • • Groups of female rats when housed together show slowing down of their estrous cycle (Lee-Boot effect) 4 • Exposure to male odour (or urine) will begin the cycle again (Whitten effect) and the cycles will synchronize • A female rat will show accelerated puberty if she is exposed to male odour (Vandenbergh effect) • These effects are caused by compounds present in the urine of ‘intact’ adult males; the urine of ac astride male has no effect • Therefore, the production of pheromone requires the presence of testosterone The Bruce Effect: • If a recently impregnated mouse encounters a male mouse other than the one she mated, the pregnancy will fail • This effect is caused by a substance in the ‘intact’ male urine • Thus, a male mouse is able to prevent the birth of infants carrying another male’s genes and subsequently impregnate the female himself • This is an important survival advantage; the new male is likely to be more healthier and more vigorous thereby increasing the changes of passing genes to her offspring that are more likely to survive !  The VNO projects to the olfactory bulb which detects odours. !  The VNO responds primarily to non-volatile compounds f
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