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Lecture 10-sexual reproduction

Lecture 10-sexual reproduction - Sex and Reproduction •...

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Unformatted text preview: Sex and Reproduction • Gonadal hormones • Sexual differentiation • Copulation • Parental behavior Sexual differentiation For • For species that reproduce sexually, each individual must become either male or female Sexual differentiation is the Sexual process by which individuals develop with male or female develop bodies and behavior behavior For mammals, this process For begins before birth and continues throughout adult life life • • Genotype of sperm determines sex The • The key event in sex determination is whether the sperm contains an X or Y chromosome chromosome Mammals that receive an X Mammals chromosome from the father will become female father Those that receive a Y Those chromosome will become male male The mother always The contributes an X chromosome chromosome XY = male; XX = female • • • • Gonad development Very • Very early in development, individuals have a pair of indifferent gonads gonads During • During the first month of gestation in humans, the indifferent gonads begin changing into ovaries or testes ovaries SRY: sex determination Sex • Sex chromosomes direct sexual differentiation of the gonads the n • IIn mammals, the Y chromosome contains the SRY gene SRY SRY • SRY = sex determining region of the Y chromosome chromosome The • The SRY gene is responsible for the development of the testes development SRY: sex determination Very • Very early into development, in individuals with a Y chromosome, the indifferent gonad make Sry protein protein The • The Sry protein causes the indifferent gonad to develop into the testes into f • IIf no Y chromosome (or no functional SRY gene), then indifferent gonad develops into the ovary into Masculinization Gonadal • Gonadal hormones direct sexual differentiation of the body body Developing testes produce Developing several hormones several Developing ovaries produce Developing very little very Bodies are ‘preset’ to develop Bodies female… but masculinize if testes are present and secrete testosterone testosterone • • • Wolffian and Mullerian systems The • The early fetus has a genital tubercle that can form either a clitoris or a penis clitoris As well as two ducts As that connect the indifferent gonads to the out body wall… the wolffian ducts and the mullerian ducts mullerian In females, the In mullerian ducts develop into fallopian tubes, uterus and inner vagina • • Wolffian and Mullerian systems n • IIn males, hormones secreted by the testes cause the wolffian ducts to develop into the epididymis, vas deferens, and seminal vesicles and This system is This masculinized by testosterone (which promotes the development of the wolffian system of And anti-mullerian And hormone (which induces regression of the mullerian Wolffian duct system) system) • • Wolffian and Mullerian systems n • IIn the absence of testes, these hormones are not present and the genital tract develops into a feminine pattern (i.e. the wolffian ducts regress and the mullerian ducts develop into components of the female internal reproductive tract; fallopian tubes, uterus) uterus) Mullerian duct Androgens masculinize Testosterone • Testosterone masculinizes non-wolffian derived structures structures Testosterone is converted Testosterone to dihydrotestosterone and this causes issue around the urethra to form the prostrate gland, scrotum and penis and • Androgens masculinize Testosterone • Testosterone masculinizes non-wolffian derived structures structures Testosterone is converted Testosterone to dihydrotestosterone and this causes issue around the urethra to form the prostrate gland, scrotum and penis and If androgens are absent, the prostrate fails to form and the external skin grows into the labia and clitoris clitoris • • Hormones guide sexual differentiation So • So the chromosomes determine the sex of the gonad gonad The gonadal hormornes The then drive sexual differentiation for the rest of the body of Later in life, both Later hormones and experience guide sexual differentiation and the development of gender identity identity • • Androgen receptors Androgen • Androgen insensitivity • • • • syndrome syndrome The gene for the androgen The receptor is located on the X chromosome chromosome An XY individual that has a An dysfunctional androgen receptor gene does not respond to androgen that is produced produced They have SYR so they have They testes development testes The testes then produce The androgen androgen Anti­mullerian hormone And • And the testes produce AMH which inhibits the mullerian duct structures duct In the absence of working In androgen receptors, the wolffian ducts fail to develop and the external tissue forms labia and a clitoris labia These individuals look like XX These females at birth and develop breasts at puberty breasts But they lack ovaries and a But uterus, so AIS identified when no menstrual cycle no • Testosterone & AMH • • Preoptic area of the hypothalamus There • There is a region in the preoptic area of the hypothalamus that is much larger in males than females larger The • The sexually dimorphic nucleus of the POA nucleus Organizationally • Organizationally controlled, castrated males have smaller SDN-POA, SDN-POA, Females • Females adrogenized at birth have large male-like SDNhave POA Hypothalamus to gonad Hypothalamus to gonad The • The gonads produce steroid hormones and regulate reproduction reproduction Gonads consists of two Gonads different sub-compartments, one produces the hormones and one produces the gametes gametes Gonadal hormones are critical Gonadal for triggering both reproductive behavior controlled by the brain and gamete production gamete • • Testes Testes • Testes are sperm producing cells that secrete the sex steroid testosterone (an androgen) androgen) The hypothalamus releases The gonadotropin-releasing hormone (GnRH) into the anterior pituitary anterior Anterior pituitary releases Anterior luteinizing hormone (LH) and follicle stimulating hormone (FSH) (FSH) Which travels through the Which blood and acts to release testosterone from the testes testosterone • • • Gonadal Hormones: Male Testosterone • Testosterone is produced in • • • • Leydig cells of testes Leydig Testosterone is responsible Testosterone for the development and maintenance of male reproductive organs reproductive generates male secondary sex generates characteristics characteristics development/differentiation of development/differentiation reproductive organs reproductive muscle mass Gonadal Hormones: Male Gonadal Hormones: Male Androgens and Brain Testosterone • Testosterone found in both males and females (> males) females Interacts with androgen receptors in brain Sexual motivation (desire) in both men and women; aggression?? May have role in memory Male-typical sexual behavior (mounting) Ovaries Female • Female gonads that produce mature gametes, ova (eggs) and sex steroid hormones and Hormone secretion from Hormone ovaries is more complicated than it is in the testes than Ovarian hormones are Ovarian produced in cycles produced The duration of the cycle The differs depending on the species species Human ovarian cycle is 4 Human weeks weeks Rat cycle is 4 days • • • • • Ovaries The • The ovary produces two major • • • • • classes of steroid hormones classes Progestins (hormones that Progestins help maintain pregnancy) help Progesterone Estrogens (important for Estrogens sexual receptivity) sexual Estradiol Estrus- scientific term for Estrusperiodic sexual receptivity in females of many species females Gonadal Hormones: Female • Estrogens (estradiol) produced in ovaries secondary sex characteristics development and differentiation of reproductive organs reproductive cycle and sexual behavior (lordosis) in rats Estrogens and Brain Estrogen • Estrogen found in both males and females (>females) Interacts with estrogen receptors in brain Role in memory and cognition Hormone replacement therapy may improve memory Female-typical sexual behavior (lordosis) Gonadal Hormones: Female Progestins • Progestins (progesterone) (progesterone) produced in ovaries thicken uterine wall for egg implantation reduce uterine contractility fall in progesterone at childbirth triggers milk production Progesterone and Pregnancy Progesterone • Progesterone levels increase greatly during pregnancy pregnancy Prepare • Prepare breasts for lactation lactation Reduce • Reduce contractility of uterus (reduces chance of spontaneous abortion) spontaneous Reproductive behavior • 1) sexual attraction • 2) appetitive behavior • 3) copulation 4) • 4) postcopulatory behavior behavior Sexual attraction To • To reproduce, males and females must produce a set of behaviors in a precise and intricately coordinated sequence to successfully reproduce reproduce The first stage in bringing males The and females together and Sexual attraction is most often Sexual synchronized with physiological readiness to reproduce readiness Attraction and sexual response Attraction influenced by experience influenced • • • Sexual attraction n • IIn the lab, attractiveness is assessed by how quickly potential mates approach potential By manipulating By appearance it can be determined which physical traits are important for sexual attraction Males often attracted to Males sight or smells of females that are in heat caused by increased estrogen production production • • Sexual attraction Since • Since estrogen secretion is associated with the release of eggs, mechanisms that increase attractiveness during increased estrogen synchronize desire to mate and peak fertility mate Appetitive behavior f • IIf animals are mutually attracted they engage in appetitive behaviorbehaviors that establish, maintain, or promote sexual interaction interaction Females approach the male Females and ‘hop’ and ‘dart’ and Thus…advertising that they Thus…advertising are ready to mate (proceptive) (proceptive) Males are less complicated, Males they approach and stay near the female near • • • Copulation When • When both male and female show appetitive behaviors, they move on to copulation to When stimulation When reaches a threshold, the male ejaculates spermmale bearing semen into the bearing female female After one bout of After copulation, animals will not mate for a bout of time (this is called the refractory period) refractory • • Copulation The • The refractory phase varies from minutes to months (depending on species to circumstances) circumstances) Many animals will resume Many mating faster if they are provided with a new partner (called the Coolidge effect) (called In most species, the female In chooses when copulation occurs and is based on if the female is in heat (i.e. in estrus; or sexually receptive) or • • Copulation: females Postcopulatory behavior • Grooming • Copulatory lock n • IIn dogs, the penis swells for 10 to 15 minutes and cannot be removed during this period this Bringing gametes together Copulation • Copulation brings gametes • • • together for reproduction together Successful reproduction Successful occurs when there is fertilization (fusion of sperm and egg) and In most fish and frogs, males In and females release their gametes into the water and fertilization takes place outside of the body outside In mammals, birds and In reptiles this takes place inside the body Mating in rats Rats • Rats engage in brief • • • copulation copulation Female rats are Female spontaneous ovulators Ovulate (release their Ovulate eggs from the ovary) every 4 to 5 days every For those few hours For around the time of ovulation, the female seeks out a male and displays proceptive behavior behavior Mating in rats The • The most important proceptive behavior by females is lordosis females • Raise rump, move tail, and allow intromission Mating in rats Rats • Rats perform several intromissions and then males will • ejaculate ejaculate Several intromissions are necessary for female brain to Several secrete hormones that support pregnancy secrete Mating in rats • After copulation, male and female separate and groom n • IIn about 5 minutes, females engage in proceptive behaviors again and another mating bout can/will occur (inter mating interval; i.e. pacing) (inter Mating in rats: pacing For • For mating to be rewarding in females they have to • control the pace control This facilitates successful impregnation Hormones and mating: Males Testosterone • Testosterone mediates the • • • males interest in copulation copulation If you castrate male rats, they will eventually stop mating (in couple of weeks) weeks) Testosterone restores Testosterone mating mating In this case, the hormone In (testosterone) transiently alters behavior and this is referred to as an ‘activational’ effect of the hormone hormone Hormones and mating: Females Estrogens • Estrogens secreted at the beginning of he 4- to 5day ovulatory cycle facilitate the proceptive behavior of the female rat behavior And the subsequent And production of progesterone increases proceptive and activates receptivity receptivity An adult female rat with An ovaries removed do not show proceptive or receptive behaviors receptive • • Hormones and mating: Females However, • However, 2 days of estrogen treatment followed by a single injection of progesterone will restore proceptive and receptive behavior for a couple of hours couple The proper order and The timing is required timing • Brain regulation of reproduction nformation • IInformation regarding the neural regulation of copulatory behavior comes from rats from One successful strategy One has been to lesion particular regions of the brain and determine if copulatory behavior is altered altered Autoradiography shows Autoradiography that many sub-regions in the hypothalamus contain estrogen and progesterone sensitive neurons sensitive • • Brain regulation of reproduction The • The ventromedial hypothalamus (VMH) has many… many… Lesions of the VMH Lesions eliminates lordosis eliminates Estrogen treatment also Estrogen increases dendritic branching in the VMH and stimulates the production of progesterone receptors of The VMH projects the The periaqueductal gray (PAG) periaqueductal • • • Brain regulation of reproduction • Lesion PAG also eliminates lordosis PAG • PAG projects to medullary reticluar formation which then projects to the spinal cord then Brain regulation of reproduction When • When the VMH and PAG are signaling appropriately (estrogen mediated), sensory information provided by the male (mounting etc) causes the spinal cord to trigger the lordosis response the Brain regulation of reproduction Thus, • Thus, the role of the VMH is to monitor steriod hormone concentrations and (at the right time in the ovulatory cycle) activate the pathway that causes the spinal cord to contract back muscles and produce lordosis to Brain regulation of reproduction: males Steroid • Steroid hormones also activate male copulatory behavior in rodents rodents Brain regions that are Brain important are also regions of the hypothalamus that have high density of androgen receptors receptors The hypothalamic medial The preoptic area (mPOA) has a high density of ‘steroidhigh sensitive’ neurons Lesions of the mPOA Lesions eliminates male copulatory behavior behavior • • • Brain regulation of reproduction: males Experiment: • Experiment: Castrate male and mating stops; then infuse testosterone into the mPOA… mating is restored infuse mPOA lesioned rats will press a bar for a female • Brain regulation of reproduction: males mPOA • mPOA projects to dopamine neurons in the midbrain, which project to the basal ganglia to coordinate mounting (including spinal cord) mounting ...
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