Chapter 13 Hormones and Sex What’s Wrong with the Mamawawa This multimedia product and its contents are protected under copyright law. The following are prohibited by law: any public performance or display, including transmission of any image over a network; preparation of any derivative work, including the extraction, in whole or in part, of any images; any rental, lease, or lending of the program. Copyright © 2006 by Allyn and Bacon

Developmental and Activational Effects of Sex Hormones Developmental – “organizational” - influencing the development of anatomical, physiological and behavioral characteristics that differentiate the sexes Activational – activating reproduction-related behavior in mature individuals Copyright © 2006 by Allyn and Bacon

Copyright © 2006 by Allyn and Bacon Glands Exocrine – Release chemicals into ducts which carry them to their targets. Sweat glands, for example. Endocrine – Ductless. Release hormones directly into the circulatory system. Only organs whose primary function is hormone release are referred to as endocrine glands. Copyright © 2006 by Allyn and Bacon

Copyright © 2006 by Allyn and Bacon Hormones Amino acid derivatives Epinephrine, for example (adrenal medulla) Peptides and proteins Short and long chains of amino acids Steroids Synthesized from cholesterol (fat) Fat-soluble – able to enter cells and bind to receptors in cytoplasm or nucleus Copyright © 2006 by Allyn and Bacon

Copyright © 2006 by Allyn and Bacon Gonads Male testes produce sperm cells Female ovaries produce ova Sperm and ova each have 23 chromosomes Fertilization Sperm cell + ovum = zygote 23 pairs of chromosomes X and Y – sex chromosomes XX = female, XY = male Copyright © 2006 by Allyn and Bacon

Sex Steroids – Released by Gonads Androgens - e.g., testosterone Estrogens - e.g., estradiol Adult testes release more androgens and ovaries more estrogens Progestins – also present in both sexes progesterone prepares uterus and breasts for pregnancy Adrenal cortex – also releases sex steroids Copyright © 2006 by Allyn and Bacon

Hormones of the Pituitary “Master gland” Tropic hormones influence the release of hormones by other glands Posterior pituitary – hormones synthesized in the hypothalamus Anterior pituitary – tropic hormones Copyright © 2006 by Allyn and Bacon

Copyright © 2006 by Allyn and Bacon Sexual Development We are dimorphic – exist in 2 forms Initially there is a primordial gonad Cortex – potential to be ovary Medulla – potential to be a testis If XY, Y triggers the synthesis of H-Y antigen and promotes development of the medulla No H-Y antigen, cortex develops into ovary Copyright © 2006 by Allyn and Bacon

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Copyright © 2006 by Allyn and Bacon Sexual Development 6-weeks post-conception: H-Y antigen > testes No H-Y antigen > ovaries Both sexes begin with 2 sets of reproductive ducts Wolffian system – male – seminal vesicles, vas deferens Mullerian system – female – uterus, vagina, fallopian tubes Differentiation occurs in the 3rd prenatal month Copyright © 2006 by Allyn and Bacon

Copyright © 2006 by Allyn and Bacon Sexual Development 6-weeks: gonads develop 3rd prenatal month: differentiation of ducts Testes produce testosterone and Mullerian-inhibiting substance Wolffian system develops, Mullerian degenerates, testes descend No testes – no testicular hormones Mullerian system develops, Wolffian degenerates Copyright © 2006 by Allyn and Bacon

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Copyright © 2006 by Allyn and Bacon A terminology note Ovariectomy – removal of ovaries Orchidectomy – removal of testes Gonadectomy or castration – removal of gonads, either ovaries or testes Such procedures are often used to study the effects of sex hormones Copyright © 2006 by Allyn and Bacon

Copyright © 2006 by Allyn and Bacon Sexual Development External reproductive structures – genitalia – develop from one bipotential precursor Differentiation occurs in 2nd month Testosterone > male No testosterone > female Copyright © 2006 by Allyn and Bacon

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Sexual Dimorphisms in the Brain Pfeiffer (1936) – gonadectomized and implanted gonads in neonatal rats Gonadectomy > cyclic hormone release Transplant of testes or ovaries > steady Perinatal hormones lead to male pattern Why do both ovaries and testes lead to male pattern? What masculinizes the brain? Copyright © 2006 by Allyn and Bacon

Sexual Dimorphisms in the Brain What masculinizes the brain? Sex steroids are all derived from cholesterol and are readily converted from one to the other Aromatize testosterone > estradiol Evidence suggests that estradiol masculinizes the brain Copyright © 2006 by Allyn and Bacon

Evidence that Estradiol (E) Masculinizes the Neonatal Brain Neonatal injections of E masculinize Dihydrotestosterone can’t be converted to E – doesn’t masculinize Block aromatization or E receptors – interferes with masculinizing effects of testosterone Why doesn’t E masculinize female brains? Copyright © 2006 by Allyn and Bacon

Copyright © 2006 by Allyn and Bacon Alpha fetoprotein In blood during perinatal period - protects the female brain from E Binds to circulating E, so none gets to the brain How does E get into male brain? In males, testoterone enters the brain and then is converted to E Copyright © 2006 by Allyn and Bacon

Copyright © 2006 by Allyn and Bacon Sexual Dimorphisms Not just a consequence of absence or presence of testosterone (T) XX and XY cells differ prior to hormone exposure Female brain development may not automatically occur in absence of T Various dimorphisms emerge at different stages under different influences Copyright © 2006 by Allyn and Bacon

Perinatal Hormones and Behavioral Development Masculinize – promoting male behavior, mounting, etc. Defeminize – preventing female behavior, lordosis Perinatal T masculinizes and defeminizes Neonatal castration of male rats – feminizes and demasculinizes Copyright © 2006 by Allyn and Bacon

Copyright © 2006 by Allyn and Bacon Puberty Fertility achieved, secondary sex characteristics develop Features that distinguish sexually mature men and women Increase in release of anterior pituitary hormones Growth hormone – acts on bone and muscle Gonadoptrophic hormone Adrenocorticotrophic hormone Copyright © 2006 by Allyn and Bacon

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Copyright © 2006 by Allyn and Bacon Puberty Relative levels of androgens and estrogens determine whether male or female features develop Androstenedione – androgen necessary for the growth of axillary and pubic hair in both sexes Copyright © 2006 by Allyn and Bacon

Andrenogenital Syndrome Androgenic insensitivity leads an XY individual to look female (Anne S.) Andrenogenital Syndrome is caused by congenital adrenal hyperplasia Too little cortisol leads to compensatory excessive release of adrenal androgens No problem for males May masculinize female genitalia and behavior – surgical and hormonal treatments needed at puberty Copyright © 2006 by Allyn and Bacon

Male Reproduction-Related Behavior and Testosterone (T) Effects of orchidectomy Bremer (1959) Reduced sexual interest and behavior Rate and degree of loss varies Still have adrenal T Level of male sexuality is NOT correlated with T levels Increasing male T levels does NOT increase sex drive Copyright © 2006 by Allyn and Bacon

Female Reproduction-Related Behavior and Gonadal Hormones Rats and guinea pigs – surges of estrogen and progesterone initiate estrus, a period of fertility and receptivity Women – sexual motivation and behavior not tied to cycle Sex drive may be under androgenic control Copyright © 2006 by Allyn and Bacon

Human Female Sexuality and Androgens T increases the proceptivity of ovariectomized and adrenalectomized female rhesus monkeys Correlations seen between sexual motivation and T T found to rekindle sexual motivation in ovariectomized and adrenalectomized women Copyright © 2006 by Allyn and Bacon

Copyright © 2006 by Allyn and Bacon Anabolic Steroids Anabolic – growth-promoting No firm scientific evidence that muscularity and strength are increased Sex-related side effects High circulating hormones cause a reduction of natural release Men - testicular atrophy, sterility, gynecomastia (breast growth in men) Women – amenorrhea (cessation of menstruation), sterility, hirsutism (excessive growth of body hair) Copyright © 2006 by Allyn and Bacon

Neural Mechanisms of Sexual Behavior Sexually dimorphic nucleus (SDN) medial preoptic area of rat hypothalamus larger in males, due to estradiol shortly after birth size of male SDN correlated with T levels and aspects of sexual activity Nuclei in preoptic, suprachiasmatic, and anterior regions of the hypothalamus are larger in men than in women Copyright © 2006 by Allyn and Bacon

Medial Preoptic Area of the Hypothalamus Contains the SDN Destruction abolishes sexual behavior of all mammalian males studied, but does not affect female sexual behaviors females Stimulation elicits copulatory behaviors Copyright © 2006 by Allyn and Bacon

Ventromedial Nucleus of the Hypothalamus Contains circuits critical for female rat sexual behavior Lesion eliminates lordosis Microinjections of E and progesterone induce estrus Lesions of periaqueductal gray (PAG) or the tracts to it eliminate lordosis Copyright © 2006 by Allyn and Bacon