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Hormones, Sexual Development,

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Increased M/F sex hormone activity Secondary characteristics. maturation of genitals ... African Spotted Hyena. vicious predators. Females dominate ... – PowerPoint PPT presentation

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Title: Hormones, Sexual Development,


1
Hormones, Sexual Development, Sexual Behavior
  • Lecture 11

2
Sexual Dimorphism
  • Two forms
  • male and female
  • What determines your sex?

3
Genetic determinants
  • XX or XY
  • XO ?
  • Turners syndrome
  • no ovaries
  • default FEMALE
  • MALE
  • Override genetic program

4
Genotypic vs Phenotypic Sex
  • Genotype
  • complete genetic makeup
  • Phenotype
  • expression of genes

5
Olympics Sex
  • Gene tests
  • Stella Walsh
  • XY
  • Disqualify her?

6
Sexual Differentiation of Body
  • Chromosomal sex - XX or XY
  • single gene
  • Sex-Determining Region on the Y Chromosome
  • SRY

7
SRY
  • Turns on switch
  • testes development
  • XX SRY?
  • male
  • XY - SRY
  • female
  • Monozygotic nonidentical twins?

8
Development of Reproductive Organs
9
Primordial Gonad
  • Indifferent gonad
  • Potential for both sexes
  • Medulla
  • testes
  • Cortex
  • ovaries

10
Differentiation
  • at 6 weeks
  • SRY
  • medulla ----gt testes
  • No SRY
  • cortex ----gt ovaries

11
Internal Reproductive Ducts
  • lt 6 weeks
  • 2 sets
  • Mullerian system female
  • upper vagina
  • uterus
  • fallopian tubes

12
  • Wolffian system male
  • seminal vesicles
  • vas deferens
  • 3d month development
  • 1 set withers
  • SRY ---gt testes
  • testosterone
  • Mullerian Inhibiting Hormone - MIH

13
Mullerian Inhibiting Hormone
  • Testes ---gt scrotum
  • Mullerian degenerates
  • Testosterone stimulates wolffian
  • Testosterone to female
  • get both systems
  • No MIH
  • Critical periods
  • No MIH ---gt Mullerian

14
External Genitalia
  • Dihydrotestosterone (DHT)
  • critical period
  • testosterone ------------------------gt DHT
  • 5-alpha-reductase
  • M F - same tissue

15
Sexual Differentiation of the Brain
16
Masculinization
  • Gonadotropin release patterns
  • Female natural pattern
  • Brain masculinized by...
  • testosterone?
  • Structural differences?
  • Hypothalamus
  • Sexually Dimorphic Nucleus - SDN
  • Spinal Nucleus of the Bulbocavernosus

17
Masculinization of the Brain
  • testosterone -------------------gt estradiol
  • aromatase
  • Aromatase present in neonates
  • inject estradiol into neonate female
  • brain masculinized
  • What protects females?
  • Rats - alpha-fetoprotein
  • Primates - placenta?

18
Secondary sex characteristics
  • Puberty
  • Increased M/F sex hormone activity Secondary
    characteristics
  • maturation of genitals
  • breasts
  • body shape
  • Pubic axillary hair
  • females- androstenedione
  • from adrenal cortex

19
African Spotted Hyena
  • vicious predators
  • Females dominate -
  • bigger, stronger, more aggressive than
    males

20
Why?
  • ovaries ---gt androstendione during pregnancy
  • converted to T rather than E
  • low aromatase levels
  • Masculinizes offspring
  • highly aggressive
  • Siblicide -

21
Sexual Development Syndromes
22
Adrenogenital Syndrome
  • Congenital adrenal hyperplasia
  • prenatal adrenal cortex hyperactivity
  • high levels of androgens
  • partially masculinized external genitalia

23
Androgen Insensitivity Syndrome
  • What sex?
  • Phenotype?
  • Genotype?

24
Androgen Insensitivity Syndrome
  • Genetically XY -
  • No androgen receptors
  • Genetic mutation - X chromosome gene
  • Born with vagina, raised as female
  • Undescended testes become functional at puberty.
  • NOW WHAT HAPPENS?

25
5-alpha Reductase Syndrome
  • Genetically XY
  • Fetal 5-alpha reductase deficiency
  • T not converted to DHT
  • Born with vagina - raised as female

26
At puberty
  • Undescended testes become functional at puberty
  • NOW WHAT HAPPENS?

27
Hormones Sexual Behavior
28
Female behavior rats
  • Proceptive
  • ear wiggling
  • darting
  • hopping
  • Receptive - lordosis
  • head down
  • haunches up

29
Male behavior rats
  • Mounts
  • no testosterone ---gt no mounting
  • Intromits several times
  • Ejaculates
  • 4-5 times
  • 5 min refractory period

30
Organizational Effects of Hormones
  • SDN SNB
  • Critical periods
  • Humans - prenatal
  • Rats - Perinatal
  • easily manipulated

31
Hormones Sexual Behavior
  • Castrate XY males at birth
  • Later...
  • testosterone ---gt no male behavior
  • estrogen?
  • lordosis
  • Brain not masculinized

32
  • Ovariectomize female at birth
  • give testosterone
  • Later...
  • estrogens ---gt no female behavior
  • testosterone ---gt male behavior
  • Brain masculinized

33
Human Sexual Behavior
  • No stereotypical M F behaviors
  • Men are like rats
  • T plays a activational role
  • Castration -
  • decline in sexual behaviors
  • variable rate
  • Role of oxytocin?
  • probably not
  • knockout mice

34
Hormones - Women
  • Estrogen Progesterone
  • no activational effects
  • Ovariectomy has no effect
  • Some fx on willingness to copulate increased
    during ovulation
  • E P are high

35
  • Testosterone levels
  • correlated with frequency of intercourse
  • Oxytocin
  • uterine and vaginal contractions - sensations
    associated with orgasm

36
Brain Mechanisms Rats
  • Male - Medial preoptic area
  • lesion SDN ---gt no sexual behavior
  • NOT sexual motivation
  • barpress for female
  • Female - Ventromedial nucleus
  • lesion- no sexual behavior
  • Masculinizes by preventing cell death

37
Homosexuality
  • Sex hormones role?
  • rats - yes
  • Humans?
  • NOT SURE
  • Learning experiences?
  • or biologically determined?

38
Biological Factors
  • Levels of circulating sex hormones?
  • No
  • Differences in brain structure?
  • Perhaps - Where?

39
Homosexuality
  • Simon LeVay
  • Brains of male AIDS victims
  • Anterior Hypothalamus
  • Anterior commissure
  • SDN (rats)
  • Humans 3rd interstitial nucleus

40
3d interstitial nucleus
.15 .10 .05
Volume mm3
F H-M M
  • Anterior commissure larger in females
  • Similar relationship

41
Homosexuality 2 Hypotheses
  • 1. Androgen levels
  • low in XY fetuses that---gt gay high in XX
    fetuses ---gt lesbian

42
Homosexuality 2 Hypotheses
  • 2. Genetic differences in
  • fetal brains response to androgens
  • Xq28 - tip of the X chromosome
  • shared by large of gay brothers -
  • gene influences M sexual orientation?
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