Download What sex?

Hormones,
Sexual Development,
& Sexual Behavior
Lecture 11
Sexual Dimorphism
Two forms
male and female
 What determines your sex?

Genetic determinants
XX or XY
 XO ?
Turner’s syndrome
no ovaries
 default = FEMALE
 MALE
Override genetic program

Genotypic vs Phenotypic Sex
Genotype
complete genetic makeup
 Phenotype
expression of genes

Olympics & Sex
Gene tests
 Stella Walsh
 XY
 Disqualify her?

Sexual Differentiation of Body
Chromosomal sex - XX or XY
 single gene

 Sex-Determining
Chromosome

SRY
Region on the Y
SRY
Turns on switch
testes development
 XX + SRY?
male
 XY - SRY
female
 Monozygotic nonidentical twins?

Development of Reproductive
Organs
Primordial Gonad
Indifferent gonad
Potential for both sexes
 Medulla
testes
 Cortex
ovaries

Differentiation
at 6 weeks
 SRY
medulla ----> testes
 No SRY
cortex ----> ovaries

Internal Reproductive Ducts
< 6 weeks
2 sets
 Mullerian system = female
upper vagina

uterus
fallopian tubes

Wolffian system = male
seminal vesicles
vas deferens
3d month development
1 set withers
 SRY ---> testes
testosterone
Mullerian Inhibiting Hormone - MIH

Mullerian Inhibiting Hormone
Testes ---> scrotum
 Mullerian degenerates
Testosterone stimulates wolffian
 Testosterone to female
get both systems
No MIH
 Critical periods
No MIH ---> Mullerian

External Genitalia

Dihydrotestosterone (DHT)
critical period
testosterone ------------------------> DHT
5-alpha-reductase
 M & F - same tissue
Sexual Differentiation of the
Brain
Masculinization
Gonadotropin release patterns
Female natural pattern
 Brain masculinized by...
testosterone?


Structural differences?
 Hypothalamus
 Sexually Dimorphic Nucleus - SDN
 Spinal Nucleus of the Bulbocavernosus
Masculinization of the Brain
testosterone -------------------> estradiol
aromatase
 Aromatase present in neonates
 inject estradiol into neonate female
brain masculinized
 What protects females?
 Rats - alpha-fetoprotein
 Primates - placenta?
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

African Spotted Hyena
vicious predators
 Females dominate bigger, stronger, more
aggressive than males

Why?
ovaries ---> androstendione during
pregnancy
 converted to T rather than E
low aromatase levels
 Masculinizes offspring
highly aggressive
 Siblicide 
Sexual Development
Syndromes
Adrenogenital Syndrome
Congenital adrenal hyperplasia
 prenatal adrenal cortex hyperactivity
 high levels of androgens
 partially masculinized external
genitalia

Androgen Insensitivity Syndrome
What sex?
 Phenotype?
 Genotype?

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?

5-alpha Reductase Syndrome
Genetically XY
 Fetal 5-alpha reductase deficiency
 T not converted to DHT
 Born with vagina - raised as female

At puberty
Undescended testes become
functional at puberty
 NOW WHAT HAPPENS?

Hormones & Sexual Behavior
Female behavior: rats
Proceptive
ear wiggling
darting
hopping
 Receptive - lordosis
head down
haunches up

Male behavior: rats
Mounts
no testosterone ---> no mounting
 Intromits several times
 Ejaculates
4-5 times
5 min refractory period

Organizational Effects of Hormones
SDN & SNB
 Critical periods
Humans - prenatal
Rats - Perinatal
easily manipulated

Hormones: Sexual Behavior
Castrate XY males at birth
 Later...
testosterone ---> no male behavior
estrogen?
lordosis
 Brain not masculinized

Ovariectomize female at birth
give testosterone
 Later...
estrogens ---> no female behavior
testosterone ---> male behavior
 Brain masculinized

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

Hormones - Women
Estrogen & Progesterone
no activational effects
Ovariectomy has no effect
 Some fx on willingness to copulate
increased during ovulation
E & P are high

Testosterone levels
correlated with frequency of intercourse
 Oxytocin
uterine and vaginal contractions sensations associated with orgasm

Brain Mechanisms: Rats
Male - Medial preoptic area
lesion SDN ---> no sexual behavior
NOT sexual motivation
barpress for female
 Female - Ventromedial nucleus
lesion- no sexual behavior
Masculinizes by preventing cell death

Homosexuality
Sex hormones role?
rats - yes
Humans?
NOT SURE
 Learning experiences?
 or biologically determined?

Biological Factors
Levels of circulating sex hormones?
No
 Differences in brain structure?
Perhaps - Where?

Homosexuality
Simon LeVay
Brains of male AIDS victims
Anterior Hypothalamus
Anterior commissure
 SDN (rats)
Humans: 3rd interstitial nucleus

3d interstitial nucleus
.15
Volume
mm3
.10
.05
F
H-M
M
 Anterior commissure larger in females
 Similar relationship
Homosexuality 2 Hypotheses

1. Androgen levels
low in XY fetuses that---> gay
high in XX fetuses ---> lesbian
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?