Biology of Reproduction Summers |
Endocrinology Homeostasis/Feedback Adult Female Steroid Production Ovulation |
 |
Adult Male Gonadal Axis Regulation Sexual Differentiation Sexual Behavior Puberty |
Reproductive Cycling Estrous Cycles Menstrual Cycle Menopause Fertilization |
Fertilization Systems Gamete Interaction Pregnancy Labor and Parturition Lactation |
Sexual Response & Behavior Pheromones STDs text: Human Reproductive Biology4th Edition- RE Jones & KH Lopez,: pp 303-319, 149 - 152 Acronyms/Abbreviations end |
XIII. Development of Sexual Behavior A. T (from testes) masculinizes the brain (hypothalamus) 1. converted to E2 intracellularly a. aromatase in mPOA & VMH 2. E2 binding to E-Ra or b produces male sexual behavior a. E-Ra promotes increased & clustered A-R & P-R i. A-R also important for male sexual behavior b. but... DA via D1 receptors can also activate E-Ra c. female rats have a-feto-protein ® binds to E2 and keeps it from entering the brain 3. Critical Period = Window of Effectiveness a. time during development when "T" has an effect masculinizing the brain producing male behavior
| MAMMAL | GESTATION LENGTH IN DAYS |
CRITICAL PERIOD DAYS (time after fertilization) |
DAYS AFTER TESTES APPEAR |
| Hamster | 16 | 16-21 | 4.5 |
| Mouse | 19-20 | 20 | 7.5 |
| Rat | 21-22 | 18-28 | 5.0 |
| Guinea Pig | 68 | 30-35 | 5.0 |
| Human | 270 | T goes up 84-126 | 21 |
b. fetal hormone organize sexual behavior in males
i. postpubertal hormones maintain behavior
in males and females
c. Evidence for critical period in humans
i. Guevedoces
(1) raised as females, plenty of T,
male behavior as adults
ii. Adrenogenital Syndrome
(1) high androgens - more male-like behavior
iii. Progestogens (given to prevent loss of pregnancy)
via P-R or A-R, females born to women with
this treatment have more male-like behavior
iv. Estrogen +feedback in homosexuals
(1) other studies have refuted this finding,
and even suggested positive feedback in heterosexual males
XIV. Sexual Orientation or Preference
A. Theory of Evolution of Sexual Preference
1. Depends on bi-directional selection
a. females choosing males
b. males choosing females
2. Evolution of Different Sexual Preferences
a. Preference for same sex (homosexuality)
i. 1.6% gay and lesbian demographic
b. different species
c. nothing (asexuality)
d. individuals to old to reproduce
e. too young to reproduce
3. Depends on
a. individuals with different preference
i. do not suffer reproductive disadvantage
b. realized attractiveness
i. more attractive individual is choosier
1) increased popularity
ii. choosier individual rejects most
1) Selective lack of interest
iii. the most disinterested one (choosiest)
1) shows no interest in the opposite sex at all
B. Determining Sexual Orientation
1. Self-labeling and past behavior are unreliable
2. Physiological genital arousal
a. clitoral or penile plethysmography
i. to sexual imagery
ii. sexual fantasy or feelings
b. males - bimodal
i. heterosexual or homosexual
1) rarely bisexual
c. females - positive responses bisexually
i. toward both male and female images
ii. in both heterosexual and lesbian women
3. Sexual orientation develops before sexual reward learning
C. Genes associated with homosexuality in males
1. X chromosome region Xq28 (tip of long arm)
shared by some (up to 67%) homosexual brothers
a. X-linked recessive
i.also autosomal markers at 7q36, 8p12 and 10q26
1) but not linked to Xq28
b. heritability: 53% of the variance
in homosexuality is genetic
i. identical twin studies
c. adopted brothers of homosexuals have a higher
than normal incidence of homosexuality
2. genes code for proteins (mostly enzymes)
a. genetic background represents a predisposition
i. triggered or supressed by external factors
D. Genes and homosexuality in females
1. 52% heritability
associated with same-sex orientation in women
E. Testicular Feminization Syndrome
1. no androgen receptors (Xq11)
a. normal testis, female external genitalia
2. XY heterosexual female
F. neuroanatomical sexual dimorphism:
3rd interstitial nucleus of the mPOA (=INAH3)
1. smaller in women
2. smaller in homosexual men
G. multimorphisms and sexual orientation: SCN
1. shape (not size) of SCN differ
in heterosexual males and females
a. AVP secreting cells
2. SCNAVP 2x larger in homosexual men
3. SCN = biological clock
® homosexual men arise and retire earlier
a. SCN also regulates reproductive function + rhythmicity
4. male-to-female transexuals - smaller female-like cBNST
H. Differences in hypothalamus suggest hormonal variability
1. fetal environment can influence androgen and estrogen levels
a. may influence masculinization during critical period
i. maternal stress (increased CRH, ACTH and F)
decreases androgen and estrogen levels
1) advance fetal adrenal conversion
of DHEA to F
2) increased homosexuality in males and females
ii. however, Human male without aromatase
was heterosexual (N = 1)
1) DA via D1 may be able to organize
morphological and functional sex differences
in the abscence of steroid
iii. masculinization limits E provoked LH surge
1) 50% of homosexual men had LH surge
2) 33% of heterosexual men had LH surge
a) those with lowest [T] (both groups)
i) no masculinization
of human brain?
ii) E will never provoke
LH surge in male rat
iv. PET - stronger hypothalamic response to 5-HT challenge
a) in heterosexual than in homosexual men
2. male homosexuality may appear as a mosaic of traits
(some sex-typical, others sex-atypical and yet others that are sex-exaggerated)
a. differences in the timing and/or concentration
of T (A-R, ERa, PR, D1) exposure
i. homosexual men may be exposed to particularly
high androgen levels very early in development
I. Fetal environment can affect non-steroidal events
1. increased # of older brothers increased chance of homosexuality
a. each older brother increases chance by 33%
i. multiply by chance of homosexuality (1-2%)
to get overall increase
2. progressive immunization of mothers
to minor Y-linked histocompatibility antigens
a. non-self immune action against H-Y antigen, protocadherin
or neuroligin by maternal antibodies impedes male sexual
differentiation of the brain
i. male mice whose mothers are immunized to H–Y prior
to pregnancy show reduced sexual behaviour
towards receptive females
ii. H-Y antigen was once thought to determine gonadal sex
(1) before discovery of TDF
J. Evolution of Homosexuality outcomes
1. 67% of lesbian women are mothers
a. 75% of lesbian women had sex with men
b. 72% of straight women are mothers
2. 83% of bisexual and homosexual men are fathers
3. therefore... no reproductive disadvantage