1. Sexual Differentiation Berthold’s Experiment (1849)
Arnold Adolph Berthold
( )
University of Göttingen
Germany
Bob the Chicken

2. Organizational and activational effects of steroids
Organizational: To guide the organization of brain, endocrine glands, and
behavior during hormone-sensitive “critical periods” or
epochs of fetal and postnatal life.
Activational: At puberty and afterward, to generate the growth of
secondary sex characteristics, to activate endocrine
systems involved in sperm and egg production, to mature
neuroendocrine systems required for pregnancy, and to
stimulate the appropriate “adult” behaviors required for
those functions.
Masculinization: Active process of acquiring “male-typical” anatomy, physiology,
and behavioral functions.
Demasculinization: Active process of losing “male-typical” functions.
Feminization: Default or “passive” process in mammals of acquiring
“female-typical” anatomy, physiology, and behavioral functions.
Defeminization: Active process of losing “female-typical” functions.

3. Genetic → Hormonal differentiation

4. Internal differentiation

5. External differentiation

6. Brain differentiation (pre and postnatal)
(Sexually dimorphic nucleus of the medial preoptic area)
Male Female
TP-treated Castrated
Female Male

7. Differentiation of spinal cord
(Spinal nucleus of the bulbocavernosus muscle)
Castrated male TP-treated female
Female Male

10. Sexual differentiation requires Prostaglandin E2 in hypothalamus
Margaret M. McCarthy
( )
University of Maryland
Baltimore
Discovered that COX-2
inhibitors disrupted
formation of SDNs in
males.
Also disrupted display
of masculine sexual
behavior after puberty.
Effects irreversible.
Replacement with PGE2 in perinatally castrated males could restore both growth of SDNs
and masculine sexual behavior.

12. (with conversion to estradiol
in mammals, and functional
activation of prostaglandin E2!)