SEX HORMONES (1)

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Sex Hormones, the brain and behavior

• M.Prasad Naidu
• MSc Medical Biochemistry, Ph.D,.

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Definitions of Sex
Genetic
Gonadal
Hormonal
Morphological
Behavioral (gender role behavior)
Identity
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Effects of Sex Hormones

• Organizational Effects
• structural
• sensitive period
• irreversible
• masculinization/defeminization
• Activational Effects
• act on existing structure
• no sensitive period
• reversible

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testes differentiate
ovaries differentiate
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Sexual Dimorphisms
Phenotypic differences between males and females
They can be anatomical physiological behaviora
l cognitive
They can be qualitative quantitiave
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Control of Sex Hormones
Hypothalamus
Indirect Loop
Short Loop
GnRH
Adenohypophysis
LH, FSH
Direct Loop
Testes or Ovaries
Testosterone or Estrogen Progesterone
Target tissues
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Bipotential tissues Undifferentiated
tissue that can differentiate into either a male
or female form.
Sexual Dimophisms Structures, functions or
behaviors that differ qualitatively or
quantitatively between the sexes.
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Prototypical Experiment (Males)
Castrate male hamster at birth
(before period of brain differentiation)
Test in adulthood
inject with testosterone
place with receptive female
male typical behavior low
mounting, intromission (ejaculation not possible)
inject with estrogen and progesterone
place with male
female-typical behavior high
darting, ear-wiggling, lordosis
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Prototypical Experiment (Females)
Neuter female hamster at birth and inject with
testosterone
(before period of brain differentiation)
Test in adulthood
inject with testosterone
place with receptive female
male typical behavior high (mounting)
inject with estrogen and progesterone
place with male
female-typical behavior low (ear-wiggling,
darting, lordosis)
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Differentiation of the Brain
Two processes
both are dependent on fetal androgens
Masculinization
Induction of male characteristics
Defeminization
Suppression of female characteristics
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Why arent all females masculinized?
a-fetoprotein binds to estradiol
extracellulary and prevents entry into cell
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Ripple effects in brain sexual dimorphisms
Kelley, D.B. (1988) Ann. Rev. Neurosci., 11,
225-251.
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Steroid Hormones
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cholesterol
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Control of Sex Hormones
Hypothalamus
Indirect Loop
Short Loop
GnRH
Adenohypophysis
LH, FSH
Direct Loop
Testes or Ovaries
Testosterone or Estrogen Progesterone
Target tissues
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Control of Stress Hormones
Hypothalamus
Indirect Loop
Short Loop
CRF (aka CRH)
Adenohypophysis
Corticotrophin (aka ACTH)
Direct Loop
Adrenal Cortex
Cortisol or Corticosterone
Target tissues
This is usually referred to as the HPA
axis, but is now often called the LHPA axis.
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Suppose there is a deficiency of
either 21-hydroxylase or 11-ß hydroxylase.
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cholesterol
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cholesterol
aromatase
5-alpha reductase
estrodiol
DHT
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Sex differences in cognition
Studies of mathematically gifted
Effects of brain damage
Anatomical studies of brain laterality
Functional (fMRI) studies of brain laterality
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Brain Laterality
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Geshwinds Theory of Cerebral Lateralization
Geschwind, N. Galaburda, A.S. (1987) Cerebral
lateralization. Cambridge, MA MIT Press
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McManus, I.C. Bryden, M.P. (1991) Geschwinds
theory of cerebral lateralization Developing a
formal, causal model. Psych. Bull., 110,
237-253.
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Control of Sex Hormones
neural inputs
Hypothalamus
Indirect Loop
Short Loop
GnRH
Adenohypophysis
LH, FSH
Direct Loop
Testes or Ovaries
Testosterone or Estrogen Progesterone
Target tissues
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Activational Effects of Sex Hormones on Cognition
Possible activational effects of sex hormones on
cognition
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Splenium
de Lacoste-Utamsing, C. Holloway, R.L.
(1982) Sexual dimorphism in the human corpus
callosum. Science, 216, 1431-1432.
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Gladue, Green Hellman (1983) Science, 225,
1496-1499.
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Gladue, Green Hellman (1983) Science, 225,
1496-1499.
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LeVay, S. (1991) Science, 253, 1034-1037
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Size related to sexual identity not sexual
orientation
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THANK YOU