Chap 17. Sex and the brain

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Chap 17. Sex and the brain
XX, XY and XXY?
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SRY encodes testis-determining factor If the
SRY is incorpo- ted into XX, the mouse
develops as a male SRY is not everything, for
instance, sperm production depends on other genes
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SRY--gt testosterone
Mullerian inhibiting factor
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Aromatase
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Estradiol receptors in the brain
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- Inverse relationship between light and
melatonin ,and melatonin inhibits GnRH release -
Stress and emotional regulation
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Neural control of human sex organs
Four phases in sexual response cycles -
arousal - plateau - orgasm - resolution Simple
reflex! Ach, VIP, NO Neural mechanisms for
climax are entirely mysterious.
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The neurochemistry of reproductive
behavior Prairie vole After intense period of
initial matings, form a tight pair-bond, live
together in one nest nurture their young
together Montane vole Asocial Promiscuous Liv
e in an isolated nest Males take no part in
parenting Female care for their offsping only
briefly
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Evidence that vaso and oxy regulate reproductive
behavior 1. Plastic changes of the Rc map of
montane vole after giving birth. 2. When prairie
vole copulates, level of vaso (in male) and
oxy (in female) rise sharply (love NT) 3. Vaso
antagonist, but not oxy antagonists, given to
male prevents the pair-bond 4. When a male is
given vaso while exposed to a female, he forms a
strong preference for her (a dart of cupid!) 5.
Vaso enhance nurturing behavior. Oxy to
female. 6. What happens if vaso is given to
montane vole? - No pair-bonding and parenting,
still promiscuous - Rc distribution pattern is
more important than ligand
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Sexual dimorphism of the CNS
Somatosensory map plasticity
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Sexually dimorphic nucleus (SDN) in the
hypothalamus 5 to 8 times larger in male
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Sexual dimorphism in the CNS Sexually dimorphic
nucleus (SDN) Within the preoptic area of
anterior hypothalamus Lesions in the preoptic
area disrupts the estrous cycle reduce the
frequency of copulation Interstitial nuclei of
the anterior hypothalamus (INAH) Subregion 1, 2,
3 and 4 INAH-2 and INAH-3 are about twice as
large in men as in women. Corpus Callosum
size and shape difference Anterior
commissure Motor neurons in the spinal cord for
BC muscles
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Sexual dimorphism of cognition
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Tasks at which women excel Naming objects in the
same color Listing words beginning with the same
letter Verbal memory Tasks at which men
outperform Map reading Maze learning Mathematic
al reasoning Mental rotation Interpretation Horm
one? 1) Better spatial learning when estrogen
levels are lowest during the mestrual cycle 2)
Enhancement of spatial learing in old men by
adminstrating testosterone Conclusion no good
correlation between performance and hormone
levels
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Sex hormones, the brain and behavior
1) Metabolites of progesterone, like
benzodiazepine, stimulate GABAA receptor 2)
Estradiol binds to receptor and stimulates gene
expression Note that testosteron is converted to
estradiol (by aromatase) and binds to
estradiol receptor Timing of estrogen surge
masculinize brain early surge of testo in
male no early surge in female
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Steroid hormone exerts effects on the brain
throughout life 1. Organizational effects
Irreversible organization of peripheral
tissues 2. Activational effects Temporary
activation of the brain parts that are essential
for reproduction
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Zebra finches - Live in a desert - Ready to
breed anytime whenever food and a mate are
available - The same song (ditty) all their
lives Wild canaries - Live in a
predictable environment - Breed only during
spring and summer - New repertoire (songs) every
spring
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Vocal control regions (VCRs) in zebra finches
Female finches, when exposed to testosterone
both during early development and adult, sing
like males (organization activation) Adult
female canaries, when exposed to testo for the
first time, respond to it and sing like males in
few weeks. Seasonal variation in the size of VCR
(Neurogenesis throughout adulthood) a basis for
new song?
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Determination of the sexual characteristics of
the nervous system by hormones 1. Female rats
exposed to testosterones early in
development fail to elicit the typical female
mating posture, called lordosis 2. Female guinea
pig treated in utero with testosterone
develop masculine external genitals and try to
mount and attempt to mate with female 3. The
female calf in twin calves (male and female),
exposed to testosterone in utero, becomes a
freemartin (infertile and behave like a
bull) Freemartin (??? ?? ???) ?? ?? ?? ????.
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Congenital adrenal hyperplasia (CAH) Genetically
female but Adrenal glands secretes a large
amount of androgens Testostrone early in
development Normal ovary External genitals half
in size between a clitoris and a penis Surgical
removal or medications Aggressive and tomboyish
behaviors
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Androgen Insensitivity Syndrome (AIS)
Genetically men but Defective androgen receptor
in the X chromosome Develop normal testes and
produce testosterone Develop vagina, clitoris,
labia and, at puberty, breats and a female body
shape Behaves like women, prefer to be called as
a woman and choose men as their sex partners
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Figure 17.15 Dendritic spines and
estradiol Spine density fluctuation during 5-day
estrous cycle Correlation between estradiol
levels and spine density New spines with
NMDAR Estradiol enhances LTP (smart
women?) Estradiol receptor in inhibitory
interneurons where no spines exist --gtReduced
inhibitory circuit increased the excitation
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Epilepsy and hormones Epilepsy potential
correlates well with the ratio of
estradiol/progesterone Implications 1)
Epilepsy and menstrual cycle 2) Epilepsy and
menopause 3) Hippocampus and spatial memory
(good for females actively seeking out mates?)
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Born-that-way theory of homosexuality
The size of INAH-3 (interstitial nuclei of the
anterior hypothalamus) is twice larger in men
than women INAH-3 is twice smaller in gay men
than straight men Simon LeVey (Box 3).
Different vs. abnormal Arguments 1) A male rat
with destroyed INAH-3 shows similar sexual
behaviors 2) The size of the INAH-3 may not be
different at the birth (a house with 1 boy and
10 girls)
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Gay gene? a genetic basis for sexual
orientation
Homosexuality maternally linked X chr. - High
probability when other males in his family are
homosexual - associated with cousins/uncles
related through a mans mother than
father. Analysis of 40 pairs of homosexual
brothers (not twins) Identification of a small
segments in the X chr Argument Some identical
twin show different sexual orientation
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A sex difference in the human brain and its
relation to transsexuality. Zhou et al. Nature
378, 68-70 (1995).  The volume of the central
subdivision of the bed nucleus of the stria
terminals (BSTc), a brain area that is essential
for sexual behaviour, is larger in men than in
women. A female-sized BSTc was found in
male-to-female transsexuals. The size of the
BSTc was not influenced by sex hormones in
adulthood and was independent of sexual
orientation. a female brain structure in
genetically male transsexuals Hypothesis
gender identity develops as a result of an
interaction between the developing brain and sex
hormones.
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Sex on the brain S. MARC BREEDLOVE. Nature 389,
801 (1997) Reports of morphological differences
between the brains of humans with different
sexual orientation or gender identity have
furthered speculation that such behaviours may
result from hormonal or genetic influences on the
developing brain. However, the causal chain may
be reversed sexual behaviour in adulthood may
have caused the morphological differences. I
report how adult sexual experience alters the
appearance of rat motor neurons as revealed by
Nissl staining, the same technique used in
post-mortem human studies.
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Figure 1 Sexual experience alters neuronal
morphology.