Sex Differences and Steroid
Hormone Receptors
NEUS 501
October 24, 2014
Sexual Differentiation of the Brain
Genetic sex determination
Steroid hormones
Sexual differentiation of the brain and behavior
Steroid hormone receptors and behavior
New genetic approaches to studying sexual
differentiation
• Effects of hormones on neuron structure and
signaling
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What determines sex?
• Genetics
– XY or XX, mammalian male or female
– ZZ or ZW, avian & fish male or female
• Sex hormones
– Estrogens
– Androgens
• Aromatase converts testosterone to estradiol
Sexual differentiation
McCarthy MM, Arnold AP. Nat Neurosci. 2011. 14(6):677-83.
Genetics: Sry gene basics
• Sry (sex determining region on Y) on Y chromosome
induces undifferentiated gonads to form testes
• Testes secrete anti-mullerian hormone and
testosterone to masculinize the rest of the body
• Without Sry expression gonad develops as an ovary,
and body is feminine
Other genes involved, See also de Vries, et al 2002
Effect of hormones on behavior
• Organizing effects
– Early periods of development, alter subsequent
brain and body development.
• Activating effects
– Acute, can be mediated by previous organizing
effects.
– Sex differences caused by activational effects are
abolished by gonadectomy of adult animals.
Landmark study, 1959
Phoenix et al., Organizing action of prenatally administered testosterone
proprionate on the tissues mediating mating behavior in the female guinea
pig. Endocrinology 65:369-382 (1959).
Female guinea pigs exposed to testosterone as fetuses
copulate like males.
Steroid Hormone Synthesis
Progestins
Androgens
Estrogens
Steroid hormones involved in sexual
differentiation
Principles of Neural Science, 4th Edition, Chapter 57
Sexual differentiation of the vertebrate nervous system. Morris JA, Jordan CL, Breedlove SM.
Nat Neurosci. 2004. 7:1034-9.
Hormones mediate sexual differentiation
of the brain
McCarthy MM. J Neuroendocrinol. 2010. 22:736-42.
Sex specific behaviors in rodents
Female: Lordosis
Male: Mounting behavior,
intromissions, ejaculation
Effects of perinatal testosterone on rat
sexual behavior
Estradiol administered to females during the critical period also masculinizes the brain
Hormone manipulation and sexual
behavior
Principles of Neural Science, 4th Edition, Chapter 57
Male aromatase knockout mice exhibit
deficits in sexual behavior
A role for estrogen in sexual differentiation of the brain
Honda, S., et al. Biochem Biophys Res Commun. 1998. 252:445-9.
Female aromatase knockout mice
Estrogen is required for female brain development.
Have you noticed the singing of the
birds?
canary
Songbird males sing
learned songs
Most females do not
sing songs
(just make calls)
zebra finch
Sexually dimorphic nuclei in songbird
Male
Female
HVC, RA, LMAN, area X
canary
zebra finch Hormones play organizational and activational roles in this system
Nottebohm and Arnold, 1976
Sexually dimorphic nuclei in rat
• Sexually dimorphic nucleus of the pre-optic area (SDN-POA).
More neurons in males.
• Size sensitive to testosterone during the perinatal period but not
after.
• Early castration feminizes, perinatal testosterone masculinizes.
Male
Female
Sexual differentiation of the vertebrate nervous system. Morris JA, Jordan CL, Breedlove
SM. Nat Neurosci. 2004. 7:1034-9.
Structural sex differences in the rat nervous system
Controls
ovulation
Controls
male sexual
behavior
Principles of Neural Science, 4th Edition, Chapter 57
Sex differences in human brain
F>M
• Fronto-orbital cortex
• Precentral, superior
frontal, and lingual gyri
M>F
• Fronto-medial cortex
• Amygdala
• Angular gyrus
Why sex matters for neuroscience. Cahill L. Nat Rev Neurosci. 2006. 7:477-84.
The nuclear receptor superfamily
Mangelsdorf et al, (1995) Cell 83:835-839
Estrogen receptors regulate many types of
behaviors
Classical function as ligand-activated transcription factors.
“Non-classical” function as activators of signaling cascades
ERα
ERβ
Female sexual behavior
Male sexual behavior
Learning and memory
Anxiety
Reward
Male aggressive behavior
GPR30
Female sexual behavior
Learning and memory
17-β-estradiol binds with equal affinity to ERα and ERβ.
Often opposing effects of ERα and ERβ on behavior
Estrogen receptors are required for
male sexual behaviors
Test
αβWT
αβERKO
αERKO
βERKO
Aggression
Number of
mice
0/7
4/8‡
0/2
0/9
Mounts
Number of
mice
6/7
0/7‡§
1/2
7/9
Mean latency*
539.17 ± 52.35
—
291
468.29 ± 36.01
Mean
number/10
min
2.26 ± 0.27
0.00 ± 0.00†‡§
1.50 ± 1.06
1.94 ± 0.24
Number of
mice
5/7
0/7‡§
1/2
6/9
Mean latency*
533.80 ± 43.27
—
412
747.17 ± 94.02
Mean
number/10
min
3.41 ± 0.54
0.00 ± 0.00†‡§
3.00 ± 2.12
4.01 ± 0.54
Number of
mice
1/7
0/7
0/2
1/9
Mean latency*
934
—
—
1,026
Mean
duration*
33
—
—
32
Intromissions
Ejaculation
Ogawa S, et al. Proc Natl Acad Sci U S A. 2000. 97:14737-41.
ERα is required for male aggressive behavior in
mice
©2000 by National Academy of Sciences
Ogawa S et al. PNAS 2000;97:14737-14741
ERα is required for female sexual
behavior in mice
Ogawa S et al. Endocrinology 1998;139:5070-5081
Mice without ERα
αERKO female mice
• no sign of lordosis behavior,
• greatly reduced pup-caring
behavior,
• and elevated levels of
infanticide and aggression
αERKO male mice
• reduced levels of intromission
• and virtually no ejaculation
• normal levels of mounts.
• testosterone-inducible
aggressive behavior reduced
• infertile
Ogawa et al 1996;1997;1998 Pfaff lab
Mice without ERβ
Male
Mounting
Intromission
Ejaculation
normal
Higher
male-male
aggression (1st
test), normal
male-male
aggression in
later tests
Female
Lordosis
normal
Ogawa S et al. PNAS 1999;96:12887-12892
Models for the Role of Testosterone in
Masculinizing the Brain and Behavior.
Scott A. Juntti , Jessica Tollkuhn , Melody V. Wu , Eleanor J. Fraser , Taylor Soderborg , Stella Tan , Shin-Ichir...
The Androgen Receptor Governs the Execution, but Not Programming, of Male Sexual and Territorial Behaviors
Neuron Volume 66, Issue 2 2010 260 - 272
Androgen receptor increases the
frequency of male mating
Scott A. Juntti , Jessica Tollkuhn , Melody V. Wu , Eleanor J. Fraser , Taylor Soderborg , Stella Tan , Shin-Ichir...
The Androgen Receptor Governs the Execution, but Not Programming, of Male Sexual and Territorial Behaviors
Neuron Volume 66, Issue 2 2010 260 - 272
Androgen receptor increases the levels
of male territorial displays (aggression)
Scott A. Juntti , Jessica Tollkuhn , Melody V. Wu , Eleanor J. Fraser , Taylor Soderborg , Stella Tan , Shin-Ichir...
The Androgen Receptor Governs the Execution, but Not Programming, of Male Sexual and Territorial Behaviors
Neuron Volume 66, Issue 2 2010 260 - 272
Mice without brain androgen
receptors
• Show only subtle degree differences in male
type behavior:
– decreased mating frequency
– decreased territorial attack on male intruder
– decreased urine marking behavior
Juntti et al 2010, Shah lab
Other behaviors influenced by
hormone exposure in infancy
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Aggression
Exploratory behavior
Play
Taste preference
Feeding
Active avoidance learning
Maze learning
Puberty begins in the brain
• Gonadotrophin releasing
hormone (Gnrh) neurons
– Start the process of
puberty
• Cascade of pulsatile
release
• GNRH
• Luteinizing
hormone (LH)
• Follicle stimulating
hormone (FSH)
Sisk and Foster, Nat. Rev. Neurosci. 2004
Estrous Cycle: circulating hormones
Humans vs rodents
Synapse density in rat hippocampus
fluctuates with estradiol levels
Gould and McEwen had
previously shown that OVX
reduced spine density.
Change in spine density
occurred during different
phases of the estrus cycle.
Catherine Wooley and Bruce McEwen, 1990
Onset of common psychiatric disease
Paus et al., 2008
Sex differences in psychiatric disease
Men>women
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ADHD
autism
Fragile X
Schizophrenia
Women>men
• Depression
• anxiety
• Eating disorders
Estrogen receptors, anxiety, and stress
• Estradiol administered to
OVX female rats
decreases anxiety and
aggressive behavior.
• OVX reduces HPA
responses to stress (cort
levels); estradiol
enhances.
• Activation of ERβ
decreases anxiety-like
behaviors in rats.
• Activation of ERα
enhances HPA responses
to stress.
• Increased anxiety-like
behaviors in ERβ KO mice.
• Activation of ERβ reduces
HPA responses to stress.
It’s not just about hormones,
chromosomes matter, too
• All female cells of the body contain XX chromosomes.
• All male cells of the body contain XY chromosomes.
• Sex differences can arise from gene expression differences
based on chromosomal (X vs. Y)complement, independent
of hormonal/gonadal status.
• Although most dosage-related sex differences in X gene
expression are essentially abolished by the sex-specific
process of X-inactivation, which transcriptionally silences
one X chromosome in each XX cell, some X genes are
incompletely inactivated.
Separating sex chromosomes from
gonadal phenotype
Delete the SRY gene
Place on an autosome
The four core genotypes to separate
chromosomal vs gonadal influence
XXM
XYM
XXF
XYF
McCarthy MM, Arnold AP. Nat Neurosci. 2011. 14(6):677-83.
Sex differences validated by 4 core genotype
model as organizational/activational effects of
sex hormones
• Male sexual behavior
• Social exploration
• Number of TH neurons in AVPV (F>M)
• Number of motoneurons in spinal nucleus of bulbocavernosus
(M>F)
• Thickness of cerebral cortex (M>F)
• Number of progesterone receptor positive cells in diencephalon,
AVPV, medial preoptic nucleus, ventromedial nucleus.
See Arnold & Chen, Front. Neuroendocrin. 2009. 30:1-9.
Sex differences mediated by sex
chromosome complement
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Aggression-home cage intruder tests
– XXF < (XXM, XYM, XYF)
– Interaction between sex chromosome and gonadal phenotype.
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Pup retrieval (parenting behavior)
– XXF > (XXM, XYM, XYF).
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Social interaction
– XX mice sniffed and groomed intruders less than XY mice.
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Pain responses (nociception)
– XX mice showed quicker/more frequent pain responses.
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Habit formation
– XX persist in responding for food even when it is devalued as a reward.
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Defects in neural tube closure
– XX show more lethality with p53 deletion
See Arnold & Chen, Front. Neuroendocrin. 2009. 30:1-9.
Pain responses in four core genotype
mice-chromosomal effects
Gioiosa, L. et al. , Sex chromosome complement affects nociception in tests of acute and
chronic exposure to morphine in mice, Horm. Behav. 53 (2008) 124–130.
Another layer: brain region specific paternal
imprinting
Silencing of one copy of a gene, depending on its parent of origin
New data suggests this is brain region and age dependent
“Custody battle for the brain” –Nirao Shah 2010
Gregg et al., 2010ab
Sexual Differentiation of the Brain
Genetic sex determination
Steroid hormones
Sexual differentiation of the brain and behavior
Steroid hormone receptors and behavior
Effects of hormones on neuron structure and
signaling
• New genetic approaches to studying sexual
differentiation
•
•
•
•
•
Read: Chapter 58, Principles of Neural
Science, 5th edition
Sexual Differentiation of the Nervous
System