Chapters 4: Sex Differences in Animals & Humans Flashcards
Sexual dimorphisms in human behavior
Men are more likely to have: Visuospatial abilities Aggression Schizophrenia Autism
Females are more likely to have:
Verbal abilities
Nurturing behavior
Depression
Nature vs Nurture
Nature (genes, hormones)
vs
Nurture (social factors, learning, culture)
Sex matters: “60 Minutes” investigates men, women and drug dosage
http://www.amara.org/en/videos/
H2FdrVnvT8Mn/info/
sex-matters-60-minutes-investigates-men-women-and-drug-dosage/
Early last year, the FDA made a surprising announcement when it cut the recommended dose of the nation’s most popular sleep drug, Ambien, by half - but only for women. Lesley Stahl reports on how much different men and women are, when it comes to medicine.
Women metabolize the drug more slowly than men.
Male and female bodies are very different, and not just on a hormonal or gonadol level, most organs, including the heart and lungs are different between the sexes.
CO-ED LAB RATS study
on The Colbert Report
http://thecolbertreport.cc.com/
videos/el90zp/co-ed-lab-rats
Scientists discover that the tradition of testing medicine exclusively on male subjects can lead to negative side effects for women.
Patterns of play behavior
diferences in girl and boy play behavior.
Sex differences in the brain are Categorized as:
Volumetric: size differences of specific brain regions or nuclei
Connective: type or number of synapses or the size of a particular type of projection within the brain
Spinal Nucleus of the Bulbocavernosus (SNB)
Region of the spinal cord
Motorneurons that innervate muscles attached to the penis that control erection
Sex difference in neuron number and dendritic arbor
Onuf’s nucleus
During fetal development, androgens spare muscles and SNB
Aromatization NOT important for masculine development of this system
Environmental effects can also influence SNB sex difference, i.e. maternal licking
maternal licking of male pups can masculinize the circuit of the spinal cord
Sex differences in mammalian brain
Raisman & Field (1971, Science)
First report of sex difference in brain
Very small connective difference in rat hypothalamus (MPOA)
Used EM to count and categorize synapses in the MPOA
Males: more shaft synapses
Females: more spine synapses
Hormone manipulations immediately after birth can affect this pattern of connectivity
Males castrated 1 day after birth
had a feminine pattern of the dendritic spine activity
Females injected with T shortly
after birth had a masculine pattern
The SNB is larger and has more complex neurons in _______?
males
Onuf’s nucleus
human SNB
It’s a similar area, called SNB in rats and Onuf’s nucleus in humans
T/F:
The SNB in females, and the muscles that control erectile function, are diminished in size or completely absent in adult female rats.
true
SNB sex differences are much _____ pronounced in humans
much more pronounced
side note- in humans it contracts rhythmically during erection and ejaculation
What happens to SNB motorneurons in female rats?
the SNB neurons die in females around the time of birth.
What happens to SNB motorneurons in male rats?
androgen treatment spares the muscles and secondarily spares the SNB, this happens in fetal development
males will lose the spare muscles and SNB unless androgens save them
Is the SNB sex difference volumetric or connective?
volumetric
Does the SNB depend on androgens or estrogens?
androgens
T/F:
Aromatization is NOT important for masculine development of the SNB system
true
Environmental effects on SNB size:
maternal licking of male pups can masculinize the circuit of the spinal cord
Are androgen treatments effective once the muscles responsible for penile erection have atrophied?
No, once the muscles have regressed, androgen treatment cannot restore the muscle cells so the critical period of androgen effectiveness in sparing motoneurons in the SNB is defined by the rate of muscular atrophy.
______ prevent cell death in the SNB
Androgens
First reported sex difference in the mammalian brain?
Very small CONNECTIVE difference in rat hypothalamus (MPOA)
Males: shaft synapses are larger than spine synapses
Females: the opposite
Males castrated 1 day after birth had a ______ pattern
feminine pattern of the dendritic spine activity
Females injected with T shortly after birth had a ______ pattern
masculine pattern
The SDN-POA (Sexually Dimorphic Nucleus of the Preoptic Area) is bigger in _____ than in _____ .
males than in females.
The sex difference in the size of the SDN-POA is due to a _______ number of cells in females and castrated males; androgens, or more precisely their estrogenic metabolites, protect neurons from apoptosis, programmed cell death.
decreased
Rats with complete androgen insensitivity syndrome (testicular feminization) exhibit what?
a deficiency in androgen receptors but normal estrogen receptors and display female typical genitalia but male-typical SDN-POA
Gorski et al (1978)
Rat tissue sections stained with Nissl
Volumetric sex difference in SDN-POA
SDN-POA
T permanently enlarges the SDN-POA but only if given during critical period in early life
Difference in cell number; cell death
Estrogens (aromatized from testosterone) protect neurons from cell death and masculinize the SDN-POA
Males who are castrated neonatally have an SDN that is female in size. Castrating male rats in adulthood does not alter the size of the POA.
Gonadal hormones and developmental apoptosis:
regional specificity.
SDN vs. nearby AVPV
Giving testosterone to a fetal female rat caused them to develop this male-typical brain SDN
MANY mechanisms produce organizational sex differences in the brain (and probably behavior)
DNA Methylation Histone Acetylation Neurogenesis Cell Death or Survival Spinogenesis Neuronal Migration.
Regional specificity in synthesis (and receptors) produce a complex mosaic
Remember: Steroid hormones are synthesized in the brain!
First reported that women have smaller brains than men
However – brain size relative to body size is not different !
Sex differences in human brain
Increased folding of the brain surface in women
Global cerebral blood flow is greater in women
Women have a higher proportion of gray matter
men have a higher percentage of white matter
Neurochemical differences
Genetic/epigenetic differences
In some studies, nuclei of the human POA subdivided into interstitial nucleus of the anterior hypothalamus (INAH) 1-4
Preoptic Area (POA)
…
INAH-3 in humans
Cause or consequence?
Organizational effects in humans
Hormones act to ‘prepare’ the brain to direct sex-specific reproductive behaviors
…so brain (and body) phenotype matches the sex-specific hormone levels the brain will experience later in life and sex-typical behavior will result
WHAT HAPPENS IF THERE IS A MIS-MATCH?
Brenda / Bruce Reimer (David)
Sad resolution to a sad story
Evolving medical standards to deal with ambiguous genitalia in infants
Disorders of Sexual Development:
Treatment and Intervention
New medical standards for dealing with disorders of sexual development and ambiguous genitalia:
DO NOT alter genitalia to ‘conform’ or make the problem go away. Wait until the child can decide
DO NOT conceal from child
DO Assign a gender AFTER appropriate genetic and hormonal tests
Diagnose 5-alpha reductase, AIS, etc and predict likely gender identity based on this
Organizational effects on human behavior:
Androgens and Congenital Adrenal Hyperplasia
Adrenal dysfunction leads to under-production of cortisol and over-production of sex steroids
Females with CAH are exposed to high levels of androgens during early development
What about the brain and behavior of CAH females?
Prenatal androgens and sex-typical play: Evidence from CAH
Not all sex differences in the brain relate to reproduction:
A majority occur in brain regions primarily related to reproductive behavior
Example: hypothalamus, spinal cord nuclei.
Others in brain regions related to reproductive and other behaviors
Amygdala: fear, territorial aggression, SEX
Periaqueductal gray: pain, SEX
…but maybe not. Sex differences in non-reproductive behaviors, too, such as spatial reasoning (hippocampus) and language (frontal cortex)
Organizational effects on human behavior:
Art in girls and boys—nature or nurture or both?
motifs in coloring
A sampling of human sex differences in cognition:
Males better:
Spatial
Aiming
If only 60 percent of seedlings will survive, how many must be planned to obtain 660 trees?
Females better:
Matching
Words
2 (15 + 3) + 12 – 15/3 = ?
Men and women use different parts of their brains to solve similar language tasks (rhyming)
Female pattern is bilateral; greater lateralization in males
Activational Effects in Humans
Individual differences in androgen levels (activational) predict performance on some tasks
There seems to be a bell curve of how much testosterone and how well they do the SPATIAL task
And there’s a line slope with PERCEPTUAL speed, where the lower the testosterone, the better they do
Studying sex differences in humans is difficult because:
1) Overlap and effect size
2) Ethics of manipulating hormones
Must take advantage of hormone manipulations for other reasons
Transexual transition….
Male to female: administered androgen receptor blockers or estrogens
Female to male: administered androgens
Female to male transexuals
Female to male transexuals taking testosterone during transition.
fMRI during transition to see brain structure changes over 4 weeks
Decrease volume due to testosterone
Transexual studies
Increased inter-hemisphere connectivity in Male to Female transexuals
Increased intra-hemisphere connectivity in female to male transexuals
Total brain volume—down in male to female transexuals on HRT
Ventricular volume—up in male to female transexuals; down in female to male transexuals
Hypothalamus size- down in male to female transexuals (match females)
MALE –> FEMALE transexuals
on anti-androgen or estrogen treatment
Animal Models for Sexually Dimorphic Behaviors
Play behavior in primates
Birdsong
Urinary posture in canines
Sex differences in play in non-human primates are Very similar patterns to those seen in CAH and in human girls and boys
Rough-and-tumble play is more common with young male primates
Rough-and-Tumble Play in Primates
Males engage in more play behavior than females, a larger proportion of their play involves simulated fighting or rough-and-tumble play
Sex difference in play is behavior organized prenatally and is not dependent on the activational effects of hormones
Pseudohermaphrodites were females treated in utero with androgens
Birdsong
Song is a learned vocalization
Stages of song learning: 1. Sensory stage (listen) 2. Sensory motor stage (Listen and try) 3. Crystallization (Become proficient)
Sex difference in amount of singing is species specific
Sex differences in birdsong reflect sex differences in brain regions that control singing
Song circuit
AREA X: Like the Basal Ganglia
HVC: PreMotor Cortex
Efferent motor pathway: song production
Anterior forebrain pathway: song learning
Zebra finch
In species where there is a large sex difference in the amount of song, brain structures involved in song are sexually differentiated.
Area X can’t be discerned in females
HVC & RA: males > females
Due to larger, more numerous and scattered neurons in these nuclei
Sex differences in brain and singing are either organized by estrogen or activated by androgens
Gurney & Konishi (1980, Science)
If females treated with estradiol after hatching, and with T in adulthood:
RA and HVC almost the size of untreated males
They sing!
Organizational /activational hypothesis in action
But…
Castration after hatching does not demasculinize the song system or singing behavior
Treating hatchling males with antiestrogens, antiandrogens or aromatase inhibitors does not demasculinize males
No consistent sex differences in chick plasma estradiol or testosterone (but brain?)
No sex differences in brain estrogen receptors or brain aromatase
Treating genetic females with an aromatase inhibitor during development will produce a genetic female with testes…
…testes insufficient to masculinize female brain!
Perhaps a gene on the sex chromosomes play a role ?
Both sides of brain exposed to same hormonal milieu
Perhaps the sex chromosomes compensate for some hormone issues
Normal male song and copulation
Urinary posture in canines
Sexually dimorphic
Female dogs treated with T in utero and immediately after birth –> had masculinized genitalia and male urinary posture
Males castrated as puppies still shift from the juvenile to male position when normal males do
Male typical posture organized by perinatal androgen exposure but does NOT require hormones for activation
Changes in perceptual processing of environment too, seem to be organized. Male adults prefer to urinate on things in vertical orientation of at least a certain height
