sex differences in animals and humans

schizoprenia

autism

ADHD

parkinson’s

aggression

spatial tasks

males > females

depression

multiple sclerosis/autoimmune

alzheimer’s

verbal tasks

nurturing

female > males

genetically different

biochemically different

immunologically different

neuronally different

neurobiologically different

males and females differ in variety of ways that can impact disease 

1993

NIH mandated enrollment of women in human clinical trials

2016

NIH required pre-clinical research to include males and females and to consider sex as a biological variable

behavioral sex differences

hormones sculpt and fine tune the brain in ways that could account for sex differences in adult behavior

sexual dimorphism

two distinct forms or opposing characteristics between sexes

sex differences

differences, subtle or not, between males and females

sex convergence and divergence

endpoint is the same in males and females, but mechanisms are different

volumetric

connective

neurochemical

sex differences in the nervous system

volumetric

size differences of specific brain regions or nuclei

connective

type and number of synapses or the size of particular type of projection within the brain

neurochemical

differences in hormonal/NT secretion, receptor number and receptor distribution patterns

gonadal steriod hormones

genes

environment

contribute to brain sex differences

spinal nucleus of bulbocavernosus

region of spinal cord that contains motor neurons that innervate bulbocavernous muscle

• larger and contains more neurons in males

bulbocavernous muscle

muscle that is attached to the penis and controls penile erection

testosterone and environment

testosterone is responsible for the masculine development of spinal nucleus of bublocavernous 

reduced maternal licking in male pups leads to a smaller spinal nucleus of bublocavernous 

MPOA

small connective difference between male and female rats in this region of the brain

shaft synapses > spine synapes

male MPOA

spine synpases > shaft synpases

female MPOA

sexually dimorphic nucleus 

volumetric sex difference; bigger in males compared to females 

• evidence suggests that it might act to inhibit female sexual behaviors in males 

estrogens

aromatized from testosterone; protect neurons from cell death and masculinze the SDN

AVPV

regulates ovulation and controls maternal care; larger in females compared to males

estradiol

promotes apoptosis of AVPV in males

vasopressin

neurochemical sex difference 

• estradiol masculinizes vasopressin expression

• males have 2-3x more vasopression-expressing neurons as females in limbic regions and projections of these cells are denser as well

4 core genotypes models

used to detect direct chromosome effect on a sex difference

• mice are genetically modified so that sex chromosomes are unrelated to the animal’s gonadal sex

• used to show chromosomal sex differences in behaviors and disease

sex steriods

sex differences tend to be evidence in regions that are known to possess receptors for

global cerebral blood flow and gyrification

greater in females compared to males

gray matter

females have more of this type of matter than males

white matter

males have more of this type of matter compared to females

INAH-3

brain structure that is bigger in males compared to females

mosaicism

brain of any one individual is likley to be a mosaic of relative maleness, femaleness, and sameness with the brain of no two individuals being exactly alike