Lecture 24- Sex and sexuality Flashcards
How is sex genetically determined?
- XX= females -XY= male
What gene on the Y chromosome determines male development?
-there are few genes on the Y chromosome -SRY gene determines this -SRY leads to development of testosterone secreting cells in early development
What does absence of SRY result in?
-female phenotype (this is the default phenotype)
What are the sex hormones (3)?
- Testosterone= (androgen) male sex hormone 2. Estradiol (estrogen)=female sex hormone 3. Progesterone (other main female sex hormone)
What is the pathway by which sex hormones are made?
-
What is really important for sex hormone production?
-presence of cholesterol
What does aromatose do?
-converts testosterone to estradiol (estrogen)
What is 5-alpha dihydrotestosterone?
-converted by 5-alpha reductase from testosterone -stronger type of the androgen
When do sex steroids appear in males?
-In males, circulating testosterone seen early in foetal development – Falls to very low levels after birth – Rises again at puberty
When do sex steroids appear in females?
-In females, circulating estrogen and progesterone appear at or around puberty – Fall to very low levels at menopause – Testosterone synthesized in adrenal cortex- present throughout life
What does testosterone do in females after menopause?
as the other hormones in females disappear from 45-55 -then testpsterone takes up the function of the steroid hormones tp keep the whole system functioning
What is the difference between males and females in presence/absence of sex steroids in utero?
males have testosterone and some and progesterone circulating
When is testosterone the highest in males?
-higheset at 20 and falls to a third by 75
What are the sites of estrogen action in a rat brain?
–At synapses, membrane action –In cell bodies, DNA transcription, estrogen receptors (ER)
What are the effects estrogen in the brain?
-alter neurotransmitter synthesis, releaser and re-uptake -alter membrane permeability -promotes or inhibits transcription (protein synthesis)
How is PMS mood explained?
-estrogen and progesterone and testosterone can act on cell membrane directly= this is likely to account for the mood of PMS!!!! -alter the action of GABA receptors
What are the brain areas with estrogen receptors?
-Most regions with ER involved in sexual behaviour or regulation of steroid production
Are the androgen and progesterone receptors found in overlapping but distinct regions?
-yes -similar subcellular sites of action
How does hypothalamus come into sex steroids?
-sets their levels by feedback •Hypothalamus acts to cause release of hormones (FSH, LH) from the pituitary that regulate production of estrogen or testosterone •Hormone secretion depends on environment and levels of the relevant sex steroid -at this level the hormones have neural effect as it has feedback!
Can sex steroids get through the blood brain barrier?
-yes as they are steroids= lipid soluble
What are the gender dimorphisms in humans? (4)
- Sexual behaviour 2. Pain 3. Cognitive function 4. Maternal behaviour
What are the differences in sexual behaviour between the genders?
- – Mating,courtship,bonding,rhythms
- rats=females get into position for sex if injected with testosterone then try to mount instead= must be hormone mediated
What is stress-mediated analgesia?
if you stress an animal they feel pain less= males and females have different versions and are different pharmacologically
How do females and males differ in cognitive function?
1.Males score better than females on spatial rotation tasks 2.Males score higher, and lower, than females on tests of higher mathematical skills (at low end of mathematical skills= more males than females -females have a tighter grouping around the mean) 3. Females perform better in learning during period after puberty
What is the sexually dimorphic nucleus of preoptic area (SDN-POA)?
-differs in male and female rats -larger in males -subthalamic nuclei -function in sexual behaviour and response to mating -humans have a similar thing but at least 4 nuclei
If you inject a female rat with testosterone shortly after birth how is the SDN-POA affected?
- converted to male structure by testosterone treatment around birth
- see it is larger in a male but similar if female with testosterone= these females will try to mount
- part of the brain driving the mountaing
- can masculinize the brain by progesterone too as it is then converted by the nucleus to testosterone
What is the firing of SDN-POA of a female rat at different stages of mating?
*insertion of penis, ejaculation arrows
What is the firing of neurons of SDN-POA in a male monkey when exposed to a receptive female?
-reacts on seeing the female already
Does stress reduce reaction to painful stimuli?
-yes
How does male and female mediated analgesia differ?
1: Swim in warm water analgesia depends on endogenous opioids -Males more sensitive to antagonists than females 2:• Swim in cold water analgesia depends on NMDA receptors in males, but not in females - Difference disappears if estrogen is removed
What are the organizational effects of steroids?
-Occur during development and determine structure -will not change, like the preoptic nuclei thing -happens at a time when no estrogen circulating in females so all detrmined by testosterone or its absence
What is androgen insensitivity?
-lack of testosterone receptors or not working – Androgen-insensitivity syndrome leads to genotypic males being phenotypic females
What do the individuals with androgen insensitivity look and behave like?
• More feminine than women in several ways –more female behaviour than females as they do not have any testosterone and none of the responses to it even females have -tall, fair hair -some breasts, usually quite attractive -do not get periods usually -organiational effect
Are there many effects in brain due to conversion of testosterone to estradiol via aromatase within neurons?
-yes -local conversion as it is in a neuron, within it -organisational effect
What are the activational effects of steroids?
• Responses to levels of circulating hormones once development is complete
What are examples of activational effects of steroids? (5)
1 .Estradiol increases number of dendritic spines in hippocampus (means more potential synapses in hippocampus at certain times of the month=following menopause women are more vulnerable to dementia due to this (and that they live longer) 2. Premenstrual syndrome 3. Stress mediated analgesia 4. Aggression due to use of anabolic steroids (androgens) 5. Regulation of steroid hormone production
What is the social life of prairie and montane voles?
•Prairie voles pair bond, although not strictly monogamous, first mating leads to strong changes in behaviour •Montane voles are polygamous – No pair bonds,love them and leave them
How does the social bonding or lack of happen in the voles?
•Difference is in expression of oxytocin receptors in females and in form of vasopressin synthesised in males
–Markedly different between two types of vole
–Oxytocin receptors more dense in reward system of females
–Vasopressin molecule longer in males
- Mating releases vasopressin in males and oxytocin in females
- Blocking vasopressin prevents pairing in prairie vole males
- Giving long vasopressin to an unmated male induces pairing with novel female even when mating does not take place
- Blocking oxytocin prevents pairing in females
