Chapter 4 Flashcards
(42 cards)
Organizational/Activational Hypothesis also referred to as:
linear model
linear model states (in males):
1)while the organism is developing androgens are present (ex: organism has testes) and those androgens are converted into estrogens will masculinize CNS and defeminize CNS 2)then in adulthood, if there are masculine hormones present (testosterone), this will lead individual to engage in classic male behaviour
linear model states (in females)
1) Early on the individual is chromosomal female, undifferentiated gonad develops into ovaries, ovaries do not produce many hormones (not much androgen) which feminize and demasculinize leading individual to engage in female typical behaviour if specific hormones are there to activate as adults estrogen + progesterone are there. Hormones produced in adults act on system that already developed in female like fashion
Two stage model for organizational effects of steroids
hormones are very present during perinatal but also see a peak of androgens during pubertal stage: presence of hormones continue to reorganize system
differentiate linear model and two stage model:
Linear model: only organization happening at perinatal then activation of that system during adulthood
Two stage model: there is organization in perinatal but further organization in pubertal/adolescent stage as well
Sex differences in the brain (4)
(1) Connective differences
(2) Volumetric differences
(3) Lesions or stimulation of Medial Preoptic Area (MPOA) alter sexual behavior
(4)Connective sex differences
sex differences in the brain describe (1/4):Connective differences
Connections: synapses (amount synapses, location)
One can look at if there are differences in the types of synapses or amount of synapses in specific brain regions between sexes
sex differences in the brain describe volumetric differences (2/4):
Size difference: size of the brain, is there a difference in regards to specific regions or specific nucleus?
sex differences in the brain (3/4):Lesions or stimulation of Medial Preoptic Area (MPOA) alter sexual behavior***
MPOA very important for sexual behaviour especially in males: you lesion MPOA – reduces sexual behaviour, electrically stimulate MPOA – increase sexual behaviour***
sex differences in the brain:* Connective sex differences
MPOA: females more synapses formed on dendritic spines, male more synapses on dendritic shaft
Do hormones play a role In this difference connectivity MPOA synapses dendrites vs dendritic spines ?
YES
what happens if you castrate male rats on day 1 of life in terms of connective sex difference
These males would show more synapses forms on dendric spines instead of on the shaft (in a female like manner)
what happens if u treat a 4 day old female rate with testosterone in terms of connective sex difference
These females will form more synapses on dendritic shaft instead of how they normally would on dendritic spine
Volumetric sex differences in the brain have been found: __ larger in males
Sexually Dimorphic Nucleus of the Preoptic Area (SDN-POA) larger in males
SDN POA will be bigger (like male) if a female was
exposed to androgens (converted to estrogen
what causes big size of SDN POA in males?
androgens converted to ESTROGENS: we know this because in males inhibit aromatase and end up with SDN POA size of female
can you differentiate sex of rat early on by looking at SDN POA
no early on SDN POA same size in males and females:Male and female rats born with similar number of neurons in SDN-POA
The sex difference in size of SDN POA is due to ↓number of cells in female SDN-POA. So what might testosterone be doing here?
In females absence androgens (absence estrogen): cause most cells specifically in SDN POA to die (apoptosis)
In males, testosterone (converted to estrogen in rats) seems to be inhabiting apoptosis so SDN POA stays same size
What happens if a male does not have reductase? SDN POA will still shrink
SDN POA plays a role in sexual preference and typical male mounting
It is not testosterone directly inhibiting: testosterone once it goes into cell it goes into cell converted to estradiol via aromatase: estradiol binds to receptor to form steroid receptor complex which will bind to DNA in presence of coregulator which will
SDN POA plays a role in
sexual preference and typical male mounting
Another volumetric sex difference:
__ is larger in females
Anteroventral periventricular nucleus (AVPV)
kisspeptin neurons (neurosecretory cells) are located where
AVPV
kisspeptin neurons are positively activated by:
estrogen during positive feedback
AVPV Important in
LH surge which gives rise to estrogen followed by progesterone surge ultimately leading to ovulation
In this region we have neurosecretory cells which produce and release kisspeptin, when kisspeptin binds to its receptors on neurosecretory cells leads to release of GTRH.. secretion LH + FSH
GNRH not only impacted by kisspeptin
Typically what happens is that certain neuro secretory cells in hypo produce and secrete GNRH in portal system to anterior pituary which secretes FSH and Lh: these bind to receptors on female gonads and lead to production of various hormones importantly peak in estrogen and progesterone for ovulation
Typically progesterone and estrogen feed back negatively
One every cycle the system moves away from negative feedback to positive feedback: increase estrogen leads to more estrogen being released: that surge estrogen followed by surge progesterone is important for ovulation
APVN important because
it has neurosecretory cells that produce kisspeptin: when kisspeptin is released neurosecretory cells that produce GRH produce even more GRH
**SCN seems to be important as well: important in biological rythms: surge happens once per month we need to know when that is : SCN behaves like clock machine
