Sex Differences in Behavior: Sex Determination and Differentiation - The Effects of Hormones on Sexually Dimorphic Behaviors
13 important questions on Sex Differences in Behavior: Sex Determination and Differentiation - The Effects of Hormones on Sexually Dimorphic Behaviors
What does the injection of a ovariectomized rat with high doses of estrogen do?
causes an increase of GnRH and LH concentrations due to positive feedback.
What are artricial animals?
Animals that have young that can not yet work for themselves
When do concentrations of testosterone reach levels of adulthood in Rat pups?
After 6 hours, the release of the infants testes from negative feedback suppression by placental gonadotropins and retarded steroid clearance rates as steroid metabolism shifts from maternal systems to the infant's own liver funstion.
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What is the difference in GnRH release between males and females?
Both have surges, however with females, when GnRH surges coincide with high estrogen levels in the blood, extra GnRH is released, resulting in a GnRH and LH surge.
When does masculinization and defeminization occur in rats?
When rats are exposed to testosteron prior to 10 days of age. Otherwise feminization and demasculinization occurs.
Where in the brain are positive and negative feedback of GnRH found?
Positive: hormone release is triggerd by the arcuate nuclei and the ventromedial nuclei of the hypothalamus (VMN). Most of the female GnRH cells are located in the rostral aspects of the preoptic and suprachiasmatic nuclei. The medial basal hypothalamus seems to be where the negative feedback is regulated in rodents.
What is the role of androgens and oestrogens in defeminization and masculinization of the brain: fig 3.30?
female male
remove gonads before day 10? --> / no \ / no \ / yes \
Inject with testosterone before day 10? / No \ / yes \ / no \ / yes \ /no \ / yes \
Remove gonads in adulthood? / Yes \ / yes \ / yes \ / yes \ / yes \ / yes\
Inject with testosterone in adulth? / no yes \ / no yes \ /no yes \ / no yes \ / no yes \ /no yes \
Male-typical behaviour? / no no \ / no yes \/ no yes \ / no yes \/ no no \/ no yes\
What two hypothesis are there that explain that no estrogen treatment can in adulthood can evoke GnRH surge in male rodents or female rodents that are treated with androgens perinatally?
- early exposure to androgens destroy neural connections between the surge and the pulse generators.
- the androgenization may diminish puberal estrogen binding to cytosol receptors so that surges are not observed.
How does the brain of a rat masculinize?
a-fetoprotein is not so much effective in the binding of estrogens so the testosterone produced by the gonads of the males travels through the bbb to the brain where it is automatized into estrodiol where it masculinizes the brain.
What happens to male a and b estrogen knockout mice? (aERKO/bERKO)
Normal mounting behaviours, reduced levels of intromissions, no ejaculation, less aggressive,
What happens to male a + b knockout mice? (abERKO)
fail to express any sexual behaviours.
What do male and female ARKO mice show (androgen knockout)
Male: reductions in male-typical aggression and reproductive behaviours.
Female: Normal
Does maternal stress affect adult reproductive behaviour of offspring?
Yes, male fetuses produce less androgen.. More like females..
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