Before birth, the rodent brain is sexually undifferentiated. It is only in the first few days following birth, during a period referred to as the critical period, that the rodent brain differentiates along male or female lines. The hormone testosterone plays a critical role in this development. Specifically, sexual differentiation is determined by the presence of estradiol, an estrogen derivative of testosterone, in certain areas of the brain. Testosterone is converted to estradiol in critical brain cells that contain the enzyme aromatase.To study the effects of testosterone on the neonatal rodent brain, the following experiments were conducted: The above research, combined with additional studies, concluded that testosterone has two "organizational" effects on the male rodent brain:DefeminizationModerate levels of testosterone-derived estradiol during the critical period are sufficient for defeminization of the brain. Defeminization of the rodent brain results in loss of estrogen positive feedback on LH and FSH secretion and the ensuing loss of cyclicity, as well as loss of female sex behavior.MasculinizationHigh levels of estradiol due to high levels of testosterone during the critical period results in masculinization of the brain. Masculinization leads to the induction of male sex behavior including antagonism towards other males and the mounting of females.A researcher proposes that very low doses of estradiol are required for induction of female sex behavior and cyclicity in the rodent brain. Which of the following observations would best support this hypothesis?
Answer(s): A
The passage indicates that estradiol is an estrogen. Choice A states that tamoxifen is an antiestrogen.Therefore, injecting tamoxifen blocks all estradiol activity. So, as predicted by the given experiments, masculinization would not occur in female neonates injected with tamoxifen and male sex behavior would not be induced. The lack of female sex behavior and cyclicity, and lack of male sex behavior, indicates that induction of female sex behavior and cyclicity also requires estradiol.Choice B is incorrect because aromatase is only responsible for converting testosterone to estradiol. So, lacking aromatase would have no effect on estradiol present in females that is not testosterone-derived. And, most of the estradiol in females is not derived from testosterone. This experiment, then, provides no information about the role of estradiol in inducing female sex behavior.Choice C is incorrect because large doses of estradiol lead to defeminization and masculinization as expected.This does not support the hypothesis.Choice D is incorrect because males convert testosterone to estradiol in the brain, leading to normal male development. This does not support the hypothesis. Note that while the incorrect choices did not oppose the hypothesis, they did not support the hypothesis either.
Before birth, the rodent brain is sexually undifferentiated. It is only in the first few days following birth, during a period referred to as the critical period, that the rodent brain differentiates along male or female lines. The hormone testosterone plays a critical role in this development. Specifically, sexual differentiation is determined by the presence of estradiol, an estrogen derivative of testosterone, in certain areas of the brain. Testosterone is converted to estradiol in critical brain cells that contain the enzyme aromatase.To study the effects of testosterone on the neonatal rodent brain, the following experiments were conducted:The above research, combined with additional studies, concluded that testosterone has two "organizational" effects on the male rodent brain:DefeminizationModerate levels of testosterone-derived estradiol during the critical period are sufficient for defeminization of the brain. Defeminization of the rodent brain results in loss of estrogen positive feedback on LH and FSH secretion and the ensuing loss of cyclicity, as well as loss of female sex behavior.MasculinizationHigh levels of estradiol due to high levels of testosterone during the critical period results in masculinization of the brain. Masculinization leads to the induction of male sex behavior including antagonism towards other males and the mounting of females.In Experiment 2, researchers most likely waited 2-3 months before implanting ovaries:
Answer(s): C
The experiments were designed to demonstrate the effects of testosterone on sexual differentiation. The ovaries were transplanted to allow the rodent to demonstrate whether or not it had the ability to cycle normally.Thus, it is important that transplantation of the ovaries did not influence the development of the rodent. To make sure that the transplantation of ovaries had no effect on the sexual differentiation of the rodent brains, the ovaries had to have been transplanted once the sexual differentiation of the rat brain had already occurred.According to the passage, this differentiation occurs during the critical period which begins a few days after birth. The researchers castrated the neonate and waited for the rodent to mature past the critical period before implanting the ovaries.Choice A is incorrect because it would not take 3 months for the rat to recover from surgery. Also, the rat is castrated at birth indicating that surgery is not an obstacle. Implanting the ovaries would require another surgery.Choice B is incorrect because testosterone levels would not rise in the castrated rat (no testes).Choice D is incorrect because defeminization would be promoted by estradiol (or testosterone converted by aromatase).
Before birth, the rodent brain is sexually undifferentiated. It is only in the first few days following birth, during a period referred to as the critical period, that the rodent brain differentiates along male or female lines. The hormone testosterone plays a critical role in this development. Specifically, sexual differentiation is determined by the presence of estradiol, an estrogen derivative of testosterone, in certain areas of the brain. Testosterone is converted to estradiol in critical brain cells that contain the enzyme aromatase.To study the effects of testosterone on the neonatal rodent brain, the following experiments were conducted: The above research, combined with additional studies, concluded that testosterone has two "organizational" effects on the male rodent brain:DefeminizationModerate levels of testosterone-derived estradiol during the critical period are sufficient for defeminization of the brain. Defeminization of the rodent brain results in loss of estrogen positive feedback on LH and FSH secretion and the ensuing loss of cyclicity, as well as loss of female sex behavior.MasculinizationHigh levels of estradiol due to high levels of testosterone during the critical period results in masculinization of the brain. Masculinization leads to the induction of male sex behavior including antagonism towards other males and the mounting of females.An adult male rat that is acyclic is observed to mount females. However, the rat also allows itself to be mounted by male rats. According to the passage, the most likely Explanation: for these observations is that:
The rat has been masculinized and so exhibits male sex behavior. However, the rat has not been fully defeminized in that it exhibits some female sex behavior.Choice A is incorrect because the passage does not discuss hermaphrodites. It focuses on the sexual differentiation of the brain, not the sex organs.Choice B is incorrect because the passage does not discuss demasculinization.Choice D is incorrect. The passage defines masculinization as the development of male sex behavior, which the rat exhibits by mounting females. Thus, the rat has been masculinized. The passage's definition of defeminization includes the loss of female sex behavior. Since the rat still demonstrates some aspects of female sex behavior, (i.e., allowing itself to be mounted by males), it has not been fully defeminized.
Before birth, the rodent brain is sexually undifferentiated. It is only in the first few days following birth, during a period referred to as the critical period, that the rodent brain differentiates along male or female lines. The hormone testosterone plays a critical role in this development. Specifically, sexual differentiation is determined by the presence of estradiol, an estrogen derivative of testosterone, in certain areas of the brain. Testosterone is converted to estradiol in critical brain cells that contain the enzyme aromatase.To study the effects of testosterone on the neonatal rodent brain, the following experiments were conducted:The above research, combined with additional studies, concluded that testosterone has two "organizational" effects on the male rodent brain:DefeminizationModerate levels of testosterone-derived estradiol during the critical period are sufficient for defeminization of the brain. Defeminization of the rodent brain results in loss of estrogen positive feedback on LH and FSH secretion and the ensuing loss of cyclicity, as well as loss of female sex behavior.MasculinizationHigh levels of estradiol due to high levels of testosterone during the critical period results in masculinization of the brain. Masculinization leads to the induction of male sex behavior including antagonism towards other males and the mounting of females.Steroid hormones bind to receptors in the nucleus and directly regulate:
Steroid hormones diffuse into the nucleus and bind to receptors. The steroid/receptor complex binds to DNA and regulates mRNA transcription. In contrast, peptide hormones bind to receptors on the surface of the cell and exert their effects through secondary messenger systems.Choice B is incorrect because protein translation by ribosomes is not regulated by steroid hormones.Choice C is incorrect because cAMP production is generally associated with protein hormones binding to cell membrane receptors. It is part of a single transduction mechanism, acting as a second messenger.Choice D is incorrect because DNA replication is not regulated by steroid hormones.
Before birth, the rodent brain is sexually undifferentiated. It is only in the first few days following birth, during a period referred to as the critical period, that the rodent brain differentiates along male or female lines. The hormone testosterone plays a critical role in this development. Specifically, sexual differentiation is determined by the presence of estradiol, an estrogen derivative of testosterone, in certain areas of the brain. Testosterone is converted to estradiol in critical brain cells that contain the enzyme aromatase.To study the effects of testosterone on the neonatal rodent brain, the following experiments were conducted: The above research, combined with additional studies, concluded that testosterone has two "organizational" effects on the male rodent brain:DefeminizationModerate levels of testosterone-derived estradiol during the critical period are sufficient for defeminization of the brain. Defeminization of the rodent brain results in loss of estrogen positive feedback on LH and FSH secretion and the ensuing loss of cyclicity, as well as loss of female sex behavior.MasculinizationHigh levels of estradiol due to high levels of testosterone during the critical period results in masculinization of the brain. Masculinization leads to the induction of male sex behavior including antagonism towards other males and the mounting of females.A normal female rat injected with estradiol will respond by:
Answer(s): B
Estradiol has a positive feedback effect on the pituitary, causing it to secrete LH and FSH. Estradiol also has a positive feedback effect on the hypothalamus, causing it to secrete GnRH. Estradiol injection will lead to an LH surge in rodents capable of cycling.Choice A is incorrect because LH secretion increases.Choice C is incorrect because GnRH secretion increases.Choice D is incorrect because progesterone is not secreted by the follicle. It is secreted by the corpus luteum or placenta.
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