sex

How do early life events influence long-term brain development?

Early exposures, such as hormones or life experiences around the time of birth, can shape brain circuitry and behavior throughout life.

What are hormones, and how do they differ from neurotransmitters?

- Hormones are chemicals that enter the bloodstream and act at distant locations in the body, whereas neurotransmitters act at synapses in the brain.

- Certain neurotransmitters also function as hormones if they meet the bloodstream criterion.

What parallels exist between the stress axis and the reproductive system?

Both systems involve a hierarchy of hormonal actions and negative feedback loops to regulate their processes. For example, in the stress axis, cortisol exerts feedback on the brain to modulate the response.

How does cortisol regulate the stress response?

Cortisol binds to glucocorticoid receptors in the hippocampus, providing negative feedback to the hypothalamus to reduce stress hormone production.

0 - Hippocampus (negative feedback loop to hypothalamus)

1 - Hypothalamic CRF hormone

2 - Pituitary ACTH

3 - Adrenal cortisol

goes back to hippocampus

What are the primary functions of the testes?

The testes produce sperm (spermatogenesis) and release the hormone testosterone, also known as androgen. They are instructed to make testosterone through gonadotropins (FSH and LH release gonadotropins) (their cell bodies are in the hypothalamus GNRH neurons)

What hormones regulate testosterone production in males?

Testosterone production is regulated by two gonadotropins—FSH (follicle-stimulating hormone) and LH (luteinizing hormone)—which are released from the anterior pituitary gland.

What stimulates the release of FSH and LH?

Gonadotropin-releasing hormone (GnRH), produced by neurons in the hypothalamus, stimulates the release of FSH and LH from the anterior pituitary.

What is the role of GnRH neurons, and how are they affected in Kallmann syndrome?

GnRH neurons release hormones to stimulate gonadotropin production. In Kallmann syndrome, these neurons fail to migrate from the nose to the hypothalamus, resulting in a failure to initiate puberty.

How does negative feedback operate in the reproductive system?

Hormones like testosterone or cortisol provide feedback to the brain or pituitary gland to regulate further hormone release, ensuring the system does not produce excessive hormones.

What is the primary male hormone, and what are its functions?

Testosterone is the primary male hormone, responsible for male reproductive functions and secondary sexual characteristics.

What are gonadotropins, and what is their role?

Gonadotropins (FSH and LH) are hormones released by the pituitary gland that stimulate the gonads (testes in males and ovaries in females) to produce sex hormones and gametes.

What is the relationship between GnRH and gonadotropins?

GnRH (gonadotropin-releasing hormone) from the hypothalamus stimulates the pituitary to release gonadotropins, which then act on the gonads.

What role do hormone receptors play in the regulation of testosterone, FSH, LH, and GnRH?

Hormone receptors are essential for the desired effects of hormones like testosterone, FSH (follicle-stimulating hormone), LH (luteinizing hormone), and GnRH (gonadotropin-releasing hormone). These receptors allow the hormones to interact with cells and trigger biological responses necessary for processes like reproduction.

How does negative feedback work in the testosterone system?

Testosterone exerts negative feedback on the hypothalamus and pituitary. It shuts off the release of GnRH from the hypothalamus and the release of FSH and LH from the pituitary. This reduces further production of testosterone, maintaining hormonal balance.

What happens when a male animal is castrated?

Castrating a male animal removes the testes, eliminating testosterone production. As a result, there is no negative feedback on the hypothalamus or pituitary, which then increases the release of GnRH (gonadotropin releasing hormone), FSH, and LH (gonadotropins) in an attempt to stimulate testosterone production, even though the testes are absent.

What are the effects of anabolic steroid use on hormone production in men?

Anabolic steroids artificially increase testosterone levels, resulting in negative feedback that shuts off the natural production of GnRH, FSH, and LH. The reduced stimulation from FSH and LH can cause the gonads (testes) to shrink since the natural support for sperm production and testosterone secretion is diminished.

How do the reproductive hormone systems in females compare to those in males?

Both males and females rely on similar hormone axes involving GnRH, FSH, and LH. Unlike males, whose system is dominated by negative feedback, females experience positive feedback during certain phases of their menstrual cycle, which triggers ovulation.

What are the functions of FSH and LH in females?

FSH stimulates the ovarian follicles to mature, leading to ovulation. LH triggers ovulation, the process where the mature egg is released from the ovary. After ovulation, what's left of the follicle turns yellow (luton means yellow)

Why are the hormones FSH and LH named as such?

FSH (follicle-stimulating hormone) and LH (luteinizing hormone) are named based on their actions. FSH stimulates the development of ovarian follicles, and LH triggers ovulation and the transformation of the follicle into the corpus luteum, which produces progesterone.

How do estrogen and progesterone function in the feedback system in females?

In females, estrogen and progesterone generally provide negative feedback on the hypothalamus and pituitary, keeping the levels of FSH and LH low. However, during a specific phase of the menstrual cycle, estrogen triggers a switch to positive feedback, leading to a surge in LH and FSH that induces ovulation.

What is the pattern of testosterone levels during a human male's life.

During fetal development, particularly after the first trimester, male fetuses are exposed to high levels of testosterone, which are crucial for sexual differentiation (and then a short spike after birth). These testosterone levels remain elevated until the fetus is born, and they are the highest levels of testosterone the individual will experience until puberty. Then testosterone decreases after old age.

How does the testosterone system change during puberty?

At puberty, typically around ages 10-14, the testosterone system "kicks in," and levels of testosterone rise significantly. This surge is responsible for the development of male secondary sexual characteristics and the onset of reproductive capabilities. Testosterone remains high throughout much of adulthood.

What debates exist regarding low testosterone in older men?

There is ongoing debate about how to manage the natural decline in testosterone levels as men age. Some argue for testosterone replacement therapy to address symptoms of low testosterone, while others question the efficacy and safety of such treatments.

What are the consequences of manipulating the hormonal feedback loop using exogenous testosterone?

The introduction of external testosterone (such as through anabolic steroids) disrupts the normal feedback loop. This causes the hypothalamus and pituitary to reduce the production of GnRH, FSH, and LH, leading to decreased natural testosterone production and potential shrinkage of the gonads due to lack of hormonal stimulation.

How does the absence of testosterone affect the feedback loop in a castrated animal?

Without testosterone, the body detects a lack of this hormone, which leads to an increase in the production of GnRH, FSH, and LH as the hypothalamus and pituitary try to stimulate the gonads to produce more testosterone. However, because the gonads are no longer present or functional, testosterone production does not occur, leading to an imbalance in the system.

What is the impact of neutering (castration) on hormone levels in animals?

Neutering removes the testes, which stops the production of testosterone. This removal of testosterone removes the negative feedback on the hypothalamus and pituitary, resulting in a significant increase in the production of GnRH, FSH, and LH as the body attempts to compensate for the lack of testosterone.

What is the primary hormone that is analogous to testosterone in females?

Estrogen. FSH (follicle-stimulating hormone) and LH (luteinizing hormone) are typically shown, as they support estrogen production.

What happens to FSH and LH levels in the female lifespan?

During pregnancy, FSH and LH levels rise significantly and then drop just before birth. There is also a spike in these hormones shortly after birth, though their exact function during this time is not entirely clear. In puberty, these hormones rise a little and eventually they get monthly surges (menstrual cycle). It continues until they go through menopause, then these hormones shoot through the roof (lost negative feedback).

What is the cause of the hormone levels rising after menopause in women?

After menopause, women no longer produce estrogen and progesterone from the ovaries due to the depletion of eggs. As a result, the negative feedback mechanism is lost, causing FSH and LH levels to rise dramatically and remain high.

What is the debate regarding hormone replacement therapy (HRT) for menopausal women?

The debate surrounding HRT focuses on the potential benefits, such as improving bone density, versus the risks, such as increased cancer risk. Some women may choose to take estrogen and progesterone replacement, but it depends on individual health circumstances.

How are testosterone and estrogen synthesized in the body?

Testosterone and estrogen are both synthesized from cholesterol through a series of enzymatic processes. Cortisol, a stress hormone, is also synthesized in a similar way. (estradiol comes from testosterone)

What is the role of the enzyme aromatase in hormone conversion?

Aromatase is an enzyme that converts testosterone into estrogen.

How does testosterone affect muscle growth in the body?

Testosterone acts on androgen receptors located in muscles. When testosterone binds to these receptors, it stimulates muscle growth, which is why testosterone is often associated with increased muscle mass.

What is the role of 5-alpha reductase in testosterone conversion?

The enzyme 5-alpha reductase converts testosterone into a more potent form called dihydrotestosterone (DHT). DHT is more powerful than regular testosterone and also acts on testosterone receptors in the body.

What behavior was initially studied in rodents to understand the impact of hormones on sexual behavior?

The behavior initially studied in rodents was lordosis, a female mating posture where the female arches her back and allows the male to mount her. This behavior was shown to be dependent on hormones.

What is the male mating behavior counterpart to lordosis in rodents?

The male counterpart to lordosis is the mounting behavior, where the male climbs onto the female to copulate with her.

How do hormonal levels affect mating behaviors in rodents?

Hormonal levels, particularly estrogen and testosterone, are crucial for sexual behaviors like lordosis (female) and mounting (male). These behaviors are triggered and influenced by the presence and fluctuations of these hormones.

Ex: females show lordosis when their estrogen is high, one day out of five

What is meant by the "activational effects" of hormones?

The "activational effects" of hormones refer to how hormones activate specific behaviors in an organism. These effects are temporary and can be reversed when hormone levels change. For example, hormones like estrogen and progesterone activate the mating behavior of lordosis in female rodents, and testosterone activates mounting behavior in male rodents.

How often do female rodents show lordosis behavior during their reproductive cycle?

Female rodents show lordosis behavior about once every four to five days, which corresponds to a particular day in their reproductive cycle, similar to the 28-day cycle in humans.

What happens to female rodents' ability to show lordosis when their gonads are removed?

When the gonads (ovaries) of female rodents are removed, they stop producing estrogen and progesterone, and as a result, they will no longer show lordosis behavior.

How can the behavior of lordosis be restored in a gonadectomized female rodent?

If estrogen and progesterone are administered to a gonadectomized female rodent, she will begin showing lordosis behavior again. The presence of these hormones activates the behavior, and if the hormones are removed, the behavior ceases, demonstrating the reversible (activational) nature of this activation.

How does the male rodent respond when its testis are removed?

When the testis are removed from a male rodent, he will no longer show the mounting behavior, as testosterone, which is produced by the testis, is necessary for this behavior.

Do male rodents show mounting behavior constantly?

Yes, male rodents typically show mounting behavior constantly because they continuously secrete testosterone, unlike females, who have a cyclic reproductive pattern.

Can female rodents show mounting behavior if given testosterone?

No, female rodents do not show mounting behavior even if given testosterone. They require estrogen and progesterone to show lordosis behavior, and they do not respond to testosterone with mounting behavior like males.

What happens if males are given estrogen and progesterone? What if you give females testosterone? (all without gonads)

If males are given estrogen and progesterone, they do not show lordosis or mounting behavior. Females will not show either as well.

What is the key difference in how males and females respond to hormones like testosterone and estrogen?

Males and females respond differently to hormones due to the specific hormonal environment they are exposed to, particularly early in life. Males need testosterone to display male-typical behaviors, and females need estrogen and progesterone to show female-typical behaviors. Simply giving the opposite sex hormones to an adult will not induce the opposite sex behaviors.

What discovery did the 1950s study by Phoenix, Goy, Gerall, and Young make regarding hormones and sexual behavior?

- Expose some female rats to testosterone in early life or male rats to progesterone/estrogen in early life

- Remove gonads

- The female rats exposed to T and given T later in life exhibit mounting. The ones that were given E/P later in life did not show any response

- The male rats exposed to E/P and given E/P later showed lordosis. The ones that were given T later in life did not mount.

- The male rats that were given T early in life and T later showed mounting

What is the difference between activational effects and organizational effects?

- Activational effects are reversible changes that occur in adulthood due to hormone exposure, typically turning specific behaviors on or off.

- Organizational effects are permanent changes that occur during a critical period early in development, usually shaping the structure or behavior for later hormonal activation.

What happens if male rodents are castrated early in life?

If male rodents are castrated early in life, they do not produce testosterone.

What is the critical period for testosterone's effect on sexual behavior in rodents?

The critical period for testosterone's effect on sexual behavior in rodents is the first week after birth. If testosterone is administered outside this narrow window, it will not produce the same effect on sexual behavior.

What is the SDN-POA and how does it relate to sexual behavior in rodents?

The sexually dimorphic nucleus of the preoptic area (SDN-POA) is a brain structure in rodents that is larger in males (5x) than in females. This size difference is influenced by early testosterone exposure, which leads to masculinization. The SDN-POA seems to be involved in coordinating sexual behavior.

How does estrogen contribute to the masculinization of female rodents?

In female rodents, estrogen is converted from testosterone during early development. If a female is given high levels of estrogen early in life, especially when her alpha fetal protein levels are not enough to bind the estrogen, it can masculinize her brain and behavior, leading to behaviors like mounting and a larger SDN-POA.

How does alpha fetal protein influence estrogen's effects on female rodents?

Alpha fetal protein binds to estrogen and prevents it from reaching estrogen receptors in the brain, limiting estrogen's masculinizing effects in the female SDN-POA.

If a female is exposed to high levels of estrogen early in life, and there is insufficient alpha fetal protein to bind to it, the estrogen can masculinize the brain, leading to male-like sexual behaviors.

What did studies with rats show about spatial learning differences between males and females?

Studies showed that male rats tend to learn spatial tasks faster and make fewer errors than female rats. However, both males and females eventually learn the task equally well, with males reaching the stable performance stage more quickly.

How do early hormonal manipulations affect spatial learning in rats?

Early hormonal manipulations can alter spatial learning. For example, castrating male rats early in life leads to slower learning, resembling the pattern seen in female rats. Conversely, giving high doses of estrogen to female rats early in life can accelerate their learning, making their performance more similar to that of male rats.

What does the study of individual differences in male and female rodents suggest about hormonal influence?

Individual differences in male and female rodents, such as differences in the amount of testosterone exposure, can influence behaviors like aggression, mounting, and the size of the anogenital distance. Even without experimental manipulation, natural variation in testosterone exposure can shape behaviors in predictable ways.

Why is it important to study the organizational effects of hormones in rodents?

Studying the organizational effects of hormones in rodents helps us understand how early hormonal exposure can permanently shape behavior and brain development. This knowledge can be used to explore how similar processes might influence human behavior, cognition, and even issues like gender identity and sexual orientation.

What evidence supports the idea that individual differences in hormone exposure affect behavior?

Evidence from rodent studies shows that females exposed to varying levels of testosterone, due to the presence of male siblings, exhibit differences in behaviors like aggression, mounting, and the size of the anogenital distance. These differences suggest that even naturally occurring variations in hormone exposure can shape behavior.

How does the concept of "masculinization" apply to female rodents exposed to testosterone early in life?

In female rodents, early exposure to testosterone can lead to masculinization, meaning they may exhibit male-typical behaviors, such as mounting, rather than female-typical behaviors like lordosis. This masculinization is an organizational effect, occurring during a critical period early in life.

How does the SDN-POA grow larger in male rats?

Testosterone gets converted to estrogen and finds estrogen receptors, which is what sculpts the SDN-POA to be larger.

True or false? Masculinization occurs via conversion of estrogen to testosterone

False, it's T to E

True or false? Aromatase blockers prevent masculinization

True