Sex and the brain

Question 1

What are the sex hormones and what do they secrete?

Answer 1

-ovaries and testes secrete sex hormones –> outside the nervous system but activated but the brain –> hormones released by anterior pituitary regulate secretions from ovaries and testes

Question 2

what is sex?

Answer 2

biological state of being male or female, determined by chromosomes, hormones and body anatomy

Question 3

What is gender?

Answer 3

Set of behaviours and attributed a culture associate with men and women (i.e., masculine and feminine)

Question 4

what is gender identity?

Answer 4

our perception of our own gender

Question 5

Where is DNA and what does it provide?

Answer 5

-nucleus of every human cell, provides a person’s genetic blueprint, with all the information needed to build and individual.

Question 6

How DNA organised?

Answer 6

-into 46 chromosomes –> 23 from the father and 23 from mother
-Each of us has two versions of the chromosomes 1 through 22, conventionally numbered in order of decreasing size –> only exception to this pair system are the sex chromosomes, X and Y
-Thus, its usually stated that there are 44 autosomes (22 pairs of matching chromosomes) and 2 sex chromosomes.
-females have 2 X chromosomes, one from each parent (i.e., XX genotype)
-males have an X chromosome from mother and a Y chromosome from the father (i.e., XY genotype)

Question 7

What do genotypes specify?

Answer 7

a persons genetic sex – in humans a father’s contribution of X or Y determines the genetic sex – other animals can be different such as birds where mother determines sex of offspring

Question 8

What does a piece of DNA comprising a single gene provide?

Answer 8

the unique information needed to construct a particular protein – about 25,000 genes in human genome

Question 9

describe the size and number of genes on X and Y chromosomes

Answer 9

• X chromosome significantly larger
• X chromosome contains about 800 genes, Y chromosome contains about 50

Question 10

what are some medical consequences males suffer for having a XY genotype (more specifically for having a Y chromosome)?

Answer 10

-If a female has a defective gene on an X chromosome, she may experience no negative consequence if her gene on the other X chromosome is normal. However, any defect in a single X chromosome of a male can lead to a developmental defect, such a defect is called a X-linked disease, and there are many, e.g., red-green colour blindness relatively common in males, haemophilia and Duchenne muscular dystrophy.

Question 11

What is the sex-determining region of the Y chromosome (SRY)?

Answer 11

• a gene in the Y chromosome
• codes for a protein called testis-determining factor (TDF)
• human with Y chromosome and SRY gene develops as a male, without it, the individual develops as a female
• located on short arm of the Y chromosome
• not the only gene involved in sex determination, as SRY is known to regulate genes on other chromosomes. Also, male-specific physiology, such as sperm production, relies on other genes on the Y chromosome. Nonetheless, we will see shortly that expression of the SRY gene causes the development of the testes, and the hormones from the testes are largely responsible for making a male foetus develop differently from a female foetus.

Question 12

What is turner syndrome?

Answer 12

• a partial or complete absence of one X chromosome in a female (XO genotype), affecting one in 2500 female births, miscarriages occur with most XO foetuses. girls who survive have variety of charateristics
  —> including short stature, a receding jaw, webbed neck, and visuospatial and memory difficulties. Ovaries are abnormal, and oestrogen replacement therapy generally needed for breast development and menstruation
  -no known males with loss of X chromosome (YO)

Question 13

what is Klinefelter syndrome?

Answer 13

-extra X chromosome, one in 1000 male births
-these XXY individuals are male because of the presence of the SRY gene on the Y chromosome
-some cases there are no obvious indications of XXY genotype, but possible symptoms include less muscular body, less body hair, and increased breast tissue because of lower testosterone production

Question 14

describe the development of the gonads and external genitals

Answer 14

-during first 6 weeks of pregnancy, gonads are in an indifferent stage that can develop into either ovaries or testes.
-the uncommitted gonads possess two key structures, the Mullerian duct and Wolffian duct
-if the foetus has a Y chromosome with an SRY gene, testosterone is produced, and the wolffian duct develops into the male internal reproductive system –> at the same time, the Mullerian duct is prevented from developing by a hormone called Mullerian-inhibiting factor
-if there is no Y chromosome and no upsurge of testosterone, the Mullerian duct develops into the female internal reproductive system, and the Wolffian duct degenerates
-external genitals of males and females develop from the same undifferentiated urogenital structures. Which is why it is possible for a person to be born with genitals intermediate in form between those of typical males and females, aka hermaphroditism

Question 15

what are hormones?

Answer 15

-chemicals, released into the bloodstream, regulates physiological processes

Question 16

what releases sex hormones? and what do they do?

Answer 16

-endocrine glands in the ovaries and testes, pituitary gland regulates the release of sex hormones which are steroids
-crucial to the development and function of the reproductive system and sexual behaviour

Question 17

What are steroids?

Answer 17

-molecules synthesised from cholesterol that have four carbon rings. Small alternations in the basic cholesterol structure have profound consequences for the effects of hormone –> for example, testosterone is the most crucial hormone for male development, but it differs from the important steroid oestradiol in only a few places on the molecule
-Steroids act differently from other hormones because of their structure. Some hormones are proteins and, therefore cannot cross the lipid bilayer of a cell membrane. These hormones act at receptors with extracellular binding sites. In contrast, steroids are fatty and can easily pass through cell membranes and bind to receptors within the cytoplasm, giving them direct access to the nucleus and gene expression. Differences in the concentration of various receptors result in steroid
effects localized to different areas of the brain

Question 18

what are steroid sex hormones often referred to and explain what that means?

Answer 18

-Steroid sex hormones often referred to as “male” or “female,” but men also have “female” hormones and women also have “male” hormones. Designation reflects men have higher concentrations of androgens or male hormones, and women have more oestrogens, or female hormones. For example, testosterone is an androgen and oestradiol is an oestrogen. In the series of chemical reactions that lead from cholesterol to sex hormones, one of the principal female hormones, oestradiol, is actually synthesized from the male hormone testosterone. This reaction takes place with the aid of an enzyme called aromatase.

Question 19

describe the release of androgens and their role

Answer 19

-testes primarily responsible for release of androgen, although small amounts secrete in the adrenal glands and elsewhere.
-testosterone is most abundant androgen and its responsible for most masculinizing hormonal effects
-Prenatally, elevated testosterone levels are essential for the development of the male reproductive system.
-Increases in testosterone much later, at puberty, regulate the development of secondary sex characteristics, ranging from increased muscular development and facial hair in human males to the mane of a lion. Oddly, for those with a genetic predisposition, testosterone also causes baldness in men.
-Female concentrations of testosterone are roughly 10% of those found in males. Male testosterone levels vary during the course of the day because of numerous factors, including stress, exertion, and aggression. It is not clear whether an increase in testosterone is a cause or an effect, but it is correlated with social challenges, anger, and conflict.

Question 20

describe the release of oestradiol and progesterone and its role

Answer 20

-principal female hormones are oestradiol and progesterone –>secreted by the ovaries. -oestradiol is an oestrogen; progesterone is a member of another class of female steroid hormones called progestins.
-Quite low during childhood, oestrogen levels increase dramatically at puberty and control the maturation of the female reproductive system and the development of breasts.
-As in the male, blood concentrations of sex hormones are quite variable in the female. However, whereas in men fluctuations occur rapidly each day, in women, hormonal levels follow a regular cycle of approximately 28
days.

Question 21

What are gonadotropins and gonadotropin-releasing hormone? and describe them

Answer 21

-Anterior pituitary gland secretes two hormones that are particularly important for normal sexual development and function in both women and men: luteinizing hormone (LH) and follicle-stimulating hormone (FSH)
- LH and FSH are secreted by specialized cells scattered throughout the anterior pituitary, comprising about 10% of the total cell population.
-secretion of hormones from the anterior pituitary is under the control of hypophysiotropic hormones released by the hypothalamus.
-Gonadotropin-releasing hormone (GnRH) from the hypothalamus does what the name suggests, causing the release of LH and FSH from the pituitary. GnRH is also
referred to as LHRH, for luteinizing hormone-releasing hormone because it causes a much greater increase in LH than FSH. Neuronal activity in the hypothalamus is influenced by numerous psychological and environmental factors that indirectly affect the secretion of gonadotropins from the anterior pituitary

Question 22

Describe the chain of events from hypothalamus input to the secretion of gonadal hormones from retina

Answer 22

-Neural input from the retina to the hypothalamus causes changes in the release of GnRH based on daily variations in light level. In some nonhuman species, strong seasonal variations in reproductive behaviour and gonadotropin secretion occur. Light inhibits the production of the hormone melatonin in the pineal gland, increasing gonadotropin secretion because of the inhibitory effect of melatonin on gonadotropin release. By means of this circuit, reproductive activity can be influenced by the length of daylight during the course of the year, and offspring are born seasonally when they have the best chance of survival. In humans, there is also an inverse relationship between gonadotropin release and melatonin levels, but whether melatonin actually modulates reproductive behaviour is not known

Question 23

what releases the gonadotropins and their role in males

Answer 23

LH stimulates the testes to produce testosterone. FSH is involved in the maturation of sperm cells within the testes. Sperm maturation also requires testosterone, meaning LH and FSH play key roles in male fertility. Because there is cortical input to the hypothalamus, it is possible for psychological factors to decrease male fertility by inhibiting gonadotropin secretion and sperm production

Question 24

what releases the gonadotropins and their role in females

Answer 24

-LH and FSH cause the secretion of oestrogens from the ovaries.
-absence of gonadotropins –> ovaries are inactive, which is the situation throughout childhood.
-Cyclic variations in LH and FSH levels in adult females cause periodic changes in the ovaries, and the timing and duration of LH and FSH secretion determine the nature of the reproductive cycle, or menstrual cycle.
-In the follicular phase of the cycle, these hormones (particularly FSH) increase the growth of a small number of follicles, the cavities in the ovaries that enclose and maintain the ova (egg cells).
-In the luteal phase after egg expulsion, the small cells that surround the egg undergo chemical changes in a process called luteinization, which depends on LH release from the pituitary. The duration of the follicular and luteal phases of the reproductive cycle vary significantly for different mammals. The phases are roughly equal in length in the primate menstrual cycle

Question 25

describe the oestrous cycle

Answer 25

-Non-primate mammals, such as rats and mice, the luteal phase is much shorter.
-In other oestrous animals, such as dogs, cats, and farm animals, the phases are more nearly equal in duration.
-Many oestrous animals have only one cycle per year, usually in the spring. Presumably, this timing is for the production of offspring when the weather and food supply are optimal.
-At the other extreme are animals such as rats, which are said to be polyoestrous because they have short periods of oestrus, or “heat,” throughout the year.

Question 26

what is a full sexual response cycle consist of?

Answer 26

Arousal followed by plateau, orgasm, and resolution phases

Question 27

Where does the neural control of sexual response come from

Answer 27

From the cerebral cortex—where erotic thoughts occur—but the spinal cord coordinates this brain activity with sensory information from the genitals and generates the critical outputs that mediate the sexual responses of the genital structures

Question 28

What does sexual arousal cause?

Answer 28

-certain parts of the external genitals in men and women to be engorged with blood, and thus to swell
-In women, these structures include
the labia and the clitoris; in men, it is primarily the penis

Question 29

What sort of receptors cause engorgement and erection?

Answer 29

The external genitals are densely innervated by mechanoreceptors, particularly within the clitoris and the glans of the penis.
Stimulation of these sensory endings can, by itself, be enough to cause engorgement and erection

Question 30

What is the best evidence that engorgement can be generate by simple spinal reflex?

Answer 30

Most men who have suffered a complete
transection of the spinal cord at the thoracic or lumbar level can nevertheless experience an erection when their penis is mechanically stimulated

Question 31

describe the pathway of the genitals

Answer 31

The mechanosensory pathways from the genitals are components of the somatosensory system, and their anatomy follows the usual pattern: Axons from mechanoreceptors in the penis and clitoris collect in the dorsal roots of the sacral spinal cord. They then send branches into the dorsal horns of the cord, and into the dorsal columns, through which they project toward the brain

Question 32

What is engorgement and erection primarily controlled by

Answer 32

the parasympathetic division of the ANS

Question 33

how can the parasympathetic neurons be activated (with reference to sexual arousal)

Answer 33

Within the sacral spinal cord, the parasympathetic neurons can be excited by either mechanosensory activity from the genitals (which can directly trigger reflexive erection) or by axons descending from the brain (which account for responses mediated by more cerebral stimuli)

Question 34

what do parasympathetic nerve endings release from sexual arousal?

Answer 34

-release a potent combination of acetylcholine, vasoactive intestinal polypeptide (VIP), and nitric oxide (NO) directly into the erectile tissues

Question 35

What do the neurotransmitters released by the parasympathetic nerves into erectile tissue cause?

Answer 35

-relaxation of smooth muscle cells in the arteries and the spongy substance of the clitoris and penis –> the usually flaccid arteries then become filled with blood, thereby distending the organs

Question 36

how does sildenafil (aka viagra) treat erectile dysfuntion

Answer 36

by enhancing the effect of NO

Question 37

describe what happens at the penis become longer and thicker

Answer 37

the spongy internal tissues swell against two thick, elastic outer coverings of connective tissue that give the erect penis its stiffness. In order to keep the organs sliding easily during copulation throughout the plateau phase, parasympathetic activity also stimulates the secretion of lubricating fluids from the woman’s vaginal wall and from the man’s bulbourethral gland.

Question 38

describe the process of emission in men

Answer 38

The sympathetic efferent axons then trigger the process of emission: Muscular contractions move sperm from storage sites near the testes through two tubes called the vas deferens, combine the sperm with fluids produced by various glands, and propel the resulting mixture (called semen) into the urethra. During ejaculation, a series of coordinated muscular contractions expel the semen from the urethra, usually accompanied by the intense sensations of orgasm

Question 39

describe the process of orgasm for women

Answer 39

Stimulation adequate to trigger orgasm probably also activates the sympathetic system. Sympathetic outflow causes the outer vaginal wall to thicken and, during orgasm itself, triggers a series of strong muscular contractions.

Question 40

describe the timeframe for orgasms in men and women

Answer 40

Following an orgasm, some time must pass before another orgasm can be triggered in men. The orgasmic experience of women tends to be considerably more variable in frequency and intensity. The resolution phase, which ends the sexual response cycle, includes a draining of blood from the external genitals through veins, and a loss of erection and other signs and sensations of sexual excitement

Question 41

what is the objective of mating behaviour

Answer 41

To maximise the survival of offspring and parental genes. Species variations in preferred mating systems seem to depend on the investment that males and females make in raising their offspring, although there are exceptions

Question 42

what is polygyny

Answer 42

The male mates with many females but the
female mates with only one male for one or multiple mating seasons

Question 43

What is polyandry

Answer 43

One female mates with many males but the males mate with only that female, is rare among mammals and vertebrates in
general. One exception is the phalarope, a shorebird that breeds in the cold tundra

Question 44

what is polygamy?

Answer 44

Polygyny and polyandry both examples of this — i.e., having more than one mate

Question 45

What is monogamy

Answer 45

a male and a female form a tightly bound
relationship that includes exclusive (or nearly exclusive) mating with each other

Question 46

describe pair bonding in different species of voles

Answer 46

Prairie voles (Microtus ochrogaster): social and monogamous –> After mating, a female prairie vole spends more time with its partner than by itself or with a strange

Montane voles (Microtus montanus): asocial and promiscuous –> Female montane voles, spend most of their time in a neutral area alone rather than with their recent mating partner or a stranger.

Question 47

Describe the role of oxytocin and vasopressin receptors in reproductive behaviours and bonding in voles

Answer 47

Prairie voles: more oxytocin (female) and vasopressin (male) –> Vasopressin antagonists given to a male prairie vole before mating prevent him from forming a pair-bond relationship. This disruption of pair bonding can be produced with the antagonist selectively infused into the ventral pallidum (the anterior portion of the globus pallidus). Oxytocin antagonists have no such effect. When a male is given vasopressin while he is exposed to a new female, he quickly forms a strong preference for her even without the intense mating that usually precedes pair-bonding. In females, oxytocin appears to be necessary to establish a preference for her mate, while vasopressin has little effect

Montane voles: fewer receptors for oxytocin and vasopressin –> A virus was used to deliver genes to the ventral pallidum of male montane voles, causing an overexpression of vasopressin receptors. Consequently, the male montane voles had numbers of vasopressin receptors in the ventral pallidum comparable to prairie voles. The manipulated montane voles also pair-bonded like prairie voles. If this cause-and-effect link is supported by further studies, it will dramatically show that a complex social behaviour can be altered by the overexpression of a single protein at one location in the brain

Question 48

Describe the role of oxytocin and vasopressin receptors in parenting habits in voles

Answer 48

-Vasopressin increases the male prairie vole’s paternal proclivities, causing him to spend more time with his pups, and oxytocin similarly stimulates maternal behaviours in the female

-administering vasopressin or oxytocin to the naturally promiscuous montane voles does not evoke the effects on pair-bonding and parenting seen in prairie voles, perhaps because they don’t have receptors in the necessary places

Question 49

What is the role of oxytocin in human relationships?

Answer 49

There is evidence that human plasma oxytocin levels increase during activities like breastfeeding in mothers and sexual intercourse in men and women, suggesting its role in bonding and attachment.

Question 50

What did the experiments by Bartels and Zeki reveal about brain activity in response to loved ones?

Answer 50

the experiments showed that several brain areas, including the anterior cingulate cortex, caudate nucleus, and striatum, are more activated when people view pictures of their children and partners compared to unrelated individuals.

Question 51

What do the activated brain areas in response to loved ones have in common with the vole story?

Answer 51

Many of the brain areas activated in response to loved ones are rich in oxytocin and vasopressin receptors, similar to the vole story, suggesting a connection between these chemicals and bonding in humans.

Question 52

What do fMRI studies suggest about the role of oxytocin and vasopressin in human bonding?

Answer 52

fMRI studies suggest that oxytocin and vasopressin play roles in human bonding, potentially similar to what is observed in voles

Question 53

What did the study on vasopressin gene variants reveal in relation to human pair-bonding?

Answer 53

-In men, there was a correlation between a particular vasopressin gene variant (V1aR) and lower scores on measures of the quality of their marriage. These men were also twice as likely to report experiencing a marital crisis in the year before the survey.
-In women, there was no connection between the vasopressin gene variants and the quality of their marriage as assessed by a variety of questionnaires

Question 54

What was the impact of the vasopressin gene variant (V1aR) in men on their wives’ perception of their marital quality?

Answer 54

Wives of men with the vasopressin gene variant also reported lower marital quality compared to the wives of men without the variant.

Question 55

What is the significance of the gene variant’s function in relation to pair-bonding in humans?

Answer 55

The function of this gene variant is not known, but the study’s results suggest that, even in humans, vasopressin receptors might play a role in pair-bonding.

Question 56

Why do we predict that male and female brains are different?

Answer 56

Male and female brains are expected to have differences, known as sexual dimorphisms, due to the different neural systems required to control unique body parts and behaviours associated with each sex.

Question 57

What is the function of the bulbocavernosus (BC) muscles?

Answer 57

The BC muscles, located at the base of the penis in men and around the opening of the vagina in women, have a role in penile erection, assisting in ejecting urine, and slightly constricting the vagina in women.

Question 58

Where is Onuf’s nucleus located, and what is its role in sexual dimorphism?

Answer 58

Onuf’s nucleus, located in the sacral spinal cord, controls the BC muscles. It is moderately dimorphic, with more motor neurons in men due to the larger BC muscles in males.

Question 59

Which brain region in mammals exhibits the most distinct sexual dimorphisms and what role does it play?

Answer 59

The preoptic area of the anterior hypothalamus, clustered around the third ventricle, exhibits the most distinct sexual dimorphisms in the mammalian brain and appears to play a role in reproductive behaviours.

Question 60

How do histological sections of male and female preoptic areas from rats differ?

Answer 60

-In rats, histological sections of male and female preoptic areas show an obvious difference: the sexually dimorphic nucleus (SDN) is five to eight times larger in males than in females.
-lesions of the preoptic area disrupt the oestrous cycle in females and reduce the frequency of copulation in males

Question 61

Are there sexual dimorphisms in the preoptic area of the human brain, and if so, what are they?

Answer 61

There are small and controversial sexual dimorphisms in the preoptic area of the human brain. Four clusters of neurons called the interstitial nuclei of the anterior hypothalamus (INAH) have been studied, with INAH-1, INAH-2, and INAH-3 reported to be larger in men than women. INAH-3 is the clearest dimorphism, reported to be twice as large in men.

Question 62

Are there potential differences in the size of certain hypothalamic nuclei that correlate with sexual orientation in humans?

Answer 62

There may be subtle differences in the size of certain hypothalamic nuclei that correlate with sexual orientation in people.

Question 63

What happens in the medial preoptic area of male rhesus monkeys during sexual behavior?

Answer 63

Various neurons of the medial preoptic area in male rhesus monkeys fire vigorously during specific phases of sexual behaviour, including arousal and copulation.

Question 64

What does the conclusion about sexual dimorphisms in human brain structure suggest?

Answer 64

the most reliable conclusion about sexual dimorphisms in human brain structure is that there are very few of them, likely because the vast majority of men’s and women’s behaviours are very similar.

Question 65

What is the evolutionary explanation sometimes associated with cognitive dimorphisms?

Answer 65

An evolutionary explanation suggests that men evolved as hunters and relied more on their navigation abilities, while women evolved behaviours like staying closer to home to care for children, making them more social and verbal

Question 66

What cognitive abilities have studies reported women to excel at relative to men? and When do girls tend to perform slightly better on tests of comprehension and writing?

Answer 66

Studies have reported that women excel at verbal tasks, including naming objects of the same colour, listing words beginning with the same letter, and verbal memory. Starting at around age 11 years, girls tend to perform slightly better on tests of comprehension and writing, and this effect is sometimes said to extend through high school and beyond.

Question 67

What tasks are reported to favour men in terms of performance? why do researchers speculate that men have advantages in tasks like map reading and maze learning? What is one of the largest reported differences in performance between the sexes? What are some important considerations when thinking about dimorphisms of cognition?

Answer 67

Tasks that reportedly favour men in performance include map reading, maze learning, and mathematical reasoning. Researchers speculate that these advantages evolved from the days when men roamed large areas to hunt wild animals. One of the largest reported differences is in the mental rotation of objects, a task that appears to favour men. Considerations include that not all studies yield the same results, there are huge performance differences across large groups, and the differences may result from individual variations or differences in experience.

Question 68

What evidence supports the idea that hormones may affect cognitive function?

Answer 68

Evidence includes correlations between spatial reasoning and the menstrual cycle in women, as well as improved spatial performance in older men with low testosterone levels after receiving testosterone.

Question 69

What factors can make a behavior more common in one sex than the other?

Answer 69

A variety of factors, including genetics, culture, and life experiences, may make a behavior more common in one sex than the other, but ultimately, all behaviors are controlled by the brain

Question 70

In what ways can steroids influence neurons?

Answer 70

Steroids can influence neurons by acting quickly to alter membrane excitability, sensitivity to neurotransmitters, or neurotransmitter release through direct binding to various enzymes, channels, and transmitter receptors. For example, certain metabolites (breakdown products) of progesterone bind to the inhibitory GABA receptor and potentiate the amount of chloride current activated by GABA. The effects of these progesterone metabolites are quite similar to the sedative and anticonvulsant effects of the benzodiazepine class of drugs.

They can also diffuse across the outer membrane and bind to specific steroid receptors in the cytoplasm and nucleus, promoting or inhibiting the transcription of specific genes.

Question 71

What is the role of specific types of steroid receptors in the cytoplasm and nucleus?

Answer 71

Specific types of steroid receptors in the cytoplasm and nucleus can promote or inhibit the transcription of specific genes in the nucleus, a process that can take minutes to hours, depending on the type of sex hormone and receptor involved.

Question 72

What is meant by the organizational effects of hormones during development?

Answer 72

The organizational effects of hormones during development refer to the ability of hormones like testosterone to alter young genitals and brain circuitry in ways that lead to distinctly male genitals and masculine behaviours later in life. These effects are irreversible and allow for the generation of male functions after sexual maturity.

Question 73

What are activational effects of steroid hormones on the nervous system?

Answer 73

Activational effects refer to the temporary effects of steroid hormones on the nervous system in mature animals, often required for the full expression of sexual behaviors. These effects can activate changes in certain brain regions necessary for specific behaviors

Question 74

What hormone is responsible for masculinization of the male brain during prenatal development?

Answer 74

The hormone responsible for masculinization of the male brain during prenatal development is estradiol, which results from the conversion of testosterone into estradiol within neuronal cytoplasm, catalyzed by the enzyme aromatase.

Question 75

What is the role of α-fetoprotein in protecting the female fetus from masculinization?

Answer 75

α-fetoprotein, found in high concentrations in fetal blood, binds estrogens and protects the female fetus from masculinization by preventing the effects of maternal estrogens on the developing brain.

Question 76

What are prostaglandins, and what role do they play in brain masculinization?

Answer 76

(Role of elevated testosterone and oestradiol level) Prostaglandins are compounds derived from arachidonic acid and have various roles, including inducing pain and fever after tissue damage. Prostaglandins are involved in brain masculinization, with COX inhibitors reducing copulatory behavior in male rats and inducing male-like copulatory behaviors in female rats.

Question 77

What are the diagnostic implications of measuring α-fetoprotein levels in maternal blood or amniotic fluid?

Answer 77

Unusually high levels of α-fetoprotein are a possible indicator of neural tube defects, while unusually low levels are found in Down syndrome when measuring α-fetoprotein levels in maternal blood or amniotic fluid.

Question 78

Can hormonal function alterations lead to individuals having brains that do not match their genetic sex? and how does treatment with testosterone early in development affect adult female sexual behaviour in mammals?

Answer 78

-Yes, in situations where hormonal function is altered, it is possible for genetic males to have female brains and genetic females to have male brains.
-Treatment with testosterone early in development in mammals leads to decreases in at least some features of adult female sexual behaviour

Question 79

What is the impact of exposing genetically female rats to testosterone during a few days around birth?

Answer 79

If genetically female (XX) rats are exposed to testosterone during the few days around birth, they will fail to elicit the typical female mating posture, called lordosis, when they reach maturity

Question 80

What happens in genetic males (XY) with a defective androgen receptor gene.

Answer 80

-androgen receptor gene located on X chromosome males thus only have one copy and males with the defective gene cannot produce function androgen receptors
-Genetic males with a defective androgen receptor gene may experience profound androgen insensitivity. They develop normal testes, but these remain undescended in the abdomen. While they produce ample testosterone, their tissues cannot respond to androgen, resulting in outwardly female appearance

Question 81

What are some physical characteristics of individuals with androgen insensitivity?

Answer 81

Individuals with androgen insensitivity may have a vagina, a clitoris, and labia, and they may develop breasts and a female body shape during puberty.

Question 82

What is the impact of normal levels of Müllerian-inhibiting factor in androgen-insensitive genetic males?

Answer 82

Normal levels of Müllerian-inhibiting factor prevent the development of the female reproductive system, leading to the absence of menstruation and infertility in androgen-insensitive genetic males.

Question 83

How do androgen-insensitive genetic males typically identify themselves and behave?

Answer 83

Androgen-insensitive genetic males typically identify themselves as women, dress like women, and choose men as their sex partners, even when they understand the circumstances of their biology.

Question 84

What is congenital adrenal hyperplasia (CAH) in genetic females?

Answer 84

Congenital adrenal hyperplasia (CAH) is a condition in genetic females where the adrenal glands secrete unusually large amounts of androgens, leading to abnormally high levels of circulating androgens early in development.

Question 85

How do the external genitals of CAH females typically appear at birth? and what are the usual treatments for CAH females after birth?

Answer 85

-At birth, CAH females have normal ovaries and no testes, but their external genitals are intermediate in size between a normal clitoris and a penis.
-Surgery and medications are the usual treatments for CAH females after birth to address the condition.

Question 86

How do CAH girls and CAH women often describe their behaviour?

Answer 86

CAH girls (and their parents) are more likely to describe their behaviour as aggressive and tomboyish. As adults, most CAH women are heterosexual, but a higher percentage of them are homosexual compared to other women.

Question 87

What is the potential cause of somewhat male-like organization of certain brain circuits in CAH women?

Answer 87

Prenatal exposure to high levels of androgens is presumed to cause a somewhat male-like organization of certain brain circuits in CAH women, analogous to animal studies

Question 88

Why is it challenging to draw conclusions about the causes of human behavior in CAH females?

Answer 88

It is challenging to determine whether masculine behavior in CAH females is solely due to early androgen exposure and male-like brain dimorphisms or if it is influenced by subtle differences in the way they are treated by others, particularly parents dealing with a child with ambiguous genitals.

Question 89

What role can genes play in complex sex behaviors in organisms like the fruit fly Drosophila melanogaster? and what are some of the courtship behaviors exhibited by male fruit flies towards females? How do males learn these courtship behaviors, and what does this suggest about their genetic coding?

Answer 89

-Genes can play a role in complex sex behaviors in organisms like the fruit fly Drosophila melanogaster.
-Male fruit flies exhibit courtship behaviors, including orienting toward and following the female, singing a courtship song, and tapping her with his forelegs before attempting to mate.
-Males know how to court even if they have never seen courtship by other flies, suggesting that these behaviors are genetically coded.

Question 90

What is the role of the fru gene (fruitless) in male courtship behaviors in fruit flies?

Answer 90

The fru gene (fruitless) may be essential for male courtship behaviors in fruit flies. In males, the fru gene is expressed in various cell types, leading to the development of a male central nervous system that automatically triggers male courtship behaviors.

Question 91

How do females without fru expression differ in terms of their central nervous system and behaviors?

Answer 91

Females without fru expression develop a complete central nervous system, but its wiring is somewhat different, and female courtship behaviors are “built-in.”

Question 92

What happens to male courtship behaviors in the absence of the fru gene, and what occurs when females express fru?

Answer 92

In the absence of the fru gene, male courtship behaviors are significantly reduced or nonexistent. Conversely, females that express fru exhibit male courtship behaviors and resist courtship by males.

Question 93

What is the role of the dsx gene (double sex) in sexual differentiation?

Answer 93

The dsx gene plays an important role in the sexual differentiation of the body, including the development of male or female genitals. It also interacts with fru in controlling sexual differentiation of the central nervous system (CNS) and sex-specific behaviours

Question 94

How does the expression of the fru gene differ between males and females? and then how does the dsx gene differ in its expression between males and females?

Answer 94

In the case of the fru gene, it is either expressed in males or not expressed in females. The dsx gene is expressed in both males and females, but alternative splicing leads to the production of male-specific and female-specific proteins.

Question 95

How does testosterone interact with sexual behavior in men?

Answer 95

In men, testosterone has a two-way interaction with sexual behavior. It can rise in anticipation of a sexual act or while fantasizing about it, and reduced testosterone levels are associated with decreased sexual interest.

Question 96

What has been reported regarding women’s likelihood to initiate sex and their hormone levels?

Answer 96

It has been reported that women are more likely to initiate sex when estradiol levels are highest during their menstrual cycle.

Question 97

What happens to food intake and appetite in rats during pregnancy despite rising leptin levels?

Answer 97

In rats, during pregnancy, even though leptin levels rise, appetite and food intake increase instead of decreasing due to hormonal changes associated with pregnancy leading to leptin resistance in the hypothalamus.

Question 98

What unique behavior occurs in maternal rats during lactation and nursing?

Answer 98

During lactation and nursing, maternal rats experience a unique behavior related to somatosensory cortex changes. The somatosensory cortex in female rats has a sensory representation of the ventral skin surrounding the nipples.

Question 99

What happens to the tactile stimulation during nursing in rats?

Answer 99

Tactile stimulation during nursing leads to a dramatic increase in the representation of the ventral skin and a shrinkage of receptive fields to half their normal size.

Question 100

Is the somatosensory map plasticity observed during nursing permanent?

Answer 100

No, this somatosensory map plasticity appears to be temporary and reversible. Several months after weaning, the receptive fields return to their normal size.

Question 101

How do addictive drugs and maternal behaviors relate to the dopamine system in the brain?

Answer 101

Both addictive drugs and maternal behaviors appear to enhance the influence of dopamine released by neurons projecting from the ventral tegmental area (VTA) into the nucleus accumbens (NA). This activation of the dopamine system is associated with reward and addiction. In the case of maternal behavior, the tactile stimulation of suckling pups activates this system, reinforcing mother-infant bonding and promoting pup survival.

Question 102

What was observed in fMRI scans of lactating female rats and virgin female rats after an injection of cocaine?

Answer 102

Surprisingly, brain activation was quite similar in both groups, particularly in the nucleus accumbens (NA). This similarity suggests that both nursing and cocaine injection stimulate the dopamine system associated with reward and addiction. This finding highlights the reinforcing nature of maternal behavior during lactation.

Question 103

What might be the purpose of brain changes and dopamine system activation during nursing?

Answer 103

The hypothesis is that the tactile stimulation of suckling pups during nursing activates the dopamine system, making nursing a reinforcing behavior. This reinforcement promotes mother-infant bonding and, ultimately, the survival of the pups. These brain changes are significant for ensuring the care and well-being of the offspring.

Question 104

How can fatherhood potentially alter brain structure in species like marmosets?

Answer 104

Fatherhood in species like marmosets might alter brain structure of the prefrontal cortex by increasing the density of dendritic spines on pyramidal cells and potentially increasing the number of vasopressin receptors on these spines.

Question 105

What are the activational effects of estradiol on neurons? How quickly can estradiol exert its effects on neurons? What structural changes can estradiol induce in neuronal tissue?

Answer 105

-By modulating the flow of potassium ions, oestradiol depolarizes some neurons and increases their firing of action potentials.

-estradiol can exert its effects on neurons within minutes of experimental application.

-Estradiol treatment of tissue taken from the hypothalamus of newborn mice can lead to neurite outgrowth, increased cell viability, and higher spine density in neurons.

Question 106

What did Elizabeth Gould and her colleagues discover about estradiol’s effects on dendritic spines in the hippocampus of female rats?

Answer 106

They found that the number of dendritic spines on hippocampal neurons fluctuated during the 5-day estrous cycle, with spine density and estradiol levels peaking together. Additionally, injected estradiol increased spine numbers even in animals with low natural estradiol levels.

Question 107

How does the variation in spine density relate to hippocampal excitability during the estrous cycle?

Answer 107

The variation in spine density, which tracks estradiol levels, is thought to influence hippocampal excitability. When estradiol levels increase, the hippocampus in experimental animals is more prone to generate seizures.

Question 108

During which phase of the estrous cycle do estradiol and progesterone levels peak, and what is the effect on seizure thresholds?

Answer 108

Estradiol and progesterone levels peak during the proestrus phase of the estrous cycle. During this time, seizure thresholds are lowest, meaning that the likelihood of seizures occurring is increased

Question 109

What did Woolley and McEwen confirm regarding estradiol’s effects on hippocampal neurons?

Answer 109

Woolley and McEwen confirmed that estradiol itself triggers the increase in spine numbers on hippocampal neurons. As spine density increases, so does the growth of excitatory synapses in these neurons.

Question 110

How does estradiol alters synaptic plasticity in the hippocampus?

Answer 110

-Estradiol enhances synaptic plasticity in the hippocampus by increasing the postsynaptic responses to glutamate in the presence of estradiol, resulting in stronger excitatory synapses.
-Estradiol may also alter hippocampal function by decreasing synaptic inhibition. Estradiol causes some inhibitory cells to produce less GABA, their neurotransmitter, and therefore synaptic inhibition becomes less effective. Less inhibition increases neural activity, complementing the estradiol effect at excitatory synapses. When the pieces are put together, it seems that estradiol produces a hippocampus with less effective inhibitory synapses and stronger excitatory synapses, thereby triggering an increase in the number of spines on the pyramidal cells

Question 111

How does reduced inhibition relate to the effects of estradiol?

Answer 111

Reduced inhibition, as induced by estradiol, leads to increased neural activity, which complements the strengthening of excitatory synapses caused by estradiol.

Question 112

What is the role of the hippocampus in rats?

Answer 112

The hippocampus in rats is particularly important for spatial memory and navigational skills.

Question 113

How does estradiol affect memory formation in rats?

Answer 113

Estradiol enhances memory formation in rats when administered shortly before or after training on memory tasks.

Question 114

What happens if estradiol is given 2 hours after training on memory tasks in rats?

Answer 114

If estradiol is given 2 hours after training, the memory benefit associated with estradiol disappears. Evidently, estrogens must be present near in time to the learning experience to facilitate memory.

Question 115

What does the peak in hippocampal spine number in female rats coincide with?

Answer 115

The peak in hippocampal spine number coincides with the rat’s peak in fertility.

Question 116

What behaviors might benefit from a more excitable, NMDA-receptor-filled hippocampus?

Answer 116

Behaviors such as heightened spatial ability, which could be beneficial for seeking out mates.

Question 117

How often does the female rat’s brain fine-tune itself to meet changing reproductive needs?

Answer 117

The female rat’s brain fine-tunes itself on a 5-day cycle to meet changing reproductive needs.

Question 118

What protective effects does estradiol have on neurons?

Answer 118

Estradiol helps neurons survive hypoxia, oxidative stress, and exposure to neurotoxic agents.

Question 119

How does estrogen replacement therapy potentially benefit women with neurological disorders?

Answer 119

Estrogen replacement therapy may delay the onset of Alzheimer’s disease, reduce tremors in Parkinson’s disease, and alleviate the severity of multiple sclerosis when pregnant.

Question 120

What is the relationship between tamoxifen and stroke risk in women?

Answer 120

Tamoxifen, an estrogen receptor antagonist used in breast cancer treatment, is associated with an increased risk of stroke in women.

Question 121

What cell types in the brain express estrogen receptors, and how might this affect estrogen’s actions in neurological diseases?

Answer 121

Both neurons and astrocytes express estrogen receptors, and the benefits of estrogen in neurological diseases may arise from its effects on both cell types.

Question 122

Is there a biological basis for sexual orientation? Do administering androgens or estrogens to adults, or removing the gonads, affect sexual orientation?

Answer 122

-While there is no evidence that sexual orientation is related to the activational effects of hormones in adults, some believe it may be influenced by structural differences in the brain due to organizational effects.
-No, administering androgens or estrogens to adults, or removing the gonads, has no effect on sexual orientation

Question 123

What is the SDN, and where is it located in the brain of rats?

Answer 123

The SDN (sexually dimorphic nucleus) is a brain region located in the preoptic area of the anterior hypothalamus in rats.

Question 124

How does a surgical lesion to the SDN affect the sexual preferences of male rats?

Answer 124

After a surgical lesion to the SDN, male rats spend more time with sexually active males than with sexually receptive females, reversing their preference before surgery.

Question 125

What is unclear regarding the relationship between SDN size and sexual orientation?

Answer 125

The causal relationship between the size of hypothalamic nuclei, such as the SDN, and sexual orientation is unclear.

Question 126

What is the INAH-3 nucleus, and what are the observed size differences between men and women?

Answer 126

The INAH-3 nucleus is one of the interstitial nuclei of the anterior hypothalamus. It is about twice as large in men as in women.

Question 127

How has the size of the INAH-3 nucleus been correlated with sexual orientation in men?

Answer 127

Studies have suggested that gay men tend to have an INAH-3 nucleus size similar to that of women, which is about half the size of the nucleus in straight men.

Question 128

What is the significance of the size differences in the INAH-3 nucleus in relation to sexual orientation?

Answer 128

While the differences in INAH-3 size have been observed in relation to sexual orientation, it is challenging to interpret these findings in terms of complex human behavior. Moreover, subsequent studies have not always confirmed a consistent correlation between INAH-3 size and sexual orientation.

Question 129

What other brain structures besides INAH-3 have been found to be larger in male homosexuals than in male heterosexuals?

Answer 129

The anterior commissure and suprachiasmatic nucleus.

Question 130

Which brain nucleus is reported to be larger in men than women, and what was the finding for male-to-female transsexuals

Answer 130

The bed nucleus of the stria terminalis is larger in men than women, and male-to-female transsexuals have a nucleus comparable in size to females.