Chapter 12: Sex Flashcards
Describe the male twin (Brian and Bruce) story
- In 1965 male twins (brian and bruce) were born in Canada.
- At 8 months old they both were circumsized, but Bruce’s was botched, causing his penis to fall off.
- Bruce has a sex arrangement surgery at 22 months old, and was raised as “Brenda”.
- The doctors encouraged the family to raise Brenda as a girl, followed by giving her estrogens during puberty
- Brenda was bullied and became suicidally depressed.
- At 14 Brenda learned what had happened and decided to live as “David Reimer”. He eventually had a reversed assignment, got married, but committed suicide at 38.
What did the story of Brenda alter?
The way that scientists view gender.
What conclusions did the Brenda story lead to?
Early life hormones are important
What skepticism was left after the Brenda story?
If genital reconstructive surgery was a good idea for infants.
Describe the story of Caster Semanya.
- Caster was born and raised as a girl and made it to the olympics for running.
- People began to question if she was a man or woman due to her appearance.
- After medical testing, it was found that she mad much higher than normal levels of testosterone.
- It was discovered that she has a 5a Reductase deficiency, XY chromosomes, undescended testes, and a shallow vagina.
- She also appeared to have no uterus or fallopian tubes
- This occurred since without 5a Reductase, no masculinization of the genitals can occur.
- She still continues to identify as a woman.
What does the story of Caster Semanya point to?
The complexity of sex and gender
Sexual Behavior
Neural circuity of the brain regulates behavior
Sexual behavior is ________.
Highly diverse
What is identified in rodents in regards to sexual behavior?
Specific neural circuits
Pheromones
Guide reproductive behavior in many species
What are the 4 stages of reproductive behavior?
- Sexual Attraction
- Appetitive Behavior
- Copulation
- Post Copulatory Behavior
Stage 1: Sexual Attraction
Brings males and females together
What 2 things can sexual attraction occur with?
- Physiological readiness to reproduce
- Learned associations (appearance)
What is an example of physiological readiness to reproduce?
Odors (pheromones) reflect estrogen levels in females
Stage 2: Appetitive Behavior
Establish, maintain, or promote sexual interaction
What is an example of appetitive behavior in female rats?
A proceptive female rat may approach males or perform “ear wiggling”
Proceptive
A state in which an animal advertises its readiness to mate through typical species behaviors
What are examples of proceptive male behaviors in rats?
- Staying near the female
- Sniffing
-Singing - Nest building
(dependent on species)
Species Specific Behavior
Appetitive behaviors differ based on the species
Stage 3: Copulation
Involves one or more insertions of the male penis into the female vagina
What occurs after the stimulation of the genitals?
The male ejaculates sperm into the female
What differs in rats copulation compared to humans?
In rats, there are multiple insertions (and rounds) prior to ejaculation
Why are multiple intromissions (insertions) necessary?
Repeated stimulation of the cervix and vagina is needed for the brain to release hormones that support pregnancy.
What occurs after copulation?
A refractory phase (length varies based on species)
Coolidge Effect
A natural tendency of an animal that appears to be sexually satisfied with a present partner to resume sexual activity when provided with a better partner.
If the female is willing to copulate, she is…
sexually receptive or in estrus
When is the female willing to mate?
If offspring are likely (around ovulation)
Stage 4: Post Copulatory Behavior
Occurs after copulatory behavior and varies across species
- Can include parental behaviors to nurture offspring
Copulatory Lock
The penis swells and cannot be withdrawn from the female.
What species does the copulatory lock occur in?
Dogs and some mice
Internal Fertilization
Sperm fertilizes eggs inside the female’s body
External Fertilization
Eggs are released outside the female’s body
What animals perform internal fertilization?
Mammals, birds, and reptiles
What animals perform external fertilization?
fish and frogs (amphibians)
- release gametes into water
How often do female rats ovulate?
Every 4-5 days
What occurs during estrus in female rats?
The female will display proceptive behavior and adopt a position called lordosis, allowing for insertion.
Estrus
The period during which female animals are sexually receptive.
Lordosis
A female receptive posture in quadrupeds in which the hindquarters are raised and the tail is turned to one side, facilitating intromission by the male.
What happens in some rodents that live together before and after copulation?
Pair bonds form
Pair Bonds
A durable and exclusive relationship between two individuals of the same species (mates)
What is an example of a species that forms pair bonds?
Prairie Voles
Are prairie voles monogamous?
They are socially monogamous, but not sexually monogamous
What are sex steroid hormones important in?
Mating behaviors
What happens to a castrated male rat?
Testosterone is no longer produced, which causes the male to lose interest in mating.
What can restore normal mating behavior in castrated males?
Testosterone treatments
Activational Effect
A temporary change in behavior resulting from the administration of a hormone to an adult animal.
What is an example of an activational effect?
testosterone treatment
What occurred when 3 castrated guinea pigs were given testosterone?
An incline in their copulatory scores
- Amount of testosterone given did not determine the score (just needed enough)
What is estrogen important for?
Female proceptive behavior
When is estrogen produced?
The beginning of the ovulatory cycle
What are the effects of progesterone?
- Increases in proceptive behavior
- Makes females sexually receptive
What hormones will a female without ovaries respond to?
A combination of estrogen and progesterone
- makes her more proceptive and receptive
In female rats, what is crucial for the lordosis response through steroid actions?
The VMH
What 2 things does estrogen cause in female rats?
- Increase in dendritic trees of neurons in the VMH
- Production of progesterone receptors
What do progesterone receptors contribute to?
Lordosis through protein production
What happens when both estrogen and testosterone are in circulation?
The effects of estrogen on the length and connectivity of VMH dendrites are reversed.
What is the path of the VMH sending axons?
- VMH
- Periaqueductal Gray
- Medullary Reticular Formation
- Spinal cord via reticulospinal tract
What happens when the male mounts the female?
The sensory information via the spinal cord evokes lordosis.
Ventromedial hypothalamus (VMH)
Monitors steroid hormone concentrations and activates a multi synaptic pathway that induces spinal motor neurons to contract back muscles in response to male mounting, producing lordosis.
When does the sending of axons from the VMH occur?
During the right time in the ovulatory cycle
Medial Preoptic Area (mPOA)
Coordinates male copulatory behavior in rats
How does the mPOA work?
- Sends axons to the ventral midbrain, then to the basal ganglia to coordinate mounting.
- Axons also project through the brainstem nuclei to the spinal cord.
Paragigantocellular Nucleus (PGN)
A region of the brainstem reticular formation that normally inhibits the erection response
How does mPOA interact with PGN?
The mPOA signals counteract the inhibition of erection created by PGN.
The mPOA and PGN are…
antagonists of each other
Do humans have pheromones?
No
Pheromones
Chemical signals that communicate information between animals to help coordinate their reproductive activities
What is an example similar to pheromones in humans?
The menstrual cycles of women living together may schnchronize
Vomeronasal Organ (VMO)
Detects pheromones which activate male arousal
What is the path of pheromones?
- VMO
- Meidal Amygdala
- mPOA
What are hormones and pheromones key in determining?
Sexual behavior in both males and females
Major Histocompatibility Complex (MHC)
A group of immune related genes with many alleles
What scent of MHCs do women prefer on men?
Not too similar/dissimilar from their own
What do humans differ from other species in?
Reproductive behaviors
(Face to face positions are most common in human reproduction, while rear is most common in other species)
What is an example of a subjective response in humans?
Orgasm
What are the 4 stages of sexual response?
- Excitement
- Plateau
- Orgasm
- Resolution
Stage 1: Excitement
The phallus (penis in males and clitoris inn females) becomes erect and there is an increased blood flow to the vagina, leading to the production of lubricating fluid.
Stage 2: Plateau
Increased stimulation prior to the orgasm.
Stage 3: Orgasm
The peak of sexual experience, marked by extremely pleasurable sensations
Mens Sexual Response
Tend to have an absolute refractory phase following the orgasm.
Women Sexual Response
Greater variety of responses, with 3 typical patterns (copulatory sequences)
What images causes the brain to activate in the same regions?
Sexual images and cocaine with images
What imaging techniques allows for the indication of active brain regions?
fMRI
What parts of the brain are activated during an orgasm?
- Amygdala
- Cingulate cortex
- Nucleus accumbens
- Hippocampus
What are the hypothalamic regions responsible for after orgasm?
The release of oxytocin
How can women with spinal cord injuries still have orgasms?
The vagal nerve detects stimulation, which leads to the same activation of brain structures in non-paralyzed women.
What gender has a higher sex drive?
Males
What is the first problem with researching the differences in sexes?
Research may describe differences, but it does not reveal the source of differences
What is the relationship between differences in sexes?
The differences BETWEEN sexes are almost always smaller than differences WITHIN sexes.
What is the second problem with researching the differences in sexes?
It can be very difficult to identify and rule out potential confounds
What are women more selective in choosing?
Someone for potential romance
What are the role does low doses of androgens have in males with low testosterone levels?
It can stimulate sexual interest and activity
What effect does additional testosterone have in rats?
No effect
Is there a relationship between androgen levels and sexual activity in men?
NO
What can be beneficial to postmenopausal women?
Estrogens and androgens
What has most research not identified about pre menopausal men?
There is no easy solution to premenopausal women with low sexual interets.
What do many vertebrates require for survival?
Significant parenting
Precocial
Animals born in a developed state and can survive with little maternal care
What is an example of a precocial animal?
Horses
Altricial
Animals born in an underdeveloped state and depend on maternal care
What is an example of an altricial being?
Humans
4 Rat Mother’s Materal Behaviors
- Nest building
- Crouching over pups
- Retrieving pups
- Nursing
What does the exposure of hormones during pregnancy result in?
It prepares the mothers brain to display maternal behaviors immediately after giving birth.
Parabiotic
A surgical preparation that joins two animals to share a single blood supply
What does parabiotic show?
The effects of maternal hormones on behavior
What happens when a non pregnant female rat is exposed to the circulating hormones of a pregnant rat?
The non pregnant rat will display the same maternal behaviors as the pregnant rat.
What is included in the circulating hormones of a pregnant rat?
- Estrogens
- Progesterone
- Prolactin
What two brain structures play a large role in different maternal behaviors?
mPOA and PAG
Sexual Differentiation
The PHYSICAL process by which individuals develop either male or females’ body and behavior
When does sexual differentiation begin in mammals?
Fertilization of the egg
Where does typical development begin?
The fetus
- begins at fertilization
How is sex determined in turtles and alligators?
The temperature at which the eggs incubate.
Sexual Determination
The GENETIC determination of developing male or female body/behaviors
What does each egg (ovum) carry?
1 X chromosome from the mother
What does the sperm from a father carry?
Either an X or Y chromosome
XX represents…
female
XY represents…
male
What does sexual determination lead to?
The determination of gender
What does the embryo have during early development?
Indifferent gonads that can potentially become testes or ovaries in the 1st month
SRY Gene
A gene on the Y chromosome that directs the developing gonads to become testes.
What does it mean by saying the development of the testes/ovaries is a domino effect?
The development of the testes/ovaries leads to the typical male/female body and behavior.
What occurs when there is no SRY gene present?
The gonads develop into ovaries
= female
What directs sexual differentiation?
Hormones secreted by the gonads
(mainly testes)
What happens when the developing fetus is exposed to testicular hormones?
Many tissues of the body begin developing masculine characters
-if the cells are not exposed to testicular hormones, they develop feminine characters
What does differential exposure to sex steroids lead to?
Differences in gene expression throughout the body.
What tissue types do early embryos have?
Tissues for both male and female structures.
Wolffian Ducts
The embryo will develop into male strictures if testicular hormones are present.
What happens to the mullerian ducts if the wolffian ducts develop?
They will shrink
Mullerian Ducts
The embryo will develop into female structures if testes are not present.
What happens to the wolffian ducts when the mullerian ducts develop?
Only part of them remain
What is the purpose of the Wolffian and Mullerian Ducts?
Connect the gonads to the body wall
What 2 hormones from the testes help masculinize the embryo?
- Testosterone
- Anti-Mullerian Hormone (AMH)
Testosterone
Promotes the development of the wolffian system.
What specific structures does testosterone masculinize?
- Prostate Gland
- Scrotum
- Penis
What is the process of testosterone masculnizing the body?
- 5a Reductase converts testosterone into DHT.
- DHT masculinzes the other structures of the body.
5a Reductase
An enzyme that converts testosterone into DHT
Where is 5a Reductase found?
Genital skin
Dihydrotestosterone (DHT)
An androgen responsible for the masculization of the other structures
What occurs without DHT production?
The genitals only become partially masculinized.
What happens to the developing fetus when there is no testosterone at all?
The genitals become the labia and clitoris (female systems)
Anti-Mullerian Hormone (AMH)
Induces the regression of the mullerian system
(causing it to shrink)
Turner’s Syndrome
A condition when a person carries a single X chromosome but no other chromosome.
What happens to an individual with Turner’s Syndrome?
The individual develops as a female due to no SRY gene present.
- ovaries are recognizable but underdeveloped
What happens when an XX individual (female) is exposed to androgens in the utero?
Depending on the degree, the body may become masculinized.
What is an example of XX individuals being exposed to androgens in the utero?
A female rat that is sandwiched between two male siblings in the uterus can be exposed to prenatal androgens.
What is the physical effect of a female rat being exposed to androgens in the utero?
The females anogenital distance (anal to genitals) will be greater, like male structure than that of developing sisters in the uterus
There are different ___ where we can talk about the sex of an individual.
levels
At each ___, there are ____ that can occur, leading to mismatches.
level, “differences”
Congenital Adrenal Hyperplasia (CAH)
The result of a female due to exposure to androgens before birth
What causes CAH?
The adrenal glands fail to produce sufficient corticosteroids, and produce androgens instead.
What happens to the appearance of individuals who have CAH?
They have an intersex appearance.
- Genetically they are females, but the ovaries are underdeveloped due to androgens.
What factor makes it possible to determine that a newborn is an XX female with CAH?
No testes present
What characteristics are CAH females more likely to acquire?
- described as tomboys
- have enhanced spatial abilities on tests (usually found in males)
- more likely to report as gay
Clocal Exstrophy
Genetic males born with testes, but no penises
What is the best treatment for clocal exstrophy?
Let the child decide their sex at puberty.
What is a secondary treatment for clocal exstrophy?
Sex reassignment surgery (male to female) decided at birth.
What is the case ratio regarding clocal exstrophy cases?
-8/14 later declared themselves to be males
-5/6 were comfortable being female
Androgen Insensitivity Syndrome (AIS)
A mutation of the androgen receptor gene that causes insensitivity to testosterone effects.
What happens to the testes with an individual who has AIS?
The lack of response from receptors prevents the development of the male features.
- testes remain internal while external genitals develop into female genitals
Do the testes still produce testosterone in AIS?
Yes
What gender do individuals with AIS usually identify as?
Females
When do females usually discover they have AIS?
They discover they are
- infertile
- have no uterus/ovaries
-no menstruation
Most people usually have….
masculine or feminine traits
(patterns)
What concept is harder to define as masculine or feminine?
Behavior
What can differences with sexes be driven by?
Social and cultural concepts
What do the same hormones masculinize in the body?
The genitals and brain
What is an example of sexual differentiation of the brain?
Female guinea pigs that are exposed to testosterone in utero will not show lordosis as adults
Organizational Effect
A permanent alteration of the nervous system, resulting in a change in behavior due to steroid hormones in early development
What hormone is an example of an organizational effect?
Steroids
When are steroids present?
Sensitive period in early development
Sensitive Period
The period during development in which an organism can be permanently altered by a specific experience/treatment.
When does the specific period occur?
It is dependent on the species
- can be before birth or directly after (neonatal)
Neonatal Period
Newborns
What is the second sensitive period for organizational effects on the body?
Puberty
Organizational Hypothesis
A single steroid signal (androgen) diffuses through all tissues, masculinizing the body, brain, and behavior.
What does the organizational hypothesis result in?
Male development
What happens if rodents are exposed to androgens in early life?
They behave as males
What happens if rats are not exposed to androgens?
The behave as females
What happens if females are treated with testosterone?
- Show mounting behaviors
- Indicates that early estrogens had masculinized the brain
What happens if female newborn rats are exposed to estrogen?
They fail to show lordosis (mounting) as adults
- female hormone
Aromatization
The chemical reaction that converts testosterone to estradiol, and other androgens to estrogens.
What specific enzyme in aromatization performs the conversion?
Aromatase
Aromatization Hypothesis
Testosterone enters the brain and is converted into estrogen. These estrogens masculinize the developing rodent brain.
a Fetoprotein
A protein within the blood of fetuses that binds estrogens and prevents them from entering the brain
What does a Fetoprotein prevent?
Aromatization and masculinization
What does a Fetoprotein not do?
Bind to testosterone
Explain The Process of Aromatization
- Testes release testosterone into the bloodstream.
- Testosterone molecules enter neurons in the brain.
- Many hypothalamic neurons produce aromatase (convert testosterone to estrogen) = estradiol
- Estradiol binds to the estrogen receptor, which binds DNA in the nucleus
- The estrogen receptor increases transcription of certain genes while decreasing others. Altered gene expression in hypothalamic neurons prevent the appearance of feminine behaviors
(lordosis in adulthood) - Estrogen molecules are bound by a-Fetoprotein until they are metabolized by the liver.
- Protects females from being masculinized by circulating estrogens - The a-Fetoprotein does not bind to androgens so they are free to enter and masculinize the brain.
Why does giving estradiol to female newborn rats prevent lordosis as adults?
The estradiol injection overwhelms the amount of a-Fetoprotein in the blood, causing the estradiol to enter the brain and masculinize
What species is aromatization not important for masculinizing the brain?
Primates (unknown why)
What does hormonal masculinization of the brain organize?
Masculinization of the brain
Sexual Dimorphism
Males and females show obvious sex differences in appearance
What is an example of sexual dimorphism in birds?
The syrinx (vocal organ) is 5x larger in males than females.
- similar with brain structure size
What happens if you expose hatchling birds to testosterone/estradiol?
It can make the HVC and RA larger
What is an example of sexual dimorphism in rats?
A nucleus in the pre-optic area (POA) is larger in males than females.
What is the SDN-POA?
The nucleus in the preoptic area of rats.
“sexually dimorphic nucleus of the POA”
What happens if the SDN-POA area of rats experience a lesion?
Disrupts ovulatory and copulatory behaviors
What can increase the size of the SDN-POA in rats?
Testicular androgens during development
What gender has a larger SNB in rats?
Males
Spinal Nucleus of the Bulbocavernosus (SNB)
A group of motor neurons in the spinal cord that innervate muscles controlling the penis.
Explain the Process of SNB in rats.
- Before birth, there is an equal number of SNB in neurons and their target muscles.
- Androgens act on the BC muscles in males to prevent their breakdown.
- The innervating SNB motoneurons survive due to ciliary neurotrophic factors (CNTF).
- If the CNTF receptor i knocked out in mice, the SNB neurons die = female
Bulbocavernosus Muscles (BC)
Muscles that surround the base of the penis
Where are BC motoneurons found in non-rodent mammals?
Onuf’s Nucleus in the spinal cord
Onuf’s Nucleus
The area in the spinal cord that contains the spinal nucleus of the bulbocavernosus (SNB) in rats.
What do most female mammals retain into adulthood?
BC muscles
Where are BC muscles in females?
Surrounding the vagina
Is the BC larger in men or women?
Men
- men have more of Onuf’s Motoneurons too
What factors can modulate masculinization?
Environmental and social influences
What is an example of environmental/social influences in rats?
A mother rat cares for males differently than for females.
- Greater amounts of urogenital licking helps masculinize the developing nervous system by increasing SNB cell survival.
What happens when female baby rats experience more urogenital licking?
They will have an increased level of attentiveness as mothers.
What is a environmental/social influence in human babies?
The babies will experience different interactions with peers based on their gender
- influences sexual differentiation process including gender
What can amplify biological differences?
Socialization
What do the behavioral differences between men and women suggest?
There should be differences in the brain.
What does it mean by saying “many parts of the human brain are sexually dimorphic”?
There are different characteristics within the brain parts based on gender.
What is it difficult to know regarding dimorphisms?
If dimorphisms are caused by prenatal hormone exposure or by social influence.
Explain the details of the Guevedoces Theory.
- A genetic mutation of the 5a- Reductase enzyme results in incomplete masculinization of the genitals.
-Normally this enzyme is converts testosterone to DHT, leading to masculinized external genitals.
- At puberty, the testosterone leads to the development of a small penis
= body becomes masculinized
How are the babies who experience a genetic mutation of 5a Reductase raised?
- Raised as females
- Usually take on masculine roles
- Sexually interested in women (gay)
What are the 3 explanations for the Guevedoces theory?
- People who are raised as girls and later behave as boys may have brains that were exposed to prenatal testosterone, causing masculinization.
- masculine development at puberty - The early hormones have no effect on the body and this is simply a way of the Dominican culture recognizing the girls who become boys.
- social influence on gender development - Combination of both
What are the 2 influences on sexual orientation?
- Society’s instruction on how one should behave when grown up
- The biological factor focused on varying levels of fetal androgen directing future behavior (strong in animal models)
Explain the details of brain structures differing in gay individuals?
The INAH-3 nucleus of the POA is larger in men than in women, and in straight men than gay men.
= not clear if size difference is a result/cause of being gay
Simon LeVay
Who examined the INAH-3 Nucleus of the POA?
What are signs/markers of fetal androgen?
- Otoacoustic emissions from the ears
- Finger length patterns
- Eye blinks
- Skeletal features
What do the signs/markers of fetal androgen exposure indicate?
Lesbians as a group were exposed to slightly more androgens than straight women
- but considerable overlap between both groups
What can we not fully explain regarding sexual orientation?
How sexual orientation develops
What is fetal androgen exposure not as understood in?
Gay men
What influences the sexual orientation of men?
The number of brothers born from the same mother before the male.
- Caused by antibody exposure from previous siblings in the womb
(not related to growing up with brothers)
What does research indicate about sexual orientation in both sexes?
Sexual orientation is determined in early life (significant genetic component)
Sexual orientation is partly…
heritable
Do monozygotic twins have the same orientation?
Not always
