Reproductive Behavior Flashcards
compare and contrast asexual and sexual reproduction.
Asexual reproduction in some animals (parthenogenisis)
All eggs genetically identical to mother
Came from sexual reproduction but these animals lost the ability to sexually reproduce
Vast majority of vertebrates sexually reproduce
Sexual reproduction produces more genetic variation
In hopes that one will survive better
why are female gametes larger than male gamete?
Females gametes/ eggs carry the organelles for the reproduction, so larger gamete, limited by number gametes
Sperm generally carries DNA, have flagellum
Male gametes are smaller and designed for motility to find the eggs, smaller than female gametes, limited in number of mates.
precursors to female and male internal structures?
Mullerian ducts are precursors to female internal structures
Wolffian ducts are precursors to male internal structures
what causes differentiation into male genitals?
Gene on the male’s Y chromosome the SRY gene (sex determining region on the Y chromosome causes those differentiating gonads to develop into testes, the sperm producing organs
Testes produce androgens (hormones more abundant in males) and increases the growth of testes which would then produce more androgens
Androgens cause wolffian ducts to develop into seminal vesicles (stores semen) and the vas deferens (ducts from testes to penis)
Testes produce mullerian inhibiting hormone (MIF) that causes mullerian ducts to degenerate
Male testes produce more androgens than estrogens (hormone abundant in females)
what causes differentiation in external genitals?
In mammals differentiation of external genitals depends mainly on T
High levels of T causes external genitals to develop male pattern and low levels leads to a female pattern
First trimester is the human sensitive period for genital formation
Male developing testes secrete testosterone , certain enzymes convert it into dihydrotestosterone - very effective at promoting penis growth: if dihydrotestosterone levels is high enough the tiny genital tubercle grows and develops into a penis but if levels are low, the tubercle develops into a clitoris
Depending on levels of T and dihydrotestosterone , the embryo develops either a scrotum or labia
what causes differentiation into female genitals?
do not have the SRY gene, their gonads develop into ovaries and their wolffian ducts degenerate
Ovaries do not produce MIH- females’ mullerian ducts develop and mature into oviducts, uterus, and upper vagina
Female ovaries produce more estrogens than androgens
prominent androgens and estrogens
Prominent androgen =testosterone
Prominent estrogen = estradiol
have similar effects in some ways and opposing effects in others
progesterone
Progesterone- another prominent female hormone- prepares uterus for implantation of a fertilized ovum and promotes the maintenance of pregnancy
Progesterone released by the corpus luteum in the ovary peaks a bit later -different from rodents; to create a good place for the egg to develop- progesterone stimulates uterine development
genes and sex differences
Y and x chromosomes control some biological differences independently of hormones
Y chromosome has many sites that alter the expression of genes on other chromosomes
Genes on X and Y chromosomes produce effects beyond those that we can trace to androgens and estrogens
sexual selection
genes that make an individual more appealing to the other sex will increase the probability of reproduction
Male sexual behavior- dopamine mesocorticolimbic system
Appetitive (motivation)- sex drive, libido courtship
E.g. vocalizations, movement in search of mates
Consummatory- copulatory behavior
Sexual attraction is largely driven olfactory & auditory
Mounting (latency)
Intermount (interval)
Intromission (insertion of penis) number
Ejaculation (number)
Ultrasonic vocalizations esp after copulation and self grooming
Sensitive to Environmental context & testing paradigm
testosterones effects on male sexual behavior
T is essential for male sexual arousal, and acts partly by increasing the sensitivity in the penis
Sex hormone bind to receptors that increase responses in parts of the hypothalamus, including the ventromedial nucleus, the medial preoptic area (MPOA) and the anterior hypothalamus
T primes the MPOA and several other brain regions to release dopamine
MPOA neurons release dopamine strongly during sexual arousal
Both men and women with high T levels are more likely than average to seek additional partners
Decreases in T levels generally decrease male sexual activity
Androgen do not “cause male sexual behavior, but rather androgens change the probability that male sexual behavior will be elicited within a particular context- like a dimmer not a switch
dopamine effects on male sexual behavior
in moderate concentrations, dopamine stimulates mostly type D1 and D5 receptors which facilitate erection of the penis in the male and sexually receptive postures in the female
in higher concentrations of dopamine, dopamine stimulates type D2 receptors which lead to orgasm
dopamine stimulates sexual activity, the neurotransmitter serotonin inhibits it by blocking dopamine release.
many antidepressant drugs increase serotonin activity, and one of their side effects is decreased sexual arousal
inability to have an erection is likely due to
Low T is not usual basis for impotence, the inability to have an erection (usually caused by impaired blood circulation, especially in older men
how does viagra work
The drug sildenafil (Viagra) increases male sexual ability by prolonging the effects of nitric oxide which increases blood flow to the penis and blood flow to the brain
activational effects
Activational effects- after reproductive maturity, transient modification behavior, usually after puberty (day 40-50 in rats)- can be both genomic and non-genomic
Genomic effects are mediated by effects in transcription and tend to be longer lasting
Non-genomic effects are quite rapid and do not involve transcription and translation and can involve second messengers
Temporary effects continuing only while a hormone is present or shortly beyond
Current hormones influence the degree of sex drive
Bursts of hormone during pregnancy produces temporary effects on emotional arousal , aggressive behavior and learning and cognition
Organizing effects set the stage for activating effects
organizational effects
Organizational effects - early development, long lasting structural effects and often epigenetic in nature, small increase in testosterone after birth to masculinization the brain
Hormones injected early in life have much stronger effects
Sensitive period in early development (e.g. first trimester of pregnancy for humans, sex hormones determine whethter the body develops into female or male genitals and alters certain aspect of brain development)
Organizational effects during puberty: breast development on women, facial hair and penis growth in males, changes in voice, and male-female differences in the anatomy of certain parts of the hypothalamus; some of the differences in brain anatomy between males and females increases during this time
Organizing effects set up the female hypothalamus such that later hormones can activate the menstrual cycle
distinction between organizational and activational effects
Distinction between organizing and activating effects is not absolute, hormones often produce a combination of temporary and longer-lasting effects
how can we test the effects of T and other hormones
Remove testes, give back testosterone
Slow release implants: Silastic capsule-silicon implants- made of silicon, tubing filled with crystalline testosterone and sealed; the longer the tube, the more testosterone- way of administering testosterone without injection and lasts for weeks in the system for longer and less stressful effects.
ICB administration- brain or part of exposed to androgen, received in the ventricle
Testosterone
Testosterone crosses BBB quite easily and effects all around body as it is a small lipophilic molecule
aromatase
Aromatization in specific brain regions is crucial Important for male sexual behavior which is counter-intuitive since it creates estrogens Converts androgen (testosterone) into estrogen (estradiol) the estradiol then binds to estrogen receptors which has effects on gene expression (genomic effects)
in castrated male rats, what did T and E2 administration, and aromatase inhibitor (block activity of enzyme) show?
systemic T, androstenedione-weak androgen precursor to testosterone (also restoration to male sexual behavior), and E2 (estradiol) restore appetitive and consummatory behaviors
T+ aromatase inhibitor (block activity of enzyme)
Reduction in male sexual behavior
how do you increase amount of aromatase, inhibit aromatase in the brain, and locate it?
Increase amount of aromatase with viral vector to over express aromatase
inhibit neurons containing aromatase with optogenetics
Located aromatase in brain- in situ hybridization- mRNA
Look for aromatase protein using immunohistochemistry
Take tissue and homogenize i test tube and add radiolabeled testosterone and see active aromatase that produces radiolabeled estradiol
how are rats masculinized?
In male rats, testosterone begins masculinizing the external genitals during the last several days of pregnancy and first few days after birth and continues masculinizing at declining rate for the next month
female rats injected with T
Female rat is injected with testosterone during last few days of pregnancy or after birth is partly masculinized, just as if her own body had produced the T: exhibiting larger cliterous and shows male sexual behavior and thus, early T promotes male patterns and inhibits female patterns
male rats given estrogen
Injecting male with estrogens produces little effects on his external anatomy but if he lacks androgen receptors, he develops female typical pattern of anatomy and behavior
cause of low androgen receptors
could be an outcome of castration, genetic deficiency of an androgen receptors, or prenatal exposure to drugs that interfere with androgen response (e.g. alcohol, weed, haloperidol- antipsychotic drug, phthalates- common in manufactured products and cocaine)- amount of interference depends on type of drug and amount of exposure, even aspirin interferes with male pattern of development
effects of phthalates
Phthalates inhibit T production: sons of women with high phthalate levels showed less interest in typical boys toys and more interest in typical girls toys and suggests that prenatal hormones especially T alter the brain in many ways that influence differences between boys and girls activities and interest
prostate glands
gland that produces a fluid accompanies and protects sperm cells when ejaculated during intercourse
females lacking estradiol
Female that lack estradiol during early life develops rather normal female external anatomy but does not develop normal sexual behavior or normal internal anatomy; even if she is given estradiol injections , she will show little sexual response to anyone; estradiol is essential for female development
sexual differentiation in the brain for rats in terms of estrodiol and T
Rats Early development (shortly before or after birth) the blood contains high levels of alpha-fetoprotein that binds to circulating estradiol and prevents from entering cells; Female brain is not exposed to estradiol at this time
male T is free to enter the hypothalamus where the enzyme converts much of it to estradiol, and exerts masculinizing effects at this time
For early developing rodents, T is a way of getting estradiol to the hypothalamus
prolactin
Mammalian mother delivers her babies, she increases her secretion of oxytocin and prolactin which promote milk production and several aspects of maternal behavior
Prolactin inhibits sensitivity to leptin, promoting feeding
Man’s testosterone level declines and his prolactin level increases when a baby is born but only if the man has a close relationship with the mother and only in societies where men contribute to infant care
Men with lower T levels and higher prolactin levels spend more time playing with and caring for their children but these are correlational data
vassopressin
Vasopressin synthesized by the hypothalamus and secreted by the posterior pituitary gland
Vasopressin is important for social behavior in many species partly by facilitating olfactory recognition of other individuals
Males with highest vasopressin levels show highest levels of sexual fidelity to their mates
Low vasopressin levels, mate and then ignore the female and her young
Men with genes for less active forms of vasopressin receptor are less likely to marry, more likely to have marital conflicts or threat of divorce- less likely to show altruistic behavior
Women with the less active form of the receptor were less attentive to their young children
Female rats ignore or avoid baby rats mainly because of aversion of the odor
animals with plenty of T, if aromatase is inhibited
there is a gradual decrease in appetitive sexual behavior
Non-genomic (rapid) effects of estrogens on male appetitive sexual behavior
Single s.c. injection of vehicle control ( C) or vorozole (VOR) an aromatase inhibitor
Half of VOR- treated subjects received E2 concurrently
After 30 min (shorter than previous test), measured time at window
Vorozole rapidly decreases time at window
With estradiol- more time at window, if anything higher than control, possibly because estradiol dose was higher
Suggesting estradiol as non-genomic effects
Other ways to test non-genomic effects
Give estradiol that is conjugated (connected) to a large protein and thus cannot cross cell and cannot bind to the receptors of the nucleus but could bind to receptor at the plasma membrane- and thus still have a rapid effect
Other studies have given an inhibitor of transcription (low dose for short amount of time to not kill the cell) and shown that estrogens can have an effect on behavior or some effect on brain even with the presence of inhibitor
autoradiography
using radiolabeled hormones (testosterone or estradiol), and injecting into animals that has been gonadectomized (removing endogenous hormones) doesn’t compete with regular production of testosterone.
The tissue is then sectioned and applied to autoradiographic film and develop the film to expose where there is radioactivity.
Not as sensitive as immunohistochemistry
In Situ Hybridization or PCR to look for mRNA for the receptors
Social behavior network
Pattern of activation is important for various behaviors
Important for all kinds of behavior regulated by network
Interconnected parts of the brain
Cfos protein is expressed after some stimulus, indirect way of looking at neuronal activation
