Chapter 6: Female Sexual Behavior Flashcards
Estrus
Reproductive function in females is cyclic
“Estrus” means “in a frenzy”
In many species, females advertise their reproductive capability and availability during estrus (“heat”)
Strong motivation of female to gain access to males and mate
e.g., willingness to cross electrified grid in rats
Anestrus (not in estrus) will not sustain pain or exert much effort to interact with males
Females are active participants
Estrous Cycle
Estrous cycle: cycle between mating and non-mating conditions in female (4-5 days in rats)
4 stages: diestrus 1, diestrus 2, proestrus (behavioral estrus), estrus
Mating behavior coupled in
time with ovulation
Estrogen and progesterone
- ->ovulation
- ->affect the brain to influence the female’s behavior and induce receptivity
The ovary
Prior to ovulation (diestrus & proestrus):
GnRH from the hypothalamus—> FSH and LH from the pituitary—>
FSH follicles to grow and mature
On the afternoon of proestrus :
Pulses of GnRH become larger and more frequent —>
rapid increase in FSH and LH
FSH—> Theca and granulosa cells of mature.
(Graffian) follicles produce surge in estrogen (“estrus-inducing”) and progesterone
LH from pituitary stimulates ovulation
This is positive feedback
After ovulation (estrus):
Estrogen levels decline
Follicles are converted to corpora lutea which produce large amounts of progesterone (“pro-gestational”)
After ovulation cont’d
Does not mate and not pregnant —> corpora lutea degenerates, P levels drop and the cycle begins anew
Sufficient vaginal stimulation through copulation:
fertile and pregnant —> corpora lutea remain large, estrus cycle suspended
Hormonal Induction of Estrous Behavior:
THEY ARE ALL ACTIVATION
When the ovaries are removed from a female rat through ovariectomy (OVX), estrous behavior disappears
If treated with E alone some, but not all rats dispay estrous behavior
If treated with P alone no estrous behavior
E followed by P normal estrous behavior
Mimics the estrous cycle
In rats, p treatment is 2 dYA AFTER ESTROGEN AND TESTING IN A 4HOUR AFTER PROGESTERONE
ESTRADIOL PRIMES HTE BRAIN TO BE SENSITIVE TO P
Termination of receptivity
P has biphasic effects
AFTER OVULATION, THE LARGE AMOUNTS OF PROGESTERONE SECRETED FROM THE CORPORA LUTEA TERMINATE ESTROUS BEHAVIORAL
Knockout mice
Progesterone receptor knockouts (PRKO)
WHEN OVK, neither wild types nor the PRKO displayed lordosis after treatment with E
P treatment after E estrogen priming induced lordosis in almost all of the wild type mice
Estrogen receptor knockout mice (ERKO)
After OVX:
α estrogen receptor knockout mice (αERKO):
are unreceptive to males even after treatment with estrogen & progesterone
β estrogen receptor knockout mice (βERKO):
Display lordosis to same extent as Wild Type mice
αβ estrogen receptor knockout mice (αβERKO):
like alpha ERKO mice, fail to display lordosis after appropriate hormonal priming
Components of female sexual behavior (Beach, 1976)
Attractivity: stimulus value of a female for a given male
Proceptivity: female initiation of copulation
Receptivity: responsiveness to sexual initiation by the male
All 3 components are at their highest level during behavioral estrus when E levels peak
Attractivity
How attractive the female is to males
Usually measured in terms of preference
Hormones associated with ovulation mediate attractivity in females
E enhances attractivity in OVX females
E-Induced attractivity reduced or abolished by P
Stimulus basis of female attractivity:
Morphological changes that coincide with ovulation
eg, genital swelling in female primates
Chemical cues, e.g. urinary & vaginal secretions
Behaviors, e.g. hopping, darting, ear wiggling in rats; genital presentation in non-human primates
Proceptivity
Appetitive phase
Reflects underlying motivational state
Sexually solicitous behavior that initiates sexual union, but is not copulatory behavior per se
eg, hopping are dating, ear wiggling in rats; solicitous in non-hymn PRIMATES
High concentrations of E facilitate proceptive behavior
IN OVX RHESUS MONKEYS, E INCREASES PROCEPTIVITY IN THE ABSENCE OF MALE….
Receptivity
Consummatory
Those female reactions that are necessary and sufficient for fertile copulation with a male
INDICATED BY A species-specific mating posture IN ALL NONHUMAN PRIMATEs
e.g. lordosis in rodents
Expressed in terms of ratios between a male’s attempts to mate with a female and his success in doing so
Rats: Lordosis Quotient = # lordosis/ # mounts
E is important in receptivity
Receptivity in primates
Female primates are able to copulate at all stages of their ovarian cycles
Suggests that hormones don’t influence female receptivity
But…hormones do play a role in receptivity under certain social conditions
Are females active participants in sexual behavior?
Females have traditionally been assumed to be passive recipients of male sexual attention
Why?
Cultural constraints
Maintaining immobility during lordosis seems passive
Single pair mating tests
Breeding deme
Small breeding units that consist of one or two adult males, several females and their offspring
Females mate with several males simultaneously
Females initiate copulation and control the pacing of mating behavior
How to recreate in lab ?
Female pacing of copulation
When females can pace copulation:
the interval between intromissions is longer (3 min vs 1 min in non-paced mating tests)
they return to the male more slowly following ejaculation
Males learn partner preference
Why is female pacing important?
May be a means of ensuring that she receives an optimal pattern of stimulation (“vaginal code”) for producing offspring
This optimal sensory stimulation induces prolactin release from pituitary, which maintains luteal function and allows for embryo implantation
without it, estrus cycle begins again
Neural mechanisms mediating female sexual behavior
Lordosis activates somatosensory receptors in flank/perineum
Axons from these receptors project to the spinal cord
From the spinal cord, sensory signals travel to the medullary reticular formation in the hindbrain and the midbrain central gray
Receptive field in the flanks increase in size during estrus
Hormones affect sensory input by increasing receptive field size of flank sensory neurons
How do hormones influence receptive field size in flanks to change sensory sensitivity to males mounting and induce lordosis reflex? Hormones affect sensory input by increasing receptive field size of flank sensory neurons
Receptive field of a sensory neuron : a region in which the presence of a stimulus will alter the firing of that neuron
Greater receptive field size increases the probability that male mounting will elicit a lordosis reflex
Ventromedial nucleus of the hypothalamus (VMN)
Lesions of the VMN:
Electrical stimulation of the VMN:
Destruction of afferent and efferent fibers to VMN:
E implanted into VMN induces receptivity
E increases the production of P receptors (PR)
If E primed rats receive infusion of PR antisense oligonucleotides into VMN (block production of PR) then lordosis can’t be elicited
What are the biphasic effects of progesterone pre- and post-ovulation? Think feedback (+ or - )
Progesterone, in concert with estradiol, initiates female sexual behavior in rats
As the cycle continues after copulation and estrogen concentrations fall, the corpora lutea secrete larger amounts of progesterone, and elevated concentrations of progesterone in the blood inhibit female sexual behavior
What happens if you lesion the VMN?
Lesions of the VMN abolishes lordosis
What happens if you electrically stimulate the VMN?
Electrical stimulation of the VMN induces lordosis
What happens if there is destruction to the afferent and efferent fibers?
Destruction of afferent and efferent fibers reduces the frequency of lordosis
Proceptive behaviors
Lesion of the VMN or destruction of the afferent and efferent fibers also reduce hopping, darting, and ear wiggling
Midbrain PAG less involved in proceptive behaviors suggesting different neural mechanisms underlie sexual motivation and sexual performance
The human menstrual cycle
Mating behavior not confined to particular phase of the ovarian cycle
Primates have menstrual cycles—longer
Ovulation and peak estrogen concentration coincide in both rats and primates
Unlike rats, humans do not display a preovulatory progesterone peak
Miller et al., 2007
Female dancers working in a gentleman’s club:
Dancers taking oral contraceptives showed no variation in tips across the study
Effects of hormones on attractivity, proceptivity, and/or receptivity?
Human attractivity
Men prefer scent of ovulating women (Singh & Bronstad, 2001)
Photos of women’s faces taken during the ovulatory period judged by men and women as more attractive (Roberts et al., 2004)
Women prefer masculine faces during ovulation
Women also willing to rate a risky male as more appealing during ovulation
Human proceptivity
Some studies have shown that sexual interest peaks around the time of ovulation (VanGoozen et al., 1997)
Activational Effects of Sex Hormones
Women
Ovarian hormones do not control women’s sexual activity, but may influence sexual interest
Sexual desire in humans rely more on androgens
Human proceptivity
Although the ability to copulate is not linked to hormones in humans, the motivation to copulate appears to be linked to androgens, not estrogens:
Blood concentrations of androgens fluctuate during the menstrual cycle peaking mid-cycle when sexual interest peaks
Plasma T levels in women positively correlated with sexual desire
Treatment with low doses of androgens can increase libido in postmenopausal women (Sherwin et al., 1985)
Both testosterone and estradiol levels in females are positively correlated with self-reported orgasms (van Anders et al., 2008)
Sexual behavior influences hormones in females too:
T slightly increased by intercourse and cuddling
Average change in T bigger if orgasm achieved
Watching erotic film increases T and E, decreases cortisol
Even just thinking ‘sexy thoughts’ increases T
Individual differences in libido
“Some forms of variants in this gene were shown to have a depressing effect on sexual desire, arousal and function, while other common variant had the opposite effect an increase in the sexual desire score. The latter is believed to be a relatively new mutation, and it is estimated that it appears in Homo sapiens “only” 50,000 years ago at the time of humankind’s great exodus from Africa. Approximately 30% of many populations carry the heightened arousal mutations, while around 60% carry the depressant mutation.”
Psych Central
Individual differences in libido
DRD4 receptor associated with novelty seeking
Gambling, risky behavior, drug taking, etc
May also make receptor more active
Having the DRD4 receptor polymorphism associated with having more sexual desire also associated with more partners, more one-night stands, more cheating (Garcia et al., 2010)
Treatments for low libido
Low dose testosterone treatment in women
Viagra?
First drug specifically for low libido just approved by FDA this month:
Fibanserin:
5-HT1A receptor agonist:
Also -HT2A receptor antagonist:
Side effects, low effectiveness
Woman’s BRAIN while having an ORGASM : fMRI Scan
Genital area of the sensory cortex
Limbic system comes into action (long-term memory and emotions)
When the orgasm is about to arrive, the cerebellum and the frontal cortex become much more active
Activity reaches a peak in the hypothalamus during orgasm.
The nucleus accumbens, a region in the brain linked to pleasure and reward, also becomes very active
After the orgasm subsides, so does activity in all the stimulated brain regions
http://www.youtube.com/watch?v=Xqj9auWq-hc
