Lecture 10 - Sexual Behaviour Flashcards
Female sexual behavior in rodents
- Solicitation, hops and darts, ear wiggle
- Lordosis to intromission
- Pacing is essential for female sexual pleasure
- Conditioned place preference
- Where female can control pacing
- She will preferrentially choose this place and delay sex for her own pleasure (intermission)
Male sexual behavior in rodents
-Pursuit and investigation
-Mounts, intromission and
ejaculation
Why study rats
We hope there are analogous processes in humans (and have reason to believe there is)
Hormonal Basis of Rat Sex
Cannot experimentally manipulate hormones in humans
Use gonadectomy and hormone replacement in rats
Castration/orchidectomy
Ovariectomy
Effect of Testosterone (and estrogens?!) on male sexual behavior
Effect of estrogens (and progesterone) on female sexual behavior
Dissolve these hormones in oil
Use oil with no T as control
What is the effect of adult castration on sexual behavior?
What role do androgens play in this?
Experimental set up
Male rats castrated after first sexual experience
4 groups:
(1) subcutaneous oil
(2) T
(3) Androstenedione
(4) DHT
1mg, 500ug, 250ug each for 6 weeks decrease by 50ug every 2 weeks
Tested sexual behavior weekly with receptive female rats
Letting rats learn sex
Rats are not good at sex the first time so these experiments always allow for a first sexual experience (so they may learn)
What is the effect of adult castration on sexual behavior?
What role do androgens play in this?
Results
Oil rats do nothing
Test/And support behaviour down to 300 micrograms
And is as affective as Test
DHT does not maintain sexual behaviour as well
At the MAXIMUM does, DHT was ok, below this, no activity
What brain regions do androgens act in?
Experiment set up
Try to restore copulation after castration
Assessed effects of T implants in the hypothalamus
Ventromedial hypothalamus (VMH) and medial preoptic area (MPOA)
Also assessed estradiol (E2) implants
Looked at sexual behavior after castration
Effect of E and T in hypothalamus
What brain regions do androgens act in?
Results (VMH)
Sexual behaviours increases with experience
Decreases over 4 weeks following castration
Ventromedial hypothalamus
T partially recovers mounts and intromissions
Does not recover ejaculations
E2 partially recovers mounts
What brain regions do androgens act in?
Results (MPOA)
Medial Preoptic Area
T recovers mounts, intromissions, and ejaculation
-All 3 fully recovered
E2 partially recovers mounts, intromissions, and ejaculation
-Partial recovery of all 3
No recovery in control
Expression of sexual behavior: MPOA critical in males
The Menstrual/Estrous Cycle
- Ovulation is triggered by a peak in estrogen
- This is released by the follicle
- When it peaks = ovulation
- The follicle when discarded goes on to form the corpus luteum and makes progesterone
- Hormones fall > menstruation
- These low levels cause the next follicle to develop
- In rodents there is an estrogen peak then a progesterone peak
- The cycle lasts 4 days in rats
Estrogens + Progesterone for sexual behavior in female rats
An experiment to work out what hormones were needed and in what order
Ovariectomized (OVX) females to eliminate gonadal hormones
Administered E and tested “heat” (aka receptive period aka estrous)
ONLY not in estrus if the male was rejected
Respond to a male rat/flank stimulation with lordosis
E induced heat alone at high doses ~1/3 attempts
Not very good….
Added progesterone into the mix
E for 12 hours then P then 2-4 hours before testing (miics real life)
E + P induced heat at lower doses ~90% attempts
E+P maximal lordosis
Mechanism: E increases P receptors./ This is why it takes a while, these receptors must be built
You need both
What brain area is E+P acting in to induce sexual behavior?
OVX rats implanted with E2 in the VMH and MPOA
Injection of P 4-6hrs before lordosis test
Do females exhibit lordosis following these implants?
VMH: 12 of 13 rats exhibited lordosis
10 solicitations too
MPOA – almost no effect (1 in 10)
Other brain regions also showed no effect of E2 implants
E2 in the VMH elicits consummatory sexual behavior in female rats
Rats sexual brain areas
mPOA - male
VMH - female
Estrogen and male sexual behaviour
Estrogens have similar effects to T on sexual behavior in adulthood
Aromatase convers T into E2
Ts effects on sexual behavior partially mediated by estrogen
Men have higher brain aromatase than women
What have rats told us about sex?
Gonadal homones (T, E, P) are necessary for sex
Castration and ovariectomy abolish sexual behavior
Recover sexual behavior with T in males
E works in the brain
Recover sexual behavior with E+P in females
MPOA (with the sexually dimorphic nucleus) critical in males (SDN) while VMH critical in female consummatory sexual behaviour
Changes of male sexual behavior with age
The decrease in sexual behavior with age is not associated with the change in hormone concentrations
What other factors could be mediating the hormone-behavior relationship?
What other factors could be mediating the hormone-behavior relationship?
Hormones organize the soma, determining what sexual reactions will be brought to expression in adulthood (male/female)
Different organization = different effect of circulating hormone
Individual differences related to sexual behaviour
Before castration there were individual differences in sexual behaviour in rats (high, medium and low drive)
With the same dose of test these individual differences re-emerge
Suggests that the same level of test can have different results
Might be organizational
A receptor must exist for a hormone to do anything, these are set up during organization
“Heat” in female mammals
Heat/Estrous/Receptive period = Increase in sex at ovulation
Common in most mammalian species
Some debate over whether this occurs in women because they have sex throughout month
Examine evidence that there is an estrous period in women
-E high, P low
Attractivity
Definition:
“Female’s stimulus value in evoking sexual responses by the male” (Beach, 1976)
Adaptive functions of attractivity:
Bringing the female in contact with a male
-Change in female behaviour
- Allow male to identify female’s reproductive status
- Male alters behaviour in response
Attractivity in non-human mammal examples
Attractivity in other mammalian species has been shown to be affected by ovarian
hormones, with estrogen being the most prominent
○ Goal is to maximize the likelihood of reproduction
● Cats in receptive period: super loud, yell, assume a position that’s similar to lordosis in
rats
● Primates: changes in coloration (increased reddening) of the hindquarters and a little bit
in the face
Study looking at vocal cues of ovulation in human females
● Looking at how the female voice changes across the menstrual cycle
○ Looking for consistent changes that occur in the voice around the time of
ovulation
● Some definitions
○ Fundamental frequency: pitch of a sound
○ Formant dispersion: distance between adjacent resonant frequencies, fluctuation
in vocal frequencies
● Hypothesis: At the time of ovulation
○ Increased fundamentally frequency
○ Greater formant dispersion: more increases and decreases in pitch
● Estimated the days to ovulation based on luteinizing hormone surge
○ LH drives ovaries to produce estrogen
○ Surge in LH causes ovulation to occur
○ Use LH to get a hormonal measure of when ovulation is occuring
● Compared fundamental frequency during ovulation and the luteal phase (which occurs
after ovulation, when progesterone rises then falls)
● Looked at the pitch of women’s voices and subtracted the fundamental frequency of their
voice in the fertile period minus luteal period
○ If vocal pitch is higher during the fertile phase (ovulation), then the score should
be positive
● 5 days prior to ovulation (based on LH measure), vocal frequency is the same as it is
during the luteal phase
● But as ovulation approaches, there’s an increase in vocal pitch that seems to peak around the time of ovulation
● Also looked at formant dispersion it didn’t differ across the cycle
Clothing choice
● Do women alter their behavior around ovulation?
● Had women come into lab twice: during late follicular (around ovulation) and late luteal phase
○ Looked at outfits worn to the lab
○ Also asked women to sketch outfit they’d like to wear on a night out
● Had blind raters examine the outfits sketched and rate which ones they thought were more attractive based on our society’s standard
○ High reliability among raters
● More attractive outfits were desired and worn during the follicular phase
● Most clear cut example
Sexual Desire around ovulation
● Do females have higher sexual desire around ovulation?
● Used saliva to measure hormones
● Looked at self-reports of sexual desire and self-reports of sexual behavior
● Increase in progesterone → occurs after ovulation, moving out of receptive period
● As progesterone increases, sexual desire decreases
○ Sexual desire is reduced with progesterone which is indicative of the luteal phase
● Increase in estradiol might increase some sexual behavior
○ But data is not super clean
○ Sexual activity increases 24-48 hours following a peak in estradiol
○ Why the delay? Estradiol has relatively slow genomic effects
■ E has to change protein production in order to have effects (think about
the direct mechanism of action that steroid hormones use)
-must change protein production via gene expression and this takes time
Do men find women more attractive at ovulation?
Strip Club Study
● 18 women working at strip club
● Within subject design, women were the control for themselves
● Study lasted 60 days
● Women self-reported menstrual cycle and daily tips
● Looked at the amount of money earned per shift across the cycle
○ During most fertile period: women made more money
● Split women into 2 groups: naturally cycling vs those using oral contraceptives
○ Much less variability in those who use oral contraceptives (don’t have the same
fluctuations in ovarian hormones, birth control works by preventing the peak in
estradiol which causes ovulation)
● Authors suggested that men may be able to detect a receptive period
○ They tip more during this phase so maybe they find women more attractive
during it
● However, it could be that women behave differently at different points in the cycle and not that men can detect ovulation
Because this was a within participant design, it is not confounded by individual differences such as attractiveness
Do men find women more attractive at ovulation?
Smell and ovulation
● Measure how the smell of a women’s t-shirt might alter male’s testosterone levels
● Debate over whether human pheromones exist
○ Pheromones: olfactory cues that indicate info to another member of the same
species, present in rodents and other mammals
○ Not sure if humans are able to detect scent cues and pass information to other
humans using them
● Had four women wear t-shirts for 2 nights during different phases of their menstrual cycle
○ 13-15 days after menstruation (approximately the time of ovulation) → follicular
phase
○ 20-22 days after menstruation → beginning of luteal phase
● Control: t-shirts not worn by anyone
● Methods
○ All t-shirts were new and washed in odorless soap
○ T-shirts were put in the freezer in an odor-protecting ziplock bag
○ Women had to wash their bed covers in odorless soap each night
○ Given odorless shampoo and body wash to use
○ Were not supposed to smoke, wear perfume, or use deodorant
○ Were not supposed to have someone else sleep in the bed with them nor engage
in any sexual activity
● Had 37 men come into lab
○ All men self-reported as heterosexual
○ Took initial testosterone levels
○ Had men smell the t-shirts
○ Took another testosterone measurement
● Observed greater levels of testosterone in men who smelled shirts worn by women when
they were ovulating
● Observed a rise and fall in testosterone elicited by t-shirts based on when women were
ovulating
● Suggests that smell/pheromones contribute to men’s abilities to determine ovulation in
females
● Men also rated the odor from t-shirts worn by women who were ovulating as more
pleasant
Do females respond to male pheremones?
- If males respond to female pheromones (axillary odours) do females respond to males?
- 4,16-androstadien-3-one (AND) and estra-1,3,5(10),16-tetraen-3-ol (EST)
- PET scans of blood flow – women + AND increased flow to ventromedial and preoptic, men + EST increased paraventricular and dorsomedial
- Other studies: women rate higher T men as more attractive
- Male axillary smell increases LH release
Sexual orientations and smells
- Homo males respond similarly to AND as Hetero females
- Homo females respond similarly to EST as Hetero Males
-No observable increase in hypothalamic blood flow to EST in Homo Males or AND in Homo Females
Estrus in women: not so different from other mammals after all…..
- Female sexual desire changes across the month
- More desire and activity when estrogen levels are high
- Altered voice and dress (attractivity)
- Males are more attracted to women when fertile
- Partially based on smell
- T levels increase, linked to consummatory sexual behavior
-Suggests that there is a human version of estrus!
- Do not confuse biological increase in sex drive as consent
- Human psychological capacity greater than other mammals so sexual behavior less governed by biological drive
- Why sex occurs across the cycle
