Estrogen

1
Estrogen

• isolated first from the urine of pregnant women
  in 1929, and later directly from ovarian tissues
  in 1936
• The fluid within the Graafian follicles is
  enriched with E
• E elevation during proestrus induces behavioral
  estrus and cornification of vaginal epithelial
  cells
• 40 OVX female rats fail to mate after E

2
Progesterone

• isolated from ovarian tissues in mid 1930s
• synthesized in the ovary and corpora lutea
• implantation and pregnancy
• operates with E to have biphasic actions
• with E, initiates sexual behavior
• when E titers fall, inhibits behavior

3
Beachs concept of females sexual activity

• Attractivity the stimulus values to a given male
• Proceptivity the extent to initiate copulation
• Receptivity the stimulus value to elicit
  ejaculation

4
Female sex behavior can also be divided into

• Precopulatory phase
• to attract a male to initiate copulation
• Copulatory phase
• response to sexual initiation of a male

5
Attractivity

• The proximity score (PROX)
• Estrogen and PROX
• Estrus females have higher PROX while OVX females
  are rarely attractive
• E increases females PROX
• Both non-behavioral and behavioral components
• Morphological changes
• Chemosensory cues
• Behavioral solicitation
• Individual preferences

6
E increases attractivity of OVX rhesus monkeys
7
Proceptivity

• behavior that initiates sexual union, but is not
  copulatory behavior per se
• affiliative behavior
• solicitations
• influenced by the attractiveness of a male

8
Receptivity

• females reactions necessary for a fertile mating
  
• species-specific mating posture
• measured by ratios between a males attempts and
  success in mating
• E is important
• OVX females do not show lordosis
• is E important for primates?

9
E and receptivity in female rhesus monkeys
10
Female control of copulation

• solicitation to initiate mating
• choosing a male to sire her offspring
• pacing ensures an optimal pattern of vaginal
  stimulation (vaginal code)

11
Paced mating enhances reproduction
12
Multiple intromissions in rats and mice

• stimulate sperm transport
• maintain corpora luteal functions to secrete P to
  build up the uterine wall for the ova
  implantation
• stimulate prolactin secretion to support the
  corpora lutea

13
Estrous cycles in rodents and primates

• E peak coincides with ovulation in both
• In rodents
• no luteal phase
• several follicles develop together
• sexual motivation and performance are mediated by
  gonadal hormones
• In primates
• ability to copulate is not linked to hormones

14
Steroid hormones are critical for female sexual
behavior

• E and P receptors are in critical brain regions
• Hormonal manipulations that mimic hormonal
  profile of natural estrus induce estrus behavior
• E induces production of E and P receptors
• E in VMH
• E implants with P injections induce lordosis
• E causes changes in the firing rates of VMH
  neurons

15
Hypotheses for E regulation of lordosis

• The trigger hypothesis one brief pulse of E sets
  off chain events.
• the esterified estrogens affected neural tissues
  gt 30 min
• The maintenance hypothesis E is present
  continuously throughout the behavioral test.
• two discontinuous exposures to E facilitate
  P-evoked lordosis

16
The Cascade Hypothesis

• An initial E treatment induces specific events in
  VMH neurons
• These events are required for later E-dependent
  events to occur
• continued occupation is not required, E must
  occupy receptors at specific times
• all components of cascade events are critical for
  the onset of lordosis

17
Social environment influences female reproductive
cycles

• The Lee-Boot EffectFemale mice, 4/cage without
  males, display cycles of extended length
• Chemosensory cues suspend estrous cycles

18
The Whitten Effect
(1) Estrus induction and synchronization

• 50 female mice came into estrus on the 3rd night
  following a male exposure
• If prior exposure to a male for 2 days, mating
  occurred on the first night
• Urine/odor from intact, but not castrated, males
  had similar effects
• The substance from male urine has effects on
  estrus induction and synchronization in an
  androgen dependent manner.

(2) estrus suppressionWhen caged together in
large numbers (20-30/cage), females estrus and
ovulation were suppressed.
19
The Bruce Effect If a pregnant female mouse is
exposed to a strange male, pregnancy is
terminated followed by a subsequent mating with
the new male.

• 25-80 pregnancy blocks (48 hrs exposure induces
  the maximum blocks)
• No effects if reunion with the original male
  after 24-hr separation
• Does not occur if a new male is introduced while
  the stud male remains
• Castrated or juvenile males or other females had
  no effects
• After a pregnancy block, females returned to
  estrus

20
The Vandenbergh Effect social environment
affects the rate of sexual maturation.

• Female pups handled daily display estrus earlier
• Handled females that were housed with males
  attained puberty earlier than females without
  males
• Female mouse pups exposed to adult males matured
  earlier than those exposed to adult females

A pheromone emitted by female rodents can delay
sexual maturation in other female conspecifics -
isolated female mice attain puberty sooner than
females reared in all-female groups.
21
The role of pheromones

• Social effects on female reproductive cycles are
  mediated by chemosensory cues.
• Female cues suppress ovarian functions by
  suspending estrus or inhibiting puberty -
  suppressing gonadotropin release.
• Male cues accelerate puberty, induces estrus, or
  interrupts pregnancy -inducing LH/FSH releases -
  follicular growth
• Chemosensory cues are from urine or feces. The
  male primer cues are androgen-based component.
• It is not limited to rodents
• McClintocks studies