9 – Female Reproduction IV

Question 1

Spontaneous ovulators

Answer 1

• Ovulation in response to hormonal changes (no stimulation required)
  o Estradiol turning surge center on
• Ex. human, cat, dog, horses

Question 2

Induced (reflex) ovulators

Answer 2

• Require stimulation of the vagina and/or cervix for ovulation to occur (past finding)
  o SPINAL CORD (received signal from sensory neurons) turns surge center on=pre-ovulatory GnRH surge=LH surge
• Present in most mammalian orders (not primates)

Question 3

What is ovulation the consequence of in both spontaneous and induced ovulators?

Answer 3

• LH discharged by pituitary gland (Pre-ovulatory LH peak)
• *due to surge of GnRH

Question 4

Production of GnRH and estradiol

Answer 4

• GnRH neurons in 3rd ventricle have NO direct receptor for estradiol
• Estrogen receptors alpha and beta in hypothalamus = those bind with kisspeptin neurons=produce kisspeptin
• Kisspeptin=responsible for GnRH surge

Question 5

Relationship between GnRH and LH in pulse secretion

Answer 5

• Frequency of GnRH pulses VARIES during the estrous cycle
• Pre-ovulatory surge=GnRH surge increased significantly =LH surge

Question 6

When might induced ovulation be most value?

Answer 6

• Species that regularly undergo marked population fluctuations (ex. California voles)
• Solitary, nongregarious animals where encounters with members of opposite sex are infrequent and unpredictable (ex. musk shrews)
  *female still needs to copulate in order to ovulate (engage depending on state of estrus)

Question 7

Behavioural estrus of induced (reflex) ovulators: 2 ‘types’ of species

Answer 7

1. Exhibit well-defined periodic cycles of receptivity lasting several days, weeks or months
2. NEVER display sexual receptivity unless exposed to signals from conspecific male

Question 8

Reflex ovulators that never display sexual receptivity unless exposed to signals from conspecific males

Answer 8

• In absence of male cues: females are permanently anestrus and remain sexually UNRECEPTIVE
• *pheromonal and tactile stimuli from male=significant increases in uterine circulation estradiol level

Question 9

Exogenous stimuli for inducing LH surge: categories

Answer 9

• Category one
• Category two
• Category three

Question 10

Category one: induced ovulators

Answer 10

• Require minimal copulatory stimulation
• Ovulation induced RAPIDLY (ex. minutes or less)
• Ex. rabbit, ferret, mink

Question 11

Category two: induced ovulators

Answer 11

• Require (at minimum) a SINGLE copulatory series
  o Multiple intromissions followed by ejaculation
• Ex. racoons, hares, squirrels, camels

Question 12

Category three: induced ovulators

Answer 12

• Require MULTIPLE ejaculatory series
  o Consecutively on same day or over course of several days
• Ex. voles, shrews, cats

Question 13

Patterns of LH release in induced ovulators: species variability in

Answer 13

• in pattern of mating behaviour preceding a preovulatory surge in LH
• latency, duration and magnitude of this LH peak after mating
  *number of ejaculation is not that important for the LH surge to happen
  *CATS: more copulations they had=increased LH surge

Question 14

What actually causes ovulation in induced ovulators? (research)

Answer 14

• Stimuli or NGF?
• Tried to do artificial vaginal-cervical stimulation but get LOWER rates of ovulation and LH than normally achieved with natural copulation
• Camelids: got LH and ovulation with AI (absence of coital stimulation)

Question 15

Nerve growth factor (NGF)

Answer 15

• protein involved in neuronal survival
• present in abundant concentrations in CAMELID SEMEN
• thought to act on hypothalamus

Question 16

Is it NGF or mating in llamas that cause ovulation?

Answer 16

• Can be induced to ovulate by seminal plasma in ABSENCE of copulation
• Copulation alone CANNOT elicit ovulation in absence of seminal plasma

Question 17

If it is NGF in llamas, then why is estradiol inducing ovulation in them?

Answer 17

• Endogenous production of ovarian estradiol does NOT reach threshold necessary to trigger ‘spontaneous’ ovulatory response
  o But if give estradiol=goes over threshold= ovulation
• *rely on NGF to ovulate

Question 18

Is it NGF or mating in cats to cause ovulation?

Answer 18

• Natural mating: 100% ovulation
• Seminal plasma treatment(cats): 67% effect
• Beta-NGF treatment(llamas): 17%
  *maybe mechanical stimulus is a critical factor for ovulation

Question 19

Potential ovulatory pathways (3) in mammalian species:

Answer 19

1. Sensory
2. Estradiol
3. NGF