Induced Ovulators Flashcards
What is the history of science around induced ovulators?
- 1905: description of mating-induced ovulation in rabbits
- 1929: purification of the first steroid (esterone)
- 1947: establishment of a role for NE on induced ovulation
- 1960: establishment of the 1st radioimmunoassay
-1970: characterization of hormonal dynamics - 2005: description of an ovulation inducing factor in the semen of camelids
What is the difference btwn spontaneous vs induced ovulators?
- in spontaneous ovulators, ovulation is brought about totally in response to hormonal changes (no stimulation required)
- the reflex (induced) ovulator requires stimulation of the vagina &/or cervix for ovulation to occur
What is the pathway for induced ovulation?
- copulation stimulates sensory nerves in the vagina & cervix
- impulses are then relayed to the spinal cord
- impulses are then relayed to the surge center in the hypothalamus
- if the stimulus is of sufficient magnitude, neurons in the preovulatory center fire, causing large quantities of GnRH to be released that in turn stimulates the LH surge
How does the LH surge induce ovulation?
- both in spontaneous & induced ovulators, ovulation is the consequence of a discharge of luteinizing hormone (LH) secreted by the pituitary gland
- at the time of ovulation, the plasma concentration of LH reaches v high values, known as the pre-ovulatory LH peak
- A surge of GnRH will result in a surge of LH
How is the production of GnRH related to estradiol?
- GnRH neurons dont express the relevant E2 receptor
- E2 secreted from ovarian follicles acts on kisspeptin (KP) neurons in the hypothalamus to regulate KP expression & release. KP acts on GnRH neurons to induce GnRH release in the hypothalamic-pituitary (H-P) axis. GnRH stimulates the gonadotrophs in the anterior pituitary to induce gonadotropin (FSH & LH) secretion.
What is the relationship btwn LH & GnRH in pulse secretion?
the frequency of GnRH pulses varies during the estrus cycle
What is the phylogenetic distribution of mating-induced ovulation?
- w/ the exception of primates, induced ovulation is present in most mammalian orders that have been examined
Why are some spp induced ovulators?
induced ovulators might be most valuable in:
- spp that regularly undergo marked population fluctuations, ex: California voles (Microtus californicus)
- solitary, nongregarious animals in which encounters w/ members of the opposite sex were infrequent & unpredictable
What is behavioral estrus in reflex ovulators?
- the female must copulate in order to ovulate (the female engages in sexual activity depending on her state of estrus & behavioural receptivity)
- some spp (ex: Fe, California voles, ferrets) exhibit well defined periodic cycles of female receptivity lasting several days, weeks, or months
- in some spp (Ex: musk shrews, pine voles) will never display sexual receptivity unless they are first exposed to signals from a conspecific male (in the absence of male cues, females of these spp are permanently anestrus & remain sexually unreceptive (pheromonal & tactile stimuli from a male causes significant increases in uterine circulating estradiol lvls)
What are the 3 categories of exogenous stimuli for inducing the LG surge & ovulation in reflex ovulators?
- category one: includes spp which require minimal copulatory stimulation & in which ovulation can be induced rapidly (w/in minutes or less) (rabbit, ferret, mink, short-tailed vole)
- Category two: require, @ minimum, a single complete copulatory series, usually consisting of multiple intromissions followed by an ejaculation (racoons, hares, squirrels, camels, california voles)
- Category three: require multiple ejaculatory series, occurring either consecutively on the same day or over the course of several days (voles, shrews, Fe)
- however, no info available for Lemmings, woodchucks, numerous vole & insectivore spp, & several of the larger carnivores (bears, skunks, lions, etc.)
what are the patterns of LH release in induced ovulators?
- there is sp variability in the pattern of mating behavior preceding a preovulatory surge in LH & in the latency, duration, & magnitude of this LH peak after mating
- in both the rabbit & the ferret, the magnitude of the preovulatory LH surge is independent of the amount of mating stimulation received
- by contrast, in the cat the duration & magnitude of the LH surge is related to the amount of mating stimulation received
What causes ovulation? (studies done)
- using artificial vaginal-cervical stimulation (AVS) w/ glass rods or vibrating probes, ovulation has been induced in several reflex ovulators including mink, ferrets, bank voles, rabbits, & cats
- HOWEVER, lower rates of ovulation & LH release than normally are achieved w/ natural copulation
- in 11 induced ovulating spp in which AVS data is available, 63% did not ovulate when AVS was given alone
- several member of Camelidae showed (75-100%) LH surge & ovulation w/ just artificial insemination alone (absent of coital stimulation)
How is nerve growth factor (NGF) related to LH surge?
- NGF is a protein discovered 90 year ago involved in neuronal survival
- NGF is present in abundant concentrations in camelid semen
- NGF is thought to act at the hypothalamus
Is it nerve growth factor or mating that induces ovulation in llamas?
results demonstrate that llamas can be induced to ovulate by seminal plasma in the absence of copulation & that copulation along cannot elicit ovulation in the absence of seminal plasma
If it is NGF inducing ovulation in llamas, then why does estradiol also induce ovulation in llamas?
- it could be b/c in camelids, the endogenous production of ovarian estradiol does not reach the threshold necessary to trigger a “spontaneous” ovulatory response, & instead, the female camelid relies on seminal NGF to ovulate
