Puberty, anestrus

Question 1

GnRH during late fetal/neonatal periods

Answer 1

GnRH neurons are capable of and do secrete GnRH

Question 2

GnRH during juvenile period

Answer 2

• GnRH secretion decreases and is maintained at very low levels
• if you stimulate GnRH neurons, they can secrete it
• if supplied with GnRH, pituitary responds with secretion of FSH/LH
• if stimulated with FSH/LH, the ovaries will respond
• tl;dr: the hypothalamo-pituitary-gonadal axis is held in check by suppression of GnRH secretion from the hypothalamus –> puberty is a reactivation

Question 3

how are GnRH pulses held in check during juvenile period then re-activated in puberty

Answer 3

• developmental clock that times genetic program for puberty and sets a lower age limit on its occurrence
• clock receives input from permissive signals that may delay puberty if they are limiting
• cannot advance puberty earlier than genetically preset lowest age

Question 4

what is the critical change for puberty

Answer 4

in the hypothalamus –> increase in frequency of GnRH pulses (reverse the decreased stimulatory inputs on GnRH neurons and increased inhibitory inputs from juvenile period)

Question 5

direct drive hypothesis

Answer 5

• when alterations do not involve gonadal steroid feedback (steroid independent)
• puberty is simply the result of an increased drive for GnRH secretion
• different cell types in hypothalamus provide inhibitory or stimulatory inputs to GnRH neurons

Question 6

gonadostat hypothesis

Answer 6

• when inputs involved in suppression and reactivation of GnRH neurons include re-setting of sensitivity to gonadal steroid feedback (negative feedback inhibition from gonadal steroids)
• during puberty, sensitivity to inhibitory steroid feedback decreases

Question 7

inhibitory and stimulatory influences in direct drive hypothesis

Answer 7

• inhibitory: GABA, NPY

- stimulatory: glutamate

Question 8

what is the initiation of puberty tied to

Answer 8

body growth (somatic development), not necessarily chronologic age

Question 9

peripheral signals that trigger puberty

Answer 9

glucose, insulin, IGF-1, leptin

Question 10

photoperiod influence on puberty

Answer 10

• seasonal breeders can only attain puberty within the breeding season
• whether puberty is achieved during the first available breeding season after birth depends on growth rate and their time of birth in the previous spring (how long they have to achieve target and how long it will take)

Question 11

food supply influence on puberty

Answer 11

• seasonal variations in nutrition influence growth rate

- vital in short-lived species

Question 12

social factors in attainment of puberty

Answer 12

• pheromonal, perhaps tactile

- pheromone in urine of male mice accelerates puberty in females

Question 13

sex differences in time of puberty

Answer 13

-sexually imprinted differences in controls over GnRH secretion

Question 14

genetic influences on age at puberty

Answer 14

• alterations in developmental clock

- alterations in the time taken to achieve certain permissive cue goals (somatic development/body composition)

Question 15

7 types of anestrus

Answer 15

• juvenile: prior to puberty though there will be follicular development (not mature)
• nutritional: periods of nutritional stress and poor body condition
• seasonal: in seasonal breeders during the non-breeding season
• lactational (suckling/milked)
• behavioral
• senile
• pathological

Question 16

mechanism of suckling anestrus

Answer 16

• suppression of cyclicity relies on daily frequency of suckling
• suckling acts at hypothalamus to reduce GnRH secretion
• increased sensitivity to negative feedback inhibition by estrogen

Question 17

hypothalamo-pituitary-ovarian physiology of the pregnant and early post-partum cow

Answer 17

• early/mid pregnancy: follicles emerge and regress due to high progesterone
• late pregnancy: progesterone and estrogen high –> suppression of FSH (ovary is quiescent)
• birth: progesterone and estrogen fall, FSH release –> follicular growth
• post-partum anestrus due to defects in attainment of follicular dominance and final maturation of dominant follicles

Question 18

milked anestrus info

Answer 18

• increase in GH following calving drives nutrient partitioning to support lactation
• energy balance!
• GnRH inhibited until cow is past worst negative energy balance (1-2 wks post-partum) and then increases

Question 19

principles of milked anestrus (BCS, etc)

Answer 19

• cows in poor body condition and those with lowest voluntary intake (fattest cows) are in greatest negative energy balance, lose most BCS, take longest time to return to cyclicity
• cows with low feed intake and/or catabolizing lots of body tissue have high circulating non-esterified fatty acids but low cholesterol, glucose, insulin –> prevents GH receptor formation –> IGF-1 stays low
• increased feed intake in high producing cows increases clearance of estradiol –> lower circulating levels of estrogen

Question 20

what does low estrogen as a result of continued low LH mean

Answer 20

• reduced expression of estrus

- LH surge not induced, follicle is anovulatory and becomes atretic, new follicle emerges

Question 21

what happens with improved energy balance

Answer 21

• central inhibition of GnRH pulses lifted permitting increased LH pulses
• increased insulin stimulates receptors for GH
• dominant follicles can fully mature and secrete sufficient estrogen to give LH surge and ovulation

Question 22

behavioral anestrus

Answer 22

• social: first time breeding, mate preference
• seasonal: first of breeding season often silent
• post-partum: presence of offspring
• juvenile: first ovulation without estrus

Question 23

senile anestrus

Answer 23

menopause (humans mostly)

Question 24

pathological anestrus

Answer 24

• systemic disorders suppress hypothalamo-pituitary axis
• excess cortisol from adrenal in cushings
• insufficient cortisol in addisons
• hypothyroidism
• any disease affecting reproductive organs
• disorders of sexual differentiation