Puberty

definition:

puberty

-process of acquiring reproductive competence – not a single event

puberty definitions:
age at first estrus

-First indications of sexual receptivity, particularly in response to a male

puberty definitions:

age when a female can support a pregnancy

Most practical definition, but harder to use

GnRH threshold:

B4 puberty

-GnRH neurons highly sensitive to -ve feedback

-Low E2 from ovary

= low GnRH secretion, no LH surge

GnRH threshold:

during puberty

-GnRH neurons sensitivity to -ve feedback decreases

-High E2 from ovary (dom follicles)

= higher GnRH secretion (tonic centre), LH surge

The major limiting factors in a pre-pubertal female are inhibited GnRH signalling and low E2.

What would happen if we gave 6 week old ewe lambs a short series of FSH injections?

Why might we be interested in doing this?

-follicular development without ovulation (E2, follicles grow on ovaries, FSH dependent even in pre-pubescent ewes)

-no ovulation: inhibited GnRH, low/no LH pulse, immature pos response

-why? to research ovulation and follicle dependence on FSH and E2 (not used to stimulate ovulation)

what are the key factors driving female puberty? (2)

-metabolic rate (MR)

-body fat

(generate GnRH pulse freq)

if weight is such a big factor why can’t you just feed them fast?

-not the only trigger, will not affect brain impulses

-overweight is detrimental (fat in mammary gland, pelvic region, etc)

why do small dogs reach puberty before large dogs?

-young animals reach a threshold percentage (not an age) of body weight

-small breeds reach it faster

large: prolonged skeletal growth, juvenile stage

peripuberty:

-follicular growth in waves → start of cyclic recruitment

changes in ovary during puberty

general pathway

follicular recruitment → follicular growth → growth and maturation of follicles

In the sexually mature female, the HPG axis includes GnRH (hypothalamus), gonadotropins (pituitary) and gonadal hormones (E2, P4, inhibin)

Which two HPG axis factors are critical for female puberty onset?

A.Decreased GnRH sensitivity to –ve feedback, high levels of E2

B.Increased GnRH sensitivity to –ve feedback, high levels of gonadotropins

C.Decreased gonadotropin sensitivity to –ve feedback, high levels of E2

D. Increased ovarian sensitivity to gonadotropins, high levels of gonadotropins

A

-trigger for puberty → reduced sensitivity to neg feedback from E2