Puberty

What is puberty?

→ the ability to accomplish reproduction successfully or the period during which adolescents reach sexual maturity and become capable of reproduction

→ not one single even. Complex process that occurs over time and is still not fully understood

→ need the hypothalamus/neurons to respond to signals to have sufficient stimulation

prepubertal

before the onset of puberty

peripubertal

around the time of the onset of puberty

precocious puberty

early onset of puberty

puberty in female

1) age at first ovulation

• typically, 1st ovulation is termed as “silent ovulation”

• verified by ultrasound, rectal palpation, hormone assays

2) age at first estrus

• outward behavioral signs

3) age at which female can support pregnancy without deleterious effects

4) age at mammary development/vulva development (particularly in gilts) /vaginal opening (mice)

5) age at hormonal detection (LH/FSH)

factors influencing puberty

1) body size: fat deposition/lipid accumulation- need sufficient leptin hormone levels

2) social/external factors

• exposure to male

• season of birth

• photoperiod of during pubertal onset

• number of same-sex animals in enclosures

3) breed

environmental impacts

Months of birth will influence age at puberty in seasonal breeders

→spring lambs enter puberty at 5-6 months

→ fall lambs enter puberty 10-12 months

→ heifers born in autumn reach puberty earlier than spring-born heifers

defining puberty- males

1) age when behavioral trait are expressed

• mounting, erection - happens much sooner than other methods

2) age at first ejaculation

• coordination of nerves, muscles, secretion of seminal fluids

3) age when spermatozoa first appear in the ejaculate

• need frequent collections (1x/ week)

4) age when the ejaculate contains a threshold number of spermatozoa

• need sufficient numbers

5) age when the ejaculate contains a threshold number of normal spermatozoa

• cytoplasmic droplet detection in ejaculate

breeding soundness exams (BSE)

1) physical exam

→ Is he healthy? Can he walk?

2) scrotal circumference

→ minimum circumference based on age

3) sperm motility

→ sufficient numbers of motile sperm, >30% motile

4) sperm morphology

→ >70% normal sperm

Hypothalamus Modifications

→ Estradiol (E2) inhibits GnRH synthesis and secretion at low levels

→ the hypothalamus will be modified over time (as puberty is obtained) to respond in a positive manner to E2 → this is especially true for the surge center

→ females

• the surge center will lie dormant because of insufficient E2 being produced from the ovaries

• the tonic center is highly sensitive to low levels of E2 and will inhibit GnRH synthesis

• the transition of less sensitivity = less suppression = more GnRH

→ Males:

• GnRH neurons will become less sensitive to negative feedback as puberty approaches (peripubertal period)

• less negative feedback = more steroid hormones

KNDy neurons

Kisspeptin Neurokinin B Dynorphin

basics of pubertal attainment

→ Puberty requirement - Female

• fully functioning tonic center

• fully functioning surge center - causes GnRH/LH surge for ovulation

→ Females are unable to produce enough estradiol to stimulate the surge center

→ pubertal transition, negative feedback of estradiol is decreased and more GnRH is produced

→ more GnRH → increased LH pulses → increased estradiol from ovaries → positive feedback and massive release of GnRH → ovulation

→ puberty will be initiated when GnRH neurons are able to fully respond to positive and negative feedback