Puberty

Question 1

when is sexual differentiation organized vs activated in the hypothalamus

Answer 1

organized during fetal development

activated during puberty

Question 2

hypothalamic programming

Answer 2

in utero determination of sexual differentiation based on “surge center” neurons in the hypothalamus

secretion type that is programmed in utero begins during puberty

Question 3

male hypothalamic programming

Answer 3

1. fetal testes produce testosterone
2. testosterone gets converted to estradiol
3. estradiol eliminates the “surge center” neurons in hypothalamic nuclei
4. sets a male pattern of GnRH secretion once puberty is reached

Question 4

what is the male pattern of GnRH secretion

Answer 4

tonic, pulsatile secretion ONLY

pulsatile GnRH –> pulsatile LH/FSH –> pulsatile testosterone

NO GnRH surge

Question 5

female hypothalamic programming

Answer 5

1. no fetal testes producing testosterone
2. no conversion to estradiol
3. surge center neurons persist
4. sets a female pattern of GnRH secretion once puberty is reached

Question 6

what is the female pattern of GnRH secretion

Answer 6

tonic, pulsatile secretion AND a surge of GnRH at the end of estrus

high estradiol at end of follicular development –> positive feedback on GnRH –> surge release of GnRH (superimposed on tonic pulsatile secretion) –> induces ovulation

Question 7

are prepubertal animals fertile

Answer 7

no

Question 8

can you measure testosterone in a suspected cryptorchid if the male is prepubertal

Answer 8

NO - prepubertal males have LOW testosterone, will appear the same as a castrated male

Question 9

puberty

Answer 9

onset of spermatogenesis (M) or first ovulation (F)

Question 10

what initiates puberty

Answer 10

increased GnRH, LH, FSH

preprogrammed into hypothalamus; onset is affected by:
- age
- nutrition
- season
- genetics
- environment

Question 11

age range for puberty

Answer 11

6 to 18 months
depends on species/breed

difficult to define pubertal onset in both males and females

Question 12

how does puberty affect uterine and testicular size

Answer 12

causes an increase in size
BUT large uterus/testicles does not always guarantee onset of spermatogenesis/ovulation

Question 13

peripubertal

Answer 13

around the age of the onset of puberty

Question 14

what is unique about the cyclicity of peripubertal females

Answer 14

1st/2nd cycles are often irregular in duration (very long/very short)

NOT fertile until cyclicity is regular

Question 15

how does nutrition affect puberty onset

Answer 15

puberty is initiated as animal reaches mature body weight

Question 16

effect of leptin on puberty onset

Answer 16

signals skeletal maturity to permit onset

ONLY permissive - can not be used to induce early puberty

Question 17

flushing

Answer 17

when ewes/does are expected to become pubertal, managers will increase energy intake to accelerate the onset of puberty

Question 18

what nutrition/health factors can delay the onset of puberty

Answer 18

• overnutrition
• undernutrition
• chronic disease
• decreased glucose uptake

Question 19

in what species does seasonality affect pubertal onset

Answer 19

seasonal breeders only
- horses, cats, sheep, goats

puberty will occur in the first breeding season in which their body weight approaches maturity

Question 20

what stimulates the HPG axis in short day seasonal breeders

Answer 20

increased melatonin - released during darkness

1. photoreceptors in retina detect changes in daylight
2. signals through cervical ganglion to pineal gland
3. pineal gland secretes melatonin
4. melatonin signals to hypothalamus to stimulate HPG axis

Question 21

what stimulates the HPG axis in long day seasonal breeders

Answer 21

decreased melatonin

when daylight becomes longer, less melatonin is released, triggers HPG axis

Question 22

what species are long day breeders

Answer 22

horses, cats

breed in the spring

Question 23

what species are short day breeders

Answer 23

sheep, goats

breed in the winter

Question 24

what species are non seasonal breeders

Answer 24

dogs, cows, pigs

breed based on body weight and general health

Question 25

how does genetics influence pubertal onset

Answer 25

significant role

different breeds can have different age of onset

mature testes size in bulls/stallions/rams can predict age of puberty in daughters (larger testes = earlier onset)

Question 26

whitten effect

Answer 26

introducing a male into a group of peripubertal females can induce cyclicity and synchronize ovulation

Question 27

ram effect

Answer 27

introducing a ram or goat buck into a group of peripubertal ewes/does will induce early ovulation and accelerate onset of puberty