Puberty

Question 1

Puberty depends on …?

Answer 1

…the ability of presynaptic neurons to turn on GnRH neurons -> ++GnRH secretion to “kickstart” reproductive system

Question 2

Presynaptic neurons are influenced primarily by …?

Answer 2

…degree of fatness! hahaha A threshold body size and/or composition is required for the onset of puberty - can be influenced by genetics, nutrition…

Question 3

T or F - environmental effects can alter the age of puberty

Answer 3

true - degree of influence varies between species

Question 4

What is puberty?

Answer 4

age at which animal acquires reproductive competence

Question 5

Difference between male & female hypothalamus?

Answer 5

Female has tonic AND surge centre

Male has only tonic centre

Question 6

How does defeminisation occur?

Answer 6

oestrogen acts on hypothalamus eliminating ‘surge’ centre

Question 7

How does E2 defeminise the male but not female?

Answer 7

In female, E2 released by fetal ovary -> binds to alphaFP (from liver and yolk sac) thus does not cross blood brain barrier and enter hypothalamus -> SURGE CENTRE DEVELOPS. In male, T4 released by foetal testis enters brain -> E2 -> SURGE CENTRE DOS NOT DEVELOP

Question 8

Fundamental requirement of puberty?

Answer 8

sufficient GnRH prod by hypothalamic neurons

Question 9

What does puberty result in?

Answer 9

gametogenesis
steroidogenesis
dev. of repro. tissues

Question 10

T or F - puberty is limited by gonadotrophin producing ability of anterior pituitary

Answer 10

false

Question 11

T or F - puberty is limited by ability of ovary to respond to gonadotrophins

Answer 11

false

Question 12

First ovulation requires…?

Answer 12

achievement of full neuronal activity of the surge centre

Question 13

Limiting factors in prepubertal animals…? (females/males)

Answer 13

Females - lack of gonadal oestradiol to stimulate surge centre
Males - lack of decreased hypothalamic sensitivity to -ve feedback by T4/E2

Question 14

T or F - Response of GnRH neurons to +ve and -ve feedback is essential for onset of puberty

Answer 14

true

Question 15

T or F - Decreased sensitivity to -ve feedback triggers the onset of puberty in males and females

Answer 15

true

Question 16

Post pubertal heifers have what increase?

Answer 16

LH pulse frequency (from ~4 to ~18 pulses/24hrs)

Question 17

Dev. of hypothalamic neurons in females influenced by …?

Answer 17

1. nutritional factors (body size and/or composition)

2. exposure to certain environmental cond’s (season, photoperiod) or social cues

Question 18

T or F - metabolic signals have no influence on puberty

Answer 18

false - metabolic signals influence GnRH neurons

Question 19

Which 3 presynaptic neurons can stimulate GnRH neurons?

Answer 19

1. leptin sensitive
2. glucose sensitive
3. FA sensitive

Question 20

In dairy heifers, high/moderate.low plane of nutrition…?

Answer 20

high - 2lb/day (puberty ~7 months)
mod. - 1.5lb/day (~20 m)
low - 1.2lb/day (~>28 m)

Question 21

Social cues moderating onset of puberty…

Answer 21

• presence or absence of opposite sex during prepubertal period (olfactory recognition via pheromones in urine)
• pop. density where animals housed (gilts in smaller group 2-3 -> delayed onset of puberty

Question 22

T or F - male exposure > stimulation for onset of puberty than large groups of gilts

Answer 22

true

Question 23

Fastest onset of puberty treatment for beef heifers?

Answer 23

high growth rate + bulls

Question 24

Avg age of puberty in bovines, ovine, porcine

Answer 24

bovine - 11 mths both sexes
ovine - 7 mths both sexes
porcine - 7 mths both sexes

Question 25

Advantages of accelerating or delaying puberty…?

Answer 25

Accelerating - minimise age of males -> accelerate genetic improvement by reducing generation interval
Delaying - in pets & vermin -> pop. control