2 – Puberty

Question 1

Female/male hypothalamic development

Answer 1

• Alpha fetoprotein (alpha-FP)

Question 2

Female/male hypothalamic development: Female

Answer 2

o Alpha-FP binds E2 -> prevents it from passing the BBB and entering the brain ->hypothalamus is ‘feminized’ and GnRH surge center develops

Question 3

Female/male hypothalamic development: male

Answer 3

o T freely enters brain (alpha-FP does NOT bind it) -> T in brain is aromatized into E2 -> hypothalamus if ‘defeminized’ and GnRH surge center does NOT develop

Question 4

Female/male hypothalamic development: before puberty

Answer 4

o Male and female
 GnRH neurons in tonic and surge centers release LOW amplitude and low frequency pulses of GnRH

Question 5

Female/male hypothalamic development: pubertal females

Answer 5

o High amplitude surges of LH every several weeks
 Pulsatile releases between surges
o Tonic center controls basal levels of GnRH
 higher than prepubertal as pulse frequency increases
o surge center controls PREOVULATORY surge of GnRH

Question 6

Female/male hypothalamic development: pubertal males

Answer 6

o Small LH pulses every 2-6hr throughout
 T immediately follows each LH pulse
o Do NOT develop a surge center

Question 7

Periods of reproductive system

Answer 7

1. Fetal
2. Prepubertal
3. Reproductive
4. Senescence

Question 8

prepubertal period

Answer 8

a. In second half, rate of growth for reproductive tract increases over general body growth
b. Somatic and behaviour SECONDARY sexual characteristics appear
c. Culminates with onset of puberty

Question 9

Puberty vs. maturity

Answer 9

• Sexual and physical maturation and fertility potential CONTINUE beyond onset of puberty

Question 10

Onset of puberty : females

Answer 10

o Age at first estrus: most practical (most first ovulations are silent)
o Age at first ovulation: more accurate, less practical
o Age at first attainment of ability to support pregnancy
 Can be a while after 1st estrus or 1st ovulation

Question 11

Onset of puberty: males

Answer 11

o Harder to define timeline
o *age when ejaculate contains a threshold number of spermatozoa
 Bulls: minimum of 50 million sperm with at least 10% motility

Question 12

Factors affecting rate of sexual maturation

Answer 12

-genetics (contributes to up to 50% of variation)
-nutrition
-season
-breed
-sexual/social associations
-environmental influence
-general health
-endocrine disruptors

Question 13

Nutrition

Answer 13

o Dairy heifers: at parturition should be 24mo and 1200lb
 Earlier puberty if nutrition is betterf
o Overweight kids reach puberty sooner
o *each decade for over 100 years, age at puberty has dropped by 4 months

Question 14

Season

Answer 14

o Spring born ewe lambs reach puberty at a younger age (2 month period to get pregnant)
o Fall born ewe lambs took longer but more synchronous (1 month period to get pregnant)

Question 15

Breed

Answer 15

o Genetic selection and geographical locations
o Ex. African-American reach puberty earlier compared to Caucasians
o Ex. high altitude Asia: 18 years old

Question 16

• Sexual/social associations

Answer 16

o If have bull exposure=decrease age at puberty
 High growth rate + bull exposure=youngest age
 Can be visual or olfactory cues
o Larger groups=decrease age at puberty
o *male exposure is stronger than group size

Question 17

Effect of glucose on GnRH release (ovariectomized ewes, used 2-DG=glucose oxidation inhibitor)

Answer 17

• Before treatment: low amplitude LH pulses occurred hourly
• After treatment: LH frequency and amplitude dropped
  o LH could still respond to exogenous GnRH
• *moment to moment regulation of GnRH happens when enough GLUCOSE is available

Question 18

Stimulants of GnRH neurons

Answer 18

• Kisspeptin neurons that are stimulated by indicators of nutritional and metabolic status
  o Blood glucose
  o FAs
  o Leptin

Question 19

What is the key to endocrine regulation of puberty?

Answer 19

• Lack of high FREQUENCY and amplitude GnRH pulses
  o Puberty depends on reactivation of GnRH secretion

Question 20

Gonadostat theory: before puberty

Answer 20

o Hypothalamus is highly SENSITIVE to negative feedback of E2
 GnRH will not be released even with low levels of E2
o High levels of hypothalamic estrogen receptors are presentG

Question 21

Gonadostat theory: during transition to puberty

Answer 21

o NEGATIVE sensitivity of hypothalamus to E2 is reduced
 Allows higher release of GnRH
o Reduced levels of hypothalamic estrogen receptors

Question 22

gonadostat theory: extra

Answer 22

• *removal of other central inhibitors (Ex. opioids, GABA)
• *activation of a central driver (Ex. NE, excitatory AA, kisspeptin)

Question 23

Hypothalamus is sensitive to estradiol before puberty

Answer 23

• OVX causes LH pulses to be present at a similar frequency as in adults
• Replace E2 to OVX PREVENTS LH pulses during the first part of prepubertal period