lecture 8: puberty

Puberty

Hypothalamus GnRH Control Centers in the Female (Figure 6-1 in Text)

Male Brain Development
- testosterone in the male fetus is converted to estradiol in brain and defeminizes or prevents the differentiation of the GnRH surge centers in the hypothalamus
Female Brain Development
- alpha-fetal protein binds estradiol in the female fetus and prevents it from reaching and crossing the blood brain barrier. The surge center of the hypothalamus then develop
Tonic and Surge type releases of GnRH affect LH, also estrogen triggers GnRH surge in female (Figure 6-2 in Text).

Puberty

Puberty in the Female (covered in Textbook)

Puberty in the Male (covered in Textbook)

Average Age of Puberty (Table 6-1 in Textbook)

Factors Influencing the Timing of Puberty

Hormonal - Role of GnRH Pulses

GnRH Pulses Determine Puberty
Prepubertal period
- minimal GnRH release
- FSH and LH low
- minimal to no folliculargenesis or spermatogenesis
Puberty
- increase in the pulse frequency and amplitude of GnRH release
- increase in FSH and LH pulses
- folliculargenesis and spermatogenesis occur

Hormonal Changes in the Female (Figure 6-3 and 6-4 in Text)

GnRH pulse frequency and amplitude increase in the months prior to puberty until a GnRH surge occurs
The GnRH surge is then repeated at 16 to 22 day intervals in livestock and 28 days in humans
The frequency and amplitude of the tonic GnRH pulses is also increased and sustained with puberty

Potential Regulators of GnRH Pulses at Puberty

Development of surge center (Figure 1)
- present at very early age but becomes more responsive as puberty approaches
Change in the feedback sensitivity to estradiol (Figure 2)
- key to puberty in the female
- before puberty female has strong negative feedback to estradiol produced from small follicles
- At puberty, the negative feedback effects decrease and the hypothalamus changes by releasing more GnRH (both an increase in frequency and pulse amplitude). This will lead to more follicluar estrogen production and once that estrogen is high enough, then a positive feedback will lead to a GnRH surge.
Summary diagram (Figure 3).

Silent Ovulation at Puberty (Figure 4)

first LH surge is usually not associated with estrus or ovulation
caused by lack of progesterone which is needed to enhance the effect of estradiol on behavior and positive feedback

Steroid Hormone Influence on GnRH Neurons

Estrogen, Progesterone negative feedback is via steroid receptors in Kisspeptin neurons.
Estrogen positive feedback is via steriod receptors in specific Kisspeptin neurons.

Hormonal Changes in the Male

Puberty in the Stallion (Figure 5)

increases in GnRH pulse amplitude and frequency drive an increase in LH and FSH
Leydig and perhaps sertoli cells mature in response to the increase in LH and FSH but testosterone remains low
LH and FSH decrease (implies GnRH pulses decrease) likely due to production of some steroids by testis
FSH begins to increase effecting sertoli cells (lack of inhibin production possibly)
testosterone finally increases from leydig cells in response to LH approx. 2 months prior to sperm release and drives spermatogenesis
LH, FSH and testosterone then begin to increase to adult levels (also GnRH pulse amplitude and frequency)

Effect of Genetics on Puberty (Table 6-2 in Textbook)

Effect of Nutrition on Puberty

as animal develops the energy needed for growth decreases
there are then changes in the energy available for other processes such as reproduction

Availability of Energy Changes with Growth

Effect of 2-deoxyglucose on LH and GnRH Pulses (Figure 6-5 in Textbook)
Role of metabolic signals including glucose, free fatty acids and leptin in regulation of GnRH secretion and role of glucose sensing, neuropeptide Y and fatty acid sensing neurons via impact on Kisspeptin neurons.(Figure 6-7 in textbook)

Effect of Nutrition on Puberty

Environmental and Social Conditions (Figures 6-8 and 6-9 in Textbook)