Puberty and menopause

Except for a short postnatal period in primates, the HPG axis is inactive until puberty. Inactivity of the HPG axis is due to a neural brake in the CNS and not since of the lack of gonadal steroids. The nature of this neural brake is not clear, although GABA and neuro-peptide Y and kisspeptin have all been occupied.

The accurate trigger for puberty is not known, though it includes a metabolic signal which encodes body mass. In girls, a critical mass of 30 kg appears essential for puberty to commence, with menarche taking place at around 47 kg. Female dancers, athletes, and anorexics fail to menstruate when their body mass falls below this. One candidate for the metabolic signal is leptin that is discharged by fat cells. The blood concentration of leptin is considered to signal the size of fat stores to the hypothalamus. Leptin inhibits neuropeptide-Y-containing neurons in the arcuate nucleus.The end of reproductive life, that is the menopause, is differentiated by ovarian failure; the hypothalamus and pituitary continue to function.