Neuropeptides, neurotransmitters, neurosteroids, and the onset of puberty.

Puberty results from withdrawal of the "gonadostat" mechanisms and from increased gonadotropin sensitivity to GnRH. It has been hypothesized that GnRH release may be modulated by a non-steroid-mediated mechanism. Modifications of neuropeptides, neurotransmitters, and neurosteroids may underlie the onset of pubertal processes. Neuropeptides mainly involved in the control of GnRH release are opioids, neuropeptide Y (NPY), galanin, and corticotropin-releasing factor (CRF), whereas neurotransmitters are noradrenaline, dopamine, serotonin, melatonin and gamma-aminobutyric acid (GABA). Norepinephrine, epinephrine, and dopamine stimulate GnRH, whereas the effect of serotonin on hypothalamic-pituitary-ovarian axis seems to be norepinephrine-mediated. Neurosteroids are steroid hormones that bind to the GABA-A receptor, synthesized in the brain de novo or from blood-borne precursors. DHEA, a GABA-A antagonistic neurosteroid, and allopregnanolone, a GABA-A agonistic neurosteroid, may be important in the onset of gonadarche. In conclusion, the onset of puberty derives from the complex interplay among neuropeptides, neurotransmitters, and neurosteroids that occurs in the awakening of hypothalamic-pituitary-ovarian axis.