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
-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.
