Unlike TRH and somatostatin, almost all of the GnRH in the brain of mammals is restricted to the hypothalamus and related neural structures. Small amounts are found in the circumventricular organs of the brain, including the pineal gland. GnRH has also been found in milk, suggesting that the breast, a dermally derived structure, may have embryological origins analogous to the primitive neuroectoderm, the source of neuroendocrine cells.
The most important central nervous system effect of GnRH may be that involved in the regulation of mating behaviour. Direct injection of GnRH into the hypothalamus has been reported to enhance female sexual responsivity, even in animals without a pituitary (which are therefore incapable of responding with gonadotrophin-ovarian hormone activation). Studies of the effect of GnRH on sex drive in humans have been unconvincing.
