Neuropeptide Y (NPY): a possible role in the initiation of puberty.

NPY modulates the rat hypothalamic-pituitary-gonadal axis at both the adenohypophysial and central levels. Previously published studies have consistently shown elevations of GnRH content in the preoptic area (POA) and hypothalamus starting with the appearance of GnRH immunoreactivity around fetal day 12-14 until stabilization around the time of puberty. In the present studies, irNPY content of male and female rat hypothalami and POA was examined during days 0 to 36 of postnatal development. Hypothalamic irNPY content rose steadily from 4.54 +/- 0.19 ng/fragment (males) and 2.72 +/- 0.55 ng/fragment (females) at birth to 34.14 +/- 3.94 ng/fragment (males) and 46.79 +/- 6.16 ng/fragment (females) at day 36, corresponding approximately to the time of vaginal opening. A similar elevation of irNPY content was observed in the POA. At day 0, POA content was 1.91 +/- 0.18 ng/fragment (males) and 2.02 +/- 0.25 ng/fragment (females) and progressively increased to 42.26 +/- 3.94 ng/fragment and 41.33 +/- 3.72 ng/fragment by postnatal day 36. In subsequent investigations, hypophysial-portal and peripheral plasma irNPY was determined around the time of vaginal opening, revealing a surge in portal levels of irNPY which preceded the prepubertal LH surge. The progressive postnatal increase in hypothalamic and POA irNPY content culminating in a prepubertal surge of irNPY secretion into the hypophysial-portal circulation suggests involvement of this neuropeptide in reproductive development and the onset of puberty.