Chronic administration of neuropeptide Y into the lateral ventricle starting at 30 days of life delays sexual maturation in the female rat.

The role of neuropeptide Y (NPY) in the regulation of sexual function is still controversial. Whereas central NPY administration is stimulatory during proestrus in the rat and other species, such administration is inhibitory in castrated animals and we have shown that chronic, central infusion of NPY inhibits both the gonadotropic and somatotropic axis in adult rats. Previous studies have suggested that NPY could be involved in the triggering of the first ovulatory LH surge and a recent report indicated that a single central NPY injection given at 30 days of life could advance sexual maturation. We therefore evaluated the effect of chronic NPY administration on the timing of sexual maturation in the female rat and compared the effects obtained with those induced by a single NPY injection. Constant infusion of NPY (18 micrograms/day) into the lateral ventricle delayed sexual maturation as seen by the absence of vaginal opening, delayed ovarian growth and reduced number of pituitary GnRH receptors. This inhibitory effect was seen as long as NPY was infused. In contrast, a single NPY injection either at 30 days of life or earlier, or repeated single injections between 28 and 31 days of life, did not modify the pace of sexual maturation. Unlike what is observed in adult animals, overall food intake was only minimally increased between 30 and 37 days of life in chronically NPY-infused rats, but this increase became more important thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)