LACTATION BUT NOT PROLACTIN INCREASES THE LEVELS OF PRE-PRONPY MESSENGER-RNA IN THE RAT ARCUATE NUCLEUS

Evidence mostly obtained from pharmacological studies shows that neuropeptide Y (NPY) is involved in neuroendocrine regulation of reproduction functions. In the present study, we have studied the influence of lactation, a physiological condition associated with high plasma levels of prolactin (PRL) as well as the effects of hyperprolactinemia on pre-proNPY gene expression in the rat arcuate nucleus. The amounts of pre-proNPY mRNA were measured by in situ hybridization using a 35S-labeled cRNA probe encoding for pre-proNPY. In lactating animals killed 4 days after parturition, pre-proNPY mRNA levels were 50% higher than those detected in virgin adult females. Twenty-four hours after pup removal the mRNA levels returned to those observed in virgin animals. Hypophysectomy performed 2 weeks previously decreased by 50% pre-proNPY mRNA levels. Chronic haloperidol treatment which induced high levels of circulating prolactin increased the amounts of pre-proNPY mRNA by 70 and 66% in intact and hypophysectomized animals, respectively. Intracerebroventricular injections of PRL produced no significant changes in the hybridization signal. Chronic hyperprolactinemia obtained by pituitary implants under the kidney capsule did not induce any modifications in the pre-proNPY mRNA levels. These data demonstrate that pre-proNPY gene expression in the rat arcuate nucleus is increased during lactation and that this effect is probably not a consequence of hyperprolactinemia. Moreover, the stimulatory effect of haloperidol treatment on pre-proNPY mRNA levels does not appear to be mediated by the pituitary gland. © 1992.