RELATIONSHIPS BETWEEN HYPOTHALAMIC NEUROPEPTIDE-Y AND FOOD-INTAKE IN THE LACTATING RAT

NPYergic neurons in the hypothalamic arcuate nucleus (ARC) that projec t to the paraventricular nucleus (PVN) are postulated to regulate food intake and energy balance. This projection is overactive in lactation and is thought to drive hyperphagia in this condition. We have explor ed further the relationship between hypothalamic NPY and food intake i n lactation and tested the hypothesis that hypoinsulinemia is the stim ulus to NPY neuronal activity. Compared with nonlactating controls (n = 10), freely fed lactating rats (n = 9) showed significantly increase d (p < 0.05) NPY levels in the ARC and medial preoptic area (MPO), but there was no significant increase in whole hypothalamic NPY mRNA leve ls. Lactating rats (n = 8) that were restricted to control rats' food intake for 3 days showed generally higher hypothalamic NPY levels, wit h significantly higher concentrations than controls (p < 0.05) in the ARC, MPO, PVN, and lateral hypothalamic area(LHA);NPY mRNA levels were also significantly increased (p < 0.05). Across all three experimenta l groups, there was a significant inverse correlation between plasma i nsulin concentration and hypothalamic NPY mRNA levels (r = -0.39, p < 0.01). We conclude that the ARC-PVN projection is overactive in lactat ion and that this is not a consequence of hyperphagia. Hypoinsulinemia may stimulate these neurons, as it thought to do in other conditions of energy deficit.