ELEVATED CORTICOSTERONE IS NOT REQUIRED FOR THE RAPID INDUCTION OF NEUROPEPTIDE-Y GENE-EXPRESSION BY AN OVERNIGHT FAST

Pasting stimulates corticosterone (B) secretion and the expression and secretion of hypothalamic neuropeptide Y in rats. These studies teste d the hypothesis that the rapid and marked fasting-induced increases i n plasma B are responsible for stimulation of neuropeptide Y (NPY) gen e expression. Plasma leptin and insulin were measured because they are also signals known to affect NPY messenger RNA (mRNA). Intact or adre nalectomized rats given a low fixed level of corticosterone (B replace d) were fasted for 48 h. NPY mRNA in the mediobasal hypothalamus, meas ured by nuclease protection assay, was elevated similarly above ad lib -fed controls in both intact and B replaced groups at 15 and 48 h afte r the onset of fasting. NPY immunoreactivity in the mediobasal hypotha lamus increased between 3 and 48 h after onset of the fast in intact b ut not in B replaced groups. The fasting-induced decreases in leptin o bserved in intact rats at 48 h did not occur in B replaced rats. Fasti ng-induced decreases in insulin occurred in B replaced rats but not in intact rats. We conclude that: 1) elevated B is not required for fast ing-induced increases in hypothalamic NPY gene expression; and 2) decr eases in neither leptin nor insulin alone signal the changes that occu r in NPY mRNA in fasted rats.