Elevated corticosterone is not required for the rapid induction of neuropeptide Y gene expression by an overnight fast.
Fasting stimulates corticosterone (B) secretion and the expression and secretion of hypothalamic neuropeptide Y in rats. These studies tested the hypothesis that the rapid and marked fasting-induced increases in plasma B are responsible for stimulation of neuropeptide Y (NPY) gene expression. Plasma leptin and insulin were measured because they are also signals known to affect NPY messenger RNA (mRNA). Intact or adrenalectomized rats given a low fixed level of corticosterone (B replaced) were fasted for 48 h. NPY mRNA in the mediobasal hypothalamus, measured by nuclease protection assay, was elevated similarly above ad lib-fed controls in both intact and B replaced groups at 15 and 48 h after the onset of fasting. NPY immunoreactivity in the mediobasal hypothalamus increased between 3 and 48 h after onset of the fast in intact but not in B replaced groups. The fasting-induced decreases in leptin observed in intact rats at 48 h did not occur in B replaced rats. Fasting-induced decreases in insulin occurred in B replaced rats but not in intact rats. We conclude that: 1) elevated B is not required for fasting-induced increases in hypothalamic NPY gene expression; and 2) decreases in neither leptin nor insulin alone signal the changes that occur in NPY mRNA in fasted rats.
Hanson
E S
ES
Department of Physiology, University of California, San Francisco 94143-0444, USA. hanson@itsa.ucsf.edu
Levin
N
N
Dallman
M F
MF
D000315:Adrenalectomy; D000818:Animals; D001786:Blood Glucose / Q000032:analysis; D003345:Corticosterone / Q000494:pharmacology / Q000502:physiology*; D005215:Fasting; D015870:Gene Expression; D007033:Hypothalamus, Middle / Q000378:metabolism; D007328:Insulin / Q000097:blood; D020738:Leptin; D008297:Male; D009478:Neuropeptide Y / Q000235:genetics*; D011506:Proteins / Q000032:analysis; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D001786:Blood Glucose; D007328:Insulin; D020738:Leptin; D009478:Neuropeptide Y; D011506:Proteins; D012333:RNA, Messenger; D003345:Corticosterone