Injection of α-MSH, but not β-endorphin, into the PVN decreases POMC gene expression in the ARC

β-Endorphin (β END) and α-melanocyte stimulating hormone (α-MSH), neuropeptides derived from proopiomelanocortin (POMC), have opposite effects on eating behavior. We injected rats with α-MSH (0.6 nmol) or β-END (I nmol) into the PVN (three times in a 26 h period). These doses of α-MSH and β-END decreased and increased feeding respectively. Following α-MSH administration into the PVN, mRNA levels of POMC decreased by 17%, whereas there was no significant change in gene expression of either proDynorphin or proEnkephalin. PVN injection of β-END failed to alter gene expression of POMC, proDynorphin or proEnkephalin. These data suggest that a feedback pathway exists between the PVN and ARC for α-MSH and POMC, but not for β-END and POMC.