REGULATION OF PROOPIOMELANOCORTIN GENE-EXPRESSION BY NEUROPEPTIDE-Y IN THE RAT ARCUATE NUCLEUS

In the arcuate nucleus which is richly innervated by both proopiomelan ocortin (POMC) and neuropeptide Y (NPY) neurons, it has been shown tha t NPY fibers are in synaptic contact with POMC cell bodies. In order t o determine whether NPY could influence POMC neuronal activity, we hav e studied the effects of NPY and some NPY analogs on POMC gene express ion using quantitative in situ hybridization. The following peptides N PY, [Leu(31),Pro(34)]-NPY (a Y-1 receptor agonist), and NPY13-36 (a Y- 2 receptor agonist) were injected into the left lateral cerebral ventr icle of adult male rats 4 h before being perfused for histological pro cedures. The intracerebroventricular injection of NPY and NPY13-36 ind uced a significant decrease in the number of grains overlying the labe lled neurons. On the other hand, the Y-1 receptor agonist [Leu31,Pro34 ]-NPY did not modify POMC mRNA levels. These data then strongly sugges t that NPY negatively regulates the genetic expression of POMC neurons via the Y-2 NPY receptor subtype.