Regulation of proopiomelanocortin gene expression by neuropeptide Y in the rat arcuate nucleus.

In the arcuate nucleus which is richly innervated by both proopiomelanocortin (POMC) and neuropeptide Y (NPY) neurons, it has been shown that NPY fibers are in synaptic contact with POMC cell bodies. In order to determine whether NPY could influence POMC neuronal activity, we have studied the effects of NPY and some NPY analogs on POMC gene expression using quantitative in situ hybridization. The following peptides NPY, [Leu31,Pro34]-NPY (a Y1 receptor agonist), and NPY13-36 (a Y2 receptor agonist) were injected into the left lateral cerebral ventricle of adult male rats 4 h before being perfused for histological procedures. The intracerebroventricular injection of NPY and NPY13-36 induced a significant decrease in the number of grains overlying the labelled neurons. On the other hand, the Y1 receptor agonist [Leu31,Pro34]-NPY did not modify POMC mRNA levels. These data then strongly suggest that NPY negatively regulates the genetic expression of POMC neurons via the Y2 NPY receptor subtype.