mu-Opioid receptor mRNA expression in proopiomelanocortin neurons of the rat arcuate nucleus

It has been previously demonstrated that the activity of proopiomelanocorti n (POMC)-containing neurons in the rat arcuate nucleus is regulated by opia tes, but the expression of opioid receptors in POMC neurons las never been reported. In the present study, we have applied a double-labeling in situ h ybridization technique to investigate the occurrence of mu-opioid receptor mRNA on POMC neurons. We have found that 20 +/- 3% of arcuate POMC neurons express mu-opioid receptor mRNA and that the proportion of POMC neurons exp ressing mu-opioid receptor is higher in the caudal than in the rostral port ion of the arcuate nucleus. Our data suggest that POMC neurons might be bot h auto-regulated by P-endorphin, and regulated by enkephalins. (C) 1999 Els evier Science B.V. All rights reserved.