Injection of orphanin FQ/nociceptin into the periaqueductal gray suppresses the forebrain-elicited vocalization in the guinea pig

Abstract

Electrical stimulation of the caudoventral part of the anterior cingulate cortex (AC) evokes a species-specific vocalization in the guinea pig. After injections of glutamate receptor antagonists into the periaqueductal gray (PAG) regions where the AC projected, the forebrain-elicited vocalization (FEV) was suppressed completely. This result indicated that the FEV was induced at least partly by glutamatergic activation of PAG neurons. Injection of orphanin FQ/nociceptin (OFQ/N) into the PAG profoundly suppressed the FEV. This inhibitory effect of OFQ/N was not antagonized by naloxone, an opioid receptor antagonist. Since OFQ/N was reported to modify the glutamatergic transmission, the present results suggest that OFQ/N exerts influences upon the vocalization by regulating the glutamatergic inputs into the PAG.