The effects of nociceptin/orphanin fq on trigeminal nociception induced by cortical spreading depresion in rats

Abstract

The present study aimed to determine the effect of nociceptin/orphanin FQ (N/OFQ) on development of cortical spreading depression (CSD) and trigeminal nociception. Adult male Wistar rats were divided into three groups, including control group, CSD without N/OFQ group, and CSD with receiving N/OFQ group. N/OFQ (10uM; 100ul) and vehicle (0.9% of normal saline solution; 100ul) were applied by intrathecally injection (i.t.) into the cerebrospinal fluid. CSD was induced by application of 3 mg of potassium chloride crystal on the parietal cortex. Cortical activity was monitored by inserting glass microelectrode into the frontal cortex, ipsilateral side to the potassium chloride application. Effects of N/OFQ on trigeminal nociceptive system were studied by using the expression of transient receptor potential vanilloid subtype 1 (TRPV1) in the trigeminal ganglia (TG) as well as the expression of a transcription factor Fos in trigeminal nucleus caudalis (TNC). The results showed that application of potassium chloride resulted in series of depolarization activity characteristic for CSD. The development of these CSD waves was enhanced in CSD with N/OFQ receiving group. Such enhancement was characteristic by increased frequency of CSD wave, amplitude of CSD, and area under the curve of each CSD wave. Results from the TRPV1- and Fos-immunohistochemical studies revealed the similar pattern. Greater numbers of TRPV1 in TG and Fos in TNC were observed in N/OFQ groups. These results demonstrated that N/OFQ increases cortical excitability and neuronal activity in trigeminal nociceptive system.