The Role Of Nociceptin/Orphanin FQ And Electroacupuncture On Penicillin-induced Seizures In Rats

Epilepsy is a significant public health problem. Despite the increasing number ofanticonvulsant drugs available to clinical practice, a significant proportion ofepileptics still does not respond to therapy or suffers from undesirable side effects.There is a considerable long history and a great deal of clinical experience in treatingepilepsy by using acupuncture in China. Our previous studies showed that EA mayplay a role in inhibiting the epileptic activity through a regulatory mechanism of theopioid peptides system. The opioid peptide is thought to be implicated in specific types of seizures.Nociceptin/Orphanin FQ (OFQ) is the endogenous ligand of the opioid receptor-likereceptor (ORL1 receptor), and it may play a role in epilepsy. However, previousstudies suggested OFQ has both anti-convulsive and pro-convulsive effects, and themechanism of OFQ during seizure is still not clear. Our present work studied the inhibitory effect of electroacupuncture (EA) and itsmechanism involving OFQ on experimental epilepsy, by using electrophysiological,RT-PCR, immunohistochemical and Western Blot technique. The results are asfollows: First, we investigated the effect of OFQ on penicillin-induced seizures ( PIS ) inrats. Seizure models were produced by microinjection of penicillin into rathippocampus. Thereafter, the appearance of spontaneous seizures was monitored bycontinuous video-electroencephalography ( EEG ) and estimated by power spectrumanalysis. Pretreated OFQ ( i.c.v. 0.055nmol,0.55 nmol,5.5nmol in 2μl ) depressedPIS in a concentration-dependent manner. The selective NOP receptor antagonist[Nphe1]Nociceptin(1-13)NH2, was inactive to PIS itself, but blocked the effect of 4OFQ. Furthermore, the effect of nocistatin was similar to[Nphe1]Nociceptin(1-13)NH2. Our results indicate that OFQ has preventive effectagainst PIS, and this effect was mainly through specific receptor. Second, our research focused on whether OFQ involved in the effect of EA onPIS. During PIS, EEG power greatly increased, and the bands with the peak of themain power shifted to the right. EA inhibited the epileptiform spikes induced bypenicillin, and decreased EEG total power, δ power, θ power, β power as well.Pretreatment with [Nphe1]Nociceptin(1-13)NH2 could reverse the above preventiveeffect of EA against PIS, while nocistatin could not. Furthermore, OFQ enhanced theanti-epileptic effect of EA. These data suggested that the anticonvulsive effect of EAwas mediated by ORL1 receptor. Previous studies have shown that seizure induced by penicillin could beinhibited by EA probably via decreasing enkephalin content and increasing dynorphincontent in hippocampus. To determine whether EA modulated OFQ system level inhippocampus after penicillin injection, we observed the expression of ppOFQ mRNA,OFQ and ORL1 protein after PIS with EA treatment. It was found that at 2 hoursfollowing onset of seizure, the level of ppOFQ mRNA, OFQ and ORL1 protein wasdramatically decreased in rat hippocampus. Meanwhile there was an adverse effect ofEA. After EA treatment, the reduced expression of ppOFQ mRNA, OFQ and ORL1protein was enhanced. These results suggested that EA may regulate the biosynthesisof OFQ and ORL1 in hippocampus during seizure. Together, our results mentioned above demonstrate that OFQ may play a role inepilepsy with an inhibitory effect, and it was involved the anti-epileptic effect of EA.The effect of OFQ is through its receptor. And EA may play a role in inhibiting theepileptic activity through a regulatory mechanism of the OFQ system.