BACKGROUND:Some experiments have demonstrated that injecting orphanin FQ (OFQ) into lateral ventricle, which can obviously decrease the pain threshold. It is indicated that OFQ is an anti-opiate substance. However, whether OFQ has effects on sensory neuron ion channel in cerebral cortex needs to be further studied. OBJECTIVE:To investigate the effects of OFQ, morphine or their combination on sodium channel current of somatosensory neurons in rat cerebral cortex. DESIGN:Repeated measurement trial. SETTING:Department of Physiology, Harbin Medical University. MATERIALS:Fifty healthy Wistar rats, aged 12-16 days, of either gender, were provided by the Experimental Animal Center, Second Hospital Affiliated to Harbin Medical University. OFQ was purchased from Sigma-Aldrich Company, and morphine was provided by the Shenyang First Pharmaceutical Factory. PC2C patch clamp amplifier and LabmasterTL1were purchased from Yibo Life Science Instrument Co.,Ltd. of Huazhong University of Science and Techgnology. METHODS:This experiment was carried out in the Department of Physiology (provincial laboratory), Harbin Medical University between January 2005 and May 2006. Cortical neurons were acutely isolated from rats, and prepared into cell suspension following culture. ①Sodium channel current of somatosensory neurons in rat cerebral cortex was recorded before and after administration by whole-cell Patch clamp technique after 50 nmol/L OFQ being added to extracellular fluid. ②The amplitude of sodium channel current of somatosensory neurons in rat cerebral cortex was recorded before and after administration by the same method after 20 μmol/L morphine being added to extracellular fluid, and then the change of sodium channel current was recorded after 50 nmol/L OFQ being added. MAIN OUTCOME MEASURES:The amplitude of sodium channel current of somatosensory neurons in rat cerebral cortex following the administration of OFQ, morphine separately or their combination.. RESULTS:①The amplitude of sodium channel current of somatosensory neurons in rat cerebral cortex was significantly lower after administration of 50 nmol/L OFQ than before at the clampe of the voltage of -30 mV (P < 0.05). ②The amplitude of sodium channel current of somatosensory neurons in rat cerebral cortex was significantly lower after administration of 20 μmol/L morphine than before at the clampe of the voltage of -30 mV (P < 0.05). The sodium channel current recovered to -(2 345.24±174.18)pA after 50 nmol/L OFQ was administrated. There were significant differences in the amplitude of Na+ channel current between two interventions (P < 0.05). CONCLUSION:Morphine and OFQ can respectively reduce the amplitude of sodium channel current of somatosensory neurons in rat cerebral cortex, and OFQ can reverse the effect of morphine partly. It is indicated that OFQ can produce antiopioid activity in the central nervous system by influencing sodium channel current. BACKGROUND: Some experiments have performing that injecting orphanin FQ (OFQ) into lateral ventricle, which can obviously decrease the pain threshold. It is indicated that OFQ is an anti-opiate substance. However, whether OFQ has effects on sensory neuron channel in the cerebral OBJECTIVE: To investigate the effects of OFQ, morphine or their combination on sodium channel current of somatosensory neurons in rat cerebral cortex. DESIGN: Repeated measurement trial. Department of Physiology, Harbin Medical University. MATERIALS: Fifty healthy Wistar rats, aged 12-16 days, of either gender, were provided by the Experimental Animal Center, Second Hospital Affiliated to Harbin Medical University. OFQ was purchased from Sigma-Aldrich Company, and morphine was provided by the Shenyang First Pharmaceutical Factory . PC2C patch clamp amplifier and Labmaster TL1 share purchased from Yibo Life Science Instrument Co., Ltd. of Huazhong University of Science and Te METHODS: This experiment was carried out in the Department of Physiology (provincial laboratory), Harbin Medical University between January 2005 and May 2006. Cortical neurons were acutely isolated from rats, and prepared into cell suspension following culture. ① Sodium channel current of somatosensory neurons in rat cerebral cortex was recorded before and after administration by whole-cell patch clamp technique after 50 nmol / L OFQ being added to extracellular fluid. ② The amplitude of sodium channel current of somatosensory neurons in rat cerebral cortex was recorded before and after administration by the same method after 20 μmol / L morphine being added to extracellular fluid, and then the change of sodium channel current was recorded after 50 nmol / L OFQ being added. MAIN OUTCOME MEASURES: The amplitude of sodium channel current of somatosensory neurons in the rat cerebral cortex following the administration of OFQ, morphine separately or their combination .. RESULTS: ①The amp litudeof sodium channel current of somatosensory neurons in rat cerebral cortex was significantly lower after administration of 50 nmol / L OFQ than before at the clampe of the voltage of -30 mV (P <0.05). ② The amplitude of sodium channel current of somatosensory neurons in Rat cerebral cortex was significantly lower after administration of 20 μmol / L morphine than before at the clampe of the voltage of -30 mV (P <0.05). The sodium channel current recovered to - (2 345.24 ± 174.18) pA after 50 nmol / There were significant differences in the amplitude of Na + channel current between two interventions (P <0.05). CONCLUSION: Morphine and OFQ can decreased the amplitude of sodium channel current of somatosensory neurons in rat cerebral cortex, and OFQ can reverse the effect of morphine partly. It is indicated that OFQ can produce antiopioid activity in the central nervous system by influencing sodium channel current.