BACKGROUND: Buthus martensii Karsch is a rare medicinal animal, and dried integral Buthus martensii Karsch is an important drug in traditional Chinese medicine. OBJECTIVE: To investigate the effects of scorpion venom analgesic active peptide (SAP) extracted from Buthus martensii Karsch on evoked unit discharge of the common peroneal nerve in the posterior nucleus group of the thalamus using a stereotaxic electrophysiological extracellular microelectrode recording. DESIGN, TIME AND SETTING: One-way designed study, performed in the Physiological Laboratory of Shenyang Medical College on September 15, 2006. MATERIALS: Fifty 3-4 months old Wistar rats (25 males and 25 females) were used. SAP was provided by Shenyang Pharmaceutical University. Morphine solution was made by the First Drug Manufactory, Northeastern Drug Manufacture Group (batch number: H20013351). Naloxone solution was made by Hunan Pharmaceutical Co., Ltd. (batch number: H43021669). Type ATAC-350 medical data processing equipment was made by the Photoelectricity Company, Japan. METHODS: Fifty rats were randomly divided into the SAP group (n=20), saline group (n=10), morphine group (n=10), or naloxone group (n=10). In the SAP group, the common peroneal nerve was separated and stimulated with a single square wave (17-19 V intensity; 0.2 ms width; 20 ms retardation time). Subsequently, SAP (0.01%, 2 μL) was injected into the posterior nucleus group of the thalamus. Rats in the naloxone group were injected with naloxone (1.0 mg/kg i.v.) before SAP injection. Rats in the saline group and the morphine group were injected with saline (2 μL) or morphine (0.01%, 2 μL), respectively, before SAP injection. Other procedures were the same as those in the SAP group. MAIN OUTCOME MEASURES: Evoked discharge in the posterior nucleus group of the thalamus and effects of SAP alone and SAP in combination with saline, morphine, or naloxone on discharges in the posterior nucleus group of the thalamus as measured by TQ-19 medical data processing equipment. RESULTS: SAP group: At 1-3 minutes after SAP injection, evoked discharges in the posterior nucleus group of the thalamus were inhibited, and the inhibitory time lasted for (45.0±0.7) minutes. Saline group: Evoked discharges in the posterior nucleus group of the thalamus did not change after saline injection. Morphine group: At 1-3 minutes after morphine injection, evoked discharges in the posterior nucleus group of the thalamus were inhibited, and the inhibitory time lasted for (35.0±7.8) minutes. Naloxone group: SAP had no effects on evoked potentials in the posterior nucleus group of the thalamus. CONCLUSION: The inhibitory effect of SAP on evoked potentials was superior to that of morphine at the same concentration (2 μL of 0.01% solution). Naloxone resupination demonstrated that the inhibitory effects of SAP on evoked discharges were influenced by the opioid receptor. BACKGROUND: Buthus martensii Karsch is a rare medicinal animal, and dried integral Buthus martensii Karsch is an important drug in traditional Chinese medicine. OBJECTIVE: To investigate the effects of scorpion venom analgesic active peptide (SAP) extracted from Buthus martensii Karsch on evoked unit discharge of the common peroneal nerve in the posterior nucleus group of the thalamus using a stereotaxic electrophysiological extracellular microelectrode recording. DESIGN, TIME AND SETTING: One-way designed study, performed in the Physiological Laboratory of Shenyang Medical College on September 15, 2006. MATERIALS: Morphine solution was made by the First Drug Manufactory, Northeastern Drug Manufacture Group (batch number: H20013351). Naloxone solution was made by Hunan Pharmaceutical Co., Ltd. (batch number: H43021669). Type ATAC-350 medical data processing equi METHODS: Fifty rats were randomly divided into SAP group (n = 20), saline group (n = 10), morphine group (n = 10), or naloxone group (n = 10 In the SAP group, the common peroneal nerve was separated and stimulated with a single square wave (17-19 V intensity; 0.2 ms width; 20 ms retardation time). SAP (0.01%, 2 μL) was injected into the posterior nucleus group of the thalamus. Rats in the naloxone group were injected with naloxone (1.0 mg / kg iv) before SAP injection. Rats in the saline group and the morphine group were injected with saline (2 μL) , 2 μL), respectively, before SAP injection. Other procedures were the same as those in the SAP group. MAIN OUTCOME MEASURES: Evoked discharge in the posterior nucleus group of the thalamus and effects of SAP alone and SAP in combination with saline, morphine , or naloxone on discharges in the posterior nucleus group of the thalamus as measured by TQ-19 me dicAL data processing equipment. RESULTS: SAP group: At 1-3 minutes after SAP injection, evoked discharges in the posterior nucleus group of the thalamus were inhibited, and the inhibitory time lasted for (45.0 ± 0.7) minutes. Saline group: Evoked discharges in the posterior nucleus group of the thalamus did not change after saline injection. Morphine group: At 1-3 minutes after morphine injection, evoked discharges in the posterior nucleus group of the thalamus were inhibited, and the inhibitory time lasted for (35.0 ± 7.8 ) Naloxone group: SAP had no effects on evoked potentials in the posterior nucleus group of the thalamus. CONCLUSION: The inhibitory effect of SAP on evoked potentials was superior to that of morphine at the same concentration (2 μL of 0.01% solution) . Naloxone resupination demonstrated that the inhibitory effects of SAP on evoked discharges were influenced by the opioid receptor.