Peripheral and spinal antihyperalgesic activity of najanalgesin isolated from Naja naja atra in a rat experimental model of neuropathic pain

Snake venoms are a rich source of various compounds that have applications in medicine and biochemistry. Recently, it has been demonstrated that najanalgesin isolated from the venom of Naja naja atra exerts analgesic effects on acute pain in mice. The objective of this study was to evaluate the antinociceptive effect of najanalgesin in a rat model of neuropathic pain, induced by L5 spinal nerve ligation and transaction. We observed that intraperitoneal (i.p.) administration of najanalgesin produced significant increase in hind paw withdrawal latency (HWL) in response to both mechanical and thermal stimulation. Moreover, a single dose of najanalgesin was able to induce antinociceptive activity that lasted for 1 week. Intrathecal injection of najanalgesin increased the HWL in response to mechanical stimuli. The antinociceptive effect of najanalgesin administered intrathecally was partly inhibited by intrathecal injection of naloxone or atropine. These results demonstrate that najanalgesin has antinociceptive effects on the central and peripheral system in the rat neuropathic pain model. The opioid receptor and muscatinic receptor are involved in najanalgesin-induced antinociception in the spinal cord. This research supports the possibility of using najanalgesin as a novel pharmacotherapeutic agent for neuropathic pain.