The Changes Of P2X₃ Receptor And Sensory Neuron In The Dorsal Horn Of Spinal Cord In The Neuropathic Pain Model In Rats

Objective: The purpose of our experiment is to investigate the changes of P2X₃ and sensory neurons including the number and ultrastructure in the spinal cord and to explore the relationship between the changes of P2X₃ as well as sensory neurons and the timeline of pain behavior after chronic constriction injury.Methods: Forty male SD rats weighing 200-220 g were randomly divided into two groups. CCI were performed on the left sciatic nerves in 30 rats, another 10 rats were selected as control. The thermal hyperalgesia of the rats were tested by the hot-plate apparatus. Rats were decapitated at post-operative days 3, 7 and 14. L4～5 spinal cord of CCI and control rats were dissected. ( n=8 in each group) analyses were used to observe the localization of P2X₃ in the dorsal horn of spinal cord and the changes of its expression, the number of sensory neurons with HE staining under the light microscopy. (n=2 in each group) analyses were used to observe the changes of ultrastructure under the transmission electron microscopy in the dorsal horn of spinal cord after chronic constriction injury.Results: Paw thermal withdrawl latency (PTWL) degraded obviously in the left after CCI at day 7 and 14 (P<0.01). P2X₃ immunoreactivity was concentrated in the ventral part of lamina II of spinal cord. CCI-induced neuropathic pain up-regulated the expression of P2X₃ receptor in the left, prominently at day 7 and 14 (P<0.05). After sciatic nerve injury, under the light microscope with HE, the numbers of the operated side sensory neurons of the dorsal horn of spinal cord decreased and the rate of dead neurons reached 23 % at day 14. Under the transmission electron microscopy, Paraptosis forms of programmed cell death at day 3 and the different morphological characteristics of apoptosis at day 7 and 14 were found in sensory neurons of L4-L5 left dorsal horn of spinal cord, but rarely typical neuronal apoptosis and necrosis.Conclusions: P2X₃ receptor activation and the damage of sensory neurons may contribute to the development of neuropathic pain in rats induced by sciatic nerve ligation. Further investigation of the role of P2X₃ receptor and the damage of sensory neurons in the dorsal horn of spinal cord in the neuropathic pain are required.