Effects of Sevoflurane on the discharges of wide dynamic range neurons in spinally transected rats

Objective: To study the effects of clinical concentration of sevoflurane on activity of wide dynamic range neurons. Methods: Eight Spraque-Dawley rats(male) were selected. Their spinal cords were exposed and transected at T 9-10 level. The rate of firings of single neurons in the dorsal horn in response to electrical stimulation of skin was recorded with microelectrodes. The early and late discharges were observed when rats inhaled 0.5%, 1.0%, 1.5%, and 2.0% sevoflurane. Results: Sevoflurane suppressed the early and late discharges at the concentration of 0.5%, 1.0%, 1.5%, and 2.0%. Compared with early discharges, the extent of inhibition of late discharges was wider at the concentration of 1%, 1.5%, and 2.0% of sevoflurane. Conclusion: It is indicated that sevoflurane could suppress the transmission of nociceptive and non-nociceptive stimulation at dorsal horn. The suppression on nociceptive imput is stronger than that on non-nociceptive imput when the concentration of sevoflurane is more than 1%.

Electrophysiological properties of spinal wide dynamic range neurons in neuropathic pain rats following spinal nerve ligation

Objective The present study aimed to investigate the electrophysiological properties of wide dynamic range （WDR） neurons in spinal dorsal horn of rats with neuropathic pain induced by lumber 5 （L5） spinal nerve ligation （SNL） in a large size of samples.Methods Adult Sprague-Dawley rats were divided into normal and SNL groups.Electrophysiological technique was used to record the characteristics of WDR neurons in the spinal dorsal horn.Results Compared with the WDR neurons in normal rats,the WDR neurons in SNL rats showed an increase in excitability,manifested by an enlargement of the receptive field size,an increase in the proportion of neurons that exhibited spontaneous activities,decreases in the Cresponse threshold and latency,and an increase in the C-response duration.In addition,the numbers of A-and C-fiberevoked discharges were smaller in SNL rats than in normal rats.Conclusion The excitability of spinal WDR neurons increased in rats with neuropathic pain induced by L5 SNL.The increase in excitability of WDR neurons may contribute to the development of neuropathic pain.

THE ROLE OF RED NUCLEUS IN THE MODULATION OF SPINAL NOCICEPTIVE TRANSMISSION AND IN NOCICEPTION ELICITED BY MUSCLE SPINDLE AFFERENTS

Objective To analyse the antinociceptive effect of red nucleus (RN) and its role in the antinociceptive effect of muscle spindle afferents. Methods The single units of RN or wide dynamic range (WDR) neuron in the spinal cord dorsal horn were extracelluarly recorded. The effects of RN stimulation on nociceptive responses (C fibers evoked responses, C responses) of WDR neurons were observed. The influence of muscle spindle afferents elicited by intravenous administration of succinylcholine (Sch) on the spontaneous discharge of RN neurons and on C responses of WDR neurons were observed. The effect of muscle spindle afferents on C responses of WDR neurons after unilateral lesions of RN was also observed. Results Electrical stimulation of the RN produced a significantly inhibitory effect on the nociceptive responses of WDR neurons. RN neurons were excited by muscle spindle afferents. Muscle spindle afferents significantly inhibited C response of WDR neurons and this inhibitory effect was reduced by lesions of RN. Conclusion RN neurons have a significant antinociceptive effect and might be involved in the antinociceptive effects elicited by muscle spindle afferents.