Role of δ-opioid receptor in remifentanil induced NMDA receptor miniature excitatory postsynaptic currents in rat spinal dorsal horn neurons

Abstract

Objective To investigate the role of δ-opioid receptor in remifentanil-induced N-methyl-D-aspartate (NMDA) receptor miniature excitatory postsynaptic currents (mEPSCs) in rat spinal dorsal horn neurons.Methods Male 14-18 d old Wistar rats weighing 50-60 g were used in this study.The animals were anesthetized with intraperitoneal choral hydrate 400 mg/kg and sacrificed.Their lumbar segments of spinal cord (L1-S1 ) were immediately removed and sliced.Twenty-four slices were randomly divided into 4 groups ( n =6 each): control group (group C) ; glycine group (group G) ; remifentanil group (group R) and remifentanil + naltrindole(a δ receptor antagon) (group RN).Slices were cultured in artificial cerebrospinal fluid (ACSF) (group C) or incubated in ACSF containing glycine 0.24 μmol/L (group G) or remifentanil 4 nmol/L (group R) or remifentanil 4 nmol/L+ naltrindole 1 nmol/L (group RN) for 60 min.Whole cell patch clamp technique was used to measure NMDA receptor mEPSCs.Results The amplitude and frequency of mEPSCs were significantly higher in group R than in groups C and RN ( P ＜ 0.01).There were no significant differences in amplitude and frequency of mEPSCs among gorups C,G and RN ( P ＞ 0.05).Conclusion Activation of δ-receptor can enhance NMDA receptor function in spinal dorsal horn neurons in rats which may be the mechanism of remifentanil-induced hyperalgesia. Key words: Piperidines; Hyperalgesia; Receptors, N-Methyl-D-Aspartate; Receptors, opioid,delta; Spinal cord