Abstract: Objective To investigate the role of NMDA receptors in central medial thalamus (CMT) in the unconsciousness induced by general anesthesia. Methods A total of 60 rat models for microinfusion were assigned into 4 groups (n=15 for each group). After induction with propofol, 10 mmol/L (NMDA10 group), 20 mmol/L (NMDA 20 group) and 40 mmol/L (NMDA40 group) of NMDA and normal saline (group C) with equal volume were microinfused into CMT. The incidence of purposeful movement and recovery time of righting reflex were observed in each group respectively. Infusion sites were localized by histological method. Results When the microinfusion site localized within CMT, comparing with group C, the recovery time of righting reflex reduced notably in three NMDA groups (P < 0.05). The recovery time was significantly shorter in NMDA20 group and NMDA40 group than that of NMDA10 group. The incidence of purposeful movement during propofol anesthesia was higher in NMDA20 group and NMDA40 group than that of group C (P < 0.05). When the microinfusion site localized out of CMT, the recovery time of righting reflex was remarkably longer than that within CMT in three NMDA groups (P < 0.05), and there was no significant difference in the incidence of purposeful movement and recovery time between four group (P＞0.05). Conclusion Microinfusion of NMDA agonist into CMT reverses propofol anesthesia, indicating that NMDA receptor in CMT may contribute to the propofol-induced unconsciousness.

Key words: anesthetics, general, midline thalamic nuclei, receptors, N-methyl-D-aspartate, propofol, central thalamus, NMDA receptor, loss of consciousness, intracranial microinjection