Effects of halothane and isoflurane on hyperexcitability of spinal dorsal horn neurons after incision in the rat

Background: The aim of this study was to determine whether halothane and isoflurane used during and after surgical injury attenuate subsequent hyperexcitability of spinal dorsal horn (SDH) neurons by preventing development of central sensitization. Methods: Activity of a wide-dynamic-range neuron of the SDH was isolated in decerebrate-spinal Sprague-Dawley rats, and neuronal activity (receptive field size and responses to nonnoxious and noxious stimuli) was recorded. A 1-cm-long incision was made through the skin, fascia, and muscle under anesthesia with halothane (1.1% or 2.2%) and isoflurane (1.4% or 2.8%). Anesthesia was discontinued just after the incision had been made or was continued until 30 min after the incision, and activity of the SDH neurons was measured for up to 2 h after the incision. In a control group, the incision was made without anesthesia. Results: In the control group, the incision resulted in maximum excitation in the SDH neurons during surgery; spontaneous activity significantly increased for up to 30 min after the incision (P < 0.05) but did not significantly increase thereafter, returning to the preincision value. Halothane and isoflurane suppressed excitation of the neurons during the incision in a concentration-related manner. Administration of 2.2% halothane and 2.8% isoflurane during the incision and for up to 30 min after the incision almost abolished activity of the neurons for 30 min after the incision. The magnitude of neuronal activity 2 h after the incision was not significantly different among all groups, including the control group. Conclusions: The results demonstrate that administration of halothane and isoflurane does not attenuate development of hyperexcitability of SDH neurons despite the fact that excitation and spontaneous activity during and after the incision were greatly suppressed by administration of halothane and isoflurane.