Fig. 2. N2O caused norepinephrine release in the dorsal horn of the rat spinal cord. In rats, a dialysis fiber was placed at T12 during isoflurane anesthesia. The dialysis tubing was stabilized with dental acrylic and the ends were externalized. The following day, the inflow of the dialysis tubing was connected via a swivel to a pump, which infused artificial cerebrospinal fluid at a rate of 1.3 μl/min. Microdialysate was collected during a 60-min equilibration period, with the rats breathing air, then the rats were exposed to 70% N2O for 90 min. The effluent was sampled at 30-min intervals with a fraction collector. Norepinephrine was assayed by high-performance liquid chromatography with electrochemical detection. The position of the dialysis portion of the fiber was confirmed histologically at the conclusion of the experiment. Data were analyzed by analysis of variance for repeated measures and a posteriori by Scheffé test. Data are expressed as mean ± SEM. * P < 0.05 (n = 9).