Fig. 5. Effect of A7 administered naloxone and muscimol on the number of N2O-induced c-Fos-positive cells in each lamina of the spinal cord. Rats were microinjected into the A7 bilaterally with saline (0.2 μl × 2), naloxone (0.25 μg/0.2 μl × 2), or muscimol (0.5 μg/0.2 μl × 2). This was followed by 90 min of gas exposure to either air or N2O (75%)–O2(25%), and the c-Fos-positive cells were counted in the laminae of the spinal cord at the lumbar level. Bar = mean number for three animals; error bar = SD. *P < 0.05 versus saline–air group. #P < 0.05 versus saline–N2O group.