Comparison of extracellular dopamine concentration in awake unstressed and postsurgical nitrous oxide sedated rats

Nitrous oxide (N2O), 70%, in O2 is often used as a control condition after surgical preparation in rodents undergoing neuroscience investigations. Concern has been expressed that this constitutes a stressful condition. Microdialysis was used in 15 rats to assess extracellular striatal dopamine concentrations during overnight soundproof isolation and on the following day after vascular cannulation and halothane excretion under N2O sedation with concomitant neuromuscular blockade. The overnight dialysate dopamine concentration was 22.8 +/- 8.7 pg/40 microliters. Thirty minutes after stopping halothane, the dialysate concentration was 362.6 +/- 91.6 pg/40 microliters during postsurgical N2O sedation. These data indicate that (a) compared to an unstressed baseline, significant brain dopamine effects occur with N2O sedation after surgery with halothane N2O anesthesia, and (b) baseline conditions can have a major effect on microdialysis data expressed as percentage of baseline.