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/40μl. Thirty minutes after stopping halothane, the dialysate concentration was 362.6 ± 91.6 pg/40μl 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.