COMPARISON OF EXTRACELLULAR DOPAMINE CONCENTRATION IN AWAKE UNSTRESSED AND POSTSURGICAL NITROUS-OXIDE SEDATED RATS

Nitrous oxide (N2O), 70%, in O-2 is often used as a control condition after surgical preparation in rodents undergoing neuroscience investig ations. Concern has been expressed that this constitutes a stressful c ondition. Microdialysis was used in 15 rats to assess extracellular st riatal dopamine concentrations during overnight soundproof isolation a nd on the following day after vascular cannulation and halothane excre tion under N2O sedation with concomitant neuromuscular blockade. The o vernight dialysate dopamine concentration was 22.8 +/- 8.7 pg/40 mu l. Thirty minutes after stopping halothane, the dialysate concentration was 362.6 +/- 91.6 pg/40 mu l 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 hal othane N2O anesthesia, and (b) baseline conditions can have a major ef fect on microdialysis data expressed as percentage of baseline.