Xenon inhibits but N2O enhances ketamine-induced c-fos expression in the rat posterior cingulate and retrosplenial cortices

Both nitrous oxide (N2O) and xenon are N-methyl-D-aspartate receptor antago nists that have psychotomimetic effects and cause neuronal injuries in the posterior cingulate and retrosplenial cortices. We investigated the effect of xenon, xenon with ketamine, N2O, and N2O with ketamine on c-Fos expressi on in the rat posterior cingulate and retrosplenial cortices, a marker of p sychotomimetic effects. Brain sections were prepared, and c-Fos expression was detected with immunohistochemical methods. A loss of microtubule-associ ated protein 2, a marker of neuronal injury, was also investigated. The num ber of Fos-like immunoreactivity positive cells by ketamine IV at a dose of 5 mg/kg under 70% N2O (128 +/- 12 cells per 0.5 mm(2)) was significantly m ore than those under 30% (15 +/- 2 cells per 0.5 mm(2)) and 70% xenon (2 +/ - 1 cells per 0.5 mm(2)). Despite differences in c-fos immunoreactivity, th ere was no loss of microtubule-associated protein 2 immunoreactivity in any group examined. Xenon may suppress the adverse neuronal effects of ketamin e, and combined use of xenon and ketamine seems to be safe in respect to ne uronal adverse effects.