NOx- concentrations in the rat hippocampus and striatum have no direct relationship to anaesthesia induced by ketamine

Using microdialysis, we have examined the effects of ketamine on concentrat ions of total nitric oxide oxidation products (NOx-) in the rat hippocampus and striatum in vivo to investigate the relationship between anaesthesia a nd NOx- production in the brain. Ketamine 25, 50 and 100 mg kg(-1) i.p. inc reased NOx- concentrations to mean 125 (SD 13)%, 165 (11)% and 193 (13)% of basal, respectively, in the hippocampus and to 122 (12)%, 147 (7)% and 177 (14)% of basal in the striatum. Local perfusion with ketamine 50 and 100 m u mol litre(-1) into the hippocampus or striatum increased NOx- concentrati ons to 212 (32)% and 291 (17)% of basal, respectively, in the hippocampus a nd to 148 (20)% and 201 (18)% of basal in the striatum. Ketamine 50 and 100 mg kg(-1) i.p. caused dose-dependent prolongation of loss of the righting reflex (LRR) and 100 mg kg(-1) i.p. also caused loss of the corneal reflex (LCR). Local perfusion of ketamine did not provoke LRR or LCR. Inhibition o f NOS by L-NAME 100 mg kg(-1) i.p. decreased hippocampal NOx- concentration s to 58 (7)% of basal and did not provoke LRR or LCR. Although the effect o f ketamine-induced increases in hippocampal NOx- concentrations was signifi cantly depressed by L-NAME, LRR was not affected. These data imply that NOx -concentrations in the hippocampus or striatum have no direct relationship to the anaesthetic efficacy of ketamine, although this requires further inv estigation.