Dextromethorphan reduces functional deficits and neuronal damage after global ischemia in rats

Glutamate antagonists have been shown to be neuroprotective in animal models of cerebral ischemia. Global cerebral ischemia in rats leads to selective neuronal damage in the hippocampus and striatum. Following ischemia a transient locomotor hyperactivity and a deficit in spatial learning and memory occurs. The aim of the present study was to investigate the potential neuroprotective effect of dextromethorphan, an antagonist at the N-methyl-D-aspartate receptor, with behavioural and histological measures of global ischemia in rats. Global ischemia was induced by four-vessel occlusion (4VO) for 20 min in rats. Dextromethorphan was administered 20 min before induction of ischemia at a dose of 10 or 50 mg/kg. Before and on day 1, 3 and 5 after operation the spontaneous locomotor activity was measured. One week after surgery spatial learning was tested in the Morris water maze. After behavioural testing the animals were sacrificed and the neuronal damage was assessed. Treatment with 50 mg/kg of dextromethorphan reduced the increase in locomotor activity observed on day 1 and 3 after ischemia. In the water maze dextromethorphan reduced the increase in escape latency and in swim distance induced by 4VO. Furthermore, the ischemia-induced reduction in time spent in the quadrant of the former platform position during the probe trial was increased by treatment with dextromethorphan. Neuronal damage in the CA1 sector of the hippocampus and in the dorsolateral striatum produced by 4VO was significantly attenuated by dextromethorphan. The present results demonstrate that protective effects on neuronal damage may be related to an attenuation of deficits in spatial leaning and memory following global ischemia.