Ketamine induces anterograde and retrograde amnesia in rats

The N-methyl-D-aspartate (NMDA) receptors, which have been implicated in memory formation, could be noncompetitively blocked by ketamine. The present study examines the short term effect of ketamine on induction of anterograde and retrograde amnesia in male rats using Morris water maze (MWM). Male N-MRI rats were randomly divided into nine experimental groups. MWM studies were performed to evaluate spatial learning and memory parameters. In order to examine the effect of ketamine on the induction of anterograde amnesia, 4 groups of animals received daily injections of ketamine (1, 3, 6 or 12 mg/kg, i.p.) 10 min before testing on training days. To examine the effect of drug on the induction of retrograde amnesia four other groups of rats received daily injection of normal saline (on training days) and ketamine (1, 3, 6, or 12 mg/kg, i.p.) (in probe trial) 10 min before testing. Rats of the control group received normal saline on all days of experiments. Spatial learning and memory parameters were recorded and subjected to the analysis of variance (ANOVA). Difference was considered significant if p<0.05. Data showed that injection of ketamine at the dose of 3 mg/kg and higher inhibits spatial learning and memory parameters and induces both anterograde and retrograde amnesia in rats. It seems that ketamine induces inhibitory effects on spatial learning and memory via blocking the NMDA receptors. On the other hand, ketamine induced dose dependent decrease in swim speed which was significant at the dose of 12 mg/kg.