A comparison of state dependent learning induced by electroconvulsive shock and pentobarbital

Two experiments compared the efficacy of electroconvulsive shock (ECS) and ECS preceded by footshock (FS-ECS) to produce state dependent learning relative to pentobarbital (12 and 25 mg/kg). In Experiment 1, rats were trained in a water T-maze and retrained 72 hr later. Comparison with controls indicated: (a) FS-ECS administered 24 hr prior to training but not retraining (Agent-O order) produced state dependency but did not when animals were trained in the normal state and received FS-ECS 24 hr prior to retraining (O-Agent order) as in most retrograde amnesia experiments; (b) pentobarbital, 12 or 25 mg/kg, injected just prior to either training or retraining produced state dependency in the O-Agent order but not the Agent-O order; and, (c) ECS alone was not effective in either treatment order. Experiment 2 used reversal training to determine the state dependency effect of the agents. Conclusions were the same as in Experiment 1 except that FS-ECS produced state dependency in both treatment orders. These data indicate that FS and ECS interact to produce a dissociation effect 24 hr later that is as complete as that produced shortly after pentobarbital injections. The results of Experiment 2 but not of Experiment 1 support the notion that amnesia observed 24 hr after a training trial FS followed 0.5 sec later by ECS may be due to a state dependency effect rather than the failure of memory fixation.