Effects of diazepam, piracetam and mexidol on passive avoidance response

In experiments on rats, we compared the influence of anxiolytic diazepam and nootropics piracetam and mexidol on passive avoidance conditioning (PAC) in a three compartment apparatus that consisted of a light compartment, a dark dangerous compartment in which foot shock was delivered and a dark safe one where the rats were not punished. Electric foot shock during PAC caused a sharp increase in the latent period of the central compartment leaving during the testing in the control animals, but did not lead to the safe compartment choice. Based on these data on the differential impact of the foot shock on PAC, we formulated the assumption that learning processes, which determined the motor response delay and the safe compartment selection, had different associative nature. The increase in the latent period is associated with the classical fear conditioning regardless of the place of the current impact. The safe compartment choice, on the contrary, is associated with the memory trace formation about the location of the foot shock exposure. The use of pharmacological substances that affect fear and memory in different ways gave additional arguments in favor of the assumption of various associative processes that determined PAC. Reducing the level of fear with diazepam reduced the latent period of motor response relative to the control value, but did not affect the choice of a safe compartment. In contrast, the mnemotropic properties of piracetam and mexidol increased the preference for a safe compartment without increasing the latent period. These differential pharmacological effects confirm that PAC is based on the conditioned responses of fear, which causes an increase in latent period of leaving the central compartment, and on the memory of the electrical exposure location which provides the safe compartment choice.

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