The psychostimulants amphetamine and the “bath salt” 3,4- methylenedioxypyrovalerone (MDPV) differentially affect the accuracy of memory in rats

Human studies have shown that drugs of abuse affect memory function. This study aimed to evaluate whether two psychostimulants, Amphetamine and the ‘bath salt’ MDPV, affect memory accuracy. Male rats were first trained in a Inhibitory Avoidance apparatus (Non-Shock box) and, after 1 or 2 min delay, in a second one (Shock box) they received an inescapable footshock. Amphetamine (1-3 mg/Kg, i.p.), MDPV (0.5–1 mg/Kg, i.p.) or saline were administered immediately after training. Forty-eight hours later, rats were tested in a randomized order in the Shock and Non-Shock boxes as well as in a Novel box. Control rats trained with a 1 min delay did not present episodic-like memory of the association of footshock with the correct training context, whereas an increase of the interval to 2 min allowed them to discriminate the 2 contexts. Amphetamine (3 mg/kg) increased retention latencies in the Shock box in rats trained with both delays interval, indicating an increase in memory strength. It also enhanced retention latencies in both Non-Shock and Novel boxes under both conditions of delay, indicating increased generalization. MDPV (1 mg/kg) increased retention latencies of rats trained with both delays at training only in the Novel box, inducing memory generalization without altering its strength. It is tentative to hypothesize that the different effects on memory strength versus generalization induced by the two psychostimulants are due to differences in the modulation of the monoaminergic neurotransmissions, in the recruitment of different brain areas or in the interaction with the stress systems.