Modulation of long-term memory by delayed administration of the amide of L-pyroglutamyl-D-alanine, a nootropic agent, in spaced and massed training in rats.

The effects of the nootropic agent L-pyroglutamyl-D-alanine amide (given at a dose of 0.5 mg/kg i.p., 24 h after training) on long-term memory were studied in rats with contextual and conditioned reflex freezing. Spaced and massed training protocols were used; habit formation was tested 72 h after training. In massed training, which led to lower levels of learning as compared with spaced training, the dipeptide improved contextual memory, while in spaced training, which led to higher initial learning levels, dosage with dipeptide improved reproduction of the habit. Testing of responses to the conditioned signal (a sound) 96 h after training, revealed no significant differences between groups. This is evidence for the selectivity of the effect of L-pyroglutamyl-D-alanine amide for contextual memory.