Hippocampal asymmetry in serotonergic modulation of learning and memory in rats

The modulation of learning and memory after left or right microinjections of the selective 5-HTIA receptor agonist 8-OH-DPAT and of the 5-HTIA receptor antagonist NAN190 into the hippocampal CA1 area of male Wistar rats was studied. Microinjections of 8-OH-DPAT (1 mu g) into the right or left CA1 hippocampal area produced a significant decrease in the number of avoidances in a shuttle box. The impairing effect or 8-OH-DPAT was more pronounced when injected into the right hippocampus compared to the left one. Microinjections of NAN 190 (1 mu g) into the right or left CA1 hippocampal area produced a significant increase in the number of avoidances in a shuttle box. Right microinjections of NAN 190 increased the number of avoidances more strongly than compared to left injections. These effects on learning and memory were more pronounced after injection or either of the serotonergic agents into the right CA1 hippocampal area compared to the left. The stronger memory-modulating effect after injection of 8-OH-DPAT or NAN190 into the right CA1 hippocampal area suggests a rightward bias in the rat.