NITRIC-OXIDE SYNTHASE INHIBITION DOES NOT IMPAIR VISUAL OR SPATIAL DISCRIMINATION-LEARNING

Nitric oxide (NO) is a candidate retrograde messenger involved in syna ptic plasticity, and is linked to the cholinergic system in the brain. We examined the role of NO in the acquisition of visual and spatial d iscriminations by daily administration of either saline or 1-nitroargi nine methyl ester (L-NAME), an NO synthase inhibitor. Brains were assa yed for NO synthase activity and two presynaptic cholinergic markers: hemicholinium-3 (HC-3) binding, which determines the number of sodium- dependent high-affinity choline uptake sites, and activity of choline acetyltransferase (ChAT), which is the synthetic enzyme for acetylchol ine. In both behavioral tasks, the acquisition rate was not different between groups. L-NAME reduced NO synthase activity by 85% in all brai n areas assayed and HC-3 binding by 38% in hippocampus and 48% in post erior cortex. ChAT activity was not different between groups in any re gion assayed. These data suggest that NO does not play a role in visua l or spatial discrimination learning. However, NO synthase inhibition may play a role in the regulation of cholinergic activity.