Effects of nicotinamide on central cholinergic transmission and on spatial learning in rats

High-dose nicotinamide (1000 mg/kg) leads to a minor increase of plasma choline but to a major increase of the choline concentrations in the intra- and extracellular spaces of the brain. In the hippocampus, the nicotinamide-induced increase in choline was associated with an increase in the release of acetylcholine under stimulated conditions. In young rats, nicotinamide in doses between 10 and 1000 mg/kg did not influence spatial learning, as tested in the Morris water maze. In old rats, low doses of nicotinamide were ineffective whereas the high dose of 1000 mg/kg even impaired spatial learning. The combined administration of choline and nicotinamide had a synergistic effect on brain choli…