The quantitative evaluation of cholinergic markers in spatial memory improvement induced by nicotine–bucladesine combination in rats

We previously showed that post-training intra-hippocampal infusion of nicotine–bucladesine combination enhanced spatial memory retention in the Morris water maze. Here we investigated the role of cholinergic markers in nicotine–bucladesine combination-induced memory improvement. We assessed the expression of choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT) in CA1 region of the hippocampus and medial septal area (MSA) of the brain. Post-training bilateral infusion of a low concentration of either nicotine or bucladesine into the CA1 region of the hippocampus did not affect spatial memory significantly. Quantitative immunostaining analysis of optical density in CA1 regions and evaluation of immunopositive neurons in medial septal area of brain sections from all combination groups revealed a significant increase (P < 0.001) in the ChAT and VAChT immunoreactivity. The maximum increase was observed with combination of 10-µM/side bucladesine and 0.5 µg/side nicotine and in a concentration dependent manner. Also, increase in the optical density and amount of ChAT and VAChT immunostaining correlated with the decrease in escape latency and traveled distance in rats treated with nicotine and low dose of bucladesine. Taken together, these results suggest that significant increases of ChAT and VAChT protein expressions in the CA1 region and medial septal area are the possible mechanisms of spatial memory improvement induced by nicotine–bucladesine combination.