Cholinergic and dopaminergic systems are involved in spatial memory and are modulated by nitric oxide (NO); NO has well documented effects on place learning in rodents. The aim of the present study was to investigate the effect of NOS inhibition on place learning in the water maze and to evaluate the relationships between NOS inhibition, learning performance, dopamine (DA) D2 and muscarinic acetylcholine (mACh) receptors. Male Sprague-Dawley rats received the NOS inhibitor N omega-Nitro-L-Arginine (L-NA), or saline and were trained in the water maze. Rats that were not trained, but received the same treatments were also included. Following treatments with or without water maze training, [H-3]-QNB and [H-3]-spiperone binding in cortex, striatum and hippocampus were determined to assess the effects of NOS inhibition and/or learning on DA D2 and mACh receptor regulation. The overall results of the present study showed that: (1) NOS inhibition impairs performance in the MWM; (2) NOS inhibition does not affect specific binding to DA D2 (striatum and hippocampus) and mACh (cortex and hippocampus) receptors; (3) MWM training lowers D2 and mACh receptor binding in cortical regions. (C) 2005 Elsevier Inc. All rights reserved.