The role of nitric oxide in the emotional learning of rats in the plus-maze

The present study evaluated the role of nitric oxide (NO) in the transfer latency (TL) paradigm in the elevated plus-maze. Male Wistar rats received i.p. injections of either 0.9% Saline, N-w Nitro-L-arginine-methyl-ester (L-NAME, an inhibitor of NO synthesis), D-NAME (inert isomer), scopolamine (SCO, antagonist of muscarinic receptors), or MK-801 (antagonist of NMDA receptors) and, after 30 min, were submitted to TL procedure. In an independent experiment, the ability of the same L-NAME treatments in changing the arterial pressure and blood glucose level (BGL) was evaluated in conscious rats. The treatment with SCO (1 mg kg(-1)), MK-801 (0.15 mg kg(-1)) and L-NAME (10 and 50 mg kg(-1)), but not with D-NAME, impaired the TL learning. The L-NAME-induced TL deficit was counteracted by L-ARG (100 and 200 mg kg(-1)), while the co-administration of sub-effective doses of L-NAME and MK-801 failed to impair the TL learning. The L-NAME (50 mg kg(-1)) treatment failed to alter the BGL. All treatments with L-NAME induced hypertension, but the rats treated with L-NAME (5 mg kg(-1)) were still able to learn the TL task. The data indicate that the TL deficit induced by L-NAME (10 and 50 mg kg(-1)) is not due to either hypertension or changes in the BGL. It is also possible to establish that NO production is important for emotional learning underlying the TL procedure in rats. (c) 2004 Elsevier Inc. All rights reserved.