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, Nω 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.