Failure of intrabulbar and peripheral administration of N omega-nitro-L-arginine to prevent the formation of an olfactory memory in mice.

The gaseous neurotransmitter molecule nitric oxide (NO) has recently generated a lot of interest on account of its possible physiological role in several models of learning and memory, both in vitro and in vivo. The presence of its synthesizing enzyme has been reported in the granule cell and external plexiform layers of the accessory olfactory bulb (AOB) in mice and rats. We have tested the effect of different doses of the nitric oxide synthase inhibitor, N omega-nitro-L-arginine applied locally and peripherally, on the formation of olfactory recognition memory in the context of pregnancy block in mice. Local infusions of 5, 10, and 40 nmol of the NOS inhibitor into the AOB failed to prevent memory formation of the stud male without affecting the effectiveness of the strange male to induce pregnancy block. Peripheral administration of the NOS inhibitor produced a pregnancy block rate that was linearly related to the dose regardless of whether or not exposure to the familiar or no male subsequently followed. This suggests that the effect of peripheral administration of the NOS inhibitor on memory formation could not be assessed using this experimental paradigm. The observations made in this study do not enable us to envisage any critical or primary physiological role for NO in this memory model. Its role, at best, may be modulatory and not obligatory.