Local inhibition of nitric oxide synthase activity in the accessory olfactory bulb does not prevent the formation of an olfactory memory in mice.

The putative intercellular transmitter nitric oxide has been suggested to play a role in synaptic plasticity in several models of learning and memory. We have investigated the cellular localisation of nitric oxide synthase in the accessory olfactory bulb of the mouse, using immunohistochemistry and NADPH diaphorase histochemistry. The strikingly high levels of nitric oxide synthase observed in the accessory olfactory bulb were found to be due almost exclusively to its localisation in granule cell interneurons. In mice the accessory olfactory bulb has been proposed as the site of synaptic changes occurring during the formation of an olfactory memory to male pheromones. In an attempt to disrupt the formation of this olfactory memory, we used local infusions of the nitric oxide synthase inhibitor L-NG-nitroarginine, into the olfactory bulb over the critical period for memory formation. Infusions of L-NG-nitroarginine at doses that effectively inhibited nitric oxide synthase activity did not prevent memory formation. The apparent resistance of this memory to inhibition of nitric oxide synthase activity may reflect the special nature of the mitral cell to granule cell reciprocal synapse in the accessory olfactory bulb.