Increased expression of neuronal nitric oxide synthase mRNA in the accessory olfactory bulb during the formation of olfactory recognition memory in mice

The mouse accessory olfactory bulb contains a high density of nitric oxide synthase and, in females, is involved in the formation of a mating and pher omone-specific recognition memory. The exact role of nitric oxide in this m emory model is not yet clearly understood. In this study, in situ hybridiza tion was used to assess neuronal nitric oxide synthase mRNA expression duri ng the critical-interval associated with synaptic plasticity in the accesso ry olfactory bulb of female mice leading to the formation of a recognition memory for the stud male pheromones present following mating. Nitric oxide synthase mRNA was significantly increased following mating and 120-min stud male exposure compared with oestrus mice. The mRNA expression was more pre dominant in the anterior than the posterior regions of the bulb. These obse rvations indicate a stimulus-specific activation of nitric oxide gene expre ssion in the female mouse accessory olfactory bulb and support the hypothes is that nitric oxide may modulate intermediate synaptic pathways during the formation of a pheromone-dependent olfactory recognition for stud males.