Co. Okere et al., FORMATION OF AN OLFACTORY RECOGNITION MEMORY IN MICE - REASSESSMENT OF THE ROLE OF NITRIC-OXIDE, Neuroscience, 71(2), 1996, pp. 349-354
The plexiform and granule cell layers of the female mouse accessory ol
factory bulb, whose synaptic activities are modified by pheromonal inp
uts after mating, contain one of the highest densities of nitric oxide
synthase in the brain. We tested the hypothesis that exogenous nitric
oxide administration can, in principle, permit the formation of a spe
cific pheromonal memory without mating by acting in I synergy with bul
bar neurotransmitter(s) to enhance long-lasting increase in gain of th
e mitral-granule cell dendrodendritic synapse. Two infusions of sodium
nitroprusside (5 nnol; 0.5 mu l) into the accessory olfactory bulb ac
tivated recognition without mating. A single infusion produced no reco
gnition. This memory is specific to the pheromones to which the female
s were exposed during sodium nitroprusside infusions because strange m
ale pheromones evoked a significant pregnancy failure rate. Furthermor
e, the memory formation is dependent on coincident activation by phero
monal inputs and sodium nitroprusside infusions, since drug infusions
in the absence of male pheromones permitted a significant pregnancy bl
ock on test exposure. The cc-adrenergic antagonist phentolamine preven
ted sodium nitroprusside-mediated memory formation. Ih females with de
pleted bulbar noradrenergic innervation by specific neurotoxin (6-hydr
oxydopamine) injection into the medial olfactory striae or the accesso
ry olfactory bulb, sodium nitroprusside infusions failed to induce mem
ory formation. The procedure itself apparently did not interfere with
the occurrence of pregnancy. These results demonstrate that exogenous
administration of nitric oxide can induce a pheromone-specific olfacto
ry memory without mating, and that this memory is mediated, at least i
n part, by noradrenaline.