Scopolamine injection into the olfactory bulb impairs short-term olfactory memory in rats

Abstract

A previous experiment showed that systemic administration of the muscarinic antagonist scopolamine altered delayed matching in an olfactory task in rats. The present experiment tested whether the impairment could result from blockade of the cholinergic transmission in the first relay structure of the olfactory system, the olfactory bulb. Drug was infused directly into both olfactory bulbs before test sessions. Results showed that the intrabulbar infusion reproduced the effect of the systemic administration. With a 4-s delay between target odor and choice test, performances of treated rats remained unchanged; but with a 30-s delay, rats performed randomly. Results from a complementary electrophysiological experiment in anesthetized rats support the idea that scopolamine injected into the olfactory bulb was unlikely to have reached more central structures. Further evidence for the involvement of pure sensory areas in short-term memory is concluded.