Odor-induced fast waves in the dentate gyrus depend on a pathway through posterior cerebral cortex: Effects of limbic lesions and trimethyltin

Previous research has shown that the odor of a variety of organic solvents and of components of the anal scent gland excretions of various predators will elicit a burst of fast waves of about 20 Hz in the olfactory bulb, pyriform cortex, and dentate gyrus of the rat. The present experiments show that large lesions of the caudal cerebral cortex, involving particularly the entorhinal and subicular cortices and the angular bundle, abolish the olfactory fast wave response of the dentate gyrus, but not the similar response of the olfactory bulb. In confirmation of previous work, such a lesion also abolishes an average evoked response elicited in the dentate gyrus by electrical stimulation of the olfactory bulb. Systemic treatment with the neurotoxin trimethyltin abolished the olfactory fast wave response in the olfactory bulb and both the olfactory fast wave and the olfactory evoked potential in the dentate gyrus, Large lesions of the amygdala or the septal nuclei did not eliminate either the dentate olfactory evoked potential or the odor-induced dentate fast wave response. However, the septal lesion reduced the amplitude of both spontaneous and odor-induced dentate fast wave activity. It is suggested that olfactory stimuli elicit 20 Hz dentate fast waves via a pathway from the olfactory bulb through the entorhinal cortex and, further, that cholinergic interneurons in the dentate gyrus may be essential to the dentate fast wave response. (C) 1999 Elsevier Science Inc.