SCOPOLAMINE BLOCKS OLFACTION-INDUCED FAST WAVES BUT NOT OLFACTORY EVOKED-POTENTIALS IN THE DENTATE GYRUS

The presentation of some odorous materials such as xylene or toluene u nder the snout of rats has been shown to elicit 15-30 Hz fast-wave bur sts in both the olfactory bulb and dentate gyrus. Electrical stimulati on of the olfactory bulb elicits an evoked potential (latency of first peak is 16-18 ms) in the dentate gyrus. The present study demonstrate s that scopolamine or atropine blocks toluene-induced fast-wave bursts in the dentate region and to a lesser degree in the olfactory bulb wh ile leaving dentate gyrus electrically evoked potentials intact. Furth er, rhythmical burst stimulation of the olfactory bulb at fast-wave fr equencies will elicit fast-wave-like oscillations in the dentate gyrus , These fast-wave-like events, unlike evoked potentials to single-puls e stimulation, are abolished after muscarinic receptor antagonism with atropine. Mechanisms at the olfactory bulb and dentate gyrus that pro duce fast oscillations may involve muscarinic cholinergic synapses whi le the simple transmission of single, non-oscillatory olfactory signal s to the dentate gyrus does not.