High-speed optical imaging of afferent flow through rat olfactory bulb slices: voltage-sensitive dye signals reveal periglomerular cell activity

Fast, multiple-site optical recording and video imaging techniques were combined to visualize the olfactory processing stream as it flowed through rat olfactory bulb slices stained with the voltage-sensitive dye RH155. A 464 element photodiode detector array was used to record the voltage-sensitive dye signals. Focal electrical stimulation of the olfactory nerve layer evoked relatively large optical responses in the olfactory nerve and glomerular layers but only small responses within the external plexiform layer. With paired-pulse stimulation, glomerular attenuation was evident in signals recorded from the glomerular and external plexiform layers but not from the olfactory nerve layer. At very high recording speeds ( < 0.2 msec/frame), the presynaptic component of the olfactory processing stream could be followed as it flowed through the olfactory nerve layer and into the glomerular layer, where its amplitude rapidly declined. This decline was followed by a reciprocal rise in a postsynaptic depolarization that was largely restricted to the glomerular layer. Spatiotemporal interactions between overlapping afferent streams within the glomerular layer were observed and partially characterized. The optically recorded glomerular layer response was largely resistant to bath application of GABAA receptor antagonists but was sensitive to manipulations of external chloride concentration and to bath application of a stilbene derivative, 4-acetamido-4'isothiocyanatostilbene-2,2'-disulfonic acid known to block Cl- conductances. It is suggested the the voltage-sensitive dye signals recorded from the glomerular layer reflect activity in periglomerular cells and that Cl- efflux through non-GABAA chloride channels contributes to the postsynaptic depolarization of these cells after olfactory nerve stimulation.