Intracellular records of carbachol-induced theta rhythm in hippocampal slices

Intracellular recordings were made in the CA1, CA3 and dentate cell layers prior to, during and after the bath perfusion of 50 μM carbachol on hippocampal slices. Fifty-six percent of the cells in this sample were termed theta (θ)-related, ie., they exhibited membrane potential oscillations of 5–28 mV and rhythmic spike discharges related to the carbachol-induced extracellular θ-rhythm. The remaining 44% of the cells did not show the above relationship to the extracellular θ-rhythm. Carbachol produced an overall depolarization in all cells, in the range of 10–20 mV. These results demonstrated the cellular basis of carbachol-induced θ in hippocampal slices. This preparation will be a valuable model for studying cellular mechanisms and network properties underlying electroencephalographic activity.