Is the dentate gyrus an independent generator of in vitro recorded theta rhythm?

In this study we investigated the ability of the dentate gyrus to independently generate cholinergically induced theta rhythm in vitro. Two different experiments were performed. In Experiment I, new laminar profiles of theta phase, amplitude, and current sources and sinks were constructed. In this experiment a gradual phase shift of theta waves in the CA1 stratum radiatum was observed. Simultaneously, two amplitude maxima were detected: the first in the CA1 stratum oriens, and the second in the CA1 stratum lacunosum-moleculare. Moreover, during the positive peak of theta in the CA1 stratum oriens, two large sinks were observed: the first localized in the stratum oriens and the second in the stratum lacunosum-moleculare. In Experiment II the EEG activity of three different transected hippocampal slices (CA1 transected slices, CA3c transected slices, and DG transected slices) was recorded. It was demonstrated that the dentate gyrus granular cell body layer was not able to independently produce in vitro theta rhythm. Data obtained in both experiments provide strong evidence that in cholinegically treated hippocampal formation maintained in vitro there is no independent generator of theta rhythm in the region of the dentate gyrus granular cell layer.