Theta rhythm related hippocampal cell discharges in the urethane anaesthetized rat: evidence for a predominant entorhinal input.

Unit spike activity and slow wave field potentials were recorded in the CA1 pyramidal layer and the dentate granular layer of the dorsal hippocampus of urethane anaesthetized rats during theta rhythm. 70% of the units in the pyramidal layer and all units in the granular layer, having a discharge pattern related to theta rhythm, had their mean moment of discharge in the positive phase of the theta wave recorded in the pyramidal layer. Combined with the results of a modelling study (Holsheimer et al. 1982) it appears that in rat under urethane the theta modulated input to the CA1 pyramidal cells and the dentate granular cells will be mediated predominantly by pathways which terminate distally at these cells: the perforant path.