Control of sensory activation of granule cells in the fascia dentata by extrinsic afferents: septal and entorhinal inputs.

Three groups of rats were trained to perform a differential discrimination task in a 2-tone operant conditioning paradigm. One group received electrolytic lesions of the medial septal nuclei, another received electrolytic or knife cut lesions of the entorhinal cortex. These groups were compared with a normal control group. Recordings of granule cells in the fascia dentata were obtained in all animals during criterion performance of the behavioral task. Both lesions produced disruption of behavioral discrimination in the form of increased error and intertrial responding. Granule cell discharges to the tone stimuli were disrupted by each type of lesion. Septal lesions reduced the differential discharge tendency to CS+ and CS- and changed granule cell firing on all trials to statistically resemble firing on CS- trials in normal animals. Extensive lesions in the entorhinal cortex or knife cuts that severed the perforant path caused near elimination of the tone-evoked discharges to both the CS+ and CS-tones. Septal and entorhinal lesions caused marked changes in the sequential dependence of the granule cell discharge compared with intact animals. Results are discussed in terms of the control of the granule cell discharge by the remaining afferent pathways in each type of lesion condition.