Evoked potentials and long-term potentiation in the mouse dentate gyrus after stimulation of the entorhinal cortex

When the entorhinal cortex is electrically stimulated, an evoked potential is produced in the ipsilateral dentate gyrus of the mouse which is similar to this response in the rat, rabbit, and other preparations in which it has been recorded. The evoked potential consists of two components: Component I represents an extracellular monosynaptic population EPSP, and Component II represents a population spike due to the synchronous activation of the granule cells. After tetanic stimulation, responses to single-pulse stimuli increased and remained at that level for at least 30 min. This demonstrated long-term potentiation of the evoked potential, phenomenologically similar to that described in other species. A medial and lateral perforant path could be differentiated. Stimulation of the medial perforant path resulted in evoked potentials that had a short peak latency, half-width, and rise time. Conversely, stimulation of the lateral perforant path resulted in evoked potentials that had a long peak latency, half-width, and rise time. The recording electrode depth series were also different after selective activatio of the two paths. Stimulation of the medial perforant path resulted in recording electrode depth series that had their maximum negativities close to the cell body layer, whereas stimulation of the lateral perforant path resulted in depth series that had their maximum negativities farther out along the granule cell dendrites. These results are consistent with the different sites of termination of the two paths. Long-term potentiation was demonstrated in both pathways after administration of tetanic stimuli of various parameters.