[Spatial distribution of hippocampal responses to dental pulp stimulation and acoustic clicks].

Evoked potentials and unitary discharges in responses to tooth pulp and acoustic click stimuli were recorded from the hippocampus of freely moving rats. The spatial distribution of evoked field responses to tooth pulp stimulation and acoustic clicks were identical. Averaged evoked potentials consisted of a large negative deflection (N1) preceded by a small positive potential (P1). The shortest latency N1 was recorded from the middle third of the dentate molecular layer and the outer portion of apical dendrites of Ca3 (27 ms). The peak latency of N1 was significantly longer (34 ms) in the stratum radiatum of CA1. Laminar profiles of N1 in the dentate gyrus and CA3 were similar to that evoked by electrical stimulation of the perforant path and in CA1 similar to the response profile evoked by the Schaffer collaterals. The largest amplitude P1 was observed above the pyramidal layer of CA1 and the hilus. Both sensory modalities were able to modify the discharge rate of neurons in all hippocampal regions. A conclusion is made that information about sensory stimuli can reach the hippocampus by two distinctive pathways: a short-latency inhibitory input via the fimbrial fornix and a longer-latency path via the entorhinal cortex.