| Abstract: | Evoked potentials (EP) and neuronal responses produced by tooth pulp stimulation and a clicking sound were recorded at different hippocampal sites using microelectrodes in unrestrained rats. Spatial distribution of EP was found to be the same for both types of stimulation. Averaged EP consisted of a high amplitude negative preceded by a low-amplitude positive component (N1 and P1, respectively). Latency of the N1 wave reached its minimum (of 27 msec) at the middle third of the molecular layer of the dentate gyrus and the outer portion of the CA3 apical dendrites. Latency of N1 was considerably longer in the stratum radiatum layer of the CA1. Laminar profiles of the amplitude of the N1 componenent of EP produced in the dentate gyrus and the CA3 by tooth pulp stimulation resemble those observed during perforant path stimulation; in the CA1 they are similar to those evoked by stimulating the Schaffer collaterals. Maximum amplitude of the P1 component was observed above the pyramidal layer of the CA1 and the hilus. Neuronal discharge pattern changed in all hippocampal regions under the effects of both tooth pulp stimulation and the clicking sound. It is deduced that information can reach the hippocampus by two routes: via a "fast" (inhibitory) pathway through the fimbria and the fornix and a slower (excitatory) path through the entorhinal cortex.P. Flexig Institute for Brain Research, Karl Marx University, Leipzig, DR. Institute of Physiology, Pecs University Medical School, Pecs, Hungary. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 36–46, January–February, 1987. |
