Elsevier

Brain Research

Volume 182, Issue 1, 20 January 1980, Pages 47-64
Brain Research

An olfactory input to the hippocampus of the cat: Field potential analysis

https://doi.org/10.1016/0006-8993(80)90829-XGet rights and content

Abstract

Hippocampal responses to electrical stimulation of the prepyriform cortex in the cat were studied both in acute experiments under halothane anesthesia and in awake cats with chronically indwelling electrodes. Analysis of field potentials and unit activity indicated the extent to which different hippocampal subareas were activated, the laminar level at which the synaptic action took place and the dynamics of the evoked responses. It was found that: (1) the main generator of evoked responses in the hippocampus upon prepyriform cortex stimulation is localized in the fascia dentata and CA3 (CA1 pyramidal cells, and probably also subiculum cells, are activated but in a lesser degree); (2) the initial synaptic activity takes place at the most distal part of the dendrites of fascia dentata granule cells and CA3 pyramidal cells; and (3) this synaptic activity corresponds to an EPSP that leads to a transient increase in the firing rate of the hippocampal units, which is often followed by a long-lasting decrease in firing rate.

We conclude that the pathway from the prepyriform cortex via lateral entorhinal cortex to hippocampal neurons may enable olfactory inputs to effectively excite hippocampal neurons.

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      No simultaneous activation of the CA1 and the DG was observed in our experiments. In addition, because of the problems mentioned below (see next paragraph) we could not detect any direct EC–CA3 response, as previously reported (Habets et al., 1980; Wouterlood and Nederlof, 1983; Liu and Bilkey, 1997). Since EC–CA1/CA3 and EC–DG inputs are mediated by neurons located respectively in layer III and layer II of the EC (see Witter, 1993), our findings suggest that the olfactory input mediated by the activation of LOT preferentially targets neurons in EC layer II, since the largest sink we observed was located in the ML of the DG.

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    *

    Present address: Netherlands Institute for Brain Research, IJdijk 28, 1095 KJ Amsterdam, The Netherlands.

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