Elsevier

Neuroscience

Volume 77, Issue 3, 3 February 1997, Pages 629-648
Neuroscience

Morphological and electrophysiological characterization of layer III cells of the medial entorhinal cortex of the rat

https://doi.org/10.1016/S0306-4522(96)00494-0Get rights and content

Abstract

Entorhinal cortex layer III cells send their axons into hippocampal area CA1, forming the less well studied branch of the perforant path. Using electrophysiological and morphological techniques within a slice preparation, we can classify medial entorhinal cortex layer III cells into four different types. Type 1 and 2 cells were projection cells. Type 1 cells fired regularly and possessed high input resistances and long membrane time constants. Electrical stimulation of the lateral entorhinal cortex revealed a strong excitation by both N-methyl-d-aspartate and non-N-methyl-d-aspartate receptor-mediated excitatory postsynaptic potentials. Type 2 cells accommodated strongly, had lower input resistances, faster time constants and featured prominent synaptic inhibition. Type 1 and 2 cells responded to repetitive synaptic stimulation with a prolonged hyperpolarization. We identified the two other, presumed local circuit, cell types whose axons remained within the entorhinal cortex. Type 3 cells were regular firing, had high input resistances and slow membrane time constants, while type 4 cells fired at higher frequencies and possessed a faster time constant and lower input resistance than type 3 neurons. Type 3 cells presented long-lasting excitatory synaptic potentials. Type 4 neurons were the only ones with different responses to stimulation from different sites. Upon lateral entorhinal cortex stimulation they responded with an excitatory postsynaptic potential, while a monosynaptic inhibitory postsynaptic potential was evoked from deep layer stimulation. In contrast to type 1 and 2 neurons, none of the local circuit cells could be antidromically activated from deep layers, and prolonged hyperpolarizations following synaptic repetitive stimulation were also absent in these cells.

Together, the complementing morphology and the electrophysiological characteristics of all the cells can provide the controlled flexibility required during the transfer of cortical information to the hippocampus.

Section snippets

Slice preparation

Horizontal slices (400 μm thick) from adult female Wistar rats (200–250 g) containing the hippocampus, entorhinal, perirhinal and temporal cortices (as described previously[8]) were cut using a Vibroslice (Campden Instruments, Loughborough, U.K.). Earlier in the study slices were also cut using a McIlwain tissue chopper. The slices were transferred to a standard interface chamber maintained at 34°C and perfused at a rate of 1.5–1.8 ml/min with artificial cerebrospinal fluid, containing (in mM):

Results

In this study we made stable recordings from 185 medial EC layer III cells. Forty were also identified morphologically and located at a range of positions within the medial EC relative to the cortical surface (mean 436.3±15.4 μm, range 300–587 μm). Across all cell types there was no significant difference in their positions (F3,34=1.8, P=0.16, one-way ANOVA). On the basis of the morphological characteristics of the subset of labelled cells, we broadly separated the cells into two groups, those

Discussion

We describe four different cell types within layer III of the medial EC. The morphological details of the recorded cells helped to classify the cells into two major groups on the basis of whether their axons reached deep layers heading towards the angular bundle or whether they remained within the EC. Based on the absence of spines, type 1 could be differentiated from type 2, 3 and 4 cells. Type 4 cells had a very characteristic axonal arborization which made them distinct from the other

Acknowledgements

We acknowledge support from the HFSP, SFB 515 and a Royal Society Exchange Program Fellowship to R.M.E.

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    Present address: Department of Pharmacology, University of Oxford, Mansfield Road, Oxford, OX1 3QT, U.K.

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