Morphological and electrophysiological characteristics of layer V neurons of the rat lateral entorhinal cortex

Abstract

The intrinsic electrophysiological and morphological properties of lateral entorhinal area (LEA) layer V neurons were investigated by sharp electrode intracellular recording and biocytin labeling in vitro. The morphological analysis revealed that layer V of the LEA contains three distinct subtypes of principal neurons, which were classified as pyramidal, horizontal, and polymorphic neurons. Pyramidal cells were the most abundant subtype (57%) and could be further subdivided into neurons with large, small, and star-like somas. Similarly to pyramidal cells, horizontal neurons (11%) had a prominent apical dendrite. However, their distinctive basal dendritic plexus extended primarily in the horizontal plane. Polymorphic neurons (32%) were characterized by a multipolar dendritic organization. Electrophysiological analysis of neurons in the three categories demonstrated a diversity of electrophysiological profiles within each category and no significant differences between groups. Neurons in the three subgroups could display instantaneous and/or time-dependent inward rectification and different degrees of spike frequency adaptation. None of the recorded cells displayed an intrinsic oscillatory bursting discharge. Many neurons in the three subgroups, however, displayed slow (3.5-14 Hz), sustained, subthreshold membrane potential oscillations. The morphological and electrophysiological diversity of principal neurons in the LEA parallels that previously reported for the medial entorhinal area and suggests that, with respect to the deep layers, similar information processing is performed across the mediolateral extent of the entorhinal cortex. Layer V of the entorhinal cortex may undertake very complex operations beyond acting as a relay station of hippocampal processed information to the neocortex.

Dendritic morphology, local circuitry, and intrinsic electrophysiology of principal neurons in the entorhinal cortex of macaque monkeys

“…Although qualitatively similar, our findings suggest that there are quantitative speciesspecific differences in the dendritic structure of principal neurons in the superficial layers of the entorhinal cortex. Several previous studies, both in our own laboratories and in others, have used similar techniques to evaluate the dendrites of entorhinal cortical neurons in rats (Lingenhöhl and Finch, 1991;Hamam et al, 2000Hamam et al, , 2002. Although our sample of reconstructed neurons in the deep layers of primates was small, it appeared that for neurons in layers V and VI, the numbers of primary dendrites, dendritic branches, and total dendritic length in monkeys were similar to those in rats.…”

Dopaminergic Regulation of Neuronal Excitability through Modulation ofIhin Layer V Entorhinal Cortex

“…A total of 241 neurons was recorded from layer V of lateral EC that displayed electrophysiological characteristics consistent with previously identified EC layer V pyramidal neurons (Hamam et al, 2002). Thus, they displayed a baseline action potential amplitude (104.9 Ϯ 0.8 mV), half-width (1.16 Ϯ 0.02 ms), V rest (Ϫ69.3 Ϯ 0.9 mV), and input resistance (89.3 Ϯ 3.7 M⍀) consistent with previous reports, and regular spiking or adapting firing patterns.…”

“…For instance, many of these neurons display a voltage sag in response to hyperpolarization, and other indicators of hyperpolarization-activated currents (I h ) (Richter et al, 2000;Hamam et al, 2002). I h potently regulates firing and synaptic integration (Mayer and Westbrook, 1983;Spain et al, 1987;Pape and McCormick, 1989;McCormick and Huguenard, 1992;Magee, 1998Magee, , 1999.…”

State-Dependent Modulation of Amygdala Inputs by Dopamine-Induced Enhancement of Sodium Currents in Layer V Entorhinal Cortex

“…The neurons recorded within layer V of the lateral EC were located between the lamina dissecans, which was apparent because of the density of fibers and layer VI, which had neurons that appeared smaller and closer to the external capsule. When recorded in current clamp, these neurons displayed electrophysiological characteristics consistent with previously described entorhinal cortical pyramidal neurons (Hamam et al, 2002). In current clamp, the mean resting membrane potential was Ϫ71.3 Ϯ 0.8 mV, and input resistance was 87.5 Ϯ 3.3 M⍀.…”