Characterization of the electrophysiological and morphological properties of rat central amygdala neurons in vitro

Abstract

Forty central amygdala neurons labelled with 2% Neurobiotin were categorized according to their distinctive bioelectrical membrane properties and classified physiologically by their hyperpolarized resting membrane potential (-74 mV), short duration medium afterhyperpolarization (239.2 ms), and nonaccommodating response as Type A neurons (63%; N = 25/40), or as Type B neurons (37 %; N = 15/40) by their depolarized resting membrane potential (-66 mV), long slow-afterhyperpolarization (1.8 s), and accommodation response. Visualized within subnuclei of the central amygdala, Neurobiotin- labelled Type A neurons were medium-size cells [16.5 ± 3 x 10.7 ± 2 μm; length x width] with smooth, spine-free ovoid, pyramiform, and fusiform perikarya. Aspinous primary dendrites gave rise to distal dendrites covered with numerous small pedunculated spines; density of spines ranged from sparse to abundant. Type B central amygdala neurons were larger cells [23.9 ± 5 x 14.9 ± 4 μm] with smooth, aspinous ovoid, polygonal, and pyramiform somata. Dendrites were aspinous and covered with variably sized varicosities. Two distinct populations of neurons exist within the central amygdaloid complex: the medium-size, spine-laden Type A defined neuron with its non-accommodating electrophysiological response and the larger aspinous, varicosity-laden Type B defined neuron with its accommodating response. In contrast to their neighboring 'cortical-like' amygdala neurons, central amygdala neurons possess a 'striatal-like' cytoarchitecture and electrophysiology.