Morphological and electrophysiological properties of principal neurons in the rat lateral amygdala in vitro

In this study, we characterize the electrophysiological and morphological p roperties of spiny principal neurons in the rat lateral amygdala using whol e cell recordings in acute brain slices. These neurons exhibited a range of firing properties in response to prolonged current injection. Responses va ried from cells that showed full spike frequency adaptation, spiking three to five times, to those that showed no adaptation. The differences in firin g patterns were largely explained by the amplitude of the afterhyperpolariz ation (AHP) that followed spike trains. Cells that showed full spike freque ncy adaptation had large amplitude slow AHPs, whereas cells that discharged tonically had slow AHPs of much smaller amplitude. During spike trains, al l cells showed a similar broadening of their action potentials. Biocytin-fi lled neurons showed a range of pyramidal-like morphologies, differed in den dritic complexity, had spiny dendrites, and differed in the degree to which they clearly exhibited apical versus basal dendrites. Quantitative analysi s revealed no association between cell morphology and firing properties. We conclude that the discharge properties of neurons in the lateral nucleus, in response to somatic current injections, are determined by the differenti al distribution of ionic conductances rather than through mechanisms that r ely on cell morphology.