GABAergic Interneurons in the Mouse Lateral Amygdala: A Classification Study

Whole cell patch-clamp recordings were performed in GABAergic interneurons labeled by green fluorescent protein (GFP) in the lateral amygdala (LA) in vitro from glutamic acid decarboxylase 67 (GAD67)-GFP mice. Neurons were characterized by electrotonic and electrogenic parameters. Cytoplasm was collected from individual neurons, and single-cell RT-PCR was used for detection of molecular markers typifying LA interneurons. Hierarchical cluster and multiple discriminant analysis demonstrated the existence of five types of GABAergic interneurons, which can be reliably identified through electrophysiological criteria. Action potentials were of a short duration followed by pronounced fast afterhyperpolarization (AHP) in interneurons of all types, except for type V, which generated broad action potentials and displayed typical spike bursts at the beginning of depolarizing stimuli and prominent anomalous inward rectification. Interneurons of type I and II generated series of action potentials with frequency adaptation on maintained depolarizing current stimulation with overall frequencies at high levels and presented delayed firing, stuttering or fast-spiking behavior. Further distinguishing features of type II interneurons were a medium AHP following spike trains and pronounced anomalous inward rectification. Types III and IV of neurons fired regularly, whereas type IV displayed no prominent spike frequency adaptation. Additionally, interneurons of all five types contained mRNA of glutamic acid decarboxylase 65 and cholecystokinin, whereas only type I interneurons were somatostatin-positive. Overall, these data represent a detailed and reliable classification scheme of LA GABAergic interneurons and will provide a feasible basis for subsequent functional studies.