Abstract
Amygdala plays crucial roles in emotional learning. The lateral amygdala (LA) is the input station of the amygdala, where learning related plasticity occurs. The LA is cortical like in nature in terms of its cellular make up, composed of a majority of principal cells and a minority of interneurons with distinct subtypes defined by morphology, intrinsic electrophysiological properties and neurochemical expression profile. The specific functions served by LA interneuron subtypes remain elusive. This study aimed to elucidate the interneuron subtype mediating feedback inhibition. Electrophysiological evidence involving antidromic activation of recurrent LA circuitry via basolateral amygdala stimulation and paired recordings implicate low-threshold spiking interneurons in feedback inhibition. Recordings in somatostatin-cre animals crossed with tdtomato mice have revealed remarkable similarities between a subset of SOM+ interneurons and LTS interneurons. This study concludes that LTS interneurons, most of which are putatively SOM+, mediate feedback inhibition in the LA. Parallels with cortical areas and potential implications for information processing and plasticity are discussed.
Highlights
Amygdala is a collection of different nuclei (Swanson and Petrovich 1998) that play cardinal functions in the acquisition and expression of fear responses (LeDoux 2000; Pape and Pare 2010; Gründermann and Lüthi 2015)
We aimed to identify the interneuron type that mediates feedback inhibition focusing to lateral amygdala (LA) to investigate whether our observations will parallel the observations made in the basolateral complex of the amygdala (BLA) overall
We have found a proportion of low threshold spiking (LTS) interneurons to exhibit reciprocal connectivity with principal cells of the LA while fast-spiking (FS) interneuron inputs were not reciprocated by principal neurons
Summary
Amygdala is a collection of different nuclei (Swanson and Petrovich 1998) that play cardinal functions in the acquisition and expression of fear responses (LeDoux 2000; Pape and Pare 2010; Gründermann and Lüthi 2015). The BLA is a collection of smaller cortex-like nuclei and is composed ~ 75% of glutamatergic principal neurons that relay information to the output station of the amygdala, the central amygdala (CeA). The remaining population (~ 25%) constitutes a neurochemically and electrophysiologically heterogeneous set of interneurons similar to that found in cortex (McDonald and Augustine 1993; Pare and Smith 1993; Spampanato et al 2011; Bienvenu et al 2012; McDonald and Augustine 2019) and are thought to play significant roles in determining the integration and plasticity of principal cell synaptic inputs and determining the dynamic range of their action potential firing output (Gaudreau and Pare 1996), thereby regulating information processing within the basolateral amygdala under normal and pathophysiological conditions (Letzkus et al 2015; Fee et al 2017; Krabbe et al 2018). PV+ interneurons form perisomatic baskets or axoaxonic synapses on principal neurons and constitute around 50% of the total interneuron population (McDonald and Mascagni 2001; McDonald and Bettette 2001; Rainnie et al 2006; Vereczki et al 2016; Butler et al 2018) and play
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