Morphological characterization of large intercalated neurons provides novel insight on intrinsic networks of the amygdala

Background Although extinction-based therapies are effective treatments for anxiety disorders, the neural bases of fear extinction remain still largely unclear. Recent evidence suggests that the intercalated cell masses of the amygdala (ITCs) are critical structures for fear expression and extinction. They consist of clusters of densely packed medium spiny GABAergic neurons surrounding the basolateral amygdaloid complex (BLA). Five percent of ITC neurons are large cells mostly present near the cluster borders. So far, no information is available regarding the neurochemical features, afferents and efferents of large ITC cells, preventing any elucidation of their functional role. Only recently we discovered that large ITC neurons display immunoreactivity for either neurokinin 1 or metabotropic glutamate 1a (mGlu1a) receptors. We also found that dendrites of these neurons receive inhibitory inputs from medial capsular projecting ITC cells [1]. The aim of our study consists in the characterization of the morphological features, as well as the afferent and efferent connectivity, of large ITC neurons in order to further clarify their potential participation in the neuronal processes underlying fear extinction.