The intercalated cell masses project to the central and medial nuclei of the amygdala in cats.

In order to study the efferent projections of the intercalated cell masses within the amygdaloid complex, iontophoretic injections of cholera toxin B subunit were performed in several amygdaloid nuclei of the centromedial and basolateral groups in cats. Analysis of the ensuing retrograde labeling revealed that the main intra-amygdaloid targets of the intercalated cell masses are the central and medial nuclei. Most intercalated neurons projecting to the medial nucleus were found in the larger, rostrally located intercalated cell masses. In contrast, the majority of intercalated cells projecting to the central medial and central lateral nuclei were found in the smaller, caudally located intercalated cell masses. In addition, evidence for weaker projections to the basolateral nucleus and other intercalated cell masses was obtained. In light of previous immunohistochemical results showing that GABAergic cells represent the main cell type in the intercalated cell masses, these results imply that the intercalated cell masses constitute an important source of GABAergic input to the centromedial complex. The significance of this finding lies in the fact that the intercalated cell masses are located at the interface between the basolateral nuclear group and the centromedial complex, the main route through which the amygdaloid complex can directly influence hypothalamic and brainstem centers involved in the elaboration of autonomic responses and species-specific emotional behaviors.