Coexistence of somatostatin with neuropeptide Y, but not with cholecystokinin or vasoactive intestinal peptide, in neurons of the rat amygdala.

A two-color immunoperoxidase procedure was used to determine whether somatostatin (SOM) containing neurons in the amygdala also contain neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), or cholecystokinin (CCK). There was no evidence that SOM-containing neurons in any of the amygdaloid nuclei contain VIP or CCK. In contrast, there was extensive colocalization of SOM and NPY in all of the amygdaloid nuclei with the exception of the intercalated masses and the lateral subdivision of the central nucleus. The greatest number of SOM-NPY double-labeled cells was observed in the medial nucleus, lateral nucleus, and intra-amygdaloid portion of the bed nucleus of the stria terminalis. The morphology of these SOM-NPY neurons was similar in all nuclei. Most exhibited fusiform or ovoid cell bodies with one or two sparsely branched dendrites emerging from each pole of the cell. The extensive coexistence of SOM and NPY in non-pyramidal neurons of the basolateral amygdala is similar to that seen in the cerebral cortex and supports the concept that these brain regions share many important characteristics. The extensive colocalization of SOM and NPY in the medial amygdala, in conjunction with the results of previous studies, suggests that some of these cells may project to the bed nucleus of the stria terminalis and hypothalamus.