The immunocytochemical localization of somatostatin-containing neurons in the rat central nervous system

Somatostatin-containing neurons in the rat central nervous system were localized by immunocytochemical methods. The detection of somatostatin-like immunoreactivity was facilitated by (1) the use of brains from colchicine-treated rats, (2) the proteolytic pretreatment of sections with pronase and (3) a ‘double-bridge’ immunoperoxidase staining technique. In addition to the known distribution of somatostatin-like immunoreactivity we also observed immunoreactive perikarya in the following regions: the anterior olfactory nucleus, some areas of the preoptic and hypothalamic regions, the claustrum, the periaqueductal gray, the locus ceruleus, the central gray substance, the lateral parabrachial nucleus, the nucleus of the lateral lemniscus, the nucleus ambiguus, the spinal trigeminal nucleus, the nucleus of the solitary tract and various areas of the reticular formation. Immunoreactive neuronal processes were also observed in several major tracts of the brain, including the stria terminalis, the fornix and the medial forebrain bundle.Our results indicate that somatostatin-containing neurons may occur both as interneurons in some areas of the central nervous system and as projection neurons in others. The widespread but selective distribution of these neurons suggests that somatostatin is not only a hypothalamic regulator of neuroendocrine function, but may also function as a major neuromodulator mediating a variety of functions throughout the central nervous system.