Thyrotropin releasing hormone, somatostatin, and enkephalin: distribution studies using immunohistochemical techniques.

Using the indirect immunofluorescence technique of Coons and collaborators, the localization of thyrotropin releasing hormone, somatostatin, and enkephalin was studied in the rat central nervous system. These three peptides were found in neurons throughout the brain and spinal cord; the latter two peptides were also found in the peripheral nervous system and in certain endocrine cells. Utilizing the peroxidase--antiperoxidase technique of Sternberger and collaborators the neuropeptides were also traced at the ultrastructural level. They seemed to be mainly confined to so-called large dense core vesicles (diameter around 1,000 A), localized within cell bodies and nerve terminals.