25] - Light and Electron Microscopic Investigation of Somatostatin-Containing Neurons in the Central Nervous System

Abstract

The somatostatin (SOM)-containing neurons of the cerebral cortex have been a subject of considerable interest in clinical medicine as well as basic neuroscience, but their physiological role remains unclear. The SOM-containing neurons in various regions do not show identical morphological characteristics, and although they contain the same peptides, the various neuronal types may have somewhat different metabolisms and functions. This chapter discusses the SOM-containing neurons, nerve fibers, and terminals in the rat cerebral cortex, striatum, and spinal cord, with special reference to light and electron microscopic findings. Immunohistochemical procedures that avoid false-positive reactions for SOM at both light and electron microscopic levels are also presented in the chapter. The chapter further discusses how to distinguish the specific immunopositive reaction from nonspecific staining at the light microscopic level and how to analyze the electron microscopic results. In doing this, the morphological characteristics of the SOM-containing neurons in each of these selected regions in the central nervous system can be clarified. The chapter also presents the immunohistochemical procedure for neuropeptides, such as SOM at both light and electron microscopic levels, and emphasizes comparison of the findings of light with those of electron microscopy as a means of avoiding confusion of nonspecific reaction products with the specific products. It has also been emphasized that neurons containing a given peptide may occur in several subtypes with different morphologies and ultrastructural findings.