Immunocytochemical studies of actin localization in the central nervous system.

The contractile protein, actin, is a major component of the central nervous system (CNS). Its accumulation at presynaptic and postsynaptic sites has been suggested by biochemical and ultrastructural studies. The present work examines directly the distribution of actin within the CNS by immunocytochemical means. Sections of rat CNS were stained with an antiserum against chicken gizzard actin, using a peroxidase-antiperoxidase technique. In Vibratome sections, reaction product appeared widely distributed in the perikaryal cytoplasm of neurons, in axons and dendrites, and in astrocytes and blood vessels. In paraffin sections, however, much of the cytoplasmic reaction was not observed. Instead, the reaction product was concentrated in processes within the neuropil and in discrete densities about the perimeters of neurons. This latter distribution, observed in areas in which large axosomatic synapses are known to occur, was consistent with a concentration at synaptic sites. Immunocytochemistry performed at the ultrastructural level, using a pre-embedding technique, revealed a diffuse cytoplasmic staining, with increased accumulation under the neuronal plasma membrane, particularly at postsynaptic densities.