THE ALPHA-ISOFORM AND GAMMA-1-ISOFORM OF PROTEIN PHOSPHATASE-1 ARE HIGHLY AND SPECIFICALLY CONCENTRATED IN DENDRITIC SPINES

Protein phosphatase 1 (PP1) is a highly conserved enzyme that has been implicated in diverse biological processes in the brain as well as in nonneuronal tissues. The present study used light and electron micros copic immunocytochemistry to characterize the distribution of two PP1 isoforms, PP1 alpha and PP1 gamma(1), in the rat neostriatum. Both iso forms are heterogeneously distributed in brain with the highest immuno reactivity being found in the neostriatum and hippocampal formation. F urther, both isoforms are highly and specifically concentrated in dend ritic spines. Weak immunoreactivity is present in dendrites, axons, an d some axon terminals. Immunoreactivity for PP1 alpha is also present in the perikaryal cytoplasm and nuclei of most medium- and large-sized neostriatal neurons. The specific localization of PP1 in dendritic sp ines is consistent with a central role for this enzyme in signal trans duction. The data support the concept that, in the course of evolution , spines developed as specialized signal transduction organelles enabl ing neurons to integrate diverse inputs from multiple afferent nerve t erminals.