The α and γ1 isoforms of protein phosphatase 1 are highly and specifically concentrated in dendritic spines

Abstract

Protein phosphatase I (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 microscopic immunocytochemistry to characterize the distribution of two PPI isoforms, PP1α and PP1(γ1), in the rat neostriatum. Both isoforms are heterogeneously distributed in brain with the highest immunoreactivity being found in the neostriatum and hippocampal formation. Further, both isoforms are highly and specifically concentrated in dendritic spines. Weak immunoreactivity is present in dendrites, axons, and some axon terminals. Immunoreactivity for PP1α is also present in the perikaryal cytoplasm and nuclei of most medium- and large-sized neostriatal neurons. The specific localization of PPI in dendritic spines is consistent with a central role for this enzyme in signal transduction. The data support the concept that, in the course of evolution, spines developed as specialized signal transduction organelles enabling neurons to integrate diverse inputs from multiple afferent nerve terminals.