Immunocytochemical localization of the neural-specific regulatory subunit of the type II cyclic AMP-dependent protein kinase to postsynaptic structures in the rat brain

The cellular and subcellular distribution of a major cyclic AMP binding protein in the central nervous system, the neural-specific regulatory subunit of the type II cyclic AMP-dependent protein kinase (RII-B), was analyzed in rat brains with light and electron microscopic immunocytochemical methods. The distribution of the non-neural isoform of the regulatory subunit of the enzyme (RII-H) was also analyzed. It was found that RII-B immunoreactivity was predominantly localized to neurons whereas glial and endothelial cells were unlabeled. In the neurons the RII-B immunoreactivity occurred in the perikaryal cytoplasm and in the dendrites; there was no significant accumulation of immunoreaction product in nuclei, myelinated axons and axon terminals. Although immunoreactivity was never detected in axon terminals, it was characteristically associated with the postsynaptic densities and the surrounding non-synaptic sites in somata, dendrites and dendritic spines. The localization of RII-B antigenic sites did not show specificity to any type of neuron or synapse, but the amount of immunoreactivity varied. The distribution of RII-H immunoreactivity was similar to that of RII-B except that RII-H immunoreaction product was also observed in glial cells and occurred more frequently in myelinated axons. Our data confirm that RII-B is one of the major cyclic AMP binding proteins in neurons, and provide morphological support for the involvement of the type II cyclic AMP-dependent protein kinase in postsynaptic neural functions.