Immunohistochemical demonstration of a neuronal calmodulin-binding protein, NAP-22, in the rat spinal cord

Neuron-enriched acidic protein having a molecular mass of 22 kDa, NAP-22, i s a newly isolated calmodulin-binding protein and is phosphorylated with pr otein kinase C (PKC). This protein is localized to biological membrane via myristoylation and found in the membrane fraction of the brain and in the s ynaptic vesicle fraction. To reveal the NAP-22 distribution in vivo, we inv estigated the spinal cord of the 4-5-week old rats using light and electron microscopy. NAP-22 immunoreactivity was observed in the gray matter with d orsoventral gradient of reactivity. Distinct reactivity was demonstrated in the nerve terminals and dendritic spines. Some reactions were also observe d in the thin nerve fibers. NAP-22 immunoreactivity was associated mainly w ith pre- and postsynaptic membranes, synaptic vesicles and outer mitochondr ial membranes. In the nerve terminals, NAP-22 was colocalized with synaptic vesicle proteins such as synapsin I or synaptobrevin 2. About 80% of the n erve terminals having immunoreactivity for synapsin I or synaptobrevin 2 sh owed NAP-22 immunoreactivity. From these results, NAP-22 is confirmed to be distributed in the synaptic region of the spinal cord and is involved in t he synaptic function relating to PKC. (C) 1999 Elsevier Science B.V. All ri ghts reserved.