Immunohistochemical localization of a novel acidic calmodulin-binding protein, NAP-22, in the rat brain

NAP-22 is a neuronal tissue-enriched acidic calmodulin-binding protein with a molecular mass of 22,000 and is recovered in the membrane fraction durin g biochemical fractionation. mie observed the distribution pattern of this protein in the rat brain using an immunohistochemical method by light and e lectron microscopy. NAP-22 immunoreactivity was detected through the whole brain, and the most dense staining was observed in the forebrain including cerebral cortex, hippocampal formation, olfactory bulb, basal ganglia and t halamus. Immunoreactivity was distributed densely at the neuropil, whereas nerve cells and nerve fibres had little or no reaction. In the brain stem, immunonegative large nerve cell bodies were surrounded by immunopositive va ricosities. In the cerebellar cortex, mossy fibre terminals and parallel fi bres showed immunoreactivity, whereas Purkinje cells did not. Intracellular distribution was observed in the cerebral and cerebellar cortices. NAP-22 immunoreactivity was noted in the axon terminals, dendritic spines and thin nerve fibres. In these structures, reaction products were associated mainl y with synaptic vesicles, pre- and postsynaptic membranes and microtubules. This study demonstrates that the immunoreactivity of NAP-22 is distributed widely in the brain, especially in the synapse, and suggests that this prot ein is involved in synaptic transmission both in the pre- and postsynaptic region. (C) 1999 IBRO. Published by Elsevier Science Ltd.