Localization of phosphoneuroprotein 14 (PNP 14) and its mRNA expression in rat brain determined by immunocytochemistry and in situ hybridization

Distribution and ultrastructural localization of a novel phosphoneuroprotein with a molecular mass of 14 kDa (PNP 14), and expression of its mRNA were studied in the adult rat central nervous system (CNS) by immunocytochemistry and in situ hybridization histochemistry. PNP 14 immunoreactivity was abundant in the molecular layer, present moderately in the granular layer, and rare in the Purkinje cell layer of the cerebellar cortex. No PNP 14 immunoreactivity was detected in the cerebellar medulla. In the forebrain, immunoreactivity was found in the hippocampus, striatum, and throughout the cerebral cortex, especially in layer V. Electron microscopic immunocytochemical observation in the cerebellar cortex revealed many PNP 14-immunoreactive axon terminals making synaptic contact with dendritic processes in both granular and molecular layers. PNP 14 immunoreactivity was present mainly in the cytoplasmic matrix in the presynaptic axon terminals. PNP 14 mRNA was localized in the granular layer of the cerebellar cortex, in the hippocampus, and in the cerebral cortex, suggesting that PNP 14 is synthesized in neurons of the granular layer and then transported to the molecular layer by axonal transport. These morphological findings suggest that PNP 14 is likely to modulate the function of selected CNS synapses.