Distribution of GAP-43 (B50/F1) mRNA in the adult rat brain by in situ hybridization using an alkaline phosphatase labeled probe.

GAP-43 (B-50,F1, pp46) is a calmodulin binding protein which is specific to the nervous system and also a substrate for the protein kinase C. Furthermore an enrichment of this protein in the growth cone and developmental brain indicate that this protein is related to nerve development, regeneration, and outgrowth. While its level dramatically decreases after the completion of synaptogenesis, the protein is still to some extent continuously expressed in certain regions of the mature brain. In order to clarify GAP-43 localization in mature normal rats, we investigated the distribution of GAP-43 mRNA in the rat central nervous system by using a non-radioisotopic in situ hybridization histochemistry. This method demonstrated GAP-43 mRNA expressing cells with high resolution. GAP-43 mRNA was more abundant in the forebrain than in the lower brainstem. Intense hybridization signal was observed in the mitral cells of olfactory bulb, cerebral cortex, CA3 region of hippocampus, diagonal band, substantia nigra, raphe nuclei, locus coeruleus, and dorsal motor nucleus of vagus. Weak to moderate hybridization signals were also widely expressed in thalamus, hypothalamus, and midbrain. Moreover, most noradrenergic, adrenergic, serotonergic, histaminergic, and caudal part of dopaminergic cells exhibited an intense GAP-43 mRNA signal. Thus, GAP-43 mRNA is abundantly expressed under normal conditions in the brain and may play an important physiological role particularly in the forebrain and in monoaminergic neurons supporting the findings that GAP-43 could be implicated in plasticity and monoamine release.