Distribution of voltage-gated sodium channel alpha-subunit and beta-subunit mRNAs in human hippocampal formation, cortex, and cerebellum

The distribution of mRNAs encoding voltage-gated sodium channel alpha subunits (I, II, III, and VI) and beta subunits (beta1 and beta2) was studied in selected regions of the human brain by Northern blot and in situ hybridisation experiments. Northern blot analysis showed that all regions studied exhibited heterogenous expression of sodium channel transcripts. In situ hybridisation experiments confirmed these findings and revealed a predominantly neuronal distribution. In the parahippocampal gyrus, subtypes II and VI and the beta-subunit mRNAs exhibited robust expression in the granule cells of the dentate gyrus and pyramidal cell layer of the hippocampus. Subtypes I and III showed moderate expression in granule cells and low expression in the pyramidal cell layer. Distinct expression patterns were also observed in the cortical layers of the middle frontal gyrus and in the entorhinal cortex. In particular, all subtypes exhibited higher levels of expression in cortical layers III, V, and VI compared with layers I and II. All subtypes were expressed in the granular layer of the cerebellum, whereas specific expression of subtypes I, VI, beta1, and beta2 mRNAs was observed in Purkinje cells. Subtypes I, VI, and beta1 mRNAs were expressed, at varying levels, in the pyramidal cells of the deep cerebellar nuclei. These data indicate that, as in rat, human brain sodium channel mRNAs have a distinct regional distribution, with individual cell types expressing different compliments of sodium channels. The differential distribution of sodium channel subtypes suggest that they have distinct roles that are likely to be of paramount importance in maintaining the functional heterogeneity of central nervous system neurons.