SODIUM-CHANNEL MESSENGER-RNA-I, MESSENGER-RNA-II AND MESSENGER-RNA-III IN THE CNS - CELL-SPECIFIC EXPRESSION

The cellular localization of rat brain sodium channel alpha-subunit mR NAs I, II and III in the central nervous system (CNS) was examined by non-isotope in situ hybridization cytochemistry utilizing two independ ent sets of isoform-specific RNA probes, one set recognizing sodium ch annel isoforms in the coding region and the other in the non-coding re gion of the sodium channel messages. The independent sets of probes de monstrated qualitatively similar patterns of sodium channel mRNA expre ssion. In the hippocampus, sodium channel mRNA I was very weakly expre ssed in the pyramidal layer and in the granular layer of the dentate g yrus; in contrast, sodium channel mRNA II was strongly expressed by ne urons in these regions. Sodium channel mRNA III exhibited low-to-moder ate expression in some neurons of the pyramidal layer of the hippocamp us and granular layer of the dentate gyrus, and was not detectable in others. In the cerebellum sodium channel mRNA I was moderately express ed in some Purkinje cells, weakly expressed in scattered cells in the molecular layer and negligibly expressed in the granular layer. Sodium channel mRNA II was strongly expressed in Purkinje and granule cells, and was moderately expressed in some cells in the molecular layer. So dium channel mRNA III was generally not detectable in the cerebellum. In the spinal cord, motor neurons and scattered neurons throughout the gray matter exhibited moderate-to-strong expression of both sodium ch annel mRNA I and II. A population of cells in the spinal zone of Lissa uer showed heavy expression of mRNA II, but not mRNA I. Sodium channel mRNA III was not detectable in spinal cord neurons. These observation s are consistent with a general regional distribution of sodium channe l message isoforms, with mRNA II being preferentially expressed in ros tral regions of the CNS and mRNA I in caudal regions. However, the res ults also indicate that different cell types, within a given region, d isplay different patterns of sodium channel mRNA expression. Moreover, these data suggest that individual neurons may express multiple forms of sodium channel mRNA.