Developmental and regional expression of sodium channel isoform NaCh6 in the rat central nervous system

The sodium channel isoform NaCh6 is abundant in the adult rat brain and is expressed in both neurons and glia (Schaller et al. [1995] J. Neurosci. 15:3231-3242; Krzemien et al. [2000] J. Comp. Neurol. 20:70-83). With reverse transcriptase-polymerase chain reaction (RT-PCR), in situ hybridization, and immunolabeling, NaCh6 expression was investigated in the developing rat brain and spinal cord [embryonic day 15 (E15) through postnatal day 28 (P28)]. The relative abundance of the four major central nervous system NaCh subtypes was quantitated with RT-PCR. In all regions that were investigated (olfactory bulb, cortex, hippocampus, cerebellum, and spinal cord), each subtype had a unique pattern of expression. NaCh6 mRNA and protein were not detected in either brain or spinal cord at E15 and E18 by in situ hybridization and immunohistochemistry. Neurons in the hippocampus, cortex, and olfactory bulb began to express NaCh6 mRNA and protein shortly after birth. The mRNA signal peaked at P7-P14, and protein expression increased as development proceeded. NaCh6 mRNA was detected at P1 in the cerebellum, and a nonuniform distribution of NaCh6 immunoreactivity in both Purkinje cells and granule cells was observed by P7-P14. NaCh6 protein was expressed in granule cells as soon as they left the proliferative phase and began to migrate. Both NaCh6 mRNA and protein were detected in the spinal cord at P1 and were expressed clearly at P7 in motor neurons. The time course of appearance of NaCh6 in postnatal development is consistent with the development of neurologic symptoms in med and jolting mice, which have mutations in the mouse ortholog of NaCh6.