NA-1 SUBUNIT MESSENGER-RNA EXPRESSION IN DEVELOPING RAT CENTRAL-NERVOUS-SYSTEM( CHANNEL BETA)

The sodium channel beta 1 subunit (Na beta 1) is a component of the ra t brain voltage-dependent sodium channel. We have used nonradioactive in situ hybridization cytochemical techniques to demonstrate that tran script levels of Na beta 1 are differentially upregulated during postn atal development of several CNS regions, with selective labeling of sp ecific neuronal populations. In the hippocampus, labeling of the pyram idal cell layer (particularly in the CA3 region) and dentate granule c ells was initially observed at postnatal day 2 (P2) and P10, respectiv ely, and became progressively more intense with maturation. Labeled ce lls were first observed in the hilus at P10. In the developing cerebel lum, transient labeling was observed in the external granule cell laye r beginning at P1 while label increased in the internal granule cell l ayer up to P21. Purkinje cells showed significant label beginning at P 4 and increasing up to P21. Weak signal was seen in neurons of deep nu clei at P1 and increased up to P21. Na beta 1 labeling in the spinal c ord was first observed in the ventral horn at P2, and the intensity of labeling in these large motoneurons gradually increased. In addition, there was a ventral-dorsal gradient in this region, with label appear ing subsequently in neurons of Rexed laminae IX, VII and VIII, and in the dorsal horn (Rexed laminae I-VI). In these regions, the labeling r eached a plateau within the first 2-3 weeks after birth and persisted into the adult rat. The time course and regional heterogeneity of Na b eta 1 expression are consistent with the hypothesis that the expressio n of mature Na+ channels, including Na beta 1, contributes to the deve lopment of circuitry that supports complex patterns of electrogenesis.