DIFFERENTIAL UP-REGULATION OF SODIUM-CHANNEL ALPHA-SUBUNIT AND BETA-1-SUBUNIT MESSENGER-RNAS IN CULTURED EMBRYONIC DRG NEURONS FOLLOWING EXPOSURE TO NGF

Although the pattern of expression of various sodium channel alpha- an d beta-subunits changes as development proceeds, the mechanisms that c ontrol the expression of these subunits are not yet understood. To stu dy the role of nerve growth factor (NGF) in modulating the expression of sodium channel subunits, we used in situ hybridization cytochemistr y to examine the distribution of sodium channel alpha- and beta 1-subu nit mRNAs in embryonic day 16 (E16) dorsal root ganglia (DRG) neurons cultured in the absence or presence of NGF. At 4 days in vitro in the absence of NGF, sodium channel alpha-subunit II mRNA was expressed at low-to-moderate levels in DRG neurons, but the transcripts for sodium channel alpha-subunits I, III and NaG and beta 1-subunit were not dete ctable. In the presence of NGF, DRG neurons expressed low-to-moderate levels of sodium channel alpha-I, high levels of alpha-II and low leve ls of alpha-III; NaG mRNA was not detectable. Sodium channel beta 1 mR NA was up-regulated and was expressed at high levels in DRG neurons in NGF-containing media. These observations demonstrate that the NGF exe rts a differential up-regulation of sodium channel alpha- and beta-sub unit mRNAs in DRG neurons derived from E16 embryos.