Following sciatic nerve transection, the expression of sodium channel III (alpha-III) transcripts increases and SNS (alpha-SNS) transcripts decreases in small (< 25 microns diameter) dorsal root ganglion (DRG) neurons, which may reflect an interruption of retrograde transport of peripherally derived factor(s) involved in the regulation of these channels. To test the hypothesis that the neurotrophin nerve growth factor (NGF), which is abundant in peripheral targets, participates in the modulation of the expression of these sodium channel transcripts, we examined the hybridization signal of alpha-SNS and alpha-III mRNAs in small DRG neurons from adult rats that had been dissociated and maintained for 7 days in the absence or presence of exogenous NGF. Neurons maintained in control (no added NGF) cultures showed changes in alpha-III and alpha-SNS hybridization signal similar to those induced by axotomy, with increased alpha-III mRNA levels and decreased alpha-SNS mRNA levels, compared with those observed in small DRG neurons at 1 day in vitro. The addition of exogenous NGF to DRG cultures attenuated these alterations in transcript levels, decreasing alpha-III mRNA and increasing alpha-SNS mRNA expression. These results suggest that NGF participates in the regulation of membrane excitability in small DRG neurons by pathways that include opposing effects on different sodium channel genes.

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B104 neuroblastoma cells are excitable, but the ion channels underlying electrogenesis in these cells have not been identified. RT-PCR, restriction enzyme analysis and in situ hybridization were used to study sodium channel mRNAs in B104 cells. High levels of sodium channel ¢x-subunit mRNAs Ili, NaG and Na6 and [~l-subunit mRNA were detected by RT-PCR in BIIM cells. Low levels of types I and II cx-subunit mRNAs were also present. In situ hybridization with subtype-specific riboprobes detected sodium channel ct-subunit mRNAs III, NaG and Na6 and I]l-subunit mRNA in B104 cells; analysis of the percentage of B104 cells expressing each ¢x-subunit mRNA subtype suggests that some cells express the mRNAs for several ~-subunits. Key words:In situ hybridization; Neuroblastoma; mRNA; RT-PCR; Sodium channel examined whether BI04 cells express the mRNA for the 131-subunit of sodium channels (Na[31). In this paper, we confirm the work of Baines et al. [2] that B104 ceils express high levels of sodium channel III mRNA, and extend this work to demonstrate that sodium channel c~-subunits NaG and Na6 and Nal31 are also expressed at high levels in these cells. Material and methods CultureStocks of B104 cells [1] were obtained from D. Schubert (Salk Institute, San Diego) and grown in Dulbecco's modified Eagle's medium containing 20% fetal calf serum and penicillin/streptomycin (500 U/ml) on Coming 75 cm 2 plastic flasks or on 12 mm circular glass coverslips. Cells were maintained at 37°C in a 5% COJ95% air atmosphere and fed every fourth day.