Solubilization of a membrane factor that stimulates levels of substance P and choline acetyltransferase in sympathetic neurons.

The choice of which neurotransmitters will be produced by a developing neuron is influenced by the microenvironment of the neuron. In this study we show that neuronal contact with membrane-associated molecules promotes expression of peptidergic and cholinergic traits. Treatment of cultured neonatal rat sympathetic neurons with plasma membranes derived from adult rat spinal cord or sympathetic ganglia induced expression of the peptide transmitter substance P and increased levels of the cholinergic biosynthetic enzyme choline acetyltransferase. The transmitter-stimulating activity could be solubilized from spinal cord membranes by the detergent octyl glucoside but not by Triton X-100. The choline acetyltransferase- and substance P-stimulating activity also could be extracted from spinal cord membranes by 4 M sodium chloride, suggesting that the active material is membrane associated rather than an intrinsic structural membrane molecule. Trypsin or heat treatment of the extract destroyed the transmitter-stimulating activity, indicating that the factor contains a protein. Activity also was destroyed by hyaluronidase treatment, suggesting that the active material may contain a glycosaminoglycan. The choline acetyltransferase-stimulating activity in the 4 M NaCl extract was eluted in a single peak from a calibrated Sephadex G-75 column with a retention time slightly less than that of a 25-kDa standard. NaDodSO4/polyacrylamide gel electrophoresis of the active peak revealed a predominant band at 29 kDa. Thus, contact-mediated stimulation of substance P and choline acetyltransferase activity in sympathetic neurons results from neuronal exposure to a 29-kDa membrane-associated factor.