Nerve Growth Factor Stimulates Phospholipid Methylation in Target Ganglionic Neurons Independently of the Cyclic AMP and Sodium Pump Responses

Suspensions of neurons prepared from embryonic day 12 (E12) chick sympathetic ganglia were incubated with [methyl‐ 3 H]methionine in the absence of nerve growth factor (NGF). Presentation of the factor for different periods of time resulted in an approximate threefold stimulation of radioactivity incorporated into total phospholipid, followed by a rapid decline thereafter. Both the magnitude and the time of the response were dependent on the NGF concentration used. Also examined were possible relationships of phospholipid methylation to two other short‐latency responses to NGF, i.e., control of the Na + ,K + ‐pump and elevation of cyclic AMP content. Incubation of E12 sympathetic neurons with known transmethylase inhibitors (shown to be active in the present system) failed to prevent reactivation of the Na + ,K + ‐pump in response to NGF administration. E16 sympathetic neurons and E15 sensory neurons, which do not depend on exogenous NGF for control of their Na + ,K + ‐pump, still show a stimulation of phospholipid methylation when challenged with the factor. Blockage of the pump with ouabain also fails to prevent a methylation response. Thus, the pump and methylation responses to NGF occur independently of each other. Intact E8 chick dorsal root ganglia, but not E12 sympathetic ganglia, display a rapid and transient rise in their cyclic AMP content when presented with NGF. At a concentration of 10 biological units/ml, NGF elicits a peak of phospholipid methylation at 4 min, and a peak of cyclic AMP at 10 min. Methylation inhibitors prevent the methylation response, but not that of cyclic AMP. Dibutyryl cyclic AMP, which is able to cause a cyclic AMP elevation similar to NGF, failed to produce any stimulation of phospholipid methylation. These findings are discussed in terms of the role of short‐latency responses in the mode of action of NGF.