[ 3H]acetylcholine synthesis in cultured ciliary ganglion neurons: Effects of myotube membranes

Avian ciliary ganglion neurons in cell culture were examined for the capacity to synthesize acetylcholine (A Ch) from the exogenously supplied precursor, choline. Relevant kinetic parameters of the A Ch synthetic system in cultured neurons were found to be virtually the same as those of the ganglionic terminals in the intact iris. Neurons were cultured in the presence of and allowed to innervate pectoral muscle; this results in an enhanced capacity for A Ch synthesis. In particular, the ability to increase A Ch synthesis upon demand after stimulation is affected by interaction with the target. This effect is shown to be an acceleration of the maturation of the cultured neurons. Lysed and washed membrane remnants of the muscle target were able to duplicate, in part, this effect of live target tissue on neuronal transmitter metabolism. Culture medium conditioned by muscle, and by the membrane remnants of muscle, was without significant effect. Thus, substances secreted into the medium do not play a major role in this interaction. Neurons cultured with either muscle or muscle membrane remnants formed large, elongate structures on the target membrane surface. These were not seen in the absence of the target at the times examined. This morphological difference in terminal-like structures may parallel the developmental increases in size and vesicular content of ciliary ganglion nerve terminals in the chick iris, and may relate to the increased A Ch synthetic activity. The results suggest that direct contact with an appropriate target membrane has a profound, retrograde influence upon neuronal metabolic and morphological maturation.