A multiwire proportional chamber study of axoplasmic transport in frog sciatic nerve involving interruption of somatic supply.

A multiwire proportional chamber was used to detect axoplasmic transport in isolated spinal-cord-sciatic nerve preparations in which the nerve cell bodies were exposed to L-[35S]methionine. The detector collected radiation from a series of 6-mm segments of sciatic nerve for consecutive periods of 30 min for the duration of experiments lasting 16--23 h. The radioactivity of each segment showed an initial plateau at background level followed by a rise which was approximately linear through time. Plots of the time at which the rise in radioactivity took place against the position of each segment of the nerve yielded transport velocities for the most rapidly moving label; at room temperature (21--23 degrees C) these were typically 150 mm/24 h. Approximately 1.5 h after the addition of 5 mM colchicine to the bathing solution the slope of the radioactivity-time curve decreased for all segments of the nerve; this indicated that the method satisfactorily detected impaired axoplasmic transport. If the sciatic nerve were severed at the proximal end of the preparation at about 9 h after the radioactive front had been established, the slope of the radioactivity-time curve for each nerve segment subsequently changed abruptly. Plots of the time at which the transition occurred against position in the nerve yielded transport velocities which did not differ statistically from those of the radioactive front. This transition time is thought to indicate the time at which the fastest labelled material left each segment of nerve. In some experiments, an additional change in slope occurred, possibly indicating the departure of the slowest material from each segment.