The axoplasmic transport of catecholamines in sympathetic neurons was examined with the formaldehyde fluorescence method for biogenic amines. The whole course of canine colonic nerves, from the caudal mesenteric ganglion to the terminals in the colonic wall, as well as the sciatic nerve was used. Besides normal animals, various experimental conditions caused by axotomy, ligation, reserpinization, and their combinations were studied. The proximal cut end of the colonic nerve was also observed electron microscopically in comparison with the normal nerve.
1. Most nerve cells in normal caudal mesenteric ganglia possessed catecholamine specific fluorescence. Some fluorescent nerve fibers passed by them while others terminated on them. Every part of the colonic nerve weakly fluoresced. In the colonic wall the fluorescent nerve fibers entered the submucosal nerve plexus.
2. After administration of reserpine the entire length of the colonic nerve became non-fluorescent in 6hrs. In 24hrs the ganglion cells first became weakly fluorescent, in 48hrs the fluorescence was somewhat intensified and in 96hrs it returned to normal and a weak fluorescence reappeared in the terminals in the colonic wall.
3. After section at the branching site of the colonic nerve and at the root of all other nerves arising from the caudal mesenteric ganglion, fluorescent nerve cells in the ganglion decreased in number with time, whereas the fluorescent materials accumulated in the proximal cut end reaching a maximum 7 days after section and then decreasing. The fluorescence in the distal cut end and in the terminals in the colonic wall disappeared after 4 days.
4. One to 2 days after double ligations of the colonic nerve, the fluorescent material accumulated more markedly to the proximal end rather than distal end of the nerve segment between the ligations.
5. When reserpine is given after axotomy the fluorescence in the proximal cut end of the nerve almost completely disappeared in 24hrs. When the nerve is sectioned after pretreatment with reserpine, the fluorescence in the proximal cut end disappeared as late as 5 days after axotomy.
6. Fluorescent nerve fibers in the sciatic nerve lost their fluorescence 7 days after resection of the lumbar sympathetic trunk.
7. In the proximal cut end of the colonic nerve, a number of large granular vesicles with a diameter of 1, 100-1, 500Å were observed electron microscopically. Even with the use of KMnO₄ fixation small granular vesicles (500Å diameter) were never detected. The large granular vesicles were also found sparsely in normal axons of the colonic nerve.
From these findings we conclude that the fluorescent materials, representing catecholamines, are synthesized within the cell bodies of the sympathetic gangilon cells, transported distally towards the terminals, by means of an axoplasmic flow. Electron microscopical findings suggest that at least most of the catecholamines may be contained in large granular vesicles to be transported to the periphery. The relation of this type of vesicles to the small granular vesicles in the nerve terminals is unknown.