Time course and subcellular distribution of the radioactivity in a synaptic terminal after supplying the perikaryon with labelled glutamic acid

Summary The cell bodies of the preganglionic neurons of the chick ciliary ganglion were supplied with ³H-glutamic acid by intracerebral injection. The ciliary ganglia were studied with light and E.M. radioautography at 3, 18, 24 hours, 2, 6 and 16 days after injection. The reaction in the ganglion was intense over the preganglionic structures but very weak over the ganglionic cell bodies. The reaction increased in intensity from the myelinated region toward the ending; within the axon, the radioactivity was rather peripheral during early stages and more evenly distributed from the second day onward. The ending showed two peaks of radioactivity, at 18 hours and at 6 days; these peaks are interpreted as the accumulation of material which arrived in two phases; the first with an average velocity greater than 80 mm/ day and the second with a velocity of 2–5 mm/day. Within the nerve ending, the material transported in the fast phase was associated preferentially with the axoplasm rich in synaptic vesicles, close to the synaptic region, whereas the material transported in the slow phase was associated rather with mitochondria and the axoplasm devoid of synaptic vesicles that lies away from the synaptic surface. In contrast to what is observed with lysine, the density of the reaction on the preterminal axons was much lower than that on the endings. It is suggested that a protein rich in glutamyl residues with a rather long mean-life is transported to the ending in the fast phase.On leave from the Catholic University, Santiago, Chile.Supported by Institut National de la Santé et de la Recherche Médicale, France and IBRO.Acknowledgement. I express my sincere thanks to Dr. B. Droz for his hospitality and for helpful discussions throughout the work.