Direction and specificity of the axonal and transcellular transport of nucleosides.

The axoplasmic transport of nucleosides or their derivatives has been examined autoradiographically in avian and mammalian brains. Following injections of [3H]-adenosine or [3H]uridine intravitreally in chicks and rats or into the thalamus or neocortex of rats, three findings emerge: (1) axoplasmic transport of these materials occurs both in the anterograde and retrograde direction in birds and mammals; (2) anterograde transport in the axons of injected cells results in considerable cellular labeling in the region in which the axons terminate. This labeling is not exclusively transsynaptic, but probably results from some less specific, trancellular transport, since glial cells at the terminal site and along the path of the axons also become labeled; (3) injection of [3H]uridine in the chick optic and rat thalamocortical systems results in a pattern of labeling which differs considerably from that seen after injection of [3H]adenosine. After [3H]adenosine injections in the chick eye or rat thalamus, retrograde cell labeling is far more obvious than anterograde, transcellular labeling; after injections of [3H]uridine, anterograde, transcellular labeling is more intense than retrograde cell labeling.