Retrograde Labeling of Dorsal Root Ganglion Neurons after Injection of Tritiated Amino Acids in the Spinal Cord of Rats and Cats

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Abstract
The present experimetns are based upon evidence that neurons may selectively take up at their terminals, and retrogradely transport, the same chemical they use as a neurotransmitter or its analogues. In an attempt to identify dorsal root ganglion (DRG) neurons that use glutamic acid as a neurotransmitter, [3H]D-aspartate ([3H]D-Asp) was chosen as a marker, since it is a metabolicallly inert amino acid known to be taken up by the same affinity mechanism as L-aspartate and L-glutamate. The results in cases of injection with [3H]D-Asp may be interpreted as consistent with the idea that a fraction of DRG neurons use glutamate and/or aspartate as neurotransmitter(s). The results in animals administered [3H]GABA, though not consistent with the retrograde transport of selected transmitters, may underlie the internalization of the receptor-ligand complex by synaptic terminals, and the subsequent retrograde transport of it. Through this mechanism, selective retrograde transport may play a role in the regulation of neuronal activity.

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