Collateral projections of neurons of the rat globus pallidus to the striatum and substantia nigra.

Double retrograde fluorescent tracing techniques were used to evaluate the possibility that ascending and descending projections from the globus pallidus arise from divergent axon collaterals. Appropriately placed injections of different tracers (True Blue, Nuclear Yellow) into the substantia nigra and the striatum resulted in the double labelling of neurons in the globus pallidus. Conversely, simultaneous injection of two different sites within the striatum did not produce significant double labelling of globus pallidus neurons. These results indicate that at least a portion of the neurons of the globus pallidus project to both the striatum and substantia nigra, and that individual pallidal neurons do not have widespread projections to the striatum.