Subpallidal projections to the mesencephalic locomotor region investigated with a combination of behavioral and electrophysiological recording techniques.

Locomotor activity was increased as a function of current intensity in a series of rats with chronic stimulating electrodes in the tegmental pedunculopontine nucleus. Single pulse stimulation of these same mesencephalic locomotor region (MLR) sites antidromically activated more than one-quarter of the neurons sampled in the subpallidal area. In a second series of rats locomotor activity was increased by chronic stimulation of the zona incerta as well as by chronic stimulation of MLR. Approximately one-quarter of subpallidal neurons sampled were antidromically activated by single pulse stimulation of zona incerta and/or MLR. Thirty-one of the subpallidal neurons were antidromically activated by stimulation of both zona incerta and MLR and, according to the results of the reciprocal collision test, about half this number had branching projections to the zona incerta and MLR. These observations provide additional evidence that subpallidal-MLR neurons are associated with locomotion.