Electrophysiological demonstration of an excitatory subthalamonigral pathway in the rat

The subthalamonigral projection was studied with extracellular techniques in the rat. Orthodromic and antidromic stimulations of this pathway were performed in different sets of experiments in order to exclude the possible activation of passing fibers. A majority of the recorded cells in the subthalamic nucleus (STN) were antidromically activated by nigral stimulation. It was furthermore shown that the subthalamofugal fibers are excitatory to cells located in the pars compacta as well as in the pars reticulata of the substantia nigra. The possible existence of another descending STN pathway is also discussed.