The organization of nucleus tegmenti pedunculopontinus neurons projecting to basal ganglia and thalamus: a retrograde fluorescent double labeling study in the rat.

The organization of nucleus tegmenti pedunculopontinus (PPN) projections to the basal ganglia and thalamus was studied in the rat by using retrograde transport of fluorescent dyes. Fast blue was injected into the substantia nigra (SN) while Nuclear yellow was delivered to one of the following nuclei: globus pallidus (GP), entopeduncular nucleus, subthalamic nucleus (STN) or parafascicular nucleus of the thalamus. Retrogradely labeled cells were observed throughout the PPN without topographical arrangement. The cells labeled from the SN outnumbered those labeled from other structures. In all cases the majority of cells were single labeled and only a few cells double labeled from SN-GP or SN-STN were found. Labeled cells were either fusiform or multipolar in shape. These data suggest that distinct PPN cells project to their basal ganglia and thalamic targets without a prominent branched organization.