Projections of striatopallidal structures to the pedunculopontine nucleus of the tegmentum of the midbrain in dogs.

A method based on retrograde axonal transport of horseradish peroxidase was used to study the striatopallidal afferent projections of the pendunculopontine nucleus of the midbrain (PPN) in dogs. The major source of these projections was found to be the pallidum, as both the compact and diffuse zones of this nucleus received projections from all of its structures: the entopeduncular nucleus, the globus pallidus, and the ventral pallidum. The striatal complex, specifically the nucleus accumbens, showed only occasional labeled neurons, projecting exclusively to the compact part of the PPN. Since the distribution of projection fibers arising from the functionally diverse territories of the striatopallidum and directed to individual structural subdivisions of the PPN showed no topical elements, identification of functionally specific (motor and limbic) areas of the PPN was not possible on the basis of the present analysis.