Anatomical interconnections of the pedunculopontine tegmental nucleus and the nucleus prepositus hypoglossi in the cat.

The Pedunculopontine tegmental nucleus (PPT) is a mesopontine structure containing predominantly cholinergic neurons, and physiological data indicate its neurons transfer eye-movement gated ponto-geniculo-occipital (PGO) waves to thalamus during the rapid eye movement phase of sleep. The present study, using anterograde and retrograde tracing of wheat germ agglutinin-conjugated horseradish peroxidase, found that the medullary nucleus Prepositus hypoglossi (PH), whose neurons are known to have eye-movement-related information, projects densely to PPT, and PPT has reciprocal projections to PH. The PH-PPT projection has some topographic organization, with rostral PH to rostral PPT and caudal PH to caudal PPT projections dominating. The PH-PPT projection may furnish the anatomical substrate for input of eye movement-related information into the rostral PGO wave system.