Anatomy of respiratory rhythmic systems in brain stem and cerebellum of the carp.

The afferent and efferent connections of two respiratory rhythmic loci in the dorsal mesencephalic tegmentum were studied by retrograde and anterograde transport of horseradish peroxidase. The injection areas were determined with extracellular activity recording using HRP filled glass micropipettes, and then followed by electrical stimulation and subsequent iontophoretic HRP delivery. One area in the nucleus of the posterior commissure was found to be optic related respiratory in nature and possessed afferents from optic tectum, pretectal nuclei, preoptic nucleus and the bulbar reticular formation. An extensive set of efferents is present to the torus longitudinalis, nucleus rotundus, corpus cerebelli and the various levels of the reticular formation. The second respiratory rhythmic area was localized in the vicinity of the oculomotor nuclei. This area receives afferent information from corpus cerebelli, vestibular nucleus and reticular formation, and has efferent connections to corpus cerebelli, preoptic nucleus and a major projection to the various parts of the reticular formation. Stimulation of both areas resulted in respiratory movements of the lower jaw and the opercula. Several injections in the corpus cerebelli resulted in retrograde labeling in the nucleus of the posterior commissure, which suggests the involvement of cerebellar circuits in optic related respiratory reflexes.