Projections from the nucleus parafascicularis prerubralis to medullary raphe nuclei and inferior olive in the rat: a horseradish peroxidase and autoradiography study.

Horseradish peroxidase gel implants into either the nucleus raphe magnus (NRM) or inferior olive (IO) led to large numbers of retrogradely labeled cells in the prerubral subthalamic region in a cell group that surrounds the fasciculus retroflexus, which we suggest should be referred to as the nucleus parafascicularis prerubralis (nPfPr) to avoid the confusion of previous terminology. Autoradiographic studies, following injections of tritiated leucine into the nPfPr, confirmed projections to both medullary raphe nuclei (MRN) and IO. This common prerubral projection to IO, a well-established precerebellar nucleus, and MRN, again raises the question of whether the latter are involved in brainstem-mediated reflexes in addition to their well documented role in analgesic mechanisms.