Projections of the basilar pontine nuclei and nucleus reticularis tegmenti pontis to the cerebellar nuclei of the rat.

This study showed the precise projection pattern of the basilar pontine nuclei (BPN) and the nucleus reticularis tegmenti pontis (NRTP) to the cerebellar nuclei (CN), as well as the different anatomic features of BPN and NRTP projections. The staining of BPN or NRTP with biotinylated dextran labeled projection fibers to complementary topographic areas in the CN. In fact, BPN principally project to a rostrocaudally oriented column of the nucleus lateralis (NL), which at the midcentral level shifts to the lateroventral part of the nucleus, as well as to the caudolateral part of the nucleus interpositus posterioris. The NRTP projects to a rostrocaudal column of the NL, which at the midcentral level shifts medially, as well as to the nucleus interpositalis and to the caudal part of the nucleus medialis. BPN axons in the CN usually branch into short collaterals of simple morphology that involve small terminal areas, whereas NRTP axons branch into longer collaterals of complex morphology involving terminal areas of different sizes. Each site of injection is at the origin of a set of terminal areas in the CN. The set of projections from different BPN or NRTP areas were partially, but never completely, overlapping. Thus, the set of terminal areas in the CN was specific for each area of both BPN and NRTP. Injection of tetramethyl-rhodamine-dextran-amine into the CN stained cell bodies of BPN and NRTP with different repartition on the two sides. The study showed that CN are innervated by the contralateral BPN and not very much by the ipsilateral BPN, whereas they are innervated by NRTP bilaterally, even if with a contralateral prevalence. In conclusion, this study supports the hypothesis that both BPN and NRTP are concerned in the central program for skilled movements, even if they are probably involved in different functional roles. Copyright 2002 Wiley-Liss, Inc.