Axon collaterals projection from nucleus reticularis tegmenti pontis onto the cerebellar paramedian lobule in the rabbit: a fluorescent double labelling study.

Double labelling method with retrograde transport of fluorescent tracers (Fast Blue; FB and Diamidino Yellow; DY) was employed in the rabbit to investigate whether neurones of the nucleus reticularis tegmenti pontis (NRTP) give off axon collaterals to the cerebellar paramedian lobule (PML) of both sides. Following injections to various regions of the homotopic or heterotopic sublobules of the left (FB) and right (DY) PML cortex, distribution of double labelled neurones within NRTP was analyzed. NRTP of the rabbit consists of a medial principal part (the nucleus papillioformis: PLF) and smaller lateral part (the processus tegmentosus lateralis: PTL). Within PLF three subdivisions are to be distinguished: the dorsomedial part -- zone A, the main part -- zone B and the ventrolateral part -- zone C. The present study in the rabbit indicated collateral projections from neurones in some NRTP regions to the both PML. The cells of origin of these projections were located prominently through the rostrocaudal extent of zone B. Projections from zone A were sparse and those from zone C were absent. Moreover, a weak projection arose mainly from the caudal aspect of PTL. It is concluded that the rostral (e and f) and middle (c and d) sublobules are the main targets for the NRTP-PML branching projections.