Spatial arrangement of the interpositorubral projection in the rabbit. A retrograde HRP study

The objective of this investigation was to analyse the organization of rubral afferents from the cerebellar interpositus nuclear complex (NI) in the rabbit. Free HRP was employed as a retrograde tracer to identify the distribution patterns of labeled cells in the anterior and posterior interpositus nuclei. The interpositus projections distribute throughout nearly the entire contralateral red nucleus (RN) except for its rostralmost parvocellular region (RN-PA) which does not correspond to the usually distinguished parvocellular subdivision of the red nucleus (RN-P). The central and lateral regions of the posterior interpositus nucleus (NIP) project (nearly exclusively) to the medial region of the RN. The lateral region of the anterior interpositus nucleus (NIA) sends projections to both the lateral and medial regions of the caudal three-quarters of the RN. Thus, the lateral region of the RN appears to be under nearly exclusive control of NIA. The rostral one quarter of the RN receives cerebellar afferents from the NIP only and caudal pole of RN from the NIA exclusively. Comparison of labelling patterns indicates absence of topogrophic differentiation of projections from the NIP, whereas dorsoventral topography in the NIA can correlate to the rostrocaudal and mediolateral arrangement of the RN. Collectively, interpositorubral projections in the rabbit are similar to those in other species only in basic features.