Input-output connections of the ?hindlimb? region of the inferior olive in cats

Abstract

The aim of the present study was to establish whether gracile afferents to the inferior olive are topographically organized and whether such inputs coincide with the location of cells that output to the hindlimb C1 zone in the cerebellar posterior lobe. Small injections (n=15) of the anterograde tracers Fluoro-Ruby or biotinylated dextran amine were made into gracile, resulting in anterograde labelling often distributed in partially separate, rostrocaudally directed columns within the lateral half of the contralateral rostral dorsal accessory olive (rDAO). In 12 cases, anterograde labelling was also located within the caudolateral medial accessory olive. Evidence for a topographical organization was obtained, suggesting that medial gracile targets only the most lateral part of rDAO, whereas lateral gracile also targets more medial parts. Gracile injections centred dorsally also resulted in more extensive terminal fields in rDAO than similar sized injections centred ventrally which may relate to the representation of the distal hindlimb in dorsal gracile (e.g., Millar and Basbaum, 1975). Injections of retrograde tracer (green beads) into the C1 zone in the ipsilateral caudal paramedian lobule (7 cases), resulted in retrograde cell labelling in the middle one-third of contralateral DAO in two columns that fused caudally. The proportion of labelled cells that overlapped with anterograde labelled terminals was related to the dorsoventral locus of the gracile injection site: gracile injections centred dorsally produced the largest degree of overlap and therefore, potentially, the greatest functional convergence. In summary, the results suggest that a topographical organization is present within the gracilo-olivo-cerebellar projection which is discussed in relation to the functional organization of the olivocerebellar system.

A novel site of synaptic relay for climbing fibre pathways relaying signals from the motor cortex to the cerebellar cortical C1 zone

“…The retrograde tracer was used to mark the location within the inferior olive where neurones are the source of climbing fibres to the cortical zone under study. As in previous studies (see for example Apps, 1998) the beads produced distinctive granular labelling confined to cell bodies. This cell labelling could be readily differentiated from any axonal or terminal labelling arising from injections of anterograde tracer in the same experiments (see Fig.…”

Precise matching of olivo‐cortical divergence and cortico‐nuclear convergence between somatotopically corresponding areas in the medial C1 and medial C3 zones of the paravermal cerebellum

“…1(D), the population of cells retrogradely labelled from an individual cortical injection typically defined a continuous region in rDAO (usually a rostrocaudally extended column, cf. Apps 1998). To facilitate comparison between cell distributions, the retrograde labelling in individual experiments was projected onto horizontal outlines of rDAO (see Fig.…”

The Entire Trajectories of Single Olivocerebellar Axons in the Cerebellar Cortex and their Contribution to Cerebellar Compartmentalization

“…The activity of adjacent olivary neurons is functionally correlated because of the electrotonic coupling among olivary neurons (Llinás et al, 1974) and because of focal afferent projection patterns to the inferior olive (Apps, 1998;McCurdy et al, 1998). To determine the translation of such correlated olivary activities into patterns of activity across the cerebellar cortex, it is necessary to know the relationship of axonal projection patterns of adjacent olivary neurons.…”