Morphology of single olivocerebellar axons labeled with biotinylated dextran amine in the rat

Abstract

The morphology of olivocerebellar (OC) axons originating from the inferior olive (IO) was investigated in the rat by reconstructing the entire trajectories of single axons that had been labeled with biotinylated dextran amine. Virtually all of the OC axons entered the cerebellum through the inferior cerebellar peduncle (ICP) contralateral to the IO, with a few exceptions. Although most OC projection was contralateral, a few axons projected bilaterally by crossing the midline within the cerebellum. Collaterals of OC axons could be classified into thick branches and thin collaterals. Thick branches of each OC axon (6.1 ± 3.7/OC axon, mean ± SD for n = 16 axons) terminated as climbing fibers (CFs) on single Purkinje cells (PCs) in a one‐to‐one relationship. Besides terminal arborization around PC thick dendrites, CFs had terminals that surrounded a PC soma, fine branchlets that extended transversely in the molecular layer, and thin retrograde collaterals that re‐entered the PC and granular layers. Innervation of a single PC by two CFs originating from the same axon was seen, although infrequently. Concerning thin collaterals, about half of the OC axons had one or only a few collaterals terminating in the white matter of the ICP, most had 1 to 6 collaterals terminating in a single cerebellar nucleus, and all had 3 to 16 collaterals that terminated mainly in the granular layer, but occasionally in the cerebellar white matter and the PC layer. Some swellings of thin collaterals touched somata of presumed Golgi cells and PCs. No OC axons terminated solely in the ICP, cerebellar nucleus or granular layer without giving rise to CFs. J. Comp. Neurol. 414:131–148, 1999. © 1999 Wiley‐Liss, Inc.

Quantitative analysis of granule cell axons and climbing fiber afferents in the turtle cerebellar cortex

“…7). Compared with the features of BDA-labeled rat climbing fibers (Sugihara et al 1999), our observation in turtle for a paucity of labeled climbing fiber varicosities, fine collateral tendrils, and the limited radial distribution in the molecular layer requires us to seriously consider the possibility that our BDA labeling paradigm did not completely label climbing fiber terminal arbors. The consistency of labeling of small diameter parallel fibers was largely the result of orthograde transport from the granule cell body.…”

“…In rats, climbing fiber arbors are localized to the inner two-thirds or complete thickness of the molecular layer (Palay and Chan-Palay 1974;Sugihara et al 1999). Occasional varicosities on the secondary branches of climbing fibers contact Purkinje cell dendrites, but it is mainly small delicate collaterals of these secondary and tertiary branches that contact Purkinje cell dendritic appendages that constitute the bulk of climbing fiber synaptic contacts with Purkinje cells (Palay and Chan-Palay 1974;Sugihara et al 1999). Biotylinated labeled rat climbing fiber varicosities were mostly 1.2-1.6 m in diameter and each climbing fiber had about 250 swellings (Sugihara et al 1999).…”

“…Occasional varicosities on the secondary branches of climbing fibers contact Purkinje cell dendrites, but it is mainly small delicate collaterals of these secondary and tertiary branches that contact Purkinje cell dendritic appendages that constitute the bulk of climbing fiber synaptic contacts with Purkinje cells (Palay and Chan-Palay 1974;Sugihara et al 1999). Biotylinated labeled rat climbing fiber varicosities were mostly 1.2-1.6 m in diameter and each climbing fiber had about 250 swellings (Sugihara et al 1999). Similarly, BDA-labeled turtle climbing fibers were more restricted in their radial distribution in the molecular layer to the inner 15% (medially) and 21% (laterally), and slightly larger (1.83 m) varicosities were fewer in number and present only on some climbing fibers (Fig.…”

“…For example, granule cell parallel fiber lengths (Pichitpornchai et al 1994;Brand et al 1976), spacing between parallel fiber en passant synaptic contacts (Pichitpornchai et al 1994;Shepherd and Raastad 2003;Shepherd et al 2002), ascending axon en passant contacts (Gundappa-Sulur et al 1999), synaptic morphology (Pichitpornchai et al 1994;Napper and Harvey 1988a;Napper and Harvey 1988b), synaptic strength (Barbour 1993), and numerical ratios between neurons (Lange 1982) have all been quantitatively analyzed. Olivocerebellar fiber afferents have also been extensively studied for their powerful synaptic activation of Purkinje cells and highly organized topography in the cortex (Sugihara et al 1999(Sugihara et al , 2001. Furthermore, morphometric and electrophysiological analysis has largely focused on the highly foliated mammalian cerebellar cortex, thereby limiting the opportunity to make observations of widespread or even spatially contiguous cortical areas.…”

Precerebellar Cell Groups in the Hindbrain of the Mouse Defined by Retrograde Tracing and Correlated with Cumulative Wnt1-Cre Genetic Labeling

“…The inferior olivary nucleus (IO) is the major source of climbing fibers projecting to the Purkinje cells of the cerebellum [27,28]. The climbing fibers of the individual subdivisions of the IO are topographically organized into a number of sagittally oriented zones [29].…”