European Journal of Neuroscience, Vol. 8, pp.. zyxwvutsr 1051-1054, 1996 zyxwvut 0 European Neuroscience Association z SHORT COMMUNICATION Topographically Organized Climbing Fibre Sprouting in the Adult Rat Cerebellum Marta Zagrebelsky, Ferdinand0 Rossi, Richard Hawkes’ and Piergiorgio Strata Department of Neuroscience, University of Turin, Corso Rafaello 30, zyxwvu 1-10125 Turin, Italy ’Department of Anatomy and Neuroscience Research Group, University of Calgary, Calgary, Alberta T2N 4N1, Canada Keywords: Purkinje cell compartments, zebrin II bands, collateral reinnervation, projection map, olivocerebellar system Abstract Adaptive recovery following brain injury requires the topography of projection maps to be restored. In the adult mammalian brain, the regeneration of severed axons does not normally occur and repair mainly relies on collateral reinnervation from uninjured neurons. Although reinnervation can be target specific at the single cell level, it is not known if the new connections are organized correctly. The normal olivocerebellar projection has a precise topography in which subnuclei of the inferior olive terminate as climbing fibres on chemically defined bands of cerebellar Purkinje cells. This precision has been exploited to determine the topography of climbing fibre sprouting following an inferior olive lesion in the adult rat. Collateral reinnervation was found to respect the boundaries between the Purkinje cell compartments. Thus, topographical cues are available in the adult during post-lesion plasticity to guide the restoration of the olivocerebellar projection map. Precise topographical projections between neurons are formed during development through the orderly growth of axons followed by synapse formation and elimination under the control of highly specific signals (Goodman and Shatz, 1993). Following a lesion in the adult, restoration of the original projection map depends on a multitude of factors including the maintenance or re-expression of positional cues. Transected axons in the adult mammalian brain generally regenerate only if experimentally provided with a permissive environment (Bray and Aguayo, 1989; B&hr and Bonhoeffer, 1994) and normally do not do so in the intact brain. Therefore, most reinnervation of deafferented neurons is through the collateral sprouting of uninjured neighbouring axons (Cotman er al., 1981; Cotman and Nieto Sampedro, 1985; Steward, 1992). Sprouts do synapse with appropriate targets at the single cell level (Cotman et al., 1981; Rossi et al., 1989, 1991a, b; Steward, 1992), but it is not known whether they can reinstate the topography of the projection. The adult rat cerebellum consists of parasagittal bands of Purkinje cells. These can be identified by immunostaining for the Purkinje cell-specific antigen zebrin zyxwvutsr I1 (Brochu et al., 1990) [aldolase C (Ahn ef al., 1994)l. The olivocerebellar projection has a similar topography, in which subsets of inferior olivary neurons terminate in the cerebellar cortex as parasagittally oriented bands of climbing fibres (Voogd, 1989). The climbing fibre and Purkinje cell bands align (Gravel er al., 1987; Wassef et al., 1992). The Purkinje cell zebrin+’- phenotype is independent of afferent innervation (Leclerc et al., 1988; Wassef er al., 1990; Seil et al., 1995) and so the parasagittal bands provide a constant reference against which to study afferent remodelling. In the adult rat, 90-99% of inferior olivary neurons are selectively killed by a single i.p. administration of the neurotoxin 3-acetylpyridine (Desclin, 1974; Llinis er al., 1975). The surviving axons, scattered throughout the cerebellar cortex, sprout collaterals that synapse with the dendrites of nearby deafferented Purkinje cells (Rossi zyxwv et al., 1989, 1991a, b) where they generate postsynaptic activity (Benedetti et al., 1983). However, to be functionally relevant, climbing fibre plasticity should respect the original projection map such that the collaterals from an individual climbing fibre should remain confined within the boundaries of the original zebrin II-defined Purkinje cell band. Some of the present results have been published in abstract form (Zagrebelsky et al., 1995). Twelve adult Wistar rats (body wt 150-200 g) were used for this study. All surgical procedures were performed under deep general anaesthesia (ketamine 100 mgkg, xylazine 5 mgkg i.p.). In eight animals the inferior olive was lesioned by 3-acetylpyridine treatment as previously described (Llinh et al., 1975), whereas four unlesioned rats were examined as controls. Two to four months after lesion, the climbing fibre projection was anterogradely traced by the iontophoretic injection of biotinylated dextran amine (BDA, 10,OOO mol. wt, Molecular Probes, Eugene, OR) in the caudal inferior olive (Rossi et al., 1991a, 1995). After 60-120 days the animals were fixed by transcardial perfusion with 4% paraformaldehyde in 0.12 M phosphate buffer (pH 7.3) and sectioned at 30 pm on a cryostat. Sections were first stained to reveal the BDA labelled axons (Rossi et al., 1991a, 1995). then the Purkinje cell compartments were revealed by immuno- peroxidase staining using mouse monoclonal anti-zebrin I1 antibody Received 30 November 1995, accepted 27 December 1995 Correspondence to: P. Strata, as above