Journal of Neuroscience, Vol 12, 1144-1159, Copyright © 1992 by Society for Neuroscience
Synapse formation and preferential distribution in the granule cell layer by regenerating retinal ganglion cell axons guided to the cerebellum of adult hamsters
TJ Zwimpfer, AJ Aguayo and GM Bray
Centre for Research in Neuroscience, Montreal General Hospital Research Institute, Quebec, Canada.
To investigate constraints and preferences for synaptogenesis in the
injured mammalian CNS, regenerating retinal ganglion cell (RGC) axons of
adult hamsters were guided through a peripheral nerve (PN) graft to a
target they do not usually innervate: the cerebellum (Cb). When identified
by the presence of HRP anterogradely transported from the retina 2-9 months
later, such RGC axons were found to have extended into the cerebellar
cortex for up to 650 microns. Most of this growth was in the granule cell
layer (GCL) and only a few axons entered the molecular layer. The
preference for the GCL could not be explained by the position of the PN
graft in the Cb, a selective denervation of the GCL, local damage to other
neurons, or the distribution of reactive gliosis in the vicinity of the
graft. Furthermore, by EM, more than 95% of the labeled retinocerebellar
terminals and synapses were in the GCL. Retinocerebellar terminals were
larger and contained more synapses than the regenerated RGC terminals
previously studied in the superior colliculus. These results indicate that
regenerating axons of CNS neurons can form persistent synapses with novel
targets. The preferential synaptogenesis in the GCL suggests that such
unusual connections are not formed randomly in the CNS of these adult
mammals.