Journal of Neuroscience, Vol 9, 4042-4050, Copyright © 1989 by Society for Neuroscience
Regenerated retinal ganglion cell axons can form well-differentiated synapses in the superior colliculus of adult hamsters
DA Carter, GM Bray and AJ Aguayo
Center for Research in Neuroscience, Montreal General Hospital Research Institute, Quebec, Canada.
To investigate in adult animals the distribution and differentiation of the
synapses made by axotomized CNS neurons whose regenerating axons are guided
back to their natural targets in the brain, we attached an autologous
peripheral nerve (PN) graft 2-3 cm in length to the ocular stump of a
transected optic nerve (ON) in adult hamsters, inserted the distal end of
the graft into the superior colliculus (SC), and, 6-8 weeks later, labeled
the retinal ganglion cell (RGC) axons that entered the SC with HRP
orthogradely transported from the eye. By light microscopy, regenerated RGC
axons extended from the graft into the retinorecipient layers of the SC for
up to 500 microns, distances that approximate the lengths of normal RGC
arbors. We compared 698 control and 758 regenerated HRP-labeled axon
terminals from 4 intact and 4 experimental animals by electron microscopy.
The structure of the regenerated RGC terminals, the type of synaptic
contacts formed, the ratios of contacts to terminal perimeter, and the
domains of the postsynaptic neurons contacted were similar to those of
controls. These results indicate that regenerated RGC axons can form well-
differentiated synapses in the SC. Morphological differences between the
regenerated and control synapses were the larger size of some regenerated
terminals, the greater mean length of the regenerated synapses, and the
higher proportion of contacts with dendrites that contained vesicles. The
synaptic differentiation attained by these reformed retinocollicular
projections suggests that regenerating CNS axons and their target neurons
in the adult mammalian brain may retain or reexpress certain molecular
determinants of normal connectivity.(ABSTRACT TRUNCATED AT 250 WORDS)