The Journal of Neuroscience, February 1, 2001, 21(3):951-960
Topological Specificity in Reinnervation of the Superior
Colliculus by Regenerated Retinal Ganglion Cell Axons in Adult
Hamsters
Yves
Sauvé,
Hajime
Sawai, and
Michael
Rasminsky
Centre for Research in Neuroscience, Montreal General Hospital and
McGill University, Montreal, Quebec, H3G 1A4, Canada
In normal rodents there is a precise topology of the
retinocollicular projection, the nasotemporal and ventrodorsal axes of the retina being respectively projected onto the caudorostral and
mediolateral axes of the contralateral superior colliculus (SC). We
evaluated the distribution of regenerated retinal ganglion cell (RGC)
axon terminals in the SC of adult hamsters in which an unbranched
peripheral nerve graft was directed from the retina to the
contralateral SC. Responses to visual stimulation of individual RGCs
were recorded from terminal arbors of their regenerated axons in the
reinnervated SC. Retinal positions of these RGCs were inferred from the
locations of their visual receptive fields. At some sites in the
reinnervated SC, axon terminal arbors converged from widely separated
RGCs. Conversely, axon terminal arbors at widely separated sites in the
SC could emanate from contiguous RGCs. To assess whether any tendency
for order was superimposed on the apparent disorganization of the
regenerated projection, we evaluated the relative positions of pairs of
RGC terminals in the SC in relation to the relative retinal locations
of the corresponding pairs of RGCs. Among the 983 pairs of RGCs able to
be evaluated from nine animals studied 30-60 weeks after grafting,
there was a statistically significant 3/2 tendency for the more nasally
situated of two RGCs to project its terminal more caudally in the SC
than that of the more temporally situated RGC. A similar tendency
toward appropriate organization was not found with respect to the
ventrodorsal axis of the retina and the mediolateral axis of the SC.
Key words:
electrophysiology; hamster; peripheral nerve graft; regeneration; retinal ganglion cell; retinotopy; superior
colliculus; synapse; tectum
Copyright © 2001 Society for Neuroscience 0270-6474/01/213951-10$05.00/0