Journal of Neuroscience, Vol 10, 578-587, Copyright © 1990 by Society for Neuroscience
Retinal graft-mediated pupillary responses in rats: restoration of a reflex function in the mature mammalian brain
H Klassen and RD Lund
Department of Neurobiology, Anatomy and Cell Science, School of Medicine, Pittsburgh, Pennsylvania 15261.
We have shown previously that fetal retinae transplanted to neonatal rat
brains are capable of making the pretectal connections necessary for
driving a pupillary reflex in response to light. At birth, the rat brain is
still developing and presents a favorable environment for fiber outgrowth
and synaptogenesis. A remaining question is whether such grafts will also
establish functional connections within the less plastic mature brain.
Fetal retinae taken from Sprague-Dawley rats at embryonic day 13 or 14 were
implanted in the pretectal region of mature host rats ranging in age from 6
to 11 weeks. The contralateral host eye was removed to reduce afferent
competition within the pretectum between the optic input of graft and host.
The remaining host optic nerve was cut before testing to eliminate all
remaining host visual input. Beginning 1 month after transplantation, the
retinae were surgically exposed and illuminated. In 6 of 24 animals,
illumination elicited an obvious pupilloconstriction response in the host
eye. The magnitude of this graft-mediated response varied between animals.
Two animals produced very brisk responses, comparable to the best results
seen following transplantation into neonatal hosts. In these cases, the
degree of constriction was clearly dependent on the level of graft
illumination. The 4 other animals produced responses that were less brisk.
All 6 animals with clear-cut graft-mediated pupillary responses had
well-formed grafts containing numerous rosettes and ganglion cells. In
addition to these 6 animals, 9 others showed extremely small or variable
pupillary changes on graft illumination. The remaining 9 animals showed no
stimulus-associated pupillary activity. Grafts in this group tended to be
poorly formed or were located outside the pretectal area. These results
show that transplanted retinae are capable of making specific functional
connections with the mature brain, since an appropriate visual reflex can
be elicited by illuminating the graft in the absence of host visual input.
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