The Journal of Neuroscience, October 15, 1998, 18(20):8344-8355
A Role for Tectal Midline Glia in the Unilateral Containment of
Retinocollicular Axons
Da-Yu
Wu1,
Gerald E.
Schneider1,
Jerry
Silver2,
Michael
Poston2, and
Sonal
Jhaveri1
1 Department of Brain and Cognitive Sciences,
Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, and 2 Department of Neuroscience, Case Western Reserve
Medical School, Cleveland, Ohio 44106
Retinal fibers approach close to the tectal midline but do not
encroach on the other side. Just before the entry of retinal axons into
the superior colliculus (SC), a group of radial glia differentiates at
the tectal midline; the spatiotemporal deployment of these cells points
to their involvement in the unilateral containment of retinotectal
axons.
To test for such a barrier function of the tectal midline cells, we
used two lesion paradigms for disrupting their radial processes in the
neonatal hamster: (1) a heat lesion was used to destroy the superficial
layers of the right SC, including the midline region, and (2) a
horizontally oriented hooked wire was inserted from the lateral edge of
the left SC toward the midline and was used to undercut the midline
cells, leaving intact the retinorecipient layers in the right SC. In
both cases, the left SC was denervated by removing its contralateral
retinal input. Animals were killed 12 hr to 2 weeks later, after
intraocular injections of anterograde tracers to label the axons from
the remaining eye. Both lesions resulted in degeneration of the distal processes of the tectal raphe glia and in an abnormal crossing of the
tectal midline by retinal axons, leading to an innervation of the
opposite ("wrong") tectum. The crossover occurred only where
glial cell attachments were disrupted.
These results document that during normal development, the integrity of
the midline septum is critical in compartmentalizing retinal axons and
in retaining the laterality of the retinotectal projection.
Key words:
midline septum; GFAP; axon barrier; radial glia; axon
guidance; brain compartmentalization
Copyright © 1998 Society for Neuroscience 0270-6474/98/18208344-12$05.00/0