Spreading of hemiretinal projections in the ipsilateral tectum following unilateral enucleation: a study of optic nerve regeneration in Xenopus with one compound eye

Right compound eyes were formed in Xenopus embryos at stages 32–33 by the fusion of two nasal (NN), two ventral (VV) or two temporal (TT) halves. Shortly after metamorphosis the optic nerve from the compound eye was sectioned and the left intact eye removed. The retinotectal projections from the compound eye to the contralateral and ipsilateral tecta were studied by [3H]proline autoradiography and electrophysiological mapping between 6 weeks and 5 months after the postmetamorphic surgery. The results showed that NN and VV eyes projected to the entire extent of both tecta. In contrast, optic fibre projection from TT eyes, although more extensive than the normal temporal hemiretinal projection, failed to cover the caudomedial portion of the tecta. The visuotectal projections in all three combinations corresponded to typical reduplicated maps to be expected from such compound eyes, where each of the hemiretinae projected across the contralateral and ipsilateral tecta in an overlapping fashion. The rapid expansion of the hemiretinal projections of the compound eyes in the ipsilateral tectum following the removal of the resident optic fibre projection suggests that tectal markers may be carried and deployed by the incoming optic fibres themselves.

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Interactions between compound and normal eye projections in dually innervated tectum: a study of optic nerve regeneration in Xenopus

Development ◽

10.1242/dev.66.1.159 ◽

1981 ◽

Vol 66 (1) ◽

pp. 159-174

Author(s):

Charles Straznicky ◽

David Tay

Keyword(s):

Optic Nerve ◽

Nerve Regeneration ◽

Compound Eye ◽

Compound Eyes ◽

Lateral Region ◽

Optic Nerve Regeneration ◽

Xenopus Embryos ◽

Retinotectal Projections ◽

Two Populations

Right compound eyes were formed in Xenopus embryos at tailbud stages by the fusion of two nasal (NN), two temporal (TT) or two ventral (VV) halves. The left eye was kept intact. Two to four weeks after metamorphosis the optic nerve from the intact eye was severed to induce bilateral optic nerve regeneration. The contralateral retinotectal projections from the compound eye and the induced ipsilateral projections from the intact eye to the same (dually innervated) tectum were studied by [3H]proline autoradiography and visuotectal mapping from 3 to 6 months after the postmetamorphic surgery. The results showed that the NN, TT and VV projections, in the presence of optic fibres from the intact eye failed to spread across the whole extent of the dually innervated tectum. Unexpectedly the bulk of the regenerating projection from the intact eye was confined to the previously uninnervated parts of the dually innervated tecta, the caudomedial region in TT, the rostrolateral region in NN and the lateral region in VV eye animals. The partial segregation of the two populations of optic fibres in the dually innervated tectum has been taken as a further indication of the role of fibre-fibre and fibre-tectum interactions in retinotectal map formation.

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Reorganization of retinotectal projection of compound eyes after various tectal lesions in Xenopus

Development ◽

10.1242/dev.35.1.41 ◽

1976 ◽

Vol 35 (1) ◽

pp. 41-57

Author(s):

K. Straznicky

Keyword(s):

Optic Nerve ◽

Visual Field ◽

Nerve Regeneration ◽

Experimental Situation ◽

Compound Eyes ◽

Retinotectal Projection ◽

Optic Nerve Regeneration ◽

Retinal Fundus ◽

Pattern Regulation

The retinotectal connexions of double nasal (NN), double temporal (TT) and doubleventral (VV) eyes in juvenile Xenopus were mapped after post-metamorphic removal of the rostral, caudal, medial or lateral tectal halves with the subsequent cutting of the optic nerveof the operated eye. A whole visual field projection occurred from NN eyes on to residual caudal tectum, from TT eyes on to residual rostral tectum and from VV eyes on to residual medial tectum. Whenoptic fibres from NN, TT or VV eyes grew into inappropriate rostral, caudal or lateral tectal halves respectively, there was a projection deficit in the nasal and temporal or in the dorsaland ventral poles of the visual field. The persisting scotomas in the visual field indicated that only the optic fibres of the central retinal fundus had succeeded in connecting with aninappropriate tectal half whereas the peripheral optic fibres had not. The incongruous results of optic nerve regeneration obtained in the various recombinations may be taken to indicatethat the assumption of early embryonic pattern regulation is inadequate to explain the findings in this experimental situation.

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