Quantitative analysis of electrophysiological visuotectal maps using polar dimensions demonstrated uniform representation of visual field on goldfish optic tectum, with topography equally precise in normal and "mature" regenerated projections. The precision of circumferential topography exceeds and is not correlated with that of radial. Radial orderliness may he poor without diminution of circumferential order: these two dimensions of pattern could he generated separately from each other. The method of analysis also allows quantitation of the orientation of the retinotectal projection.
During development radial retinotopy in the sequence of axon growth could contribute to radial topography by confining optic terminals to specific annuli within the projection. The possibility of pattern formation by this means during regeneration was studied by examining the sequence of fibre growth by retrograde labelling of ganglion cells with horseradish peroxidase (HRP), applied to a cut through the optic tract at successive intervals after optic nerve transection in mid-orbit. Most results indicated a central-to-peripheral sequence of regeneration; others showed absence of retinotopic sequence.
Regeneration of axons from central retina was delayed by repetition of axotomy. Subsequent visuotectal maps were either normal or included electrophysiologically weak representation of central visual field on peripheral tectum, outside or superimposed upon the map of peripheral field. Some of the abnormal maps also contained normal representation of central field on central tectum. Because of the contradictions in these results, the influence of temporal sequence on spatial order of connections remains uncertain.
Formation of circumferential topography was investigated by anterograde tracing with HRP of axons from narrow sectors of retina in normal and regenerated pathways. Juxtaposition of labelled axons appears to be completely lost in the optic chiasm or at the site of optic nerve transection. Contact guidance of axons therefore cannot explain circumferential order in the map. Labelling was inadequate to show whether regenerating fibres resegregate retinotopically in the optic tract
