A study of the retinotectal projection during regeneration of the optic nerve in the frog

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Abstract
The retinotectal projection was mapped electrophysiologically in 67 experiments on Rana temporaria at various intervals (from 23 to 247 days) after section of the optic nerve. In 18 animals regeneration had not occurred at the time of recording; in the others the pro­jections could be classified in the following way, according to the degree of normality of the pattern: Pattern 1: In 14 frogs there was disorganized anomalous regeneration from small regions of the retina. Tectal responses could not be evoked from the normal stimulus positions but could be evoked only from one or two localized regions of visual field. In 8 of these frogs there was one circumscribed region in the nasal half of the field and another in the temporal half from which responses could be obtained; in 4 animals there was only one region, in the nasal field, and in 2 animals there was one region, in the temporal field, from which tectal responses could be evoked. The earliest responses recorded after nerve section were of pattern 1. Pattern 2: In 4 frogs there was an abnormal projection showing partial organization in only one axis of the retina (nasotemporal, circumferential) and in only one axis of the tectum (mediolateral). This partial organization was only found at the rostral end of the tectum. Pattern 3: In 12 frogs there was recovery of the normal retinotectal projection. Pattern 4: In 15 frogs there was partial or complete recovery of the normal projection together with an anomalous but retinotopically organized projection to the wrong half to the brain. This latter projection was organized as a mirror image of the normal ipsilateral projection. One frog combined the elements of patterns 1 and 4 and the remaining 3 animals did not conform to any of the above patterns. Most of the negative results were obtained in the early days after nerve section and all recordings made later than 77 days after section gave responses. Patterns 3 and 4 were obtained more frequently the longer the interval between nerve section and recording.