OPTOKINETIC HORIZONTAL HEAD NYSTAGMUS IN THE FROG AFTER REGENERATION OF TRANSECTED RETINAL FIBERS

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  • 1 January 1983
    • journal article
    • research article
    • Vol. 34  (4) , 371-383
Abstract
The recovery of optokinetic responses during regeneration of transected retinal fibers was studied. Regenerated optic fibers were demonstrated by the Co filling technique. After transection of the chiasma in the midline in most cases regenerating retinal fibers did not cross, but terminated in ipsilateral visual centers. Aberrant fibers were found in the telencephalon, the periventricular region of the diencephalon, anterior-, posterior- and ventral tegmental commissures and in the isthmic nucleus. In 1 group of animals optokinetic responses did not return after regeneration of retinal fibers. Reinnervation was either symmetrical on both sides from one eye, or terminal fibers were disorganized. In the 2nd group of animals normal optokinetic nystagmus (OKN) returned. In these cases the fibers were symmetrically distributed on both sides or, alternatively, the crossed fibers outnumbered the ipsilateral ones. The 3rd group of animals showed reversed OKN, spontaneous turning of the head, circling or head nystagmus. Here the majority of regenerated fibers termined ipsilaterally. When the OKN returned, the retinal projection was always restored in the pretectal region. Contrary to earlier work, the basal optic nucleus is not essential for horizontal optokinetic head nystagmus because in a few animals, retinal fibers did not invade this nucleus, and in spite of this the OKN could be evoked. The most important structure (as an input channel) for horizontal OKN of frogs may be the pretectal region.