Retention of topographic addresses by reciprocally translocated tectal re-implants in adult goldfish.

1. The topographic pattern of retinotectal projections re-established after reciprocal translocation of two tectal re-implants within a whole tectum was studied in adult goldfish with neurophysiological mapping methods. 2. Reciprocal translocations of tectal re-implants along the rostrocaudal axis resulted in retinotectal projections on to these re-implants that showed corresponding reciprocal transpositions of receptive fields along the nasotemporal axis. 3. Similarly, reciprocal translocations of tectal re-implants along the mediolateral axis resulted in retinotectal projections on to these re-implants that showed corresponding reciprocal transpositions of receptive fields along the superoinferior axis. Some regenerating optic fibres in the operated tectum abruptly changed the directions of their courses, as if they were taking direct paths towards their displaced, previous target zones in the tectum. 4. Reciprocal translocation of tectal re-implants either along the rostrocaudal or mediolateral axis, accompanied by 180 degree rotation of the re-implants about the dorsoventral axis, resulted in retinotectal projections on to the re-implants that showed not only the corresponding reciprocal transpositions along the nasotemporal or superoinferior axis but also a localized 180 degree rotation in the order of the receptive fields within these re-implants. The same results were also observed after regeneration of the optic fibres following section of the contralateral optic nerve. 5. These results indicate that translocated pieces of tectal tissue retain not only the topographic polarity indicative of their normal orientation but also the topographic addresses indicative of their original positions in the tectum, with respect to their selective reinnervation by particular groups of optic fibres.