Intertectal neuronal plasticity in Xenopus laevis: persistence despite catecholamine depletion.

In normal Xenopus, the tectum receives a direct projection from the contralateral retina and an indirect projection, via the intertectal system, from the ipsilateral eye. The two maps of binocular visual space, at each tectum, are in register. If one eye is rotated during larval development, the ipsilateral visuotectal projection compensates by changing its orientation. Rearrangement of the intertectal system brings the ipsilateral map back into register with the contralateral map. We sought to determine whether this intertectal plasticity required normal levels of brain monoamines. Animals received an eye rotation between stages 55-63 of larval life and were then placed in one of 3 groups. A first control group received no further treatment. A second control group was given intraventricular injections of ascorbate vehicle. The experimental group was given intraventricular injections of 6-hydroxydopamine in ascorbate vehicle. Two to 3 months after metamorphosis, visuotectal projections were mapped electrophysiologically and the brains were assayed for monoamines. Intertectal plasticity occurred in all 3 groups of animals, including animals in which brain catecholamine levels were severely reduced. We conclude that normal levels of brain catecholamines are not required for this form of neural plasticity.