Lack of acquisition in dopamine denervated animals tested in an underwater Y-maze

There are a number of conflicting reports in the literature on the ability of dopamine (DA) denervated animals to acquire various instrumental tasks, mostly conditioned avoidance responding. The interpretational difficulties stem partly from the difficulties to test an animal that is deficient in initiating voluntary movements and partly from the difficulties to produce complete DA denervations. We have tried to solve these problems by testing DA denervated animals in an underwater swim maze where even severely denervated animals will overcome their akinesia and swim the maze. 6-Hydroxydopamine was injected into the bundle of ascending DA axons in order to produce the best possible DA degeneration and the animals were tested as soon as the degeneration was complete (48 h) in order to avoid compensatory processes. We found that such animals were unable to acquire a brightness as well as a spatial discrimination task even when the experimental situation was such that they were able to overcome their difficulties to initiate voluntary movements. Possible explanations to the discrepancies between our studies and others are discussed.