Effects of unilateral 6-Hydroxydopamine lesions of the caudate-putamen on skilled forepaw use in the rat

This experiment reports a novel means of measuring the effect of unilateral striatal dopamine (DA) depletion on co-ordinated motor behaviour involving skilled forepaw use in rats. Hungry rats were trained to use their forepaws to remove small food pellets from a moving conveyor belt. Behaviour was scored by counting successful retrievals, attempted retrievals and omissions. The rats were trained to a stable baseline, and the forepaw which they used most accurately was determined over a period of 300 trials. 6-Hydroxydopamine (6-OHDA, 8 micrograms base in 2 microliters vehicle (ascorbic acid/0.9% saline) was injected unilaterally into the head of the caudate nucleus to produce selective DA depletion, either ipsi- or contralateral to the preferred paw. A control group received vehicle alone. There was a significant change in paw use in the 6-OHDA treated rats, but not in the controls, even though accuracy was affected similarly in both sham and lesioned groups. Ipsilaterally injected rats showed increased use of the preferred paw (90% pre-operation to 98% post-operation, while contralaterally injected rats showed reduce use (86% pre-operation to 49% post-operation). These changes appeared on the first day postsurgery and were still present 3 months later.