The effects of acetylcholine and dopamine on the caudate nucleus depleted of biogenic amines.

Because it has been proposed that the reduction of the striatal biogenic amines in Parkinson's disease leads to an imbalance between the actions of acetylcholine and dopamine, we have studied the effects of these substances, liberated from multibarrelled micropipettes, on the firing of single neurons in the feline caudate nucleus depleted of biogenic amines by long-standing nigrostriatal lesions. Compared with neurons in intact cats, those in cats with lesions were more easily excited by acetylcholine and less easily supressed by dopamine. These results suggest that the depletion of the striatal amines decreases the neuronal susceptibility to dopamine and increases that to acetylocholine, possibly by changing the sensitivity or the number of the neuronal receptors of these agents.