The striatal cholinergic interneuron: Synaptic target of dopaminergic terminals?

The original observations suggesting an important interaction between dopamine and acetylcholine in the extrapyramidal system were derived from clinical investigations on Parkinson's disease in the early sixties. Since muscarinic receptor antagonists, which decrease cholinergic tone, ameliorate Parkinsonian symptoms in the same manner as do dopamine receptor agonists, which increase dopaminergic tone. It was proposed that the endogenous neurotransmitters, acetylcholine and dopamine, had opposing functions in the extrapyramidal system. The concept emerged that, under normal conditions, cholinergic and dopaminergic tone are in a state of approximate balance.