We used lesion paradigms in normal and parkinsonian rats and monkeys.
Lesion of cholinergic pedunculopontine neurons affects dopaminergic neurons.
Dopaminergic lesion results in losses of cholinergic pedunculopontine neurons.
Double cholinergic and dopaminergic lesions aggravate neuronal losses.
Strong reciprocal interactions exist between dopaminergic and cholinergic systems.