Is the mesocortical dopaminergic system involved in Parkinson disease?

Tyrosine hydroxylase was used to identify catecholaminergic neurons in the substantia nigra and ventral tegmental area of the human mesencephalon. High enzyme activity in the normal ventral tegmental area indicated the presence of numerous cathecholaminergic neurons, most likely dopamine cells. Tyrosine-hydroxylase activity was decreased in the ventral tegmental area of parkinsonian patients, implying a lesion of the mesocortical dopamine system in Parkinson disease.