Ultrastructural relations between nigrostriatal dopaminergic neurons and cholinergic nerve endings in the human brain.

The connections between cholinergic nerve endings and nigrostriatal dopaminergic neurons were studied in the substantia nigra pars compacta of the human brain. Immunocytochemistry of tyrosine hydroxylase followed by ionic fixation of acetylcholine-like cation in synaptic vesicles allowed dopaminergic neurons and cholinergic nerve endings to be visualized on the same ultrathin section. Numerous contacts, some of them with synaptic structures, were observed between nerve endings, with or without precipitates of acetylcholine-like cation and dendrites or cell bodies of tyrosine hydroxylase-immunoreactive neurons. These results, which agree with previous studies performed in the rat, suggest that cholinergic nerve endings control the activity of the nigrostriatal neurons at the level of the dendrites and cell bodies in the substantia nigra.