On the origin of substance P and glutamic acid decarboxylase (GAD) in the substantia nigra.

Knife cuts in the frontal plane separating the anterior part of the caudate-putamen from the globus pallidus resulted in marked decreases in substances P levels in the reticular part of the substantia nigra. More caudal knife cuts were required in order to effect maximal decreases in nigral glutamic acid decarboxylase levels. Thus, there is a clear anatomical dissociation between the striatal neurons which project to the reticular part of the substantia nigra and which contain SP, and the more caudally located GAD-containing striatal and pallidal neurons, all of which travel through the globus pallidus on their way to the substantia nigra.