Loss of substance P and Enkephalin immunoreactivity in the human substantia nigra after striato-pallidal infarction

Post-mortem neuropathological material from 3 patients with striato-pallidal infarction provided the first immunohistochemical evidence for substance P- and enkephalin-containing nerve fibre projections from the striato-pallidum to the substantia nigra in the human. The nigra corresponding to the normal side showed abundant substance P and enkephalin immunoreactivity whose patterns of immunostaining were notably similar. In contrast, the substantia nigra ipsilateral to the striato-pallidal infarction showed a decrease in substance P and enkephalin immunoreactivity which was proportional to the extent of the infarction. This suggests that much of the substance P and enkephalin immunoreactivity in the nigra is present in nerve fibres projecting from the striato-pallidum. Furthermore, the similar distribution of remaining substance P and enkephalin immunoreactivity in corresponding areas of the nigra of the infarcted side indicates that the origins and/or projections of nerve fibres containing these two neuropeptides may be closely approximated anatomically. Depletion of substance P immunoreactivity in the pars reticulata of the substantia nigra in a fourth patient with anterior striatal infarction suggests a topographic projection for substance P immunoreactive fibres from the striatum. There is some evidence in one patient with cognitive and behavioural abnormalities to support the suggestion that the basal ganglia may be involved in non-motor functions.