Substance P appears reduced in Huntington's disease: immunocytochemical findings in substantia nigra and substantia gelatinosa.

Using immunocytochemistry, this report visualizes immunoreactive substance P (SP) within human postmortem specimens of rostro-medial substantia nigra and dorsal spinal cord taken at autopsy from cases diagnosed as Huntington's disease (HD), and normal or non-HD. In the non-HD specimens of postmortem midbrain, the SP-immunoreaction products form a dense meshwork of neuronal processes throughout the substantia nigra (SN) pars compacta and pars reticulata. In the HD specimens, the SP-containing processes appear reduced. Presumably the reduced numbers of SP-containing processes result from the degeneration of parent SP perikarya located in the striatum, and cause the aberrant modulation of dopaminergic neurons which then influence basal ganglia output and therefore motor control. In the dorsal spinal cord substantia gelatinosa (SG), a nociceptive relay center, preliminary data demonstrate the reduced numbers of SP-containing processes in the HD cases compared with the non-HD cases. However neuronal degeneration is reportedly minimal in the spinal cord, and nociception in HD remains intact. Although the data require verification in SG, they suggest that certain kinds of neuronal degeneration may occur throughout the HD central nervous system. Additionally, the data imply that the role of SP in pain processing may require reevaluation.