Degeneration of the centré median-parafascicular complex in Parkinson's disease

Two major noncortical inputs to the striatum originate from the substantia nigra and the thalamic centré median-parafascicular complex. Although it is established that in Parkinson's disease there is degeneration of the nigral dopaminergic neurons, there has been little analysis of the glutamatergic centré median-parafascicular complex. We therefore evaluated these and neighboring thalamic nuclei (for specificity of any changes) in 9 Parkinson's disease patients and 8 age-matched controls. Degeneration in the substantia nigra and centré median-parafascicular complex was estimated by using quantitative neuronal counts. On average, 70% of the pigmented nigral neurons degenerated and there was 30% to 40% neuronal loss in the centré median-parafascicular complex in Parkinson's disease. Thalamic degeneration was marked in neuronal subpopulations (50% loss of parvalbumin-positive neurons in the parafascicular, and 70% loss of non-parvalbumin-positive neurons in the centré median nuclei). In contrast, adjacent thalamic nuclei did not degenerate, which supports a selective neurodegeneration of the centré median-parafascicular complex. Our results show that the thalamic centré median-parafascicular complex is an additional nondopaminergic site of neurodegeneration in Parkinson's disease. Because this thalamic region provides important sensorimotor feedback to the striatum, degeneration of this region is likely to exacerbate the clinical signs and symptoms of Parkinson's disease.