Parameters of cholinergic neurotransmission in the thalamus in Parkinson's disease and Alzheimer's disease.

Loss of cholinergic cells in the basal forebrain is associated with commensurate reductions in cortical acetylcholine-related enzyme activities in both Alzheimer's disease (AD) and Parkinson's disease (PD). Nerve cell loss from the cholinergic pontine tegmental nuclei also occurs. As the latter nuclei project to the diencephalon, we used frozen tissue from 5 controls, 5 PD and 5 AD cases to study the distribution of ChAT, AChE and [3H]nicotine binding in the thalamus and subthalamic nucleus. The anterior nuclear group and the mediodorsal nucleus showed high activities of ChAT and AChE together with relatively high levels of [3H]nicotine binding. The centromedian nucleus and subthalamic nucleus contained equally high levels of ChAT but negligible levels of [3H]nicotine binding. There were no significant changes in the levels of ChAT, AChE and nicotine binding in the PD and AD groups indicating that involvement of the pedunculopontine tegmental nucleus is likely to be a secondary retrograde phenomenon rather than part of a systematic cholinergic fibre degeneration.