Different forms of brain acetylcholinesterase and muscarinic binding in Parkinson's disease

Choline acetyltransferase (ChAT) activity, the sedimentation and solubility forms of acetylcholinesterase (AChE) as well as total (3H-quinuclidinyl benzilate, QNB) and M1 (3H-pirenzepine, PZ) muscarinic binding were investigated in the temporal cortex (TC) and nucleus caudatus (NC) of both non-demented and demented parkinsonian patients and controls. ChAT activity and low-salt-soluble and detergent-soluble AChE were lower in the TC of demented patients with Parkinson's disease than in controls. ChAT activity and the solubility forms of AChE in the NC did not differ between controls and parkinsonian patients. In the TC, the activity of the intermediate form of AChE was lower in parkinsonian patients, but the activity of the light form of AChE did not differ between controls and parkinsonian patients. In the TC of patients with Parkinson's disease the Bmax of 3H-QNB binding was slightly higher than in controls, but the Bmax of 3H-PZ binding did not differ between controls and parkinsonian patients. In the NC the Bmax of 3H-QNB binding was unchanged compared to that of the controls. The concomitant decrease of ChAT with soluble as well as membrane-bound tetrameric AChE suggests a close relationship between ChAT and tetrameric form of AChE. M1 receptors (3H-PZ binding sites) are not affected in the TC, but are decreased in the NC of demented parkinsonian patients. This decrease may be secondary to the loss of dopaminergic neurons projecting from the substantia nigra to the striatum.