Inhibition of choline acetyltransferase by excitatory amino acids as a possible mechanism for cholinergic dysfunction in the central nervous system

Choline acetyltransferase (ChAT) activity was reduced by more than 85% in c ultured retina cells after 16 h treatment with 150 muM kainate (T-1/2:3.5 h ). Glutamate, AMPA and quisqualate also inhibited the enzyme in equivalent proportion. Cell lesion measured by lactate dehydrogenase (LDH) release, 3- [4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide - thiazolyl blue (MTT) reduction and microscopic observation was not detected even after 48 h with kainate. Other retina neurochemical markers were not affected by ka inate and full recovery of the enzyme was achieved 9 days after kainate rem oval. Moreover, hemicolinium-3 sensitive choline uptake and hemicolinium-3 binding sites were maintained intact after kainate treatment. The immunoblo t and immunohistochemical analysis of the enzyme revealed that ChAT molecul es were maintained in cholinergic neurons. The use of antagonists showed th at ionotropic and group 1 metabotropic receptors mediated the effect of glu tamate on ChAT inhibition, in a calcium dependent manner. The quisqualate m ediated ChAT inhibition and part of the kainate effect (30%) was prevented by 5 mM N-G-nitro-L-arginine methyl ester (L-NAME). Veratridine (3 muM) als o reduced ChAT by a Ca2+ dependent, but glutamate independent mechanism and was prevented by 1 muM tetrodotoxin.