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 cultured retina cells after 16 h treatment with 150 microM 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 kainate and full recovery of the enzyme was achieved 9 days after kainate removal. Moreover, hemicolinium-3 sensitive choline uptake and hemicolinium-3 binding sites were maintained intact after kainate treatment. The immunoblot and immunohistochemical analysis of the enzyme revealed that ChAT molecules were maintained in cholinergic neurons. The use of antagonists showed that ionotropic and group 1 metabotropic receptors mediated the effect of glutamate on ChAT inhibition, in a calcium dependent manner. The quisqualate mediated 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 microM) also reduced ChAT by a Ca(2+) dependent, but glutamate independent mechanism and was prevented by 1 microM tetrodotoxin.