Differential alterations in striatal acetylcholine function in rats during 12 months' continuous administration of haloperidol, sulpiride, or clozapine.

Rats were treated continuously for 12 months with therapeutically equivalent doses of either haloperidol (1.4-1.6 mg/kg/day), sulpiride (102-109 mg/kg/day), or clozapine (24-27 mg/kg/day). After treatment for 3 and 12 months with haloperidol or clozapine but not sulpiride, striatal acetylcholine levels were increased. Striatal choline acetyltransferase activity was not altered by any drug treatment. Vmax for striatal acetylcholinesterase activity during the course of 12 months' treatment with haloperidol or clozapine, but not with sulpiride, tended to increase; Km was not altered by any drug treatment. Bmax for specific striatal [3H]quinuclidinyl benzilate binding was not altered by haloperidol or sulpiride treatment but was transiently elevated after 6 months of clozapine treatment, thereafter returning to control levels. Kd was not altered by any drug treatment. These findings indicate that alterations in striatal acetylcholine content caused by chronic treatment with some but not all neuroleptics are due to changes in cholinergic neuronal activity rather than neurotransmitter synthesis or destruction. The effects of haloperidol but not those of clozapine may be related to the emergence of functional striatal dopamine receptor supersensitivity. Since haloperidol (which is associated with a high prevalence of tardive dyskinesias) but not clozapine (which is not) had similar effects on striatal cholinergic function, the latter may not be related to the emergence of tardive dyskinesias during chronic therapy.