Striatal synaptophysin levels are not indicative of dopaminergic supersensitivity

Recent evidence suggests that behavioral supersensitivity to dopamine (DA) agonists observed in chronic neuroleptic-treated animals might be related to changes in synaptic morphology and density. The aim of this study was to test this hypothesis using Western blotting to determine the striatal synaptophysin levels in rats chronically treated with haloperidol followed by sub-acute administration of a DA agonist. Chronic haloperidol treatment (1 mg/kg/day for 21 days) produced an 88% increase in striatal synaptophysin levels and a 73% increase in apomorphine-induced stereotypes. Sub-acute administration of the DA D-1 receptor agonist SKF38393 (10 mg/kg/day for 5 days) or the DA D-2 receptor agonist quinpirole (1 mg/kg/day for 5 days) did not modify the haloperidol-induced increase in striatal synaptophysin levels. However, sub-acute administration of SKF38393 attenuated (62%) haloperidol-induced stereotypies. We conclude that there is no direct relationship between stereotyped behavior and synaptophysin levels indicating that striatal synaptophysin levels are not a good marker of dopaminergic supersensitivity.