Prototypical antipsychotic drugs protect hippocampal neuronal cultures against cell death induced by growth medium deprivation

Hippocampal cell death induced by deprivation of growth medium constituents was strongly blocked by drugs including antipsychotics (10-10-10-6 M) that display nM affinities for D2 and/or D4 receptors (clozapine, haloperidol, (±)-sulpiride, domperidone, clozapine, risperidone, chlorpromazine, (+)-butaclamol and L-741,742). These effects were shared by some caspases inhibitors and were not accompanied by inhibition of reactive oxygen species. In contrast, (-)-raclopride and remoxipride, two drugs that preferentially bind D2 over D4 receptors were ineffective, as well as the selective D3 receptor antagonist U 99194. Interestingly, (-)-raclopride (10-6 M) was able to block the neuroprotective effect of the atypical antipsychotic clozapine (10-6 M).Taken together, these data suggest that D2-like receptors, particularly the D4 subtype, mediate the neuroprotective effects of antipsychotic drugs possibly through a ROS-independent, caspase-dependent mechanism.There is clinical evidence of cognitive dysfunction in certain schizophrenic patients that is likely to be independent of psychotic symptoms [1]. This dysfunction does not seem to involve a single brain region but rather a network that includes cortical and sub-cortical regions such as the hippocampus. The therapeutic benefits of various antipsychotic drugs are thought to be predominantly associated with their antagonistic actions on D2-like (D2, D3 and D4) dopamine receptors in the brain [2,3]. Although early studies with typical antipsychotic drugs (e.g. haloperidol, chlorpromazine) mostly failed to report significant improvements of cognitive behaviors in schizophrenic patients [4-6], more recent data especially obtained using atypical antipsychotics (e.g. clozapine, risperidone, olanzapine) demonstrated positive effects [7-12]. For example, risperidone has been associated with improved verbal working memory and executive functions whereas clozapine and quetiapine seem to improve verbal fluency [9,13,14].The benefici