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

Abstract

Background: Several clinical studies suggested that antipsychotic-based medications could ameliorate cognitive functions impaired in certain schizophrenic patients. Accordingly, we investigated the effects of various dopaminergic receptor antagonists--including atypical antipsychotics that are prescribed for the treatment of schizophrenia--in a model of toxicity using cultured hippocampal neurons, the hippocampus being a region of particular relevance to cognition.

Results: 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).

Conclusion: 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.

Figure 1

Agarose gel electrophoresis showing RT-PCR products of dopamine receptor subtypes (D1 to D5) mRNAs in rat hippocampal neurons (A) and whole striatum (B). Lanes (+) and (-) represent the PCR products amplified from hippocampal neurons cDNAs following reverse transcription in the presence or absence of reverse transcriptase, respectively. The two hippocampal cultures gave identical results. Expected size for PCR products: D1, 300 bp; D2, 538 bp and 451 bp; D3, 523 bp and 410 bp; D4, 324 bp; D5, 403 bp. Lane M, molecular size standard 100-bp ladder.

Figure 2

Effects of clozapine (A), haloperidol (B), (±)-sulpiride (C), domperidone (D), chlorpromazine (E) and (+)-butaclamol (F) against toxicity induced by growth medium deprivation in enriched hippocampal neuronal cultures. Neuronal survival is estimated using the MTT and neutral red (NR) colorimetric assays. Values represent mean ± SEM of at least three separate experiments, each performed in quadruplicate. *p < 0.05, **p < 0.01 compared to vehicle-treated groups.

Figure 3

Effects of piperidine metabolite of haloperidol (A), raclopride (B) and (+)-SCH 23390 (C) against toxicity induced by growth medium deprivation in enriched hippocampal neuronal cultures. Neuronal survival is estimated using the MTT and neutral red (NR) colorimetric assays. Values represent mean ± SEM of at least three separate experiments, each performed in quadruplicate.