FAUC 213, a highly selective dopamine D4 receptor full antagonist, exhibits atypical antipsychotic properties in behavioural and neurochemical models of schizophrenia

Rationale: 2-[4-(4-Chlorophenyl)piperazin-1-ylmethyl]pyrazolo[1,5-a]pyridine (FAUC 213) is a highly selective antagonist at the dopamine D4 receptor subtype. It was designed as a derivative of two partial antagonists and has been proven to be a complete antagonist in mitogenesis assay. Objectives: In the present study, FAUC 213 was examined for antipsychotic properties in animal models of behavioural neurobiology and neurochemistry. Methods: Different concentrations of FAUC 213 were screened for effects on spontaneous, as well as amphetamine-induced, locomotor activity and apomorphine-induced prepulse disruption. The liability of causing extrapyramidal side effects was investigated in models of catalepsy and by high-performance liquid chromatography (HPLC) detection of dopamine turnover in several brain regions. The application schedule was validated, and the bioavailability of the compound determined, by means of a HPLC-pharmacokinetic study. Results: A significant effect in both the reduction of amphetamine-induced locomotor hyperactivity and the restoration of apomorphine-disrupted prepulse inhibition was found at 30mg/kg. This dose proved not to be high enough to induce catalepsy or to increase dopamine turnover in the dorsal striatum, nucleus accumbens and medial prefrontal cortex. The selective D4 antagonist FAUC 213, therefore, is not believed to mediate the above-mentioned effects via D2 receptor antagonism, but a partial involvement of 5-HT2- and α1-receptors cannot be ruled out at present. Conclusions: We have gathered evidence that FAUC 213 exhibits atypical antipsychotic characteristic