Animal Models of Negative Symptoms: M100907 Antagonizes PCP-Induced Immobility in a Forced Swim Test in Mice

Abstract

Schizophrenia is characterized by three types of symptoms: positive, disorganized, and negative. The pathophysiology of negative symptoms is less well understood than that of positive symptoms. Consequently, there are more models of positive symptoms than negative symptoms, and the characterization of novel compounds with respect to their potential effects on negative symptoms has been limited to the use of behavioral models with face validity. Behavioral models of negative symptoms that are currently being used in the development of novel antipsychotic agents include: the social withdrawal model in rodents and nonhuman primates; and the forced swim test. In addition, our data suggest that the chronic mild stress model of anhedonia may also be predictive for compounds with efficacy for negative symptoms. In rodents, chronic administration of PCP increases the duration of immobility in the forced swim test and has been used as a model of the negative symptoms of schizophrenia, such as flattening of affect and avolition. An experiment is presented that evaluated the effects of clozapine, haloperidol, and M100907 against PCP-induced immobility in the forced swim test. M100907 is a selective serotonin 5-HT2A receptor antagonist that is currently being evaluated in clinical trials as a treatment for schizophrenia. Clozapine, which has been found to be clinically active against negative symptoms, significantly attenuated PCP-induced immobility, whereas haloperidol, which is clinically inactive against negative symptoms, had no effect. M100907 (0.3 and 1 mg/kg) significantly attenuated PCP-induced immobility, showing a similar profile to clozapine in the forced swim test. Therefore, M100907 may have a unique ability to alleviate the negative symptoms of schizophrenia without the side effects of current antipsychotic medication.