Behavioral phenotypes for negative symptoms in animal models of schizophrenia

A devastating psychiatric disorder, schizophrenia is characterized by three major symptoms, positive and negative symptoms and cognitive deficit. Almost all current therapeutic drugs for schizophrenia have efficacy for positive symptoms, and weak efficacy for negative and cognitive deficit. In particular, social withdrawal, diminished motivation, and anhedonia as the depressive aspects of negative symptoms are resistant to the treatment of antipsychotic drugs. Therefore, there is a need for development of new therapeutic drugs for negative symptoms of schizophrenia, and it is necessary to have comprehensive animal models to understand the neurobiological foundations of their symptoms. In this review, we represent the behavioral phenotypes in available animal models of schizophrenia for drug discovery, focusing on the depressive aspects of negative symptoms. We mention here animal models based on the pathology and epidemiology of schizophrenia, e.g., the pharmacological, neurodevelopmental, genetic, and gene-environment combination models. The animal models of schizophrenia are developed by various approaches and are assessed, but there are few models demonstrating negative symptoms with sensitivities to available therapeutic drugs. The development of comprehensive animal model reflecting negative symptoms and of novel compounds that can remedy them provide certain insight into the neurobiological process of schizophrenia and also point the way to a new therapeutic strategy.