4 - A ZEBRAFISH MODEL OF CLOZAPINE EXPOSURE: DRUG-INDUCED TRANSCRIPTOMIC CHANGES IN THE BRAIN

Abstract

Background Schizophrenia (SZ) is a severe neuropsychiatric disorder characterized by episodic psychosis and altered cognitive function. About 20% of SZ patients are resistant to the commonly-prescribed antipsychotic medications used to treat disease symptoms. Clozapine is an atypical antipsychotic drug often prescribed to treatment-resistant SZ patients, although the functional pathways mediating its action are not well understood. Importantly, 40–70% of patients treated with clozapine show an inadequate response and there are sever side-effects. Understanding the molecular pathways involved in antipsychotic response will help in the development of new improved therapeutics that act on pathogenicity rather than just treating the acute manifestations of SZ. Methods We exposed wild type zebrafish to high and low doses of the antipsychotic drug clozapine over 72 hours. Relevant controls were included at all stages of the experiment. We recorded the animals and analysed changes in behavior associated with clozapine exposure. We then performed RNA-sequencing in the brain and identified changes in gene expression in response to clozapine exposure. Network analysis was performed to identify modules of co-expressed genes sensitive to clozapine exposure and pathway analysis was employed to identify overrepresentation of GO terms in each of the clozapine exposure-associated modules Results The fish showed a dose-sensitive shift in behaviour in response to clozapine. We identified five genes showing significant gene expression changes in response to clozapine, including ODC1, a gene previously implicated in SZ which shows changes in expression during brain development. Using network analysis, we identified fifteen modules of co-expressed genes which present a striking change in module connectivity in response to the drug. These modules show overrepresentation of key gene ontology terms, implicating processes such as calcium ion transport, cell-cell signalling, G-protein coupled receptor activity, ribosomal activity, and the regulation of transcription. Discussion Our study highlights the utility of zebrafish as a model for assessing the molecular consequences of antipsychotic medications. Our data show marked behavioural effects induced by clozapine and significant transcriptomic alterations in important functional pathways in the brain.