Role of Neuregulin 3‐ErbB4 Signaling in a Murine Model of Co‐Morbid Nicotine Dependence and Schizophrenia

According to the NIH, rates of nicotine dependence among patients with schizophrenia are at nearly 90%, compared to smoking rates of approximately 12% in the general population. Current research shows that variations in the gene for Neuregulin 3 (NRG3), a member of the EGF superfamily and the cognate ligand for ErbB4 receptors, are considered some of the strongest genetic links contributing to schizophrenia risk. Additionally, NRG3 protein and mRNA have been found to be highly enriched following chronic nicotine exposure and withdrawal. However, specific mechanisms underpinning NRG3’s association with both increased schizophrenia risk and increased nicotine withdrawal symptomology are unknown. In this ongoing experiment, we are testing the overall hypothesis that NRG3‐ErbB4 signaling effects on NMDA receptor function may provide a discrete, mechanistic link between nicotine dependence and schizophrenia. We plan to utilize a novel genetic mouse model of both nicotine dependence and schizophrenia in a multidimensional approach to study how NRG3 mediates nicotine withdrawal‐induced alterations on behavioral and molecular levels and how the alterations relate to schizophrenic‐like dysfunction. To first begin these investigations, we examined the behavioral and molecular baseline effects of nicotine and aripiprazole, a long‐acting atypical antipsychotic used to treat schizophrenia, in wildtype littermates. Animals treated chronically for nicotine and then undergoing spontaneous nicotine withdrawal were examined in the alternating Y‐maze, social interaction test, and open field test for efficacy in reducing behavioral endophenotypes common to both nicotine withdrawal and schizophrenia in our model. Following behavioral testing, PFC tissues were analyzed to determine mRNA and protein expression of factors in the NRG3 signaling pathway. Preliminary results show differential changes in mRNA expression associated with glutamatergic and serotonergic transmission in the mPFC, OFC, and hippocampus. Ongoing experiments will extend these studies to include time‐ and site‐specific genetic deletion of NRG3 in the PFC and compare these results to those derived in wildtype littermates. Our findings will provide insight into the underlying mechanisms linking the NRG3 signaling pathway and nicotine dependence, and may provide a novel link between nicotine use and its highly co‐morbid psychiatric disorder, schizophrenia. Findings from these highly translational studies may lead to novel therapeutic development for both nicotine dependence and schizophrenia.