| Schizophrenia is a debilitating mental disorder that causes a large economic burden and is prevalent across all cultures and countries around the world. Although both environmental factors and genetics are known to play an important role in the etiology of schizophrenia, the exact role of genetics and its interaction with environmental factors in an individual's predisposition to develop schizophrenia is poorly understood. Schizophrenia is characterized by symptoms that include positive symptoms (e.g. delusions, hallucinations, disorganized thinking and speech), negative symptoms (e.g. avolition, anhedonia, depressive-like behavior), and cognitive dysfunctions (e.g. executive functioning deficits in learning and memory, attention, and vigilance). Genomic screening has identified polymorphisms of the vesicular monoamine transporter 1 (VMAT1) gene (SLC18A1) that are associated with schizophrenia and bipolar disorder. The current study represents the first extensive phenotyping of both young and aged mice in which the VMAT1 gene (SLC18A1) has been deleted. The results demonstrated behavioral effects of deleting the VMAT1 gene that may relate to aspects of schizophrenic-like behavioral changes in this model. Specifically, young VMAT1 knockout mice displayed significant deficits in sensorimotor gating in the prepulse inhibition (PPI) task and in the acquisition of operant learning in the autoshaping task. When exposed to a mild stressor (24 hours of food deprivation), young VMAT1 knockout mice displayed a significant reduction in locomotor activity that was not evident under free-feeding conditions. Thus, young VMAT1 knockout mice showed deficits in tasks that model positive symptoms and cognitive deficits seen in schizophrenia; however, they did not display differences in behaviors related to models of the negative symptoms of schizophrenia or deficits in tasks designed to measure motor skills. While less extensive phenotyping was conducted in aged VMAT1 knockout mice, there were no significant deficits evident in any of the assays conducted in older animals. These findings demonstrated that deletion of the VMAT1 gene has behavioral effects that appear to be mediated by changes in brain monoamine function and changes in response to stressors (i.e. food deprivation) that may reflect changes in adrenal gland monoamine function. |
