Among the sensory modalities, olfaction is most closely associated with the temporo-limbic and frontal regions most commonly implicated in schizophrenia pathology. Olfactory probes may therefore be ideal tools to assess the structural and functional integrity of these neural substrates. To the extent that peripheral sensory afferents are disrupted in schizophrenia, the olfactory system - owing to its strategic anatomic location - may also be especially vulnerable to disruption. So, olfactory dysfunction may be a sensitive indicator of schizophrenia pathology, and may even serve as an """"""""early warning"""""""" sign of disease vulnerability or onset. In addition, since neurogenesis and neurodevelopment persist throughout life in the olfactory neuro-epithelium and the olfactory bulb (OB), probes of the olfactory system may provide insight into the neurobiological basis of aberrant neurodevelopment. This project, now in its eleventh year, represents one of the only systematic efforts to characterize schizophrenia olfactory deficits from a neurobiological, rather than a simply behavioral, perspective. Recent studies have identified specific abnormalities implicating abnormal G protein-mediated signal transduction in peripheral olfactory receptor neurons (ORNs) and altered synaptic connectivity between ORNs and olfactory bulb as specific neurodevelopmental mechanisms that may be disrupted. This renewal application proposes a unique in vivo - in vitro translational investigation of these abnormalities. Detailed behavioral and electrophysiological studies of the peripheral olfactory system, including both epithelial and primary sensory cortical responses, will be conducted in 35 adult schizophrenia patients, 35 adolescents with a genetic risk for schizophrenia, 35 clinical-risk adolescents with prodromal symptoms, and appropriate age- matched control groups. Olfactory epithelial biopsy tissue will be acquired from the schizophrenia patients and age-matched controls. As the only accessible source of regenerating neural cells, olfactory epithelial biopsy offers an unparalleled opportunity to directly assess neuronal integrity in a living human. The epithelial biopsy tissue, along with olfactory bulbs obtained from post-mortem material, will used to investigate the cellular and molecular mechanisms that underlie the dysregulations observed in vivo. A particular focus will be G protein- mediated intracellular signal transduction and ORN-OB synaptic connectivity. The overarching hypothesis is that olfactory deficits reflect genetically-mediated abnormalities in intracellular signaling and neuron-to-neuron connectivity, which arise from developmentally disturbed processes of neurogenesis and synapse formation.
Schizophrenia is a complex genetic disorder, with early developmental abnormalities in brain structure and function being important in determining vulnerability to illness. Among the different senses, olfaction is most closely associated with the brain regions implicated in the illness. Smell abnormalities may therefore be an early warning sign of disease onset. This study will examine changes in neural responses to odors in schizophrenia patients and adolescents who are at risk for the illness. The molecular causes of these abnormalities will be studied using both olfactory epithelial biopsies and post-mortem olfactory bulb tissue. This may provide important insights into the developmental causes of schizophrenia and facilitate early intervention or prevention.
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