Pathophysiology of Schizophrenia and Dementia
Schizophrenia currently is conceptualized as a broad syndrome expressed by a heterogeneous group of brain disorders rather than as a single disease entity. In addition, schizophrenia is viewed as the most severe end of a spectrum of schizophrenia-related disorders. Although placed in the category of "functional" psychiatric disorders, schizophrenia is associated primarily with abnormalities of brain neurochemistry, neuroanatomy, and development. Genetics and intrauterine events likely play the major etiologic role in schizophrenia, with psychosocial stressors serving as precipitating or exacerbating factors. This view is a move away from the psychodynamic theories of the mid-twentieth century and a return to some of the earliest conceptions of the disease. This modern biopsychiatric model has a firm foundation in twin concordance studies and research into the actions of antipsychotic medications on the dopamine systems, and, more recently, serotonin, glutamate, and muscarine systems in the brain. As a result, antipsychotic medications are now the primary treatment for schizophrenia, with counseling and behavioral therapies playing supportive, but secondary, roles. The dopamine hypothesis suggests that the hallmark neurochemical disturbance is an overactivity of the dopamine system in the brain, particularly that involving the D2 receptors, which are blocked by all antipsychotic drugs (with the possible exception of the newest atypical antipsychotic drugs). Dopamine overactivity is thought to cause the positive symptoms of the disease. Diminished activity in the prefrontal cortex related to serotonin transmission is associated with the negative symptoms. The efficacy of the new atypical antipsychotics in reversing negative symptoms may be owing to their blockage of specific serotonin receptors. Glutamatergic and, most recently, muscarinic systems have been shown in some studies to be related to both positive and...
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