This study investigated central nervous system (CNS) integrity and neuropsychiatric status in a sample of workers with past exposure to solvents while employed in the Railroad (RR) industry. Solvent exposure was evaluated with a structured clinical interview to ascertain an estimate of cumulative lifetime exposure to solvents in the workplace. Exposed workers and a matched group of non-exposed blue collar workers underwent magnetic resonance imaging (MRI) to assess brain structure (e.g., white matter) and positron emission tomography (PET) to asses brain function. A battery of neuropsychological tests was also administered, as well as indices to assess psychiatric status. Exposed workers were selected from a sample of over 250 workers who had been seen in the Occupational and Environmental Health Clinic at the West Virginia University School of Medicine between 1995 and 2003. The subjects in the exposed group had been employed in the RR industry and had been exposed to solvents for at least 10 years. Estimates of lifetime exposure were based on years of exposure, symptoms during exposure (e.g., fresh air breaks), use of protective equipment, route of exposure (e.g., airborne, dermal), etc. Demographically matched non-exposed blue collar control workers were recruited from the surrounding community and completed the same battery of tests and compared to exposed subjects. Our specific aims were to: 1) Determine, as measured by  water PET methodology, brain regions which are associated with performance of cognitive tasks of working memory and executive function. 2) Contrast the unique aspects of brain structure and brain function of solvent-exposed subjects to demographically matched, nonexposed control subjects. 3) Assess neuropsychiatric status in all subjects with a battery of cognitive and psychiatric tests. 4) Analyze CNS integrity as a function of neuropsychological performance, psychiatric status, and exposure. Study findings to date show that the volume of the corpus callosum - an area with large white matter fibers - as measured by MRI, was reduced in subjects with solvent exposure and the volume of the corpus callosum was related to the extent of exposure and neuropsychological performance. Specifically, greater exposure was associated with smaller corpus callosum volume and smaller corpus callosum volume was associated with poorer performance on cognitive tests of executive function. We have also found that the volume of the prefrontal grey matter is reduced in subjects with solvent exposure and the volume is inversely related to extent of exposure and positively related to executive functions. In terms of the PET data, solvent exposed subjects show greater activation in the prefrontal cortex when performing cognitive tasks, relative to normal controls. The extent of activation is associated with extent of exposure such that increased exposure results in increased activation in the frontal cortex to perform the tasks. With regards to cognitive function, we found that exposed workers performed more poorly than non-exposed controls across several cognitive domains (e.g., memory and learning, executive function) and cognitive decrements in the exposed workers were significantly predicted by their overall estimate of lifetime exposure to solvents.
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