Alcoholism is one of the most costly drug use problems in the United States and can result in psychiatric and medical diseases and even ultimately in death. Serotonin deficiency in alcoholics is hypothesized based on reduced serotonin metabolites in the cerebrospinal fluid, the efficacy of serotonin agonists and uptake inhibitors in reducing alcohol consumption, biochemical abnormalities in alcohol preferring rat strains and direct observations in human brain, postmortem and in vivo. During the present funding period, we have made findings in alcoholics of changes in serotonin neurons in the dorsal raphe nucleus (DRN) of increased tryptophan hydroxylase (TPH) serotonin-synthesizing enzyme, a decrease in the amount of serotonin transporter and 5-HT1A inhibitory autoreceptor binding and in the prefrontal cortex (PFC) of reduced 5-HT2A receptor binding in alcoholics and in cases with a family history of alcoholism and a decrease in the density of cortical neurons with duration of alcoholism. Changes observed in the DRN related to the duration of alcoholism are consistent with compensatory upregulation;whereas the alterations dependent on family history suggest a biological predisposition to alcoholism. Follow up studies of the serotonin system are proposed to examine these serotonin alterations in more detail and at the cellular level. The brain of 20 subjects meeting DSM-IV criteria for alcohol abuse or dependence and 20 nonpsychiatric controls will be examined. Alcohol abuse/dependence will be diagnosed by psychological autopsy.
Aim 1 seeks to define the capacity of DRN neurons to upregulate their function in alcoholics. Computer-assisted stereology of DRN neurons in alcoholics and non-psychiatric controls will determine the total number of DRN neurons and will be compared to the number of DRN neurons that are serotonin synthesizing to determine whether non-serotonergic neurons can change their phenotype to serotonergic in alcoholics. To determine whether the increase in the amount of TPH is due to increase TPH2 gene expression we will perform in situ hybridization. Preliminary studies found a decrease in serotonin transporter (SERT) in alcoholics suggesting the amount of DRN SERT could be a predisposing factor to the reinforcing effects of alcohol. Studies are proposed to examine the amount of SERT mRNA in the DRN to examine molecular responses at a cellular level.
Aim 2 examines target neurons in the prefrontal cortex and anterior cingulate cortex. Studies will be performed to determine the density and morphology of protective brain-derived neurotrophic (BDNF) factor neurons and the amount of BDNF mRNA by in situ hybridization. Change in the relative number of GABAergic inhibitory neurons will be determined in adjacent sections. Immunocytochemistry and quantitative morphology will be performed to NeuN and GAD65/67 as markers. The data gathered will suggest mechanisms involved in the pathogenesis of alcoholism. The demonstration of serotonergic neuropathology in the brain of alcoholics may suggest possible pharmacologic therapeutics and new diagnostic approaches using functional brain imaging.
Alcoholism is one of the most costly drug use problems in the United States. Alcohol consumption caused by alcoholism can result in psychiatric illness, medical diseases and even ultimately in death. Experiments are proposed in alcoholic and normal control postmortem brain tissues defining how serotonin, a neurotransmitter involved in mood and behavior, is affected by alcoholism and how serotonin deficits can contribute to the onset and maintenance of alcoholism.
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