ABSTRACT
OBJECTIVE: This study investigates the effects of chronic alcohol exposure on rat brain THmRNA expression, TH (tyrosine hydroxylase) acitivity, and TPH (tryptophan hydroxylase) activity which are important in synthesis of dopamine and serotonin and other components of both the dopaminergic and serotonergic systems of the rat brain. METHODS: Rats were fed a liquid diet containing alcohol for 4 weeks. We investigated effects of chronic alcohol exposure on dopaminergic systems as follows. We evaluated expression of THmRNA in LC, VTA and substantia nigra by using in-situ hybridization and measured activity of TH by using immunoassay. We used HPLC for simultaneous measurement of dopamine, DOPAC and HVA in the cerebral cortex, striatum, hypothalamus, hippocampus, mid brain, hind brain, and cerebellum. Also we investigated serotonergic systems as follows. We evaluated expression of TH mRNA in the dorsal raphe nucleus by using radioprobe and measured the activity of TPH by using enzyme immunoassay. We used HPLC for simultaneous measurement of 5-HT and 5-HIAA in the cerebral cortex, striatum, hypothalamus, hippocampus, mid brain, hind brain, and cerebellum. RESULTS: Alcohol exposure for 4 weeks increased the expression of TH mRNA in the ventral tegmental area and the locus ceruleus but not in the substantia nigra. The 4 weeks of alcohol exposure did not cause significant changes in levels of dopamine and metabolites in the different areas of the brain, nor was it associated with changes in the maximal binding and affinity (Kd) of anterior striatal dopamine D2 receptor. Alcohol exposure for 4 weeks had no effect on the expression of TPH mRNA or on the activity of TPH in the dorsal raphe nucleus and the hypothalamus. CONCLUSION: We reported at first that chronic alcohol exposure could increase TH mRNA in the locus ceruleus. In a previous study of acute alcohol treatment, there is increase of dopamine metabolism but in this study, we did not observe any changes in dopamine metabolism in the different areas of the brain. Also we did not see any significant changes in the synthesis and metabolism of serotonin after 4 weeks of chronic alcohol exposure compared with control. Therefore, synthesis and metabolism of serotonin was affected in the acute phase. And, as previous reports have suggested, any changes caused by alcohol returned to previous levels via adaptation and regulatory mechanisms.