The Effects of Repeated Toluene Exposure on Amino Acid Neurotransmitters in the Rat Brain / 대한구급학회지

Introduction: It was aimed to investigate the effect of chronic toluene exposure on amino acid neurotransmitters in the rat brain, corpus striatum. METHODS: Twenty four male Sprague-Dawley rats were divided into one of three groups, control, acute, and chronic. Each groups was for the microdialysis to estimate the changes of amino acid neurotransmitters, aspartate, glutamate, and citrulline before, during, and after 3,000 ppm toluene exposure for 2 hours. RESULTS: The results were as follows; 1) Aspartate and glutamate concentration were generally decreased in the toluene inhalation groups compared with the control group and more significantly decreased in chronic inhalation group than other groups. 2) Citrulline that expressed the activity of nitric oxide synthase and taurine as an inhibitory amino acid showed no significant differences between all groups. Based on these results, it is suggested that the decreasing excitatory amino acids, aspartate and glutamate, are partly contributed to the toxic mechanisms of toluene in rat brain.

An Experimental Study on MRI and Histopathologic Findings of the Brain in Toluene Inhaled Rat

PURPOSE: To evaluate MRI and histopathologic findings of toluene inhalation rat brain. MATERIALS AND METHODS: Forty-eight Sprague-Dawley rats, weighing 200-300g, were divided into six groups : the control group and five experimental groups each of eight rats, divided as follows, according to the concentration and duration of inhalation of toluene : 2500 ppm of toluence vapor for 2 hours only, 2 hours daily for 1 week, and 2 hours daily for 3 weeks ; 4000 ppm of toluence vapor for 2 hours only and 2 hours daily for 1 week. For all these five groups, a 0.02 m3; whole body exposure chamber was used. Spin echo and field echo (FE, gradient echo) MR images were obtained at 0.5 T, and then histopathologic examination of the brain was performed. MR signal changes were statistically assessed for contrast to noise ratio (CNR). RESULTS: On T2-weighted MR images, the toluene-inhalation groups revealed diffuse hypointensity in the corpus striatum and thalamus, and diffuse hyperintensity in cerebral white matter, with statistically significant CNR change, compared with the control group. On T1-weighted and FE images, CNR differences in the corpus striatum, thalamus and cerebral white matter between the toluene inhalation groups were not statistically significant. Histopathologic study of these groups showed (1)neuronal degeneration such as shrinkage of neuronal cells and increase of the number of autophagosomes, (2)myelin degeneration and regeneration, and (3)focal axonal degeneration, In groups in which toluene inhalation was at higher concentrations and for longer, these phenomena were more extensive. CONCLUSION: As seen on MRI, toluene inhalation changes the signal intensity of the corpus striatum, the thalamus, and cerebral white matter. Neuronal, myelinic and axonal degeneration probably contribute to these signal changes.