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Antarctic Nototheniidae is an attractive group for studying metabolic and physiological responses at high temperatures. The present work investigated the metabolic responses of the carbohydrate metabolism and antioxidant system to thermal stress at 8 degrees C (for 2-144 h) in the brains of Notothenia rossii and Notothenia coriiceps. In N. coriiceps, glycogenolysis was essential in the first hours of exposure (2 h) at 8 degrees C and, in addition to inhibiting glucose-6-phosphatase activity, was important for activating the pentose phosphate pathway. In N. rossii, anaerobic metabolism was reduced in the first hours of exposure (2 and 6 h) at 8 degrees C, followed by reduced hexokinase activity, suggesting energy regulation between neurons and astrocytes. The antioxidant system results indicated the importance of the actions of the glutathione-dependent antioxidant enzymes glutathione-S-transferase and glutathione peroxidase as well as those of catalase in N. coriiceps and the action of glutathione-S-transferase, glutathione peroxidase and glutathione reductase in N. rossii, especially during the first 12 h of thermal stress exposure. These results indicate tissue-specific patterns and species-specific responses to this stress.