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Mitochondria are central regulators of energy homeostasis and play a pivotal role in mechanisms of cellular senescence. The objective of the present study was to evaluate mitochondrial bioenergetic parameters in 5 brain regions (brain stem [BS], frontal cortex, cerebellum, striatum, hippocampus [HIP]) of 4 diverse age groups (1 month [young], 4 months [adult], 12 months [middle-aged], 24 months [old age]) to understand age-related differences in selected brain regions and their possible contribution to age-related chemical sensitivity. Mitochondrial bioenergetic parameters and enzyme activities were measured under identical conditions across multiple age groups and brain regions in Brown Norway rats (n = 5/group). The results indicate age-and brain regionespecific patterns in mitochondrial functional endpoints. For example, an age-specific decline in ATP synthesis (State III respiration) was observed in BS and HIP. Similarly, the maximal respiratory capacities (State V-1 and V-2) showed age-specific declines in all brain regions examined (young > adult > middle-aged > old age). Amongst all regions, HIP had the greatest change in mitochondrial bioenergetics, showing declines in the 4, 12, and 24-months age groups. Activities of mitochondrial pyruvate dehydrogenase complex and electron transport chain complexes I, II, and IV enzymes were also age and brain region specific. In general, changes associated with age were more pronounced with enzyme activities declining as the animals aged (young > adult > middle-aged > old age). These age-and brain region-specific observations may aid in evaluating brain bioenergetic impact on the age-related susceptibility to environmental chemical stressors. Published by Elsevier Inc.