Cognitive and biochemical responses to continuous moderate and extensive interval exercise in randomized elderly male rats

BACKGROUND: Aging is associated with progressive cognitive decline and reduced neurobiological resilience that increase vulnerability to anxiety-related dysfunction. Although aerobic exercise is known to support brain health, whether different exercise modalities exert distinct behavioral and neurobiological effects remains unclear. This study aimed to investigate the effects of moderate continuous and extensive interval aerobic exercise on behavioral outcomes and underlying neurobiological mechanisms in aged male rats. METHODS: Thirty-two male Sprague Dawley rats (24 aged, 8 young adults) were randomly assigned to four groups (n = 8 per group): moderate continuous exercise (MCE; 0.5 km/h, 0° incline, 30 min), extensive interval exercise (EIE; alternating 5 min at 0.5 km/h and 1 min at 1.0 km/h, 30 min total, 0° incline), aged control, or young control. Following treadmill acclimatization, exercise was performed three days per week for six weeks. Anxiety-like behavior was assessed using the open field and elevated plus maze tests, and spatial learning and memory were evaluated with the Morris water maze. Serum, hippocampal, and gastrocnemius muscle samples were analyzed for brain-derived neurotrophic factor (BDNF), superoxide dismutase (SOD), glutathione peroxidase (GPx), and interleukin-10 (IL-10). Statistical analyses were conducted using one-way and repeated-measures ANOVA with Bonferroni post-hoc tests. RESULTS: Compared with aged controls, EIE reduced thigmotaxis in the open field test p = 0.035, d = 1.20), while no differences were observed in the elevated plus maze. Both exercise groups accelerated spatial learning across Morris water maze training days (p < 0.001). EIE was associated with improved memory retention, reflected by increased target quadrant time during the probe trial (p = 0.013, d = 1.35). Biochemically, EIE increased BDNF, IL-10, and SOD levels in serum and hippocampus (p < 0.05), whereas MCE selectively enhanced hippocampal GPx activity. Both exercise modalities elevated GPx levels in muscle and serum compared with aged controls (p < 0.05-0.001). CONCLUSIONS: Aerobic exercise was associated with changes in behavioral performance and neurobiological markers in aging rats. Interval-based training was associated with more pronounced changes in certain cognitive and biochemical parameters compared to moderate continuous exercise. These findings suggest that different exercise modalities may differentially influence selected cognitive and redox-related outcomes during aging.