Abstract
Our six-week treadmill running training (forced exercise) model has revealed that mild exercise (ME) with an intensity below the lactate threshold (LT) is sufficient to enhance spatial memory, while intense exercise (IE) above the LT negates such benefits. To help understand the unrevealed neuronal and signaling/molecular mechanisms of the intensity-dependent cognitive change, in this rat model, we here investigated plasma corticosterone concentration as a marker of stress, adult hippocampal neurogenesis (AHN) as a potential contributor to this ME-induced spatial memory, and comprehensively delineated the hippocampal transcriptomic profile using a whole-genome DNA microarray analysis approach through comparison with IE. Results showed that only IE had the higher corticosterone concentration than control, and that the less intense exercise (ME) is better suited to improve AHN, especially in regards to the survival and maturation of newborn neurons. DNA microarray analysis using a 4 × 44 K Agilent chip revealed that ME regulated more genes than did IE (ME: 604 genes, IE: 415 genes), and only 41 genes were modified with both exercise intensities. The identified molecular components did not comprise well-known factors related to exercise-induced AHN, such as brain-derived neurotrophic factor. Rather, network analysis of the data using Ingenuity Pathway Analysis algorithms revealed that the ME-influenced genes were principally related to lipid metabolism, protein synthesis and inflammatory response, which are recognized as associated with AHN. In contrast, IE-influenced genes linked to excessive inflammatory immune response, which is a negative regulator of hippocampal neuroadaptation, were identified. Collectively, these results in a treadmill running model demonstrate that long-term ME, but not of IE, with minimizing running stress, has beneficial effects on increasing AHN, and provides an ME-specific gene inventory containing some potential regulators of this positive regulation. This evidence might serve in further elucidating the mechanism behind ME-induced cognitive gain.
Highlights
Dependent upon intensity based on lactate threshold (LT; approximately 50 to 60% of maximal oxygen consumption in humans), exercise has a positive effect on the function of the hippocampus, a brain region that plays an important role in the formation of memory [1,2,3,4,5]
Based on the LT, exercise is separated into mild exercise (ME; LT), which is accompanied by exercise-derived stress [9]
DNA microarray analysis showed that ME altered some novel adult hippocampal neurogenesis (AHN) regulators, which are related to lipid metabolism (APOE), protein synthesis (IGF2, IRS1) and inflammatory response (IL1B, TNF)
Summary
Dependent upon intensity based on lactate threshold (LT; approximately 50 to 60% of maximal oxygen consumption in humans), exercise has a positive effect on the function of the hippocampus, a brain region that plays an important role in the formation of memory [1,2,3,4,5]. The LT is known as a reference point where the steady state of blood lactate accumulation breaks down during incremental exercise. ME yields greater benefits for hippocampal function than does IE; our recent study showed that rats that underwent six weeks of mild (ME), but not intense (IE), treadmill running training had increased spatial memory in a Morris water maze (MWM) compared to sedentary controls (CONT) [5].
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