Effects of Exercise Intensity on Spatial Memory Performance and Hippocampal Synaptic Plasticity in Transient Brain Ischemic Rats

Abstract

Memory impairment is commonly noted in stroke survivors, and can lead to delay of functional recovery. Exercise has been proved to improve memory in adult healthy subjects. Such beneficial effects are often suggested to relate to hippocampal synaptic plasticity, which is important for memory processing. Previous evidence showed that in normal rats, low intensity exercise can improve synaptic plasticity better than high intensity exercise. However, the effects of exercise intensities on hippocampal synaptic plasticity and spatial memory after brain ischemia remain unclear. In this study, we investigated such effects in brain ischemic rats. The middle cerebral artery occlusion (MCAO) procedure was used to induce brain ischemia. After the MCAO procedure, rats were randomly assigned to sedentary (Sed), low-intensity exercise (Low-Ex), or high-intensity exercise (High-Ex) group. Treadmill training began from the second day post MCAO procedure, 30 min/day for 14 consecutive days for the exercise groups. The Low-Ex group was trained at the speed of 8 m/min, while the High-Ex group at the speed of 20 m/min. The spatial memory, hippocampal brain-derived neurotrophic factor (BDNF), synapsin-I, postsynaptic density protein 95 (PSD-95), and dendritic structures were examined to document the effects. Serum corticosterone level was also quantified as stress marker. Our results showed the Low-Ex group, but not the High-Ex group, demonstrated better spatial memory performance than the Sed group. Dendritic complexity and the levels of BDNF and PSD-95 increased significantly only in the Low-Ex group as compared with the Sed group in bilateral hippocampus. Notably, increased level of corticosterone was found in the High-Ex group, implicating higher stress response. In conclusion, after brain ischemia, low intensity exercise may result in better synaptic plasticity and spatial memory performance than high intensity exercise; therefore, the intensity is suggested to be considered during exercise training.

Exercise and Environmental Enrichment as Enablers of Task-Specific Neuroplasticity and Stroke Recovery

“…Results show that exercise facilitated somatosensory recovery in the absence of any effect on neurogenesis [23]. Like EE, physical exercise improves recovery of general neurological function (e.g., limb placing, balance) [24,25] but not motor movements requiring a high level of dexterity such as reaching in rodents after stroke.…”

Electro-acupuncture ameliorates cognitive impairment via improvement of brain-derived neurotropic factor-mediated hippocampal synaptic plasticity in cerebral ischemia-reperfusion injured rats

“…BDNF is a member of the neurotrophin family (13,14), which is known to not only promote the activity of nerve growth, but also to modulate synaptic plasticity (15). For instance, numerous studies have indicated that BDNF enhances hippocampal synaptic plasticity by inducing local protein synthesis in the pre-synaptic terminal and post-synaptic dendrites of rats with cerebral ischemic injury (16,17). EA has been proved to protect the synaptic ultrastructure and promote the expression of P38, growth-associated protein-43 and BDNF in the ischemic cerebral cortex (18).…”

Effects of different delayed exercise regimens on cognitive performance in fimbria-fornix transected rats

“…It may be argued that exposure to forced exercise is a stressful event, however, as previously noted (see Greenwood et al 2013), stress per definition does not have to hinder the positive effects of exercise and may, under certain circumstances, even promote posttraumatic cognitive recovery (Gram et al 2015, Malá et al 2008. Several studies report a positive impact of post-injury exercise on spatial acquisition paradigms (Cechetti et al 2012, Griesbach et al 2004b, Kim et al 2010, Piao et al 2013, Shen et al 2013, Shih et al 2013, Sim et al 2004. There are also studies reporting detrimental or no effects of exercise on spatial acquisition measures (Clark et al 2008, Griesbach et al 2004a, Hicks et al 1998, Luo et al 2007, Piao et al 2013, Song et al 2012.…”

“…However, the evidence is sparse and very few studies include different administration schedules or examine the effects of varying exercise intensity (see e.g. Shen et al 2013, Shih et al 2013). …”