The benefits of voluntary physical exercise after traumatic brain injury on rat's object recognition memory: A comparison of different temporal schedules

Brain-Derived Neurotrophic Factor in Pediatric Acquired Brain Injury and Recovery

We review emerging preclinical and clinical evidence regarding brain-derived neurotrophic factor (BDNF) protein, genotype, and DNA methylation (DNAm) as biomarkers of outcomes in three important etiologies of pediatric acquired brain injury (ABI), traumatic brain injury, global cerebral ischemia, and stroke. We also summarize evidence suggesting that BDNF is (1) involved in the biological embedding of the psychosocial environment, (2) responsive to rehabilitative therapies, and (3) potentially modifiable. BDNF's unique potential as a biomarker of neuroplasticity and neural repair that is reflective of and responsive to both pre- and post-injury environmental influences separates it from traditional protein biomarkers of structural brain injury with exciting potential to advance pediatric ABI management by increasing the accuracy of prognostic tools and informing clinical decision making through the monitoring of therapeutic effects.

Effect of stress on the rehabilitation performance of rats with repetitive mild fluid percussion-induced traumatic brain injuries

Animal models of traumatic brain injury (TBI) have shown that impaired motor and cognitive function can be improved by physical exercise. However, not each animal with TBI can be well rehabilitated at the same training intensity due to a high inter-subject variability. Hence, this paper presents a two-stage wheel-based mixed-mode rehabilitation mechanism by which the effect of stress on the rehabilitation performance was investigated. The mixed-mode rehabilitation mechanism consists of a two-week adaptive and a one-week voluntary rehabilitation program as Stages 1 and 2, respectively. In Stage 1, the common over and undertraining problem were completely resolved due to the adaptive design, and rats ran voluntarily over a 30-min duration in Stage 2. The training intensity adapted to the physical condition of all the TBI rats at all times in Stage 1, and then the self-motivated running rats were further rehabilitated under the lowest level of stress in Stage 2. For comparison purposes, another group of rats took a 3-week adaptive rehabilitation program. During the 3-week program, the rehabilitation performance of the rats were assessed using modified neurologic severity score (mNSS) and an 8-arm radial maze. Surprisingly, the group taking the mixed mode program turned out to outperform its counterpart in terms of mNSS. The mixed-mode rehabilitation mechanism was validated as an effective and efficient way to help rats restore motor, neurological and cognitive function after TBI. It was validated that the rehabilitation performance can be optimized under the lowest level of stress.

Effect of Voluntary Exercise on Endogenous Pain Control Systems and Post-traumatic Headache in Mice

Traumatic brain injury (TBI) can cause acute and chronic pain along with motor, cognitive, and emotional problems. Although the mechanisms are poorly understood, previous studies suggest disruptions in endogenous pain modulation may be involved. Voluntary exercise after a TBI has been shown to reduce some consequences of injury including cognitive impairment. We hypothesized, therefore, that voluntary exercise could augment endogenous pain control systems in a rodent model of TBI. For these studies, we used a closed-head impact procedure in male mice modeling mild TBI. We investigated the effect of voluntary exercise on TBI-induced hindpaw nociceptive sensitization, diffuse noxious inhibitory control failure, and periorbital sensitization after bright light stress, a model of post-traumatic headache. Furthermore, we investigated the effects of exercise on memory, circulating markers of brain injury, neuroinflammation, and spinal cord gene expression. We observed that exercise significantly reduced TBI-induced hindpaw allodynia and periorbital allodynia in the first week following TBI. We also showed that exercise improved the deficits associated with diffuse noxious inhibitory control and reduced bright light stress-induced allodynia up to 2 months after TBI. In addition, exercise preserved memory and reduced TBI-induced increases in spinal BDNF, CXCL1, CXCL2, and prodynorphin expression, all genes previously linked to TBI-induced nociceptive sensitization. Taken together, our observations suggest that voluntary exercise may reduce pain after TBI by reducing TBI-induced changes in nociceptive signaling and preserving endogenous pain control systems. PERSPECTIVE: This article evaluates the effects of exercise on pain-related behaviors in a preclinical model of traumatic brain injury (TBI). The findings show that exercise reduces nociceptive sensitization, loss of diffuse noxious inhibitory control, memory deficits, and spinal nociception-related gene expression after TBI. Exercise may reduce or prevent pain after TBI.

Voluntary Exercise to Reduce Anxiety Behaviour in Traumatic Brain Injury Shown to Alleviate Inflammatory Brain Response in Mice

Traumatic brain injury is a leading cause of neuroinflammation and anxiety disorders in young adults. Immune-targeted therapies have garnered attention for the amelioration of TBI-induced anxiety. A previous study has indicated that voluntary exercise intervention following TBI could reduce neuroinflammation. It is essential to determine the effects of voluntary exercise after TBI on anxiety via inhibiting neuroinflammatory response. Mice were randomly divided into four groups (sham, TBI, sham + voluntary wheel running (VWR), and TBI + VWR). One-week VWR was carried out on the 2nd day after trauma. The neurofunction of TBI mice was assessed. Following VWR, anxiety behavior was evaluated, and neuroinflammatory responses in the perilesional cortex were investigated. Results showed that after one week of VWR, neurofunctional recovery was enhanced, while the anxiety behavior of TBI mice was significantly alleviated. The level of pro-inflammatory factors decreased, and the level of anti-inflammatory factors elevated. Activation of nucleotide oligomerization domain-like thermal receptor protein domain associated protein 3 (NLRP3) inflammasome was inhibited significantly. All these alterations were consistent with reduced microglial activation at the perilesional site and positively correlated with the amelioration of anxiety behavior. This suggested that timely rehabilitative exercise could be a useful therapeutic strategy for anxiety resulting from TBI by targeting neuroinflammation.

The benefits of exercise for outcome improvement following traumatic brain injury: Evidence, pitfalls and future perspectives

Traumatic brain injury (TBI), also known as a silent epidemic, is currently a substantial public health problem worldwide. Given the increased energy demands following brain injury, relevant guidelines tend to recommend absolute physical and cognitive rest for patients post-TBI. Nevertheless, recent evidence suggests that strict rest does not provide additional benefits to patients' recovery. By contrast, as a cost-effective non-pharmacological therapy, exercise has shown promise for enhancing functional outcomes after injury. This article summarizes the most recent evidence supporting the beneficial effects of exercise on TBI outcomes, focusing on the efficacy of exercise for cognitive recovery after injury and its potential mechanisms. Available evidence demonstrates the potential of exercise in improving cognitive impairment, mood disorders, and post-concussion syndrome following TBI. However, the clinical application for exercise rehabilitation in TBI remains challenging, particularly due to the inadequacy of the existing clinical evaluation system. Also, a better understanding of the underlying mechanisms whereby exercise promotes its most beneficial effects post-TBI will aid in the development of new clinical strategies to best benefit of these patients.

A Sensitive Homecage-Based Novel Object Recognition Task for Rodents

The recognition of novel objects is a common cognitive test for rodents, but current paradigms have limitations, such as low sensitivity, possible odor confounds and stress due to being performed outside of the homecage. We have developed a paradigm that takes place in the homecage and utilizes four stimuli per trial, to increase sensitivity. Odor confounds are eliminated because stimuli consist of inexpensive, machined wooden beads purchased in bulk, so each experimental animal has its own set of stimuli. This paradigm consists of three steps. In Step 1, the sampling phase, animals freely explore familiar objects (FO). Novel Objects (NO1 and NO2) are soiled with bedding from the homecage, to acquire odor cues identical to those of the FO. Steps 2 and 3 are test phases. Herein we report results of this paradigm from neurologically intact adult rats and mice of both sexes. Identical procedures were used for both species, except that the stimuli used for the mice were smaller. As expected in Step 2 (NO1 test phase), male and female rats and mice explored NO1 significantly more than FO. In Step 3 (NO2 test phase), rats of both sexes demonstrated a preference for NO2, while this was seen only in female mice. These results indicate robust novelty recognition during Steps 2 and 3 in rats. In mice, this was reliably seen only in Step 2, indicating that Step 3 was difficult for them under the given parameters. This paradigm provides flexibility in that length of the sampling phase, and the delay between test and sampling phases can be adjusted, to tailor task difficulty to the model being tested. In sum, this novel object recognition test is simple to perform, requires no expensive supplies or equipment, is conducted in the homecage (reducing stress), eliminates odor confounds, utilizes 4 stimuli to increase sensitivity, can be performed in both rats and mice, and is highly flexible, as sampling phase and the delay between steps can be adjusted to tailor task difficulty. Collectively, these results indicate that this paradigm can be used to quantify novel object recognition across sex and species.

Delayed voluntary physical exercise restores "when" and "where" object recognition memory after traumatic brain injury

Physical exercise has been associated with improved cognition and may even reduce memory deficits after brain injuries. The aims of this work were to: 1) assess whether voluntary physical exercise can reduce the deficits associated with traumatic brain injury (TBI) in two different components of episodic-like memory based on object recognition, temporal order memory ("when"), and object location memory ("where"); and 2) determine whether changes in levels of brain-derived neurotrophic factor (BDNF) in the hippocampus and prefrontal cortex, as well as alterations in hippocampal cytokines, insulin-like growth factor-1 (IGF-1) and vascular endothelial growth factor (VEGF), may influence the effects exercise has on either or both tasks. The rats were distributed into a sham group, a TBI group that remained sedentary (TBI-sed), and a TBI group that had access to a running wheel for a 25-day period from post-injury day 11 (TBI-exe). The rats were sacrificed after the "where" memory task, at post-injury day 37. Physical exercise restored the "when" and "where" memories, which had been impaired by the TBI, and increased the concentration of BDNF in the hippocampus, but not the prefrontal cortex. Neither TBI nor exercise were found to significantly affect hippocampal cytokines, IGF-1 or VEGF at this time post-injury. BDNF levels showed significant positive correlations with exercise, and with "when" (but not "where") memory. These results indicate that post-injury physical exercise restores "when" and "where" object recognition memory tasks after TBI, and that increased BDNF seems to be involved in this effect, particularly with regard to "when" memory.