Locomotor exercise alters expression of pro-brain-derived neurotrophic factor, brain-derived neurotrophic factor and its receptor TrkB in the spinal cord of adult rats

Adaptation in the spinal cord after stroke: Implications for restoring cortical control over the final common pathway

Control of voluntary movement is predicated on integration between circuits in the brain and spinal cord. Although damage is often restricted to supraspinal or spinal circuits in cases of neurological injury, both spinal motor neurons and axons linking these cells to the cortical origins of descending motor commands begin showing changes soon after the brain is injured by stroke. The concept of 'transneuronal degeneration' is not new and has been documented in histological, imaging and electrophysiological studies dating back over a century. Taken together, evidence from these studies agrees more with a system attempting to survive rather than one passively surrendering to degeneration. There tends to be at least some preservation of fibres at the brainstem origin and along the spinal course of the descending white matter tracts, even in severe cases. Myelin-associated proteins are observed in the spinal cord years after stroke onset. Spinal motor neurons remain morphometrically unaltered. Skeletal muscle fibres once innervated by neurons that lose their source of trophic input receive collaterals from adjacent neurons, causing spinal motor units to consolidate and increase in size. Although some level of excitability within the distributed brain network mediating voluntary movement is needed to facilitate recovery, minimal structural connectivity between cortical and spinal motor neurons can support meaningful distal limb function. Restoring access to the final common pathway via the descending input that remains in the spinal cord therefore represents a viable target for directed plasticity, particularly in light of recent advances in rehabilitation medicine.

The Impact of Treadmill Training on Tissue Integrity, Axon Growth, and Astrocyte Modulation

Spinal cord injury (SCI) presents a complex challenge in neurorehabilitation, demanding innovative therapeutic strategies to facilitate functional recovery. This study investigates the effects of treadmill training on SCI recovery, emphasizing motor function enhancement, neural tissue preservation, and axonal growth. Our research, conducted on a rat model, demonstrates that controlled treadmill exercises significantly improve motor functions post-SCI, as evidenced by improved scores on the Basso, Beattie, and Bresnahan (BBB) locomotor rating scale and enhanced electromyography readings. Notably, the training facilitates the preservation of spinal cord tissue, effectively reducing secondary damage and promoting the maintenance of neural fibers in the injured area. A key finding is the significant stimulation of axonal growth around the injury epicenter in trained rats, marked by increased growth-associated protein 43 (GAP43) expression. Despite these advancements, the study notes a limited impact of treadmill training on motoneuron adaptation and highlights minimal changes in the astrocyte and neuron-glial antigen 2 (NG2) response. This suggests that, while treadmill training is instrumental in functional improvements post-SCI, its influence on certain neural cell types and glial populations is constrained.

Effects of a 1 year aerobic and strength training on cognitive functioning after transient ischemic attack or minor stroke: A randomized controlled trial

OBJECTIVES

Patients who have recently suffered a transient ischemic attack (TIA) or minor ischemic stroke are at increased risk of cognitive impairment. In the present study, we aimed to investigate the effect of a 1-year exercise intervention on cognitive functioning up to 2 years post intervention.

MATERIAL AND METHODS

We conducted a single-blind randomized controlled trial to investigate the effect of an exercise intervention on cognitive functioning, compared with usual care, for up to 2 years. Patients with a TIA or minor stroke were randomly allocated to an intervention group receiving the 1-year exercise intervention (n = 60) or to usual care (n = 59). Outcome measures were assessed at baseline and after 1 and 2 years. We measured cognition with neuropsychological tests on three domains: (1) executive functioning, (2) attention-psychomotor speed, and (3) memory. Linear mixed models were used for longitudinal data to determine the effect of the exercise intervention on cognitive functioning. Statistical analyses were performed using IBM SPSS software 24.0.

RESULTS

We found that over the two years study period -and corrected for age, sex, and educational level- the intervention group on average improved significantly more in executive functioning than the control group (β = 0.13; 95 % CI [0.02 to 0.25]; p = 0.03). No significant intervention effects were found on either memory or attention-psychomotor speed.

CONCLUSIONS

Our data show that a 1-year exercise intervention significantly improved executive functioning over time, compared to usual care. We recommend that health care professionals consider broadening standard secondary stroke prevention treatment in patients with TIA/minor stroke by adding exercise and physical activity.

BDNF Spinal Overexpression after Spinal Cord Injury Partially Protects Soleus Neuromuscular Junction from Disintegration, Increasing VAChT and AChE Transcripts in Soleus but Not Tibialis Anterior Motoneurons

After spinal cord transection (SCT) the interaction between motoneurons (MNs) and muscle is impaired, due to reorganization of the spinal network after a loss of supraspinal inputs. Rats subjected to SCT, treated with intraspinal injection of a AAV-BDNF (brain-derived neurotrophic factor) construct, partially regained the ability to walk. The central effects of this treatment have been identified, but its impact at the neuromuscular junction (NMJ) has not been characterized. Here, we compared the ability of NMJ pre- and postsynaptic machinery in the ankle extensor (Sol) and flexor (TA) muscles to respond to intraspinal AAV-BDNF after SCT. The gene expression of cholinergic molecules (VAChT, ChAT, AChE, nAChR, mAChR) was investigated in tracer-identified, microdissected MN perikarya, and in muscle fibers with the use of qPCR. In the NMJs, a distribution of VAChT, nAChR and Schwann cells was studied by immunofluorescence, and of synaptic vesicles and membrane active zones by electron microscopy. We showed partial protection of the Sol NMJs from disintegration, and upregulation of the VAChT and AChE transcripts in the Sol, but not the TA MNs after spinal enrichment with BDNF. We propose that the observed discrepancy in response to BDNF treatment is an effect of difference in the TrkB expression setting BDNF responsiveness, and of BDNF demands in Sol and TA muscles.

Activation of Three Major Signaling Pathways After Endurance Training and Spinal Cord Injury

We aimed to investigate the effects of endurance training on expression of growth factors (GFs) and stimulation of neurotrophin-dependent signaling pathways (PI3k/Akt, PLCγ/PKC, PLCγ/CAMKII, Ras-Erk1/2 and Rac1-Cdc42) responsible for neuroplasticity, neuroregeneration, survival and growth after spinal cord injury (SCI). Wistar rats were divided into four groups: (i) intact controls; (ii) 6 weeks of endurance training; (iii) SCI; (iv) pre-training + SCI. The animals survived for 6 weeks after SCI. Firstly, endurance training markedly upregulated mRNA expression and protein levels (up to four times) of growth factors (BDNF, GDNF) and their receptors (TrkB, Gfrα) in low thoracic segments (Th8–Th10) compared to levels in untrained animals. Secondly, we found that spontaneous neuroplasticity seen in the SCI alone group was GF-specific and was activated through both PLCγ-PKC and PLC-CAMKII signaling pathways. In addition, training prior to SCI markedly increased the activity of PLCγ-PKC signaling at both transcript and protein levels at and around the lesion site. Similar effects were seen in expression of PI3k/Akt and Ras/Erk1/2 signaling responsible for cell survival and regeneration. Thirdly, rats which underwent physical activity prior to SCI were more active and had significantly better neurological scores at the 14th and 42nd days of survival. These results suggest that regular physical activity could play an important role after SCI, as it maintains increased expression of GFs in spinal cord tissue 6 weeks post-SCI. The BDNF- and/or BDNF + GDNF-dependent signaling pathways were significantly affected in pre-trained SCI animals. In contrast, GDNF-dependent Rac1-Cdc42 signaling was not involved in training-affected SCI response.

The Effect of Two Types of Exercise Preconditioning on the Expression of TrkB, TNF-α, and MMP2 Genes in Rats with Stroke

Despite the beneficial effects of exercise and physical activity, there is little knowledge about the effects of different types of physical activity on neural function. The present study assessed the effects of two types of selected aerobic exercises prior to stroke induction and characterized the expression of TrkB, TNF-α, and MMP2 genes in vivo. Forty male adult Wistar rats were exposed to aerobic exercises following randomization into four groups, including swimming + MCAO (Middle Cerebral Artery Occlusion) (n = 10), treadmill training + MCAO (n = 10), MCAO (n = 10), and control (n = 10). The swimming + MCAO group included swimming for 30 minutes each day, while the treadmill training + MCAO group program involved running for 30 minutes each day at an intensity of 15 m/min, for three weeks, five days a week. Neurological deficit was assessed using modified criteria at 24 h after the onset of cerebral ischemia. In the control group, the animals worked freely for three weeks without undergoing ischemia. The MCAO group also operated freely for three weeks after they underwent a stroke. Both training groups underwent ischemia after three weeks of training. TrkB, TNF-α, and MMP2 gene expressions were increased in the MCAO+ swimming training and in the MCAO + running training group compared to the control and MCAO groups, respectively. Preconditioning aerobic exercises significantly increased brain trophic support and reduced brain damage conditions in exercise groups, which support the importance of aerobic exercise in the prevention and treatment of stroke.

The Role of Brain-Derived Neurotrophic Factor in Irritable Bowel Syndrome

Several studies have implied a role of brain-derived neurotrophic factor (BDNF) in abdominal pain modulation in irritable bowel syndrome (IBS). The aim of this study was to establish BDNF protein expression in human colonic biopsies and to show variation in IBS compared to controls. BDNF protein and mRNA levels were correlated with IBS symptom severity based on the IBS-symptom severity score (IBS-SSS). Biopsies from the descending colon and IBS-SSS were obtained from 10 controls and 20 IBS patients. Total protein of biopsies was extracted and assessed by ELISA and Western Blot. Total mRNA was extracted and gene expression measured by nCounter analysis. In IBS patients, symptom severity scores ranged from 124 to 486 (mean ± sem: 314.2 ± 21.2, >300 represents severe IBS) while controls ranged from 0 to 72 (mean ± sem: 27.7 ± 9.0, <75 represents healthy subjects, p < 0.001). IBS patients reported significantly more food malabsorption, former abdominal surgery and psychiatric comorbidities. BDNF protein was present in all samples and did not differ between IBS and controls or sex. Subgroup analysis showed that female IBS patients expressed significantly more BDNF mRNA compared to male patients (p < 0.05) and male IBS-D patients had higher IBS symptom severity scores and lower BDNF mRNA and protein levels compared to male controls (p < 0.05). Scatter plot showed a significant negative correlation between IBS-SSS and BDNF mRNA levels in the cohort of male IBS-D patients and their male controls (p < 0.05). We detected a high proportion of gastrointestinal surgery in IBS patients and confirmed food intolerances and psychiatric diseases as common comorbidities. Although in a small sample, we demonstrated that BDNF is detectable in human descending colon, with higher BDNF mRNA levels in female IBS patients compared to males and lower mRNA and protein levels in male IBS-D patients compared to male controls. Further research should be directed toward subgroups of IBS since their etiologies might be different.

Diverse spinal commissural neuron populations revealed by fate mapping and molecular profiling using a novel Robo3Cre mouse

The two sides of the nervous system coordinate and integrate information via commissural neurons, which project axons across the midline. Commissural neurons in the spinal cord are a highly heterogeneous population of cells with respect to their birthplace, final cell body position, axonal trajectory, and neurotransmitter phenotype. Although commissural axon guidance during development has been studied in great detail, neither the developmental origins nor the mature phenotypes of commissural neurons have been characterized comprehensively, largely due to lack of selective genetic access to these neurons. Here, we generated mice expressing Cre recombinase from the Robo3 locus specifically in commissural neurons. We used Robo3 ^Cre mice to characterize the transcriptome and various origins of developing commissural neurons, revealing new details about their extensive heterogeneity in molecular makeup and developmental lineage. Further, we followed the fate of commissural neurons into adulthood, thereby elucidating their settling positions and molecular diversity and providing evidence for possible functions in various spinal cord circuits. Our studies establish an important genetic entry point for further analyses of commissural neuron development, connectivity, and function.

Differential impacts of brain stem oxidative stress and nitrosative stress on sympathetic vasomotor tone

Based on work-done in the rostral ventrolateral medulla (RVLM), this review presents four lessons learnt from studying the differential impacts of oxidative stress and nitrosative stress on sympathetic vasomotor tone and their clinical and therapeutic implications. The first lesson is that an increase in sympathetic vasomotor tone because of augmented oxidative stress in the RVLM is responsible for the generation of neurogenic hypertension. On the other hand, a shift from oxidative stress to nitrosative stress in the RVLM underpins the succession of increase to decrease in sympathetic vasomotor tone during the progression towards brain stem death. The second lesson is that, by having different cellular sources, regulatory mechanisms on synthesis and degradation, kinetics of chemical reactions, and downstream signaling pathways, reactive oxygen species and reactive nitrogen species should not be regarded as a singular moiety. The third lesson is that well-defined differential roles of oxidative stress and nitrosative stress with distinct regulatory mechanisms in the RVLM during neurogenic hypertension and brain stem death clearly denote that they are not interchangeable phenomena with unified cellular actions. Special attention must be paid to their beneficial or detrimental roles under a specific disease or a particular time-window of that disease. The fourth lesson is that, to be successful, future antioxidant therapies against neurogenic hypertension must take into consideration the much more complicated picture than that presented in this review on the generation, maintenance, regulation or modulation of the sympathetic vasomotor tone. The identification that the progression towards brain stem death entails a shift from oxidative stress to nitrosative stress in the RVLM may open a new vista for therapeutic intervention to slow down this transition.

Swimming Training Reduces Neuroma Pain by Regulating Neurotrophins

Introduction

Neuroma formation after peripheral nerve transection leads to severe neuropathic pain in amputees. Previous studies suggested that physical exercise could bring beneficial effect on alleviating neuropathic pain. However, the effect of exercise on neuroma pain still remained unclear. In addition, long-term exercise can affect the expression of neurotrophins (NT), such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), which play key roles in nociceptor sensitization and nerve sprouting after nerve injury. Here, we investigated whether long-term swimming exercise could relieve neuroma pain by modulating NT expression.

Methods

We used a tibial neuroma transposition (TNT) rat model to mimic neuroma pain. After TNT surgery, rats performed swimming exercise for 5 wk. Neuroma pain and tactile sensitivities were detected using von Frey filaments. Immunofluorescence was applied to analyze neuroma formation. NGF and BDNF expressions in peripheral neuroma, dorsal root ganglion, and the spinal cord were measured using enzyme-linked immunosorbent assay and Western blotting.

Results

TNT led to neuroma formation, induced neuroma pain, and mechanical allodynia in hind paw. Five-week swimming exercise inhibited neuroma formation and relieved mechanical allodynia in the hind paw and neuroma pain in the lateral ankle. The analgesic effect lasted for at least 1 wk, even when the exercise ceased. TNT elevated the expressions of BDNF and NGF in peripheral neuroma, dorsal root ganglion, and the spinal cord to different extents. Swimming also decreased the elevation of NT expression.

Conclusions

Swimming exercise not only inhibits neuroma formation induced by nerve transection but also relieves pain behavior. These effects might be associated with the modulation of NT.

Effective robotic assistive pattern of treadmill training for spinal cord injury in a rat model

The purpose of the present study was to establish an effective robotic assistive stepping pattern of body-weight-supported treadmill training based on a rat spinal cord injury (SCI) model and assess the effect by comparing this with another frequently used assistive stepping pattern. The recorded stepping patterns of both hind limbs of trained intact rats were edited to establish a 30-sec playback normal rat stepping pattern (NRSP). Step features (step length, step height, step number and swing duration), BBB scores, latencies, and amplitudes of the transcranial electrical motor-evoked potentials (tceMEPs) and neurofilament 200 (NF200) expression in the spinal cord lesion area during and after 3 weeks of body-weight-supported treadmill training (BWSTT) were compared in rats with spinal contusion receiving NRSP assistance (NRSPA) and those that received manual assistance (MA). Hind limb stepping performance among rats receiving NRSPA during BWSTT was greater than that among rats receiving MA in terms of longer step length, taller step height, and longer swing duration. Furthermore a higher BBB score was also indicated. The rats in the NRSPA group achieved superior results in the tceMEPs assessment and greater NF200 expression in the spinal cord lesion area compared with the rats in the MA group. These findings suggest NRSPA was an effective assistive pattern of treadmill training compared with MA based on the rat SCI model and this approach could be used as a new platform for animal experiments for better understanding the mechanisms of SCI rehabilitation.

Protective effects of telmisartan and tempol on lipopolysaccharide-induced cognitive impairment, neuroinflammation, and amyloidogenesis: possible role of brain-derived neurotrophic factor

Angiotensin II has pro-inflammatory and pro-oxidant potentials. We investigated the possible protective effects of the Angiotensin II receptor blocker telmisartan, compared with the superoxide scavenger tempol, on lipopolysaccharide (LPS)-induced cognitive decline and amyloidogenesis. Briefly, mice were allocated into a normal control group, an LPS control group, a tempol treatment group, and 2 telmisartan treatment groups. A behavioral study was conducted followed by a biochemical study via assessment of brain levels of beta amyloid (Aβ) and brain-derived neurotropic factor (BDNF) as amyloidogenesis and neuroplasticity markers, tumor necrosis factor alpha (TNF-α), nitric oxide end products (NOx), neuronal and inducible nitric oxide synthase (nNOS and iNOS) as inflammatory markers, and superoxide dismutase (SOD), malondialdehyde (MDA), glutathione reduced (GSH), and nitrotyrosine (NT) as oxido-nitrosative stress markers. Finally, histopathological examination of cerebral cortex, hippocampus, and cerebellum sections was performed using routine and special Congo red stains. Tempol and telmisartan improved cognition, decreased brain Aβ deposition and BDNF depletion, decreased TNF-α, NOx, nNOS, iNOS, MDA, and NT brain levels, and increased brain SOD and GSH contents, parallel to confirmatory histopathological evidences. In conclusion, tempol and telmisartan are promising drugs in managing cognitive impairment and amyloidogenesis, at least via upregulation of BDNF with inhibition of neuroinflammation and oxido-nitrosative stress.

Resistance wheel exercise from mid-life has minimal effect on sciatic nerves from old mice in which sarcopenia was prevented

The ability of resistance exercise, initiated from mid-life, to prevent age-related changes in old sciatic nerves, was investigated in male and female C57BL/6J mice. Aging is associated with cellular changes in old sciatic nerves and also loss of skeletal muscle mass and function (sarcopenia). Mature adult mice aged 15 months (M) were subjected to increasing voluntary resistance wheel exercise (RWE) over a period of 8 M until 23 M of age. This prevented sarcopenia in the old 23 M aged male and female mice. Nerves of control sedentary (SED) males at 3, 15 and 23 M of age, showed a decrease in the myelinated axon numbers at 15 and 23 M, a decreased g-ratio and a significantly increased proportion of myelinated nerves containing electron-dense aggregates at 23 M. Myelinated axon and nerve diameter, and axonal area, were increased at 15 M compared with 3 and 23 M. Exercise increased myelinated nerve profiles containing aggregates at 23 M. S100 protein, detected with immunoblotting was increased in sciatic nerves of 23 M old SED females, but not males, compared with 15 M, with no effect of exercise. Other neuronal proteins showed no significant alterations with age, gender or exercise. Overall the RWE had no cellular impact on the aging nerves, apart from an increased number of old nerves containing aggregates. Thus the relationship between cellular changes in aging nerves, and their sustained capacity for stimulation of old skeletal muscles to help maintain healthy muscle mass in response to exercise remains unclear.

Effects of a Sedentary Intervention on Cognitive Function

PURPOSE

To examine the effects of a free-living, sedentary-inducing intervention on cognitive function.

DESIGN

Randomized controlled, parallel group intervention.

SETTING

University campus.

PARTICIPANTS

Thirty-three young adults (n = 23 intervention; n = 10 control).

MEASURES

The intervention group was asked to eliminate all exercise and minimize steps to ≤5000 steps/day for 1 week, whereas the control group was asked to continue normal physical activity (PA) levels for 1 week. Both groups completed a series of 8 cognitive function assessments (assessing multiple parameters of cognition) preintervention and immediately postintervention. The intervention group was asked to resume normal PA levels for 1 week postintervention and completed the cognitive assessments for a third time at 2 weeks postintervention.

ANALYSIS

Split-plot repeated-measures analysis of variance.

RESULTS

The results of our statistical analyses showed that the group × time interaction effect was not significant ( P > .05) for any of the evaluated cognitive parameters.

CONCLUSION

These findings demonstrate the need for future experimental investigations of sedentary behavior to better understand its effects on cognitive function. However, although previous work has demonstrated favorable effects of acute and chronic PA on cognitive function, our findings suggest that a 1-week period of reduced PA does not detrimentally affect cognitive function, which may have encouraging implications for individuals going through a temporary relapse in PA.

Behavioral and biochemical effects of ketamine and dextromethorphan relative to its antidepressant-like effects in Swiss Webster mice

Ketamine has been shown to produce rapid and robust antidepressant effects in depressed individuals; however, its abuse potential and adverse psychotomimetic effects limit its widespread use. Dextromethorphan (DM) may serve as a safer alternative on the basis of pharmacodynamic similarities to ketamine. In this proof-of-concept study, behavioral and biochemical analyses were carried out to evaluate the potential involvement of brain-derived neurotrophic factor (BDNF) in the antidepressant-like effects of DM in mice, with comparisons to ketamine and imipramine. Male Swiss, Webster mice were injected with DM, ketamine, or imipramine and their behaviors were evaluated in the forced-swim test and the open-field test. Western blots were used to measure BDNF and its precursor, pro-BDNF, protein expression in the hippocampus and the frontal cortex of these mice. Our results show that both DM and imipramine reduced immobility time in the forced-swim test without affecting locomotor activity, whereas ketamine reduced immobility time and increased locomotor activity. Ketamine also rapidly (within 40 min) increased pro-BDNF expression in an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor-dependent manner in the hippocampus, whereas DM and imipramine did not alter pro-BDNF or BDNF levels in either the hippocampus or the frontal cortex within this timeframe. These data show that DM shares some features with both ketamine and imipramine. Additional studies examining DM may aid in the development of more rapid, safe, and efficacious antidepressant treatments.

The effect of physical activity on cognitive function in patients with dementia: A meta-analysis of randomized control trials

Non-pharmacological therapies, such as physical activity interventions, are an appealing alternative or add-on to current pharmacological treatment of cognitive symptoms in patients with dementia. In this meta-analysis, we investigated the effect of physical activity interventions on cognitive function in dementia patients, by synthesizing data from 802 patients included in 18 randomized control trials that applied a physical activity intervention with cognitive function as an outcome measure. Post-intervention standardized mean difference (SMD) scores were computed for each study, and combined into pooled effect sizes using random effects meta-analysis. The primary analysis yielded a positive overall effect of physical activity interventions on cognitive function (SMD[95% confidence interval]=0.42[0.23;0.62], p<.01). Secondary analyses revealed that physical activity interventions were equally beneficial in patients with Alzheimer's disease (AD, SMD=0.38[0.09;0.66], p<.01) and in patients with AD or a non-AD dementia diagnosis (SMD=0.47[0.14;0.80], p<.01). Combined (i.e. aerobic and non-aerobic) exercise interventions (SMD=0.59[0.32;0.86], p<.01) and aerobic-only exercise interventions (SMD=0.41[0.05;0.76], p<.05) had a positive effect on cognition, while this association was absent for non-aerobic exercise interventions (SMD=-0.10[-0.38;0.19], p=.51). Finally, we found that interventions offered at both high frequency (SMD=0.33[0.03;0.63], p<.05) and at low frequency (SMD=0.64[0.39;0.89], p<.01) had a positive effect on cognitive function. This meta-analysis suggests that physical activity interventions positively influence cognitive function in patients with dementia. This beneficial effect was independent of the clinical diagnosis and the frequency of the intervention, and was driven by interventions that included aerobic exercise.

Effects of hindlimb unloading on neurotrophins in the rat spinal cord and soleus muscle

The aim of the present study was to investigate the effects of hindlimb unloading (HU) on the expression of neurotrophin-3 (NT-3) and brain-derived neurotrophic factor (BDNF), together with the expression of their high-affinity receptors tropomyosin receptor kinase C (TrkC) and tropomyosin receptor kinase B (TrkB), in lumbar (L4-6) segment of the spinal cord and in the soleus muscle. The mRNA and protein levels of the genes of interest were compared using quantitative PCR and western blot assays. Immunohistochemistry for NT-3 and BDNF was used to detect the levels of protein in the motoneurons in the lateral motor column. In this study, NT-3 and BDNF mRNA and protein expression were significantly increased in the spinal cord and soleus muscle after HU. NT-3 immunoreactivity, but not BDNF immunoreactivity, was significantly increased in the large motoneurons located in lateral motor column after 14 days of HU. The level of TrkC protein in the spinal cord and soleus muscle were significantly elevated after both 7 days and 14 days of HU. However, TrkC mRNA, TrkB mRNA and TrkB protein levels did not change significantly. Elevated BDNF, NT-3 and TrkC levels in the neuromuscular system indicate that neurotrophins are involved in HU-induced neuromuscular plasticity. NT-3 is a candidate to mediate the synaptic efficacy between alpha motoneurons and group Ia afferents.

Superoxide Mediates Depressive Effects Induced by Hydrogen Sulfide in Rostral Ventrolateral Medulla of Spontaneously Hypertensive Rats

Hydrogen sulfide (H₂S) plays a crucial role in the regulation of blood pressure and oxidative stress. In the present study, we tested the hypothesis that H₂S exerts its cardiovascular effects by reducing oxidative stress via inhibition of NADPH oxidase activity in the rostral ventrolateral medulla (RVLM). We examined cell distributions of cystathionine-β-synthase (CBS) and effects of H₂S on reactive oxygen species (ROS) and mean arterial blood pressure (MAP) in spontaneously hypertensive rats (SHRs). We found that CBS was expressed in neurons of the RVLM, and the expression was lower in SHRs than in Wistar-Kyoto rats. Microinjection of NaHS (H₂S donor), S-adenosyl-l-methionine (SAM, a CBS agonist), or Apocynin (NADPH oxidase inhibitor) into the RVLM reduced the ROS level, NADPH oxidase activity, and MAP, whereas microinjection of hydroxylamine hydrochloride (HA, a CBS inhibitor) increased MAP. Furthermore, intracerebroventricular infusion of NaHS inhibited phosphorylation of p47^phox, a key step of NADPH oxidase activation. Since decreasing ROS level in the RVLM reduces MAP and heart rate and increasing H₂S reduces ROS production, we conclude that H₂S exerts an antihypertensive effect via suppressing ROS production. H₂S, as an antioxidant, may be a potential target for cardiovascular diseases.

Serotonin receptor and KCC2 gene expression in lumbar flexor and extensor motoneurons posttransection with and without passive cycling

Sacrocaudal motoneuron gene expression is altered following a spinal transection. Of interest here is the regulation of serotonin (5-HT) receptors (R), glutamate receptor, metabotropic 1 (mGluR1), and potassium-chloride cotransporter (KCC2), which mediate motoneuron excitability, locomotor recovery, and spasticity posttransection. The examination of these genes in lumbar motoneurons posttransection has not been studied, which is necessary for developing potential pharmacological interventions aimed at restoring locomotion and/or reducing spasticity. Also, if activity is to be used to promote recovery or reduce spasticity postinjury, a further examination of neuromuscular activity on gene expression posttransection is warranted. The purpose of this study was to examine motoneuronal gene expression of 5-HT receptors, KCC2, and mGluR1 at 3 mo following a complete thoracic spinal cord transection, with and without the inclusion of daily passive cycling. Physiological hindlimb extensor and flexor motoneurons were differentially identified with two retrograde fluorescent tracers, allowing for the identification and separate harvesting of extensor and flexor motoneurons with laser capture microdissection and the subsequent examination of mRNA content using quantitative RT-PCR analysis. We demonstrate that posttransection 5-HT1AR, 5-HT2CR, and mGluR1 expression was downregulated, whereas the 5-HT2AR was upregulated. These alterations in gene expression were observed in both flexor and extensor motoneurons, whereas passive cycling influenced gene expression in extensor but not flexor motoneurons. Passive cycling in extensor motoneurons further enhanced 5-HT2AR expression and increased 5-HT7R and KCC2 expression. Our results demonstrate that passive cycling influences serotonin receptor and KCC2 gene expression and that extensor motoneurons compared with flexor motoneurons may be more plastic to activity-based interventions posttransection.

Distribution and phenotype of TrkB oligodendrocyte lineage cells in the adult rat spinal cord

The distribution and phenotype of a previously undescribed population of nonneuronal cells in the intact spinal cord that expresses TrkB, the cognate receptor for brain derived neurotrophic factor (BDNF) and neurotrophin 4 (NT-4), were characterized by examining the extent of co-localization of TrkB with NG2, which identifies oligodendrocyte progenitors (OPCs) or CC1, a marker for mature oligodendrocytes (OLs). All TrkB nonneuronal cells expressed Olig2, confirming their role in the OL lineage. Similar to OPCs and OLs, TrkB cells resided in gray and white matter of the spinal cord in similar abundance. Less than 2% of TrkB cells expressed NG2, while over 80% of TrkB cells in the adult spinal cord co-expressed CC1. Most OPCs did not express detectable levels of TrkB, however a small OPC pool (~5%) showed TrkB immunoreactivity. The majority of mature OLs (~65%) expressed TrkB, but a population of mature OLs (~36%) did not express TrkB at detectable levels, and 17% of TrkB nonneuronal cells did not express NG2 or CC1. Approximately 20% of the TrkB nonneuronal population in the ventral horn resided in close proximity to motor neurons and were categorized as perineuronal. We conclude that TrkB is expressed by several pools of OL lineage cells in the adult spinal cord. These findings are important in understanding the neurotrophin regulation of OL lineage cells in the adult spinal cord.

Chronic wheel running reduces maladaptive patterns of methamphetamine intake: regulation by attenuation of methamphetamine-induced neuronal nitric oxide synthase

We investigated whether prior exposure to chronic wheel running (WR) alters maladaptive patterns of excessive and escalating methamphetamine intake under extended access conditions, and intravenous methamphetamine self-administration-induced neurotoxicity. Adult rats were given access to WR or no wheel (sedentary) in their home cage for 6 weeks. A set of WR rats were injected with 5-bromo-2'-deoxyuridine (BrdU) to determine WR-induced changes in proliferation (2-h old) and survival (28-day old) of hippocampal progenitors. Another set of WR rats were withdrawn (WRw) or continued (WRc) to have access to running wheels in their home cages during self-administration days. Following self-administration [6 h/day], rats were tested on the progressive ratio (PR) schedule. Following PR, BrdU was injected to determine levels of proliferating progenitors (2-h old). WRc rats self-administered significantly less methamphetamine than sedentary rats during acquisition and escalation sessions, and demonstrated reduced motivation for methamphetamine seeking. Methamphetamine reduced daily running activity of WRc rats compared with that of pre-methamphetamine days. WRw rats self-administered significantly more methamphetamine than sedentary rats during acquisition, an effect that was not observed during escalation and PR sessions. WR-induced beneficial effects on methamphetamine self-administration were not attributable to neuroplasticity effects in the hippocampus and medial prefrontal cortex, but were attributable to WR-induced inhibition of methamphetamine-induced increases in the number of neuronal nitric oxide synthase expressing neurons and apoptosis in the nucleus accumbens shell. Our results demonstrate that WR prevents methamphetamine-induced damage to forebrain neurons to provide a beneficial effect on drug-taking behavior. Importantly, WR-induced neuroprotective effects are transient and continued WR activity is necessary to prevent compulsive methamphetamine intake.

Overexpression of BDNF increases excitability of the lumbar spinal network and leads to robust early locomotor recovery in completely spinalized rats

Strategies to induce recovery from lesions of the spinal cord have not fully resulted in clinical applications. This is a consequence of a number of impediments that axons encounter when trying to regrow beyond the lesion site, and that intraspinal rearrangements are subjected to. In the present study we evaluated (1) the possibility to improve locomotor recovery after complete transection of the spinal cord by means of an adeno-associated (AAV) viral vector expressing the neurotrophin brain-derived neurotrophic factor (BDNF) in lumbar spinal neurons caudal to the lesion site and (2) how the spinal cord transection and BDNF treatment affected neurotransmission in the segments caudal to the lesion site. BDNF overexpression resulted in clear increases in expression levels of molecules involved in glutamatergic (VGluT2) and GABAergic (GABA, GAD65, GAD67) neurotransmission in parallel with a reduction of the potassium-chloride co-transporter (KCC2) which contributes to an inhibitory neurotransmission. BDNF treated animals showed significant improvements in assisted locomotor performance, and performed locomotor movements with body weight support and plantar foot placement on a moving treadmill. These positive effects of BDNF local overexpression were detectable as early as two weeks after spinal cord transection and viral vector application and lasted for at least 7 weeks. Gradually increasing frequencies of clonic movements at the end of the experiment attenuated the quality of treadmill walking. These data indicate that BDNF has the potential to enhance the functionality of isolated lumbar circuits, but also that BDNF levels have to be tightly controlled to prevent hyperexcitability.

Exercise training plus calorie restriction causes synergistic protection against cognitive decline via up-regulation of BDNF in hippocampus of stroke-prone hypertensive rats

One of the important organ damage of hypertension is cognitive decline. Cognitive function is determined by the function of hippocampus, and previous studies have suggested that the decrease in brain-derived neurotrophic factor (BDNF) in the hippocampus causes cognitive decline. Protection against cognitive decline is reported not only in pharmacological therapy but also in exercise training or calorie restriction. The aim of the present study was to determine whether exercise training plus calorie restriction cause synergistic protection against cognitive decline via BDNF in the hippocampus or not. Exercise training for 28 days improved cognitive decline determined by Morris water maze test via up-regulation of BDNF in the hippocampus of stroke-prone spontaneously hypertensive rats, whereas calorie restriction for 28 days did not. However, exercise training plus calorie restriction causes the protection against cognitive decline to a greater extent than exercise training alone. In conclusion, exercise training plus calorie restriction causes synergistic protection against cognitive decline via up-regulation of BDNF in the hippocampus of stroke-prone hypertensive rats.

Transection of preganglionic axons leads to CNS neuronal plasticity followed by survival and target reinnervation

The goals of the present study were to investigate the changes in sympathetic preganglionic neurons following transection of distal axons in the cervical sympathetic trunk (CST) that innervate the superior cervical ganglion (SCG) and to assess changes in the protein expression of brain derived neurotrophic factor (BDNF) and its receptor TrkB in the thoracic spinal cord. At 1 week, a significant decrease in soma volume and reduced soma expression of choline acetyltransferase (ChAT) in the intermediolateral cell column (IML) of T1 spinal cord were observed, with both ChAT-ir and non-immunoreactive neurons expressing the injury marker activating transcription factor 3. These changes were transient, and at later time points, ChAT expression and soma volume returned to control values and the number of ATF3 neurons declined. No evidence for cell loss or neuronal apoptosis was detected at any time point. Protein levels of BDNF and/or full length TrkB in the spinal cord were increased throughout the survival period. In the SCG, both ChAT-ir axons and ChAT protein remained decreased at 16 weeks, but were increased compared to the 10 week time point. These results suggest that though IML neurons show reduced ChAT expression and cell volume at 1 week following CST transection, at later time points, the neurons recovered and exhibited no significant signs of neurodegeneration. The alterations in BDNF and/or TrkB may have contributed to the survival of the IML neurons and the recovery of ChAT expression, as well as to the reinnervation of the SCG.

Enhancing proprioceptive input to motoneurons differentially affects expression of neurotrophin 3 and brain-derived neurotrophic factor in rat hoffmann-reflex circuitry

The importance of neurotrophin 3 (NT-3) for motor control prompted us to ask the question whether direct electrical stimulation of low-threshold muscle afferents, strengthening the proprioceptive signaling, could effectively increase the endogenous pool of this neurotrophin and its receptor TrkC in the Hoffmann-reflex (H-reflex) circuitry. The effects were compared with those of brain-derived neurotrophic factor (BDNF) and its TrkB receptor. Continuous bursts of stimuli were delivered unilaterally for seven days, 80 min daily, by means of a cuff-electrode implanted over the tibial nerve in awake rats. The H-reflex was recorded in the soleus muscle to control the strength of stimulation. Stimulation aimed at activation of Ia fibers produced a strong increase of NT-3 protein, measured with ELISA, in the lumbar L3-6 segments of the spinal cord and in the soleus muscle. This stimulation exerted much weaker effect on BDNF protein level which slightly increased only in L3-6 segments of the spinal cord. Increased protein level of NT-3 and BDNF corresponded to the changes of NT-3 mRNA and BDNF mRNA expression in L3-6 segments but not in the soleus muscle. We disclosed tissue-specificity of TrkC mRNA and TrkB mRNA responses. In the spinal cord TrkC and TrkB transcripts tended to decrease, whereas in the soleus muscle TrkB mRNA decreased and TrkC mRNA expression strongly increased, suggesting that stimulation of Ia fibers leads to sensitization of the soleus muscle to NT-3 signaling. The possibility of increasing NT-3/TrkC signaling in the neuromuscular system, with minor effects on BDNF/TrkB signaling, by means of low-threshold electrical stimulation of peripheral nerves, which in humans might be applied in non-invasive way, offers an attractive therapeutic tool.

Differential effects of activity dependent treatments on axonal regeneration and neuropathic pain after peripheral nerve injury

Activity treatments are useful strategies to increase axonal regeneration and functional recovery after nerve lesions. They are thought to benefit neuropathy by enhancing neurotrophic factor expression. Nevertheless the effects on sensory function are still unclear. Since neurotrophic factors also play a fundamental role in peripheral and central sensitization, we studied the effects of acute electrical stimulation and early treadmill exercise on nerve regeneration and on neuropathic pain, and the relation with the expression of neurotrophins. After sciatic nerve section and suture repair, rats were subjected to electrical stimulation (ES) for 4h after injury, forced treadmill running (TR) for 5 days, or both treatments combined. Sciatic nerve section induced hyperalgesia in the medial area of the plantar skin in the injured paw. TR and ES differently but positively reduced adjacent neuropathic pain before and after sciatic reinnervation. ES enhanced motor and sensory reinnervation, and combination with TR induced strong agonistic effects in relieving pain. The differential effects of these activity treatments were related to changes in neurotrophic factor mRNA levels in sensory and motor neurons. ES speeded up expression of BDNF and GDNF in DRG, and of BDNF and NT3 in the ventral horn. TR reduced the levels of pro-nociceptive factors such as BDNF, NGF and GDNF in DRG. Combination of ES and TR induced intermediate levels suggesting an optimal balancing of treatment effects.

Comparative effect of treadmill exercise on mature BDNF production in control versus stroke rats

Physical exercise constitutes an innovative strategy to treat deficits associated with stroke through the promotion of BDNF-dependent neuroplasticity. However, there is no consensus on the optimal intensity/duration of exercise. In addition, whether previous stroke changes the effect of exercise on the brain is not known. Therefore, the present study compared the effects of a clinically-relevant form of exercise on cerebral BDNF levels and localization in control versus stroke rats. For this purpose, treadmill exercise (0.3 m/s, 30 min/day, for 7 consecutive days) was started in rats with a cortical ischemic stroke after complete maturation of the lesion or in control rats. Sedentary rats were run in parallel. Mature and proBDNF levels were measured on the day following the last boot of exercise using Western blotting analysis. Total BDNF levels were simultaneously measured using ELISA tests. As compared to the striatum and the hippocampus, the cortex was the most responsive region to exercise. In this region, exercise resulted in a comparable increase in the production of mature BDNF in intact and stroke rats but increased proBDNF levels only in intact rats. Importantly, levels of mature BDNF and synaptophysin were strongly correlated. These changes in BDNF metabolism coincided with the appearance of intense BDNF labeling in the endothelium of cortical vessels. Notably, ELISA tests failed to detect changes in BDNF forms. Our results suggest that control beings can be used to find conditions of exercise that will result in increased mBDNF levels in stroke beings. They also suggest cerebral endothelium as a potential source of BDNF after exercise and highlight the importance to specifically measure the mature form of BDNF to assess BDNF-dependent plasticity in relation with exercise.

Telmisartan protects against cognitive decline via up-regulation of brain-derived neurotrophic factor/tropomyosin-related kinase B in hippocampus of hypertensive rats

BACKGROUND AND PURPOSE

Cognitive decline may occur as a result of hypertension, and is dependent on the function of hippocampus. Brain-derived neurotrophic factor (BDNF) mediated by angiotensin II-induced oxidative stress protects against cell death in hippocampus. Angiotensin II receptor blocker (ARB), candesartan, activates BDNF in the hippocampus. Furthermore, peroxisome proliferator-activated receptor (PPAR)-gamma activation in the brain prevents brain damage. Telmisartan, a unique ARB with PPAR-gamma stimulating activity, protects against cognitive decline partly because of PPAR-gamma activation. The aim of the present study was to determine whether telmisartan protects against cognitive decline via up-regulation of BDNF and its receptor tropomyosin-related kinase B (TrkB) in the hippocampus of hypertensive rats, partly because of PPAR-gamma activation.

METHODS AND RESULTS

We divided stroke-prone spontaneously hypertensive rats (SHRSPs), as hypertensive and vascular dementia model rats, into five groups, telmisartan-treated (TLM), TLM+GW9662, a PPAR-gamma inhibitor, -treated (T+G), GW9662-treated (GW), TLM+ANA-12, a TrkB antagonist, -treated (T+A), and vehicle-treated SHRSPs (VEH). After the treatment for 28 days, systolic blood pressure did not change in all groups. However, BDNF expression in the hippocampus was significantly higher in TLM than in VEH to a greater extent than in T+G. Cognitive performance was significantly higher in TLM than in VEH to a greater extent than in T+G, and was not different between T+A, GW, and VEH.

CONCLUSION

Telmisartan protects against cognitive decline via up-regulation of BDNF/TrkB in the hippocampus of SHRSPs, partly because of PPAR-gamma activation independent of blood pressure-lowering effect.

Treadmill training stimulates brain-derived neurotrophic factor mRNA expression in motor neurons of the lumbar spinal cord in spinally transected rats

Brain-derived neurotrophic factor (BDNF) induces plasticity within the lumbar spinal circuits thereby improving locomotor recovery in spinal cord-injured animals. We examined whether lumbar spinal cord motor neurons and other ventral horn cells of spinally transected (ST) rats were stimulated to produce BDNF mRNA in response to treadmill training. Rats received complete spinal cord transections as neonates (n=20) and one month later, received four weeks of either a low (100 steps/training session; n=10) or high (1000 steps/training session; n=10) amount of robotic-assisted treadmill training. Using combined non-radioactive in situ hybridization and immunohistochemical techniques, we found BDNF mRNA expression in heat shock protein 27-labeled motor neurons and in non-motor neuron cells was greater after 1000 steps/training session compared to the 100 steps/training session and was similar to BDNF mRNA labeling in untrained Intact rats. In addition, there were significantly more motor neurons that contained BDNF mRNA labeling within processes in the ST rats that received the higher amount of treadmill training. These findings suggested that motor neurons and other ventral horn cells in ST rats synthesized BDNF in response to treadmill training. The findings support a mechanism by which postsynaptic release of BDNF from motor neurons contributed to synaptic plasticity.

Different effects of spinalization and locomotor training of spinal animals on cholinergic innervation of the soleus and tibialis anterior motoneurons

Cholinergic input modulates excitability of motoneurons and plays an important role in the control of locomotion in both intact and spinalized animals. However, spinal cord transection in adult rats affects cholinergic innervation of only some hindlimb motoneurons, suggesting that specificity of this response is related to functional differences between motoneurons. Our aim was therefore to compare cholinergic input to motoneurons innervating the soleus (Sol) and tibialis anterior (TA) motoneurons following spinal cord transection at a low-thoracic level. The second aim was to investigate whether deficits in cholinergic input to these motoneurons could be modified by locomotor training. The Sol and TA motoneurons were identified by retrograde labelling with fluorescent dyes injected intramuscularly. Cholinergic terminals were detected using anti-vesicular acetylcholine transporter (VAChT) antibody. Overall innervation of motoneurons was evaluated with anti-synaptophysin antibody. After spinalization we found a decrease in the number of VAChT-positive boutons apposing perikarya of the Sol (to 49%) but not TA motoneurons. Locomotor training, resulting in moderate functional improvement, partly reduced the deficit in cholinergic innervation of Sol motoneurons by increasing the number of VAChT-positive boutons. However, the optical density of VAChT-positive boutons terminating on various motoneurons, which decreased after spinalization, continued to decrease despite the training, suggesting an impairment of acetylcholine availability in the terminals. Different effects of spinal cord transection on cholinergic innervation of motoneurons controlling the ankle extensor and flexor muscles point to different functional states of these muscles in paraplegia as a possible source of activity-dependent signaling regulating cholinergic input to the motoneurons.

Brain-derived neurotrophic factor ameliorates brain stem cardiovascular dysregulation during experimental temporal lobe status epilepticus

BACKGROUND

Status epilepticus (SE) is an acute, prolonged epileptic crisis with a mortality rate of 20-30%; the underlying mechanism is not completely understood. We assessed the hypothesis that brain stem cardiovascular dysregulation occurs during SE because of oxidative stress in rostral ventrolateral medulla (RVLM), a key nucleus of the baroreflex loop; to be ameliorated by brain-derived neurotrophic factor (BDNF) via an antioxidant action.

METHODOLOGY/PRINCIPAL FINDINGS

In a clinically relevant experimental model of temporal lobe SE (TLSE) using Sprague-Dawley rats, sustained hippocampal seizure activity was accompanied by progressive hypotension that was preceded by a reduction in baroreflex-mediated sympathetic vasomotor tone; heart rate and baroreflex-mediated cardiac responses remained unaltered. Biochemical experiments further showed concurrent augmentation of superoxide anion, phosphorylated p47(phox) subunit of NADPH oxidase and mRNA or protein levels of BDNF, tropomyosin receptor kinase B (TrkB), angiotensin AT1 receptor subtype (AT1R), nitric oxide synthase II (NOS II) or peroxynitrite in RVLM. Whereas pretreatment by microinjection bilaterally into RVLM of a superoxide dismutase mimetic (tempol), a specific antagonist of NADPH oxidase (apocynin) or an AT1R antagonist (losartan) blunted significantly the augmented superoxide anion or phosphorylated p47(phox) subunit in RVLM, hypotension and the reduced baroreflex-mediated sympathetic vasomotor tone during experimental TLSE, pretreatment with a recombinant human TrkB-Fc fusion protein or an antisense bdnf oligonucleotide significantly potentiated all those events, alongside peroxynitrite. However, none of the pretreatments affected the insignificant changes in heart rate and baroreflex-mediated cardiac responses.

CONCLUSIONS/SIGNIFICANCE

We conclude that formation of peroxynitrite by a reaction between superoxide anion generated by NADPH oxidase in RVLM on activation by AT1R and NOS II-derived NO leads to a reduction in baroreflex-mediated sympathetic vasomotor tone during experimental TLSE; to be ameliorated by the upregulated BDNF/TrkB signaling via inhibition of p47(phox) phosphorylation. This information offers a new vista in devising therapeutic strategy towards minimizing mortality associated with TLSE.

Acute and prolonged hindlimb exercise elicits different gene expression in motoneurons than sensory neurons after spinal cord injury

We examined gene expression in the lumbar spinal cord and the specific response of motoneurons, intermediate gray and proprioceptive sensory neurons after spinal cord injury and exercise of hindlimbs to identify potential molecular processes involved in activity dependent plasticity. Adult female rats received a low thoracic transection and passive cycling exercise for 1 or 4weeks. Gene expression analysis focused on the neurotrophic factors: brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), and their receptors because of their potential roles in neural plasticity. We also examined expression of genes involved in the cellular response to injury: heat shock proteins (HSP) -27 and -70, glial fibrillary acidic protein (GFAP) and caspases -3, -7, and -9. In lumbar cord samples, injury increased the expression of mRNA for TrkB, all three caspases and the HSPs. Acute and prolonged exercise increased expression of mRNA for the neurotrophic factors BDNF and GDNF, but not their receptors. It also increased HSP expression and decreased caspase-7 expression, with changes in protein levels complimentary to these changes in mRNA expression. Motoneurons and intermediate gray displayed little change in mRNA expression following injury, but acute and prolonged exercise increased levels of mRNA for BDNF, GDNF and NT-4. In large DRG neurons, mRNA for neurotrophic factors and their receptors were largely unaffected by either injury or exercise. However, caspase mRNA expression was increased by injury and decreased by exercise. Our results demonstrate that exercise affects expression of genes involved in plasticity and apoptosis in a cell specific manner and that these change with increased post-injury intervals and/or prolonged periods of exercise.

Brain-derived neurotrophic factor promotes adaptive plasticity within the spinal cord and mediates the beneficial effects of controllable stimulation

Brain-derived neurotrophic factor (BDNF) has been characterized as a potent modulator of neural plasticity in both the brain and spinal cord. The present experiments use an in vivo model system to demonstrate that training with controllable stimulation increases spinal BDNF expression and engages a BDNF-dependent process that promotes adaptive plasticity. Spinally transected rats administered legshock whenever one hind limb is extended (controllable stimulation) exhibit a progressive increase in flexion duration. This simple form of response-outcome (instrumental) learning is not observed when shock is given independent of leg position (uncontrollable stimulation). Uncontrollable electrical stimulation also induces a lasting effect that impairs learning for up to 48 h. Training with controllable shock can counter the adverse consequences of uncontrollable stimulation, to both prevent and reverse the learning deficit. Here it is shown that the protective and restorative effect of instrumental training depends on BDNF. Cellular assays showed that controllable stimulation increased BDNF mRNA expression and protein within the lumbar spinal cord. These changes were associated with an increase in the BDNF receptor TrkB protein within the dorsal horn. Evidence is then presented that these changes play a functional role in vivo. Application of a BDNF inhibitor (TrkB-IgG) blocked the protective effect of instrumental training. Direct (intrathecal) application of BDNF substituted for instrumental training to block both the induction and expression of the learning deficit. Uncontrollable stimulation also induced an increase in mechanical reactivity (allodynia), and this too was prevented by BDNF. TrkB-IgG blocked the restorative effect of instrumental training and intrathecal BDNF substituted for training to reverse the deficit. Taken together, these findings outline a critical role for BDNF in mediating the beneficial effects of controllable stimulation on spinal plasticity.

Enhancing recovery from peripheral nerve injury using treadmill training

Full functional recovery after traumatic peripheral nerve injury is rare. We postulate three reasons for the poor functional outcome measures observed. Axon regeneration is slow and not all axons participate. Significant misdirection of regenerating axons to reinnervate inappropriate targets occurs. Seemingly permanent changes in neural circuitry in the central nervous system are found to accompany axotomy of peripheral axons. Exercise in the form of modest daily treadmill training impacts all three of these areas. Compared to untrained controls, regenerating axons elongate considerably farther in treadmill trained animals and do so via an autocrine/paracrine neurotrophin signaling pathway. This enhancement of axon regeneration takes place without an increase in the amount of misdirection of regenerating axons found without training. The enhancement also occurs in a sex-dependent manner. Slow continuous training is effective only in males, while more intense interval training is effective only in females. In treadmill trained, but not untrained mice the extent of coverage of axotomized motoneurons is maintained, thus preserving important elements of the spinal circuitry.

Differential effects of low versus high amounts of weight supported treadmill training in spinally transected rats

Intensive weight-supported treadmill training (WSTT) improves locomotor function following spinal cord injury. Because of a number of factors, undergoing intensive sessions of training may not be feasible. Whether reduced amounts of training are sufficient to enhance spinal plasticity to a level that is necessary for improving function is not known. The focus of the present study was to assess differences in recovery of locomotor function and spinal plasticity as a function of the amount of steps taken during WSTT in a rodent model of spinal cord injury. Rats were spinally transected at 5 days of age. When they reached 28 days of age, a robotic system was used to implement a weight-supported treadmill training program of either 100 or 1000 steps/training session daily for 4 weeks. Antibodies for brain-derived neurotrophic factor (BDNF), TrkB, and the pre-synaptic marker, synaptophysin, were used to examine the expression of these proteins in the ventral horn of the lumbar spinal cord. Rats that received weight-supported treadmill training performed better stepping relative to untrained rats, but only the rats that received 1000 steps/training session recovered locomotor function that resembled normal patterns. Only the rats that received 1000 steps/training session recovered normal levels of synaptophysin immunoreactivity around motor neurons. Weight-supported treadmill training consisting of either 100 or 1000 steps/training session increased BDNF immunoreactivity in the ventral horn of the lumbar spinal cord. TrkB expression in the ventral horn was not affected by spinal cord transection or weight-supported treadmill training. Synaptophysin expression, but not BDNF or TrkB expression was correlated with the recovery of stepping function. These findings suggested that a large amount of weight-supported treadmill training was necessary for restoring synaptic connections to motor neurons within the locomotor generating circuitry. Although a large amount of training was best for recovery, small amounts of training were associated with incremental gains in function and increased BDNF levels.

Treadmill training improves motor skills and increases tyrosine hydroxylase immunoreactivity in the substantia nigra pars compacta in diabetic rats

The aim of this study was to evaluate the effects of treadmill training on motor skills and immunoreactivity to tyrosine hydroxylase in the substantia nigra pars compacta and ventral tegmental area from diabetic rats induced by streptozotocin. Male Wistar rats were divided into three groups: control, diabetic and trained diabetic. Treadmill training was performed for 8weeks. Blood glucose concentrations and body weight were evaluated 48h after diabetes induction and every 30days thereafter. Motor skills were evaluated on the rotarod and open field tests. Then, animals were transcardially perfused and the brains were post-fixed, cryoprotected and sectioned in a cryostat. Immunohistochemistry for tyrosine hydroxylase analyses was done in the ventral tegmental area and in the substantia nigra. Motor skills showed that diabetic animals had a decrease in the latency to fall and enhanced number of falls in the rotarod test compared to control and trained diabetic animals. In the open field, diabetic animals had a decrease in the number of crossed squares, rearings and spent a less time moving compared to control and trained diabetic animals. In diabetic animals, optical densitometry of immunohistochemistry showed that tyrosine hydroxylase reaction decreased in the ventral tegmental area and in the neurons and process in the substantia nigra. In the later region, that decrease was reversed by treadmill training. In conclusion, we demonstrated that treadmill training can reverse the loss of the motor skills, which was correlated to tyrosine hydroxylase immunoreactivity in the substantia nigra of diabetic animals without pharmacological treatment.

Wind-up of stretch reflexes as a measure of spasticity in chronic spinalized rats: The effects of passive exercise and modafinil

Spasticity is a common disorder following spinal cord injury that can impair function and quality of life. While a number of mechanisms are thought to play a role in spasticity, the role of motoneuron persistent inward currents (PICs) is emerging as pivotal. The presence of PICs can be evidenced by temporal summation or wind-up of reflex responses to brief afferent inputs. In this study, a combined neurophysiological and novel biomechanical approach was used to assess the effects of passive exercise and modafinil administration on hyper-reflexia and spasticity following complete T-10 transection in the rat. Animals were divided into 3 groups (n=8) and provided daily passive cycling exercise, oral modafinil, or no intervention. After 6weeks, animals were tested for wind-up of the stretch reflex (SR) during repeated dorsiflexion stretches of the ankle. H-reflexes were tested in a subset of animals. Both torque and gastrocnemius electromyography showed evidence of SR wind-up in the transection only group that was significantly different from both treatment groups (p<0.05). H-reflex frequency dependent depression was also restored to normal levels in both treatment groups. The results provide support for the use of passive cycling exercise and modafinil in the treatment of spasticity and provide insight into the possible contribution of PICs.

Clinical and experimental advances in regeneration of spinal cord injury

Spinal cord injury (SCI) is one of the major disabilities dealt with in clinical rehabilitation settings and is multifactorial in that the patients suffer from motor and sensory impairments as well as many other complications throughout their lifetimes. Many clinical trials have been documented during the last two decades to restore damaged spinal cords. However, only a few pharmacological therapies used in clinical settings which still have only limited effects on the regeneration, recovery speed, or retraining of the spinal cord. In this paper, we will introduce recent clinical trials, which performed pharmacological treatments and cell transplantations for patients with SCI, and evaluate recent in vivo studies for the regeneration of injured spinal cord, including stem-cell transplantation, application of neurotrophic factors and suppressor of inhibiting factors, development of biomaterial scaffolds and delivery systems, rehabilitation, and the combinations of these therapies to evaluate what can be appropriately applied in the future to the patients with SCI.

Transcriptional upregulation of brain-derived neurotrophic factor in rostral ventrolateral medulla by angiotensin II: significance in superoxide homeostasis and neural regulation of arterial pressure

RATIONALE

Oxidative stress in rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons for the maintenance of neurogenic vasomotor tone are located, contributes to neural mechanisms of hypertension. Emerging evidence suggests that brain-derived neurotrophic factor (BDNF) manifests "nontrophic" actions.

OBJECTIVE

We assessed the hypothesis that BDNF plays an active role in oxidative stress-associated neurogenic hypertension by maintaining superoxide anion (O⁻(.)₂) homeostasis in RVLM.

METHODS AND RESULTS

In Wistar-Kyoto rats, microinjection of angiotensin II (Ang II) bilaterally into RVLM upregulated BDNF mRNA and protein and induced cAMP response element binding protein (CREB) phosphorylation. The Ang II-induced BDNF upregulation in RVLM was attenuated by coadministration of the NADPH oxidase inhibitor apocynin; the superoxide dismutase mimetic tempol; or an antisense oligonucleotide against CREB. Intracisternal infusion of Ang II elicited phosphorylation of p47(phox) subunit of NADPH oxidase, suppression of mitochondrial electron coupling capacity, and augmentation in mitochondrial uncoupling protein (UCP)2 expression in RVLM. The former 2 cellular events were enhanced, whereas UCP2 upregulation was attenuated by gene knockdown of BDNF or depletion of tropomyosin receptor kinase (Trk)B ligands with recombinant human TrkB-Fc fusion protein. The same treatments also significantly potentiated both Ang II-induced (O⁻(.)₂) production in RVLM and chronic pressor response.

CONCLUSIONS

Ang II induces (O⁻(.)₂) -dependent upregulation of BDNF in RVLM via phosphorylation of CREB. The Ang II-activated BDNF/TrkB signaling, in turn, exerts negative-feedback regulation on tissue (O⁻(.)₂) level in RVLM through inhibition of p47(phox) phosphorylation, preservation of mitochondrial electron transport capacity, and upregulation of mitochondrial UCP2, resulting in protection against Ang II-induced oxidative stress and long-term pressor response.

Reduction of extinction and reinstatement of cocaine seeking by wheel running in female rats

RATIONALE AND OBJECTIVES

Previous work has shown that wheel running reduced the maintenance of cocaine self-administration in rats. In the present study, the effect of wheel running on extinction and reinstatement of cocaine seeking was examined. Female rats were trained to run in a wheel during 6-h sessions, and they were then catheterized and placed in an operant conditioning chamber where they did not have access to the wheel but were allowed to self-administer iv cocaine. Subsequently, rats were divided into four groups and were tested on the extinction and reinstatement of cocaine seeking while they had varying access to a wheel in an adjoining compartment. The four groups were assigned to the following wheel access conditions: (1) wheel running during extinction and reinstatement (WER), (2) wheel running during extinction and a locked wheel during reinstatement (WE), (3) locked wheel during extinction and wheel running during reinstatement (WR), and (4) locked wheel during extinction and reinstatement (WL). WE and WR were retested later to examine the effect of one session of wheel access on cocaine-primed reinstatement.

RESULTS

There were no group differences in wheel revolutions, in rate of acquisition of cocaine self-administration, or in responding during maintenance when there was no wheel access. However, during extinction, WE and WER responded less than WR and WL. WR and WER had lower cocaine-primed reinstatement than WE and WL. One session of wheel exposure in WE also suppressed cocaine-primed reinstatement.

CONCLUSIONS

Wheel running immediately and effectively reduced cocaine-seeking behavior, but concurrent access to running was necessary. Thus, exercise is a useful and self-sustaining intervention to reduce cocaine-seeking behavior.

Exercise-induced motor improvement after complete spinal cord transection and its relation to expression of brain-derived neurotrophic factor and presynaptic markers

BACKGROUND

It has been postulated that exercise-induced activation of brain-derived neurotrophic factor (BDNF) may account for improvement of stepping ability in animals after complete spinal cord transection. As we have shown previously, treadmill locomotor exercise leads to up-regulation of BDNF protein and mRNA in the entire neuronal network of intact spinal cord. The questions arise: (i) how the treadmill locomotor training, supplemented with tail stimulation, affects the expression of molecular correlates of synaptic plasticity in spinal rats, and (ii) if a response is related to BDNF protein level and distribution. We investigated the effect of training in rats spinalized at low thoracic segments on the level and distribution of BDNF immunoreactivity (IR) in ventral quadrants of the lumbar segments, in conjunction with markers of presynaptic terminals, synaptophysin and synaptic zinc.

RESULTS

Training improved hindlimb stepping in spinal animals evaluated with modified Basso-Beattie-Bresnahan scale. Grades of spinal trained animals ranged between 5 and 11, whereas those of spinal were between 2 and 4. Functional improvement was associated with changes in presynaptic markers and BDNF distribution. Six weeks after transection, synaptophysin IR was reduced by 18% around the large neurons of lamina IX and training elevated its expression by over 30%. The level of synaptic zinc staining in the ventral horn was unaltered, whereas in ventral funiculi it was decreased by 26% postlesion and tended to normalize after the training. Overall BDNF IR levels in the ventral horn, which were higher by 22% postlesion, were unchanged after the training. However, training modified distribution of BDNF in the processes with its predominance in the longer and thicker ones. It also caused selective up-regulation of BDNF in two classes of cells (soma ranging between 100-400 microm2 and over 1000 microm2) of the ventrolateral and laterodorsal motor nuclei.

CONCLUSION

Our results show that it is not BDNF deficit that determines lack of functional improvement in spinal animals. They indicate selectivity of up-regulation of BDNF in distinct subpopulations of cells in the motor nuclei which leads to changes of innervation targeting motoneurons, tuned up by locomotor activity as indicated by a region-specific increase of presynaptic markers.

Transcriptional response of the neuromuscular system to exercise training and potential implications for ALS

The transcriptional adaptive response of motoneurons and muscles to voluntary exercise has been investigated by using laser capture microdissection and microarray analysis. Our results show that motoneurons respond to physical activity by activating a complex transcriptional plan, with changes involved in neurotrophic factor signalling, electrophysiological changes and synaptic reorganization. Gastrocnemius muscle shows increases in transcripts responsible for neovascularization and new myogenesis. Both tissues show transcriptional changes involved in the growth and reinforcement of the neuromuscular junction. This study indicates that the neuromuscular system undergoes significant structural and functional alterations, aiming to optimize the transmission of both chemical and electrical stimuli, thus prompting axonal outgrowth and mechanisms similar to long-term potentiation in hippocampal neurons. Understanding the response of these cells during exercise has potentially important implications for human neuromuscular disease, including amyotrophic lateral sclerosis, by highlighting candidate genes pivotal for the balance between the physiology and the pathology of the neuromuscular system in terms of the stress response to physical exercise.

Up-regulating BDNF with an ampakine rescues synaptic plasticity and memory in Huntington's disease knockin mice

Cognitive problems occur in asymptomatic gene carriers of Huntington's disease (HD), and mouse models of the disease exhibit impaired learning and substantial deficits in the cytoskeletal changes that stabilize long-term potentiation (LTP). The latter effects may be related to the decreased production of brain-derived neurotrophic factor (BDNF) associated with the HD mutation. This study asked whether up-regulating endogenous BDNF levels with an ampakine, a positive modulator of AMPA-type glutamate receptors, rescues plasticity and reduces learning problems in HD (CAG140) mice. Twice-daily injections of a short half-life ampakine normalized BDNF levels, activity-driven actin polymerization in dendritic spines, and LTP stabilization in 8-week-old mutants. Comparable results were obtained in 16-week-old HD mice with more severe LTP deficits. Ampakine treatments had no measurable effect on the decreased locomotor activity observed in the mutants but offset their impairments in long-term memory. Given that ampakines are well tolerated in clinical trials and were effective in this study after brief exposures, these results suggest a novel strategy for chronic treatment of the cognitive difficulties that occur in the early stages of HD.

Characterization of trkB immunoreactive cells in the intermediolateral cell column of the rat spinal cord

The objective of the present study was to characterize the trkB receptor immunoreactive (-ir) cells in the intermediolateral cell column (IML) of the upper thoracic spinal cord. Small trkB-ir cells (area=56.1+/-4.4 microm(2)) observed in the IML showed characteristics of oligodendrocytes and were frequently observed in close apposition to choline acetyltransferase (ChAT)-ir cell bodies. Large trkB-ir cells (area=209.3+/-25.2 microm(2)) showed immunoreactivity for the neuronal marker NeuN, indicating their neuronal phenotype, as well as for ChAT, a marker for preganglionic neurons. TrkB and ChAT were co-localized in IML neurons primarily in cases that had received in vivo administration of nerve growth factor (NGF). These findings reveal two different cell types, oligodendrocytes and neurons, in the IML of the spinal cord that show trkB immunoreactivity, suggesting their regulation by brain derived neurotrophic factor (BDNF) and/or neurotrophin-4 (NT-4). In addition, there is evidence that NGF may play a role in the regulation of trkB-ir preganglionic neurons in the IML.

Impact of exercise on neuroplasticity-related proteins in spinal cord injured humans

The present study investigated the effects of exercise on the serum concentrations of brain-derived neurotrophic factor (BDNF), insulin-like growth factor 1 (IGF-1), prolactin (PRL) and cortisol (COR) in 11 chronically spinal cord-injured athletes. In these subjects BDNF concentration at rest was sixfold higher compared with the concentrations reported earlier in able-bodied persons, while IGF-1, PRL and COR were within normal range. Ten minutes of moderate intensity handbiking (54% of the maximal heart rate) during a warm-up period (W) induced an increase (P<0.05) of BDNF of approximately 1.5-fold from basal level at rest, while a decrease to basal level was found after an immediately succeeding handbiking time trial (89% of the maximal heart rate) over the marathon distance of 42 km (M). An increase (P<0.01) of serum IGF-1 was found after W and this levels remained elevated (P<0.01) until the end of M. W had no significant effects on the serum PRL and COR, however, M induced an increase (P<0.01) of both hormones. This is the first study showing elevated BDNF concentrations at rest in spinal cord-injured athletes. Furthermore, short moderate intensity handbiking but not immediately following long lasting high intensity handbiking further increases serum BDNF concentrations. IGF-1 response to exercise differs to BDNF response as this neuroplasticity-related protein remains elevated during the long lasting physical demand with high intensity. The augmented PRL concentration suggests that a possible mechanism by which exercise promotes neuroplasticity might be the activation of neural serotonergic pathways as 5-HT is the main PRL releasing factor. Elevated COR concentrations after M are unlikely to be deleterious to neuroplasticity as COR concentrations remain within the physiological range. The present study suggests that exercise might be beneficial to enhance neuroprotection and neuroplasticity, thereby improving recovery after spinal cord injury.

Treadmill training promotes axon regeneration in injured peripheral nerves

Physical activity after spinal cord injury promotes improvements in motor function, but its effects following peripheral nerve injury are less clear. Although axons in peripheral nerves are known to regenerate better than those in the CNS, methods of accelerating regeneration are needed due to the slow overall rate of growth. Therefore we studied the effect of two weeks of treadmill locomotion on the growth of regenerating axons in peripheral nerves following injury. The common fibular nerves of thy-1-YFP-H mice, in which a subset of axons in peripheral nerves express yellow fluorescent protein (YFP), were cut and repaired with allografts from non-fluorescent littermates, and then harvested two weeks later. Mice were divided into groups of low-intensity continuous training (CT, 60 min), low-intensity interval training (IT; one group, 10 reps, 20 min total), and high-intensity IT (three groups, 2, 4, and 10 reps). One repetition consisted of 2 min of running and 5 min of rest. Sixty minutes of CT resulted in the highest exercise volume, whereas 2 reps of IT resulted in the lowest volume of exercise. The lengths of regenerating YFP(+) axons were measured in images of longitudinal optical sections of nerves. Axon profiles were significantly longer than control in all exercise groups except the low-intensity IT group. In the CT group and the high-intensity IT groups that trained with 4 or 10 repetitions axons were more than twice as long as unexercised controls. The number of intervals did not impact axon elongation. Axon sprouting was enhanced in IT groups but not the CT group. Thus exercise, even in very small quantities, increases axon elongation in injured peripheral nerves whereas continuous exercise resulting in higher volume (total steps) may have no net impact on axon sprouting.