High-intensity treadmill running impairs cognitive behavior and hippocampal synaptic plasticity of rats via activation of inflammatory response

Comparative effects of lifelong moderate-intensity continuous training and high-intensity interval training on blood lipid levels and mental well-being in naturally ageing mice

OBJECTIVE

This study aimed to investigate the impact of lifelong exercise, including both moderate-intensity continuous training and high-intensity interval training, on blood lipid levels and mental behaviour in naturally ageing mice to identify effective exercise strategies for ageing-related health issues.

METHODS

Six-week-old male BALB/c mice were randomly assigned to one of four groups: young control (YC), natural ageing control (OC), lifelong moderate-intensity continuous exercise (EM), and lifelong high-intensity interval exercise (EH) groups. The EM group was trained at a speed corresponding to 70 % of the maximum running speed, while the EH group was trained at a running speed alternating between 50 % of the maximum running speed, 70 % of the maximum running speed, and 90 % of the maximum running speed. All exercise sessions were conducted three times per week, with each session lasting 50 min. Behavioural tests and blood sample collection were conducted at 72 weeks of age.

RESULTS

Ageing in mice led to changes in muscle and fat mass. Both the EM and EH groups showed greater muscle mass and lower fat mass than did the OC group. Ageing was associated with elevated anxiety (fewer open arm entries, time spent in the central region) and depression (lower sucrose preference) indicators. However, these changes were reversed in both exercise groups, with no differences between the two exercise groups. Blood lipid levels, including total cholesterol (TC), total triglycerides (TGs), low-density lipoprotein (LDL), and free fatty acid (FFA) levels, were greater in the OC group than in the YC group. Additionally, the OC group exhibited lower high-density lipoprotein (HDL) levels. However, both the EM and EH groups exhibited improved lipid profiles compared to those of the YC group.

CONCLUSION

Lifelong exercise, whether moderate-intensity continuous or high-intensity interval training, can preserve body health during ageing, prevent anxiety and depression, and maintain stable blood lipid levels. Both exercise types are equally effective, suggesting that exercise intensity may not be the critical factor underlying these beneficial adaptations.

Physical exercise regulates microglia in health and disease

There is a well-established link between physical activity and brain health. As such, the effectiveness of physical exercise as a therapeutic strategy has been explored in a variety of neurological contexts. To determine the extent to which physical exercise could be most beneficial under different circumstances, studies are needed to uncover the underlying mechanisms behind the benefits of physical activity. Interest has grown in understanding how physical activity can regulate microglia, the resident immune cells of the central nervous system. Microglia are key mediators of neuroinflammatory processes and play a role in maintaining brain homeostasis in healthy and pathological settings. Here, we explore the evidence suggesting that physical activity has the potential to regulate microglia activity in various animal models. We emphasize key areas where future research could contribute to uncovering the therapeutic benefits of engaging in physical exercise.

Hyperbaric oxygen preconditioning rescues prolonged underwater exercise-induced hippocampal dysfunction by regulating microglia activation and polarization

Underwater exercise is becoming increasingly prevalent, during which brain function is necessary but is also at risk. However, no study has explored how prolonged exercise affect the brain in underwater environment. Previous studies have indicated that excessive exercise in common environment causes brain dysfunction but have failed to provide appropriate interventions. Numerous evidence has indicated the neuroprotective effect of hyperbaric oxygen preconditioning (HBO-PC). The objective of this study was to investigate the cognitive effect of prolonged underwater exercise (PUE) and to explore the potential neuroprotective effect of HBO-PC in underwater environment. Rats swimming for 3 h in a simulated hyperbaric chamber (2.0 ATA) was used to establish the PUE animal model and HBO-PC (2.5 ATA for 1, 3,5 times respectively) was administrated before PUE. The results demonstrated that PUE triggers anxiety-like behaviors, cognitive impairment accompanied by hippocampal dysfunction, microglia activation and neuroinflammation. Conversely, 3 HBO-PC rescued anxiety-like behaviors and cognitive impairment. Mechanistically, 3 HBO-PC reduced microglia activation and switched the activated microglia from a pro-inflammatory to neuroprotective phenotype. These findings illustrated that PUE induces anxiety-like behaviors and cognitive impairment and HBO-PC of proper frequency may provide an appropriate and less invasive intervention for protecting the brain in underwater exercise.

Ageing, Cognitive Decline, and Effects of Physical Exercise: Complexities, and Considerations from Animal Models

In our ageing global population, the cognitive decline associated with dementia and neurodegenerative diseases represents a major healthcare problem. To date, there are no effective treatments for age-related cognitive impairment, thus preventative strategies are urgently required. Physical exercise is gaining traction as a non-pharmacological approach to promote brain health. Adult hippocampal neurogenesis (AHN), a unique form of brain plasticity which is necessary for certain cognitive functions declines with age and is enhanced in response to exercise. Accumulating evidence from research in rodents suggests that physical exercise has beneficial effects on cognition through its proneurogenic capabilities. Given ethical and technical limitations in human studies, preclinical research in rodents is crucial for a better understanding of such exercise-induced brain and behavioural changes. In this review, exercise paradigms used in preclinical research are compared. We provide an overview of the effects of different exercise paradigms on age-related cognitive decline from middle-age until older-age. We discuss the relationship between the age-related decrease in AHN and the potential impact of exercise on mitigating this decline. We highlight the emerging literature on the impact of exercise on gut microbiota during ageing and consider the role of the gut-brain axis as a future possible strategy to optimize exercise-enhanced cognitive function. Finally, we propose a guideline for designing optimal exercise protocols in rodent studies, which would inform clinical research and contribute to developing preventative strategies for age-related cognitive decline.

Walking, Running, Swimming: An Analysis of the Effects of Land and Water Aerobic Exercises on Cognitive Functions and Neural Substrates

In the brain and cognitive reserves framework, aerobic exercise is considered as a protective lifestyle factor able to induce positive effects on both brain structure and function. However, specific aspects of such a beneficial effect still need to be completely clarified. To this aim, the present narrative review focused on the potential brain/cognitive/neural reserve-construction mechanisms triggered by different aerobic exercise types (land activities; such as walking or running; vs. water activities; such as swimming), by considering human and animal studies on healthy subjects over the entire lifespan. The literature search was conducted in PubMed database. The studies analyzed here indicated that all the considered kinds of activities exert a beneficial effect on cognitive/behavioral functions and on the underlying brain neurobiological processes. In particular, the main effects observed involve the cognitive domains of memory and executive functions. These effects appear related to structural and functional changes mainly involving the fronto-hippocampal axis. The present review supports the requirement of further studies that investigate more specifically and systematically the effects of each type of aerobic activity, as a basis to plan more effective and personalized interventions on individuals as well as prevention and healthy promotion policies for the general population.

Intense long-term training impairs brain health compared with moderate exercise: Experimental evidence and mechanisms

The consequences of extremely intense long-term exercise for brain health remain unknown. We studied the effects of strenuous exercise on brain structure and function, its dose-response relationship, and mechanisms in a rat model of endurance training. Five-week-old male Wistar rats were assigned to moderate (MOD) or intense (INT) exercise or a sedentary (SED) group for 16 weeks. MOD rats showed the highest motivation and learning capacity in operant conditioning experiments; SED and INT presented similar results. In vivo MRI demonstrated enhanced global and regional connectivity efficiency and clustering as well as a higher cerebral blood flow (CBF) in MOD but not INT rats compared with SED. In the cortex, downregulation of oxidative phosphorylation complex IV and AMPK activation denoted mitochondrial dysfunction in INT rats. An imbalance in cortical antioxidant capacity was found between MOD and INT rats. The MOD group showed the lowest hippocampal brain-derived neurotrophic factor levels. The mRNA and protein levels of inflammatory markers were similar in all groups. In conclusion, strenuous long-term exercise yields a lesser improvement in learning ability than moderate exercise. Blunting of MOD-induced improvements in CBF and connectivity efficiency, accompanied by impaired mitochondrial energetics and, possibly, transient local oxidative stress, may underlie the findings in intensively trained rats.

Exercise-induced modulation of myokine irisin in bone and cartilage tissue—Positive effects on osteoarthritis: A narrative review

Osteoarthritis is a chronic degenerative musculoskeletal disease characterized by pathological changes in joint structures along with the incidence of which increases with age. Exercise is recommended for all clinical treatment guidelines of osteoarthritis, but the exact molecular mechanisms are still unknown. Irisin is a newly discovered myokine released mainly by skeletal muscle in recent years—a biologically active protein capable of being released into the bloodstream as an endocrine factor, the synthesis and secretion of which is specifically induced by exercise-induced muscle contraction. Although the discovery of irisin is relatively recent, its role in affecting bone density and cartilage homeostasis has been reported. Here, we review the production and structural characteristics of irisin and discuss the effects of the different types of exercise involved in the current study on irisin and the role of irisin in anti-aging. In addition, the role of irisin in the regulation of bone mineral density, bone metabolism, and its role in chondrocyte homeostasis and metabolism is reviewed. A series of studies on irisin have provided new insights into the mechanisms of exercise training in improving bone density, resisting cartilage degeneration, and maintaining the overall environmental homeostasis of the joint. These studies further contribute to the understanding of the role of exercise in the fight against osteoarthritis and will provide an important reference and aid in the development of the field of osteoarthritis prevention and treatment.

Exerkines and long-term synaptic potentiation: Mechanisms of exercise-induced neuroplasticity

Physical exercise may improve cognitive function by modulating molecular and cellular mechanisms within the brain. We propose that the facilitation of long-term synaptic potentiation (LTP)-related pathways, by products induced by physical exercise (i.e., exerkines), is a crucial aspect of the exercise-effect on the brain. This review summarizes synaptic pathways that are activated by exerkines and may potentiate LTP. For a total of 16 exerkines, we indicated how blood and brain exerkine levels are altered depending on the type of physical exercise (i.e., cardiovascular or resistance exercise) and how they respond to a single bout (i.e., acute exercise) or multiple bouts of physical exercise (i.e., chronic exercise). This information may be used for designing individualized physical exercise programs. Finally, this review may serve to direct future research towards fundamental gaps in our current knowledge regarding the biophysical interactions between muscle activity and the brain at both cellular and system levels.

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.

Lactate as Potential Mediators for Exercise-Induced Positive Effects on Neuroplasticity and Cerebrovascular Plasticity

The accumulated evidence from animal and human studies supports that exercise is beneficial to physical health. Exercise can upregulate various neurotrophic factors, activate neuroplasticity, and play a positive role in improving and enhancing cerebrovascular function. Due to its economy, convenience, and ability to prevent or ameliorate various aging-related diseases, exercise, a healthy lifestyle, is increasingly popularized by people. However, the mechanism by which exercise performs this function and how it is transmitted from muscles to the brain remains incompletely understood. Here, we review the beneficial effects of exercise with different intensities on the brain with a focus on the positive effects of lactate on neuroplasticity and cerebrovascular plasticity. Based on these recent studies, we propose that lactate, a waste previously misunderstood as a by-product of glycolysis in the past, may be a key signal molecule that regulates the beneficial adaptation of the brain caused by exercise. Importantly, we speculate that a central protective mechanism may underlie the cognitive benefits induced by exercise.

Silymarin and neurodegenerative diseases: Therapeutic potential and basic molecular mechanisms

BACKGROUND

Neurodegenerative diseases (NDDs) are primarily characterized by selective neuronal loss in the brain. Alzheimer's disease as the most common NDDs and the most prevalent cause of dementia is characterized by Amyloid-beta deposition, which leads to cognitive and memory impairment. Parkinson's disease is a progressive neurodegenerative disease characterized by the dramatic death of dopaminergic neuronal cells, especially in the SNc and caused alpha-synuclein accumulation in the neurons. Silymarin, an extract from seeds of Silybum marianum, administered mostly for liver disorders and also had anti-oxidant and anti-carcinogenic activities.

PURPOSE

The present comprehensive review summarizes the beneficial effects of Silymarin in-vivo and in-vitro and even in animal models for these NDDs.

METHODS

A diagram model for systematic review is utilized for this search. The research is conducted in the following databases: PubMed, Web of Science, Scopus, and Science Direct.

RESULTS

Based on the inclusion criteria, 83 studies were selected and discussed in this review.

CONCLUSION

Lastly, we review the latest experimental evidences supporting the potential effects of Silymarin, as a neuroprotective agent in NDDs.

Potential Involvement of Adiponectin Signaling in Regulating Physical Exercise-Elicited Hippocampal Neurogenesis and Dendritic Morphology in Stressed Mice

Adiponectin, a cytokine secreted by mature adipocytes, proves to be neuroprotective. We have previously reported that running triggers adiponectin up-regulation which subsequently promotes generation of hippocampal neurons and thereby alleviates depression-like behaviors in non-stressed mice. However, under the stressing condition, whether adiponectin could still exert antidepressant-like effects following exercise remained unexplored. In this study, by means of repeated corticosterone injections to mimic stress insult and voluntary wheel running as physical exercise intervention, we examined whether exercise-elicited antidepressive effects might involve adiponectin's regulation on hippocampal neurogenesis and dendritic plasticity in stressed mice. Here we show that repeated injections of corticosterone inhibited hippocampal neurogenesis and impaired dendritic morphology of neurons in the dentate gyrus of both wild-type and adiponectin-knockout mice comparably, which subsequently evoked depression-like behaviors. Voluntary wheel running attenuated corticosterone-suppressed neurogenesis and enhanced dendritic plasticity in the hippocampus, ultimately reducing depression-like behaviors in wild-type, but not adiponectin-knockout mice. We further demonstrate that such proneurogenic effects were potentially achieved through activation of the AMP-dependent kinase (AMPK) pathway. Our study provides the first evidence that adiponectin signaling is essential for physical exercise-triggered effects on stress-elicited depression by retaining the normal proliferation of neural progenitors and dendritic morphology of neurons in the hippocampal dentate gyrus, which may depend on activation of the AMPK pathway.

Preventive Effects of Different Aerobic Exercise Intensities on the Decline of Cognitive Function in High-Fat Diet-Induced Obese Growing Mice

Background and Objectives: The purpose of this study was to elucidate the effects of different exercise intensities in preventing the decline of cognitive function and lipolysis associated with a high-fat diet-induced obesity in growing mice. Material and Methods: Forty male C57BL/6 mice, aged 4 weeks, were divided into the normal diet (CO, n = 10) and high-fat diet (HF, n = 30) groups to induce obesity for 8 weeks. Subsequently, the HF group was subdivided equally into the HF, HF + low-intensity training (HFLT), and HF + high-intensity training (HFHT) groups, and mice were subjected to treadmill training for 8 weeks. Results: Following the 8-week training intervention, body weight and fat mass were significantly lower in the training groups than in the HF group (p < 0.05). Adipose triglyceride lipase (ATGL), hormone-sensitive lipase (HSL), and monoglyceride lipase levels were significantly higher in the training groups than in the HF group (p < 0.05), and the ATGL and HSL levels were significantly higher in the HFHT group than in the HFLT group (p < 0.05). The Y-maze test showed that the training groups had a higher number of total entries and percent alternation than the HF group (p < 0.05). Hippocampal nerve growth factor, brain-derived neurotrophic factor, and neurotrophin-3 levels were significantly higher in the training group than in the HF group (p < 0.05). However, there was no significant difference according to the exercise intensity among the groups. Conclusions: The results of this study suggested that low-intensity exercise is as effective as a high-intensity exercise in preventing the decline of cognitive function and lipolysis, and far more effective in terms of an expected efficiency of workload and prevention of side effects.

Intensity-dependent effects of consecutive treadmill exercise on spatial learning and memory through the p-CREB/BDNF/NMDAR signaling in hippocampus

Exercise is the most recommended non-pharmacological intervention to improve neurocognitive functions under physiological and pathological conditions. However, it remains to be elucidated concerning the influence and the underlying neurological molecular mechanism of different exercise intensity on cognitive function. In this study, we aimed to explore the effects of exercise intensity on spatial learning and memory, as well as the regulation of brain-derived neurotrophic factor (BDNF)/p-CREB/NMDAR signal. In the research, low-intensity consecutive treadmill (LICT) and high-intensity consecutive treadmill (HICT) were implied to rats for 8 weeks. We found that the performances in the Morris water maze were improved in the LICT group, while reduced in the HICT group as compared with the sedentary rats. Moreover, the expression of BDNF mRNA, phosphorylation cAMP-response-element binding protein (p-CREB), mature BDNF (mBDNF), tropomyosin receptor kinase B (TrkB), tissue plasminogen activator (t-PA), and NR2B proteins was increased, whereas the expression of precursor BDNF (proBDNF) and pan-neurotrophin receptor 75 (p75NTR) proteins was decreased in the hippocampus of LICT group compared with the sedentary rats. On the contrary, the expression of proteins and mRNA aforementioned in the LICT group showed a reversed tendency in the hippocampus of HICT rats. These findings suggest that the consecutive low-intensity exercise and high-intensity exercise exert different effects on spatial learning and memory by oppositely regulating the mutual stimulation of p-CREB and BDNF mRNA feedback loop, as well as the t-PA/BDNF/NMDAR which is the post-translation cascades of BDNF signaling.

Exercise and Parkinson's Disease

Parkinson's disease (PD) is an aging-related neurodegenerative disorder characterized by progressive motor impairment.The etiology of PD is poorly understood but likely involves both genetic and environmental factors; the management of the disease is still with symptomatic therapy without any interference on the progression of neurodegeneration. In the past two decades, the results of a series of prospective cohort studies suggested that lifestyle factors likely modify the risk of developing PD. Among these, physical activity is known to reduce the risk of a wide range of diseases and conditions, including cardiovascular disease, stroke, and diabetes.Recently, a growing body of evidence has suggested that increased physical activity may also reduce the risk of PD and partly improve motor and non-motor symptoms during the disease course.Here we report the main findings on the effect of physical activity on both mobility and cognition either in animal models of PD or in people with PD. We also highlighted the structural and functional links between gait and cognition by reporting evidence from neuroimaging studies.

Akt dependent adult hippocampal neurogenesis regulates the behavioral improvement of treadmill running to mice model of post-traumatic stress disorder

Physical exercise is well-established paradigm for improving adult neurogenesis and brain functions. As considered as an alternative therapeutic strategy, treadmill running could reduce cognitive impairment and psychiatric abnormalities associating post-traumatic stress disorder (PTSD), which might associate with the promote effects to adult neurogenesis. In current study, we aimed to address how treadmill exercise benefit adult hippocampal neurogenesis in PTSD model and the underlying molecular mechanism related with Akt signaling. PTSD was induced by exposure to aggressor and treatments were conducted with different intensity of compulsory treadmill running. We observed treadmill running improved hippocampal neurogenesis including proliferation and neural differentiation of neural stem cells (NSCs). Moreover, behavioral tests showed treadmill could attenuate the cognitive deficit and depressive/anxiety like behaviors in correlating with PTSD model. Moreover, treadmill running recovered the Akt activity in hippocampus. Interrupting treadmill running administrated mice with Akt inhibitor GSK690693 resulted in the blocked the effects of treadmill running to hippocampal neurogenesis and behavioral improvement in PTSD mice model. In conclusion, treadmill running could mediate behavioral functions and improve hippocampal neurogenesis in PTSD model by regulating Akt signaling.

The effects of moderate exercise and overtraining on learning and memory, hippocampal inflammatory cytokine levels, and brain oxidative stress markers in rats

To investigate the exercise intensity effects on rats' memory and learning, animals were divided into control, moderate training (MT), and overtraining (OT) groups. At training last week, learning and memory was assessed using Morris water maze (MWM) and passive avoidance (PA) tests. Finally, the rat's brains were removed for evaluating oxidative stress and inflammatory cytokines. Overtraining impaired animal's performance in MWM and PA tests. In MT group, hippocampal levels of interleukin 1 beta (IL-1β) and malondialdehyde (MDA) increased, and thiol contents in hippocampal and cortical tissues decreased compared to control. In OT group, tumor necrosis factor α, IL-1β, and C-reactive protein hippocampal levels increased, MDA and nitric oxide metabolite in hippocampal and cortical tissues increased, thiol contents, catalase and superoxide dismutase activity in hippocampal and cortical tissues decreased compared to control and MT groups. Overtraining might lead to learning and memory impairment by increasing the inflammatory cytokine and oxidative stress markers.

Early reduced behavioral activity induced by large strokes affects the efficiency of enriched environment in rats

The majority of stroke patients develop post-stroke fatigue, a symptom which impairs motivation and diminishes the success of rehabilitative interventions. We show that large cortical strokes acutely reduce activity levels in rats for 1-2 weeks as a physiological response paralleled by signs of systemic inflammation. Rats were exposed early (1-2 weeks) or late (3-4 weeks after stroke) to an individually monitored enriched environment to stimulate self-controlled high-intensity sensorimotor training. A group of animals received Anti-Nogo antibodies for the first two weeks after stroke, a neuronal growth promoting immunotherapy already in clinical trials. Early exposure to the enriched environment resulted in poor outcome: Training intensity was correlated to enhanced systemic inflammation and functional impairment. In contrast, animals starting intense sensorimotor training two weeks after stroke preceded by the immunotherapy revealed better recovery with functional outcome positively correlated to the training intensity and the extent of re-innervation of the stroke denervated cervical hemi-cord. Our results suggest stroke-induced fatigue as a biological purposeful reaction of the organism during neuronal remodeling, enabling new circuit formation which will then be stabilized or pruned in the subsequent rehabilitative training phase. However, intense training too early may lead to wrong connections and is thus less effective.

Effects of exercise-induced fatigue on the morphology of asymmetric synapse and synaptic protein levels in rat striatum

Corticostriatal synaptic plasticity is considered to be a cellular basis for somatic motor regulation and motor skill learning. Changes in synaptic transmission efficiency underlie functional plasticity, while structural plasticity involves changes in the ultrastructure of the synapse and the levels of synaptic proteins. Exercise-induced fatigue may impair corticostriatal synaptic plasticity, and this impairment may be an important mechanism for exercise-induced fatigue. However, prior research focused mainly on functional plasticity such that the structural plasticity was not well understood. Because corticostriatal synapses are typical asymmetric synapses, here we have used transmission electron microscopy to examine the changes of asymmetry synaptic ultrastructure in rat striatum before and after repetitive exercise-induced fatigue; we have also used western blotting to detect the levels of synaptic active region protein Munc 13, RIM1 and synaptic vesicle protein Rab3A and postsynaptic density PSD-95 protein in rat striatum before and after exercise-induced fatigue. The results showed that the ultrastructure of asymmetry corticostriatal synapses and synaptic protein levels in the striatum of rats were abnormally changed after repetitive exercise-induced fatigue. These abnormal changes in synaptic ultrastructure and related protein levels may be the structural basis for the corticostriatal plasticity impairment after exercise-induced fatigue.

Silibinin Alleviates the Learning and Memory Defects in Overtrained Rats Accompanying Reduced Neuronal Apoptosis and Senescence

Excessive physical exercise (overtraining; OT) increases oxidative stress and induces damage in multiple organs including the brain, especially the hippocampus that plays an important role in learning and memory. Silibinin, a natural flavonoid derived from milk thistle of Silybum marianum, has been reported to exert neuroprotective effect. In this study, rats were subjected to overtraining exercise, and the protective effects of silibinin were investigated in these models. Morris water maze and novel object recognition tests showed that silibinin significantly attenuated memory defects in overtrained rats. At the same time, the results of Nissl, TUNEL and SA-β-gal staining showed that silibinin reversed neuronal loss caused by apoptosis, and delayed cell senescence of the hippocampus in the overtrained rats, respectively. In addition, silibinin decreased malondialdehyde (MDA) levels which is associated with reactive oxygen species (ROS) generation. Silibinin prevented impairment of learning and memory caused by excessive physical exercise in rats, accompanied by reduced apoptosis and senescence in hippocampus cells.

Neonatal general anesthesia causes lasting alterations in excitatory and inhibitory synaptic transmission in the ventrobasal thalamus of adolescent female rats

Ample evidence has surfaced documenting the neurotoxic effects of various general anesthetic (GA) agents in the mammalian brain when administered at critical periods of synaptogenesis. However, little is known about how this neurotoxic insult affects persisting neuronal excitability after the initial exposure. Here we investigated synaptic activity and intrinsic excitability of the ventrobasal nucleus (VB) of the thalamus caused by neonatal GA administration. We used patch-clamp recordings from acute thalamic slices in young rats up to two weeks after neurotoxic GA exposure of isoflurane and nitrous oxide for 6 h at postnatal age of 7 (P7) days. We found that GA exposure at P7 increases evoked excitatory postsynaptic currents (eEPSCs) two fold by means through AMPA mediated mechanisms, while NMDA component was spared. In addition, miniature EPSCs showed a faster decay rate in neurons from GA treated animals when compared to sham controls. Likewise, we discovered that the amplitudes of evoked inhibitory postsynaptic currents (eIPSCs) were increased in VB neurons from GA animals about two-fold. Interestingly, these results were observed in female but not male rats. In contrast, intrinsic excitability and properties of T-type voltage gated calcium currents were minimally affected by GA exposure. Together, these data further the idea that GAs cause lasting alterations in synaptic transmission and neuronal excitability depending upon the placing and connectivity of neurons in the thalamus. Given that function of thalamocortical circuits critically depends on the delicate balance between excitation and inhibition, future development of therapies aimed at addressing consequences of altered excitability in the developing brain by GAs may be an attractive possibility.

Exercise training normalizes elevated firing rate of hypothalamic presympathetic neurons in heart failure rats

Exercise training (ExT) normalizes elevated sympathetic nerve activity in heart failure (HF), but the underlying mechanisms are not well understood. In this study, we examined the effects of 3 wk of ExT on the electrical activity of the hypothalamic presympathetic neurons in the brain slice of HF rats. HF rats were prepared by ligating the left descending coronary artery. The electrophysiological properties of paraventricular nucleus neurons projecting to the rostral ventrolateral medulla (PVN-RVLM) were examined using the slice patch-clamp technique. The neuronal firing rate was elevated in HF rats, and ExT induced a reduction in the firing rate ( P < 0.01). This ExT-induced decrease in the firing rate was associated with an increased frequency of spontaneous and miniature inhibitory postsynaptic current (IPSCs; P < 0.05). There was no significant change in excitatory postsynaptic current. Replacing Ca²⁺ with Mg²⁺ in the recording solution reduced the elevated IPSC frequency in HF rats with ExT ( P < 0.01) but not in those without ExT, indicating an increase in the probability of GABA release. In contrast, ExT did not restore the reduced GABA_A receptor-mediated tonic inhibitory current in HF rats. A GABA_A receptor blocker (bicuculline, 20 μM) increased the firing rate in HF rats with ExT ( P < 0.01) but not in those without ExT. Collectively, these results show that ExT normalized the elevated firing activity by increasing synaptic GABA release in PVN-RVLM neurons in HF rats. Our findings provide a brain mechanism underlying the beneficial effects of ExT in HF, which may shed light on the pathophysiology of other diseases accompanied by sympathetic hyperactivation.

A Novel scFv Anti-Aβ Antibody Reduces Pathological Impairments in APP/PS1 Transgenic Mice via Modulation of Inflammatory Cytokines and Aβ-related Enzymes

Immunotherapy for Alzheimer's disease (AD) remains promising in the improvement of cognition and memory via the clearing of amyloid-β protein (Aβ) in the AD brain, despite some side effects. Our previous studies demonstrated that the 31-35 sequence of the Aβ molecule was the shortest active center and that polyclonal anti-Aβ31-35 antibody reduced neuronal apoptosis and cognitive impairments induced with acute Aβ application. The present study designed a novel single-chain variable fragment (scFv) monoclonal anti-Aβ31-35 antibody (scFv17) that specifically recognized extracellular Aβ and observed protective effects of scFv17 on pathological impairments in APP/PS1 transgenic mice. We also investigated its cellular and molecular mechanisms and found that scFv17 and 6E10 (a positive control) exhibited similar Aβ-clearing ability and that scFv17 produced a stronger effect in clearing Aβ oligomers than 6E10. scFv17, but not 6E10, enhanced anti-inflammatory responses with significant increases in IL-10 and TGF-β. 6E10 decreased BACE1 levels, and scFv17 significantly increased the level of secreted amyloid precursor protein-α (sAPPα), which is an important physiological neurotrophin from APP generated by α-secretase. 6E10 and scFv17, especially the latter, dramatically down-regulated the expression of neprilysin, which is an enzyme expressed in proportion to Aβ concentration. Therefore, the present study demonstrated that the novel monoclonal anti-Aβ31-35 antibody scFv17 effectively reduced pathological impairments in APP/PS1 transgenic mice via modulation of inflammatory cytokines and Aβ-related enzymes, which supports scFv17 as a new alternative in the current immunotherapy of AD.

Exercise-Induced Fatigue Impairs Bidirectional Corticostriatal Synaptic Plasticity

Exercise-induced fatigue (EF) is a ubiquitous phenomenon in sports competition and training. It can impair athletes’ motor skill execution and cognition. Corticostriatal synaptic plasticity is considered to be the cellular mechanism of movement control and motor learning. However, the effect of EF on corticostriatal synaptic plasticity remains elusive. In the present study, using field excitatory postsynaptic potential recording, we found that the corticostriatal long-term potentiation (LTP) and long-term depression (LTD) were both impaired in EF mice. To further investigate the cellular mechanisms underlying the impaired synaptic plasticity in corticostriatal pathway, whole-cell patch clamp recordings were carried out on striatal medium spiny neurons (MSNs). MSNs in EF mice exhibited increased spontaneous excitatory postsynaptic current (sEPSC) frequency and decreased paired-pulse ratio (PPR), while with normal basic electrophysiological properties and normal sEPSC amplitude. Furthermore, the N-methyl-D-aspartate (NMDA)/α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) ratio of MSNs was reduced in EF mice. These results suggest that the enhanced presynaptic glutamate (Glu) release and downregulated postsynaptic NMDA receptor function lead to the impaired corticostriatal plasticity in EF mice. Taken together, our findings for the first time show that the bidirectional corticostriatal synaptic plasticity is impaired after EF, and suggest that the aberrant corticostriatal synaptic plasticity may be involved in the production and/or maintenance of EF.