Circulating insulin-like growth factor I mediates the protective effects of physical exercise against brain insults of different etiology and anatomy

The Effects of Physical Exercise and Cognitive Training on Memory and Neurotrophic Factors

This study examined the combined effect of physical exercise and cognitive training on memory and neurotrophic factors in healthy, young adults. Ninety-five participants completed 6 weeks of exercise training, combined exercise and cognitive training, or no training (control). Both the exercise and combined training groups improved performance on a high-interference memory task, whereas the control group did not. In contrast, neither training group improved on general recognition performance, suggesting that exercise training selectively increases high-interference memory that may be linked to hippocampal function. Individuals who experienced greater fitness improvements from the exercise training (i.e., high responders to exercise) also had greater increases in the serum neurotrophic factors brain-derived neurotrophic factor and insulin-like growth factor-1. These high responders to exercise also had better high-interference memory performance as a result of the combined exercise and cognitive training compared with exercise alone, suggesting that potential synergistic effects might depend on the availability of neurotrophic factors. These findings are especially important, as memory benefits accrued from a relatively short intervention in high-functioning young adults.

Sirt6 alters adult hippocampal neurogenesis

Sirtuins are pleiotropic NAD⁺ dependent histone deacetylases involved in metabolism, DNA damage repair, inflammation and stress resistance. SIRT6, a member of the sirtuin family, regulates the process of normal aging and increases the lifespan of male mice over-expressing Sirt6 by 15%. Neurogenesis, the formation of new neurons within the hippocampus of adult mammals, involves several complex stages including stem cell proliferation, differentiation, migration and network integration. During aging, the number of newly generated neurons continuously declines, and this is correlated with a decline in neuronal plasticity and cognitive behavior. In this study we investigated the involvement of SIRT6 in adult hippocampal neurogenesis. Mice over-expressing Sirt6 exhibit increased numbers of young neurons and decreased numbers of mature neurons, without affecting glial differentiation. This implies of an involvement of SIRT6 in neuronal differentiation and maturation within the hippocampus. This work adds to the expanding body of knowledge on the regulatory mechanisms underlying adult hippocampal neurogenesis, and describes novel roles for SIRT6 as a regulator of cell fate during adult hippocampal neurogenesis.

Distribution of BDNF and TrkB isoforms in growing antler tissues of red deer

Antlers are the cranial appendages of deer that regenerate each year. This renewal provides a model to explore molecules involved in mammalian organ regeneration. The cellular distributions of the brain-derived neurotrophic factor (BDNF) and the isoforms of its cognate receptor Trk tyrosine kinase receptor (TrkB) were localized by immunohistochemistry in sections of growing red deer antler. BDNF and TrkB full length were widely expressed in the integument, perichondrium, periosteum and bone. The truncated isoform receptor was particularly evidenced in integument and vascular inner dermis, but very light reaction was observed in cartilage and bone, both at the site of endochondral and intramembranous ossification. These observations were also assessed at transcriptional level by RT-PCR analyses. The highest expression of all genes significantly occurred in chondroprogenitor cells; however the full-length TrkB receptor was down regulated in osteocartilaginous compartments, in which the truncated isoform was up regulated. The truncated isoform is a dominant-negative receptor that inhibits the full length receptor signalling, even if the truncated isoform not only has this function. This study establishes the presence of BDNF and its receptor in the different cellular compartments of growing antler. Their transcripts assessed by RT-PCR indicate a local synthesis of these molecules that may contribute to the modulation of antler growth, acting as autocrine and/or paracrine factors independently of nerve supply. Among the plethora of other molecular signals and growth factors affecting the antler growth, the local production of BDNF and its cognate receptor could be of interest in understanding their role in antler renewal and to delineate the different involvement of the receptor isoforms.

The effect of exercise intensity on brain derived neurotrophic factor and memory in adolescents

Background

Brain derived neurotrophic factor (BDNF) seems to serve as an important regulatory mechanism in the growth and development of neurons in many areas of the brain.Insulin-like growth factor 1 (IGF-1) is related to neurogenesis and regulation of the BDNF gene and is involved in the growth and differentiation of neurons.Cortisol is released in response to stimuli such as psychological oppression, anxiety, and fear. Stress also induces changes in BDNF. The purpose of this study was thus to examine the effects of varying intensities of aerobic exercise on resting serum BDNF, IGF-1 concentrations, cortisol, and memory of adolescents.

Methods

Forty male students with no history of physical illness from the middle school by participated in this study. Participants were randomly assigned to low, moderate, or high intensity treadmill exercise group, or a stretching (control) group. Exercise was performed 4 times per week for 12 weeks. Body composition, brain derived neurotrophic factor levels, insulin-like growth factor 1 levels, cortisol levels, and working memory were assessed.

Results

The high intensity exercise group showed a significant increase in brain derived neurotrophic factor at rest, concentration level of insulin-like growth factor 1, cortisol, and working memory. For resting brain derived neurotrophic factor, the high intensity exercise group showed a more significant increase compared to the low intensity aerobic and stretching groups. The change in the working memory significantly increased for the high intensity exercise group compared to the low intensity aerobic group, moderate intensity exercise group, and stretching group.

Conclusions

In adolescents, whose brains are still developing, aerobic exercise of moderate to high intensity levels seems to have a positive effect on levels of serum brain derived neurotrophic factor at rest and on cognitive functioning.

Trial registration

EHPM-D-16-00107R2. ICMJE. 12 July 2016.

A CONCEPTUAL MODEL FOR PHYSICAL THERAPISTS TREATING ATHLETES WITH PROTRACTED RECOVERY FOLLOWING A CONCUSSION

Sports-related concussions are receiving growing attention in healthcare. Most concussions resolve spontaneously with little or no treatment, but twenty percent of concussions take longer than three weeks to resolve. In some cases, symptoms can last for five years following a traumatic brain injury. Physical Therapists have unique skills that can assist patients experiencing protracted recovery. The purpose of this clinical commentary is to describe a new conceptual model that provides a framework for Physical Therapy management of patients with protracted recovery following a sports-related concussion. The end product is a visual diagram that represents the full scope of clinical practice that Physical Therapy can provide to an athlete following a concussion.

LEVEL OF EVIDENCE

5.

Physical activity levels determine exercise-induced changes in brain excitability

Emerging evidence suggests that regular physical activity can impact cortical function and facilitate plasticity. In the present study, we examined how physical activity levels influence corticospinal excitability and intracortical circuitry in motor cortex following a single session of moderate intensity aerobic exercise. We aimed to determine whether exercise-induced short-term plasticity differed between high versus low physically active individuals. Participants included twenty-eight young, healthy adults divided into two equal groups based on physical activity level determined by the International Physical Activity Questionnaire: low-to-moderate (LOW) and high (HIGH) physical activity. Transcranial magnetic stimulation was used to assess motor cortex excitability via motor evoked potential (MEP) recruitment curves for the first dorsal interosseous (FDI) muscle at rest (MEP_REST) and during tonic contraction (MEP_ACTIVE), short-interval intracortical inhibition (SICI) and facilitation (SICF), and intracortical facilitation (ICF). All dependent measures were obtained in the resting FDI muscle, with the exception of AMT and MEP_ACTIVE recruitment curves that were obtained during tonic FDI contraction. Dependent measures were acquired before and following moderate intensity aerobic exercise (20 mins, ~60% of the age-predicted maximal heart rate) performed on a recumbent cycle ergometer. Results indicate that MEP_REST recruitment curve amplitudes and area under the recruitment curve (AURC) were increased following exercise in the HIGH group only (p = 0.002 and p = 0.044, respectively). SICI and ICF were reduced following exercise irrespective of physical activity level (p = 0.007 and p = 0.04, respectively). MEP_ACTIVE recruitment curves and SICF were unaltered by exercise. These findings indicate that the propensity for exercise-induced plasticity is different in high versus low physically active individuals. Additionally, these data highlight that a single session of aerobic exercise can transiently reduce inhibition in the motor cortex regardless of physical activity level, potentially priming the system for plasticity induction.

Can irisin be a linker between physical activity and brain function?

Irisin was initially discovered as a novel hormone-like myokine released from skeletal muscle during exercise to improve obesity and glucose dysfunction by stimulating the browning of white adipose tissue. Emerging evidence have indicated that irisin also affects brain function. FNDC5 mRNA and FNDC5/irisin immunoreactivity are present in various regions of the brain. Central irisin is involved in the regulation of neural differentiation and proliferation, neurobehavior, energy expenditure and cardiac function. Elevation of peripheral irisin level stimulates hippocampal genes related to neuroprotection, learning and memory. In this brief review, we summarize the current understanding on neuronal functions of irisin. In addition, we discuss the pros and cons for this molecule as a potential messenger mediating the crosstalk between skeletal muscle and central nervous system during exercise.

Insulin-Like Growth Factor 1: At the Crossroads of Brain Development and Aging

Insulin-like growth factor 1 (IGF1) is a polypeptide hormone structurally similar to insulin. It is central to the somatotropic axis, acting downstream of growth hormone (GH). It activates both the mitogen-activated protein (MAP) kinase and PI3K signaling pathways, acting in almost every tissue in the body to promote tissue growth and maturation through upregulation of anabolic processes. Overall GH and IGF1 signaling falls with age, suggesting that it is this reduced IGF1 activity that leads to age-related changes in organisms. However, mutations that reduce IGF1-signaling activity can dramatically extend the lifespan of organisms. Therefore, the role of IGF1 in the overall aging process is unclear. This review article will focus on the role of IGF1 in brain development and aging. The evidence points towards a role for IGF1 in neurodevelopment both prenatally and in the early post-natal period, and in plasticity and remodeling throughout life. This review article will then discuss the hallmarks of aging and cognitive decline associated with falls in IGF1 levels towards the end of life. Finally, the role of IGF1 will be discussed within the context of both neuropsychiatric disorders caused by impaired development of the nervous system, and neurodegenerative disorders associated with aging. IGF1 and its derivatives are shown to improve the symptoms of certain neuropsychiatric disorders caused by deranged neurodevelopment and these effects have been correlated with changes in the underlying biology in both in vitro and in vivo studies. On the other hand, studies looking at IGF1 in neurodegenerative diseases have been conflicting, supporting both a role for increased and decreased IGF1 signaling in the underlying pathogenesis of these diseases.

Exercise reverses age-related vulnerability of the retina to injury by preventing complement-mediated synapse elimination via a BDNF-dependent pathway

Retinal ganglion cells (RGCs) become increasingly vulnerable to injury with advancing age. We recently showed that this vulnerability can be strongly modified in mice by exercise. However, the characteristics and underlying mechanisms of retinal protection with exercise remain unknown. Hence, the aim of this study was to investigate cellular changes associated with exercise‐induced protection of aging retinal cells and the role of local and peripheral trophic signalling in mediating these effects. We focussed on two molecules that are thought to play key roles in mediating beneficial effects of exercise: brain‐derived neurotrophic factor (BDNF) and AMP‐activated protein kinase (AMPK). In middle‐aged (12 months old) C57BL/6J mice, we found that exercise protected RGCs against dysfunction and cell loss after an acute injury induced by elevation of intra‐ocular pressure. This was associated with preservation of inner retinal synapses and reduced synaptic complement deposition. Retinal expression of BDNF was not upregulated in response to exercise alone. Rather, exercise maintained BDNF levels in the retina, which were decreased postinjury in nonexercised animals. Confirming a critical role for BDNF, we found that blocking BDNF signalling during exercise by pharmacological means or genetic knock‐down suppressed the functional protection of RGCs afforded by exercise. Protection of RGCs with exercise was independent of activation of AMPK in either retina or skeletal muscle. Our data support a previously unidentified mechanism in which exercise prevents loss of BDNF in the retina after injury and preserves neuronal function and survival by preventing complement‐mediated elimination of synapses.

Fitness and ERP Indices of Cognitive Control Mode during Task Preparation in Preadolescent Children

A growing number of studies conducted over the past decade have demonstrated that greater aerobic fitness is associated with superior cognitive control in preadolescent children. Several studies have suggested that the relationship between fitness and cognitive control may be attributed to differential reliance on proactive vs. reactive cognitive control modes. However, this contention has remained speculative, and further studies are needed to better elucidate this relationship. We designed the present study to test the hypothesis that use of cognitive control modes would differ as a function of childhood fitness. We compared performance of lower-fit and higher-fit children on a modified AX-continuous performance task, commonly used to examine shifts in the use of proactive and reactive control, along with cue-P3 and contingent negative variation (CNV) of event-related brain potentials (ERPs). Results indicated that higher-fit children exhibited greater response accuracy for BX (non-target cue – target probe) relative to AY (target cue – non-target probe) trials, whereas lower-fit children had comparable response accuracies for AY and BX trials. Because enhanced BX performance and impaired AY performance may be attributed to the proactive use of context information, these results suggest that greater childhood fitness is associated with more effective utilization of proactive control. Higher-fit children also exhibited larger cue-P3 amplitude and smaller CNV amplitude for BX relative to AY trials, with no such effect of trial type in lower-fit children. These ERP results suggest that greater fitness is associated with more effective utilization of cue information and response preparation more appropriate to trial type, supporting the behavioral findings. The present study provides novel insights into the relationship between fitness and cognition from the perspective of cognitive control mode during task preparation.

Potential Role of Aminoprocalcitonin in the Pathogenesis of Alzheimer Disease

Increasing evidence suggests that inflammatory responses cause brain atrophy and play a prominent and early role in the progression of Alzheimer disease. Recent findings show that the neuroendocrine peptide aminoprocalcitonin (NPCT) plays a critical role in the development of systemic inflammatory response; however, the presence, possible function, regulation, and mechanisms by which NPCT may be involved in Alzheimer disease neuropathology remain unknown. We explored the expression of NPCT and its interaction with amyloid-β (Aβ), and proinflammatory and neurogenic effects. By using brain samples of Alzheimer disease patients and APP/PS1 transgenic mice, we evaluated the potential role of NPCT on Aβ-related pathology. We found that NPCT is expressed in hippocampal and cortical neurons and Aβ-induced up-regulation of NPCT expression. Peripherally administered antibodies against NPCT decreased microglial activation, decreased circulating levels of proinflammatory cytokines, and prevented Aβ-induced neurotoxicity in experimental models of Alzheimer disease. Remarkably, anti-NPTC therapy resulted in a significant improvement in the behavioral status of APP/PS1 mice. Our results indicate a central role of NPCT in Alzheimer disease pathogenesis and suggest NPCT as a potential biomarker and therapeutic target.

Serum insulin-like growth factor-I and amyloid beta protein in Alzheimer's disease: relationship with cognitive function

AIMS

Previous studies have suggested that insulin-like growth factor-I (IGF-I) deficiency may lead to cognitive deficits in neurodegenerative diseases such as Alzheimer's disease. The present study aimed to investigate the possible relationship between cognitive function and concentration of IGF-I or amyloid beta protein (Aβ) in serum in Alzheimer's patients.

METHODS

A total of 81 Japanese patients were enrolled in this study. Concentrations of IGF-I, Aβ42, and Aβ40 in serum were measured. Two neuropsychological tests, Mini-Mental State Examination and Hasegawa's Dementia Scale-Revised (HDS-R), were also performed. Linear correlations among the age, serum IGF-I, serum Aβ42 or Aβ40, Aβ42/Aβ40 ratio, Mini-Mental State Examination or HDS-R total score, and the scores for six HDS-R subscales were analyzed by regression analysis.

RESULTS

IGF-I showed a significant negative correlation with age (β = -0.357, P = 0.002) and a positive correlation with Aβ42/Aβ40 ratio (β = 0.318, P = 0.007). Serum IGF-I and both the Mini-Mental State Examination and the HDS-R total score also correlated (β = 0.505, β = 0.524, P < 0.01). Among the HDS-R subscales, 'Recall' (ρ = 0.379, P < 0.01), 'Verbal fluency' (ρ = 0.360, P < 0.01), and 'Attention and calculation' (ρ = 0.389, P < 0.01) showed significant positive correlations with serum IGF-I.

CONCLUSION

The results, specifically that lower serum IGF-I was associated with cognitive impairment, suggest that metabolism of IGF-I may be involved in the pathogenesis of cognitive deficits in Alzheimer's disease.

Synaptic Failure: Focus in an Integrative View of ALS

From early description by Charcot, the classification of the Amyotrophic Lateral Sclerosis (ALS) is evolving from a subtype of Motor Neuron (MN) Disease to be considered rather a multi-systemic, non-cell autonomous and complex neurodegenerative disease. In the last decade, the huge amount of knowledge acquired has shed new insights on the pathological mechanisms underlying ALS from different perspectives. However, a whole vision on the multiple dysfunctional pathways is needed with the inclusion of information often excluded in other published revisions. We propose an integrative view of ALS pathology, although centered on the synaptic failure as a converging and crucial player to the etiology of the disease. Homeostasis of input and output synaptic activity of MNs has been proved to be severely and early disrupted and to definitively contribute to microcircuitry alterations at the spinal cord. Several cells play roles in synaptic communication across the MNs network system such as interneurons, astrocytes, microglia, Schwann and skeletal muscle cells. Microglia are described as highly dynamic surveying cells of the nervous system but also as determinant contributors to the synaptic plasticity linked to neuronal activity. Several signaling axis such as TNFα/TNFR1 and CX3CR1/CX3CL1 that characterize MN-microglia cross talk contribute to synaptic scaling and maintenance, have been found altered in ALS. The presence of dystrophic and atypical microglia in late stages of ALS, with a decline in their dynamic motility and phagocytic ability, together with less synaptic and neuronal contacts disrupts the MN-microglia dialogue, decreases homeostatic regulation of neuronal activity, perturbs “on/off” signals and accelerates disease progression associated to impaired synaptic function and regeneration. Other hotspot in the ALS affected network system is the unstable neuromuscular junction (NMJ) leading to distal axonal degeneration. Reduced neuromuscular spontaneous synaptic activity in ALS mice models was also suggested to account for the selective vulnerability of MNs and decreased regenerative capability. Synaptic destabilization may as well derive from increased release of molecules by muscle cells (e.g. NogoA) and by terminal Schwann cells (e.g. semaphorin 3A) conceivably causing nerve terminal retraction and denervation, as well as inhibition of re-connection to muscle fibers. Indeed, we have overviewed the alterations on the metabolic pathways and self-regenerative capacity presented in skeletal muscle cells that contribute to muscle wasting in ALS. Finally, a detailed footpath of pathologic changes on MNs and associated dysfunctional and synaptic alterations is provided. The oriented motivation in future ALS studies as outlined in the present article will help in fruitful novel achievements on the mechanisms involved and in developing more target-driven therapies that will bring new hope in halting or delaying disease progression in ALS patients.

Relation between aerobic fitness and brain structures in amnestic mild cognitive impairment elderly

Mild cognitive impairment (aMCI) is a clinical condition, with high risk to develop Alzheimer's disease. Physical exercise may have positive effect on cognition and brain structure in older adults. However, it is still under research whether these influences are true on aMCI subjects with low Ab_42 and high total tau in cerebrospinal fluid (CSF), which is considered a biomarker for AD. Therefore, we aimed to investigate a possible relation between aerobic fitness (AF) and gray matter (GM) volume and AF and white matter (WM) integrity in aMCI with a CSF biomarker. Twenty-two participants with aMCI acquired the images on a 3.0-T MRI. AF was assessed by a graded exercise test on a treadmill. Voxel-based morphometry and tract-based spatial statistic methods were used to analyze the GM volume and WM microstructural integrity, respectively. We correlated AF and GM volume and WM integrity in aMCI (p < 0.05, FWE corrected, cluster with at least five voxels). There was a positive relation between AF and GM volume mostly in frontal superior cortex. In WM integrity, AF was positively correlated with fractional anisotropy and negatively correlated with mean diffusivity and radial diffusivity, all in the same tracts that interconnect frontal, temporal, parietal, and occipital areas (longitudinal fasciculus, fronto-occipital fasciculus, and corpus callosum). These results suggest that aerobic fitness may have a positive influence on protection of brain even in aMCI CSF biomarker, a high-risk population to convert to AD.

A Concerted Action Of Estradiol And Insulin Like Growth Factor I Underlies Sex Differences In Mood Regulation By Exercise

Mood homeostasis present sexually dimorphic traits which may explain sex differences in the incidence of mood disorders. We explored whether diverse behavioral-setting components of mood may be differentially regulated in males and females by exercise, a known modulator of mood. We found that exercise decreases anxiety only in males. Conversely, exercise enhanced resilience to stress and physical arousal, two other important components of mood, only in females. Because exercise increases brain input of circulating insulin-like growth factor I (IGF-I), a potent modulator of mood, we explored whether sex-specific actions of exercise on mood homeostasis relate to changes in brain IGF-I input. We found that exercise increased hippocampal IGF-I levels only in cycling females. Underlying mechanism involved activation of estrogen (E₂) receptors in brain vessels that led to increased uptake of serum IGF-I as E₂ was found to stimulate IGF-I uptake in brain endothelial cells. Indeed, modulatory effects of exercise on mood were absent in female mice with low serum IGF-I levels or after either ovariectomy or administration of an E₂ receptor antagonist. These results suggest that sex-specific brain IGF-I responses to physiological stimuli such as exercise contribute to dimorphic mood homeostasis that may explain sex differences in affective disorders.

Exercise and cerebrovascular plasticity

Aging impairs cerebrovascular plasticity and subsequently leads cerebral hypoperfusion, which synergistically accelerates aging-associated cognitive dysfunction and neurodegenerative diseases associated with impaired neuronal plasticity. On the other hand, over two decades of researches have successfully demonstrated that exercise, or higher level of physical activity, is a powerful and nonpharmacological approach to improve brain function. Most of the studies have focused on the neuronal aspects and found that exercise triggers improvements in neuronal plasticity, such as neurogenesis; however, exercise can improve cerebrovascular plasticity as well. In this chapter, to understand these beneficial effects of exercise on the cerebral vasculature, we first discuss the issue of changes in cerebral blood flow and its regulation during acute bouts of exercise. Then, how regular exercise improves cerebrovascular plasticity will be discussed. In addition, to shed light on the importance of understanding interactions between the neuron and cerebral vasculature, we describe neuronal activity-driven uptake of circulating IGF-I into the brain.

Obesity, Physical Activity and Bladder Cancer

While smoking and exposure to certain chemicals are well-defined risk factors for bladder cancer, there is no consensus as to the roles of modifiable lifestyle factors, notably physical activity, and obesity. We evaluated associations of obesity and physical activity with bladder cancer risk by performing a system-wide search of PubMed for cohort and case-control studies focused on obesity, exercise, and bladder cancer. A total of 31 studies were identified that evaluated the associations of obesity and physical activity with bladder cancer risk: 20 focused on obesity, eight on physical activity, and three on both. There was marked heterogeneity in population composition and outcomes assessment. Fifteen (65%) of the obesity studies used prevalence or incidence as the primary outcome and seven (30%) used bladder cancer mortality. Ten (44%) observed positive and 13 (56%) null associations of obesity with bladder cancer. Three (100%) of three studies also noted strong positive associations of obesity with bladder cancer progression or recurrence. Ten (91%) of the physical activity studies analyzed prevalence or incidence and one (9%) mortality. One (9%) study observed positive, seven (64%) null, and three (27%) negative associations of physical activity with bladder cancer. Study heterogeneity precluded quantitative assessment of outcomes. Obesity is potentially associated with an increased risk of bladder cancer, particularly for progression, recurrence, or death. Further studies of physical activity and bladder cancer are needed to validate these observations and elucidate the associations of exercise with bladder cancer progression and mortality.

Physical training decreases susceptibility to pilocarpine-induced seizures in the injured rat brain

There is growing evidence that physical activity ameliorates the course of epilepsy in animal models as well as in clinical conditions. Since traumatic brain injury is one of the strongest determinants of epileptogenesis, the present study focuses on the question whether a moderate long-term physical training can decrease susceptibility to seizures evoked following brain damage. Wistar rats received a mechanical brain injury and were subjected to daily running sessions on a treadmill for 21 days. Thereafter, seizures were induced by pilocarpine injections in trained and non-trained, control groups. During the acute period of status epilepticus, the intensity of seizures was assessed within the six-hour observation period. The trained rats showed considerable amelioration of pilocarpine-induced motor symptoms when compared with their non-trained counterparts. Histological investigations of effects of the brain injury and of physical training detected significant quantitative changes in parvalbumin-, calretinin- and NPY-immunopositive neuronal populations. Some of the injury-induced changes, especially those shoved by parvalbumin-immunopositive neurons, were abolished by the subsequent physical training procedure and could, therefore, be considered as neuronal correlates of the observed functional amelioration of the injured brain.

Physical exercise, neuroplasticity, spatial learning and memory

There has long been discussion regarding the positive effects of physical exercise on brain activity. However, physical exercise has only recently begun to receive the attention of the scientific community, with major interest in its effects on the cognitive functions, spatial learning and memory, as a non-drug method of maintaining brain health and treating neurodegenerative and/or psychiatric conditions. In humans, several studies have shown the beneficial effects of aerobic and resistance exercises in adult and geriatric populations. More recently, studies employing animal models have attempted to elucidate the mechanisms underlying neuroplasticity related to physical exercise-induced spatial learning and memory improvement, even under neurodegenerative conditions. In an attempt to clarify these issues, the present review aims to discuss the role of physical exercise in the improvement of spatial learning and memory and the cellular and molecular mechanisms involved in neuroplasticity.

Neurotrophic growth factor responses to lower body resistance training in older adults

Resistance exercise is an efficacious stimulus for improving cognitive function in older adults, which may be mediated by the upregulation of blood-borne neurotrophic growth factors (NTFs) like brain-derived neurotrophic factor (BDNF) and insulin-like growth factor-1 (IGF-1). However, the NTF response to resistance exercise and training in older adults is poorly understood. Therefore, the purpose of this study was to characterize the timing and magnitude of the NTF response following an acute bout of resistance exercise before and after 8 weeks of resistance training. Ten cognitively normal, older adults (ages 60–77 years, five men) were examined. The acute NTF response to resistance exercise was assessed via serum samples drawn at designated time points following exercise. This procedure was then repeated following 8 weeks of resistance training. BDNF increased immediately post-exercise (Δ9% pre-training, Δ11% post-training) then returned to resting levels while IGF-1 remained stable following resistance exercise before and after 8 weeks of resistance training. Basal levels of both NTFs were unaffected by the 8 week training period. We report a transient increase in serum BDNF following a bout of resistance exercise in older adults, which could have implications for the design of interventions seeking to maximize cognitive function in older adults.

IGF-1 protects dopamine neurons against oxidative stress: association with changes in phosphokinases

Insulin-like growth factor-1 (IGF-1) is an endogenous peptide transported across the blood brain barrier that is protective in several brain injury models, including an acute animal model of Parkinson's disease (PD). Motor deficits in PD are due largely to the progressive loss of nigrostriatal dopaminergic neurons. Thus, we examined the neuroprotective potential of IGF-1 in a progressive model of dopamine deficiency in which 6-hydroxydopamine (6-OHDA) is infused into the striatum. Rats received intrastriatal IGF-1 (5 or 50 µg) 6 h prior to infusion of 4 µg 6-OHDA into the same site and were euthanized 1 or 4 weeks later. Both concentrations of IGF-1 protected tyrosine hydroxylase (TH) immunoreactive terminals in striatum at 4 weeks but not at 1 week, indicating that IGF-induced restoration of the dopaminergic phenotype occurred over several weeks. TH-immunoreactive cell loss was only attenuated with 50 µg IGF-1. We then examined the effect of striatal IGF-1 on the Ras/ERK1/2 and PI3K/Akt pathways to ascertain whether their activation correlated with IGF-1-induced protection. Striatal and nigral levels of phospho-ERK1/2 were maximal 6 h after IGF-1 infusion and, with the exception of an increase in nigral pERK2 at 48 h, returned to basal levels by 7 days. Phospho-Akt (Ser473) was elevated 6-24 h post-IGF-1 infusion in both striatum and substantia nigra concomitant with inhibition of pro-death GSK-3β, a downstream target of Akt. These results suggest that IGF-1 can protect the nigrostriatal pathway in a progressive PD model and that this protection is preceded by activation of key pro-survival signaling cascades.

Neurotrophic factors in Parkinson's disease are regulated by exercise: Evidence-based practice

We carried out a qualitative review of the literature on the influence of forced or voluntary exercise in Parkinson's Disease (PD)-induced animals, to better understand neural mechanisms and the role of neurotrophic factors (NFs) involved in the improvement of motor behavior. A few studies indicated that forced or voluntary exercise may promote neuroprotection, through upregulation of NF expression, against toxicity of drugs that simulate PD. Forced training, such as treadmill exercise and forced-limb use, adopted in most studies, in addition to voluntary exercise on a running wheel are suitable methods for NFs upregulation.

Insulin-like growth factor-1 deficiency and metabolic syndrome

Consistent evidence associates IGF-1 deficiency and metabolic syndrome. In this review, we will focus on the metabolic effects of IGF-1, the concept of metabolic syndrome and its clinical manifestations (impaired lipid profile, insulin resistance, increased glucose levels, obesity, and cardiovascular disease), discussing whether IGF-1 replacement therapy could be a beneficial strategy for these patients. The search plan was made in Medline for Pubmed with the following mesh terms: IGF-1 and "metabolism, carbohydrate, lipids, proteins, amino acids, metabolic syndrome, cardiovascular disease, diabetes" between the years 1963-2015. The search includes animal and human protocols. In this review we discuss the relevant actions of IGF-1 on metabolism and the implication of IGF-1 deficiency in the establishment of metabolic syndrome. Multiple studies (in vitro and in vivo) demonstrate the association between IGF-1 deficit and deregulated lipid metabolism, cardiovascular disease, diabetes, and an altered metabolic profile of diabetic patients. Based on the available data we propose IGF-1 as a key hormone in the pathophysiology of metabolic syndrome; due to its implications in the metabolism of carbohydrates and lipids. Previous data demonstrates how IGF-1 can be an effective option in the treatment of this worldwide increasing condition. It has to distinguished that the replacement therapy should be only undertaken to restore the physiological levels, never to exceed physiological ranges.

Previous motor activity affects transition from uncertainty to decision-making in snails

One of the most commonly accepted benefits of enhanced physical activity is the improvement in the symptoms of depression, including the facilitation of decision-making. Up until now, these effects have been shown in rodents and humans only. Little is known about their evolutionary origin or biological basis, and the underlying cellular mechanisms also remain relatively elusive. Here, we demonstrate for the first time that preceding motor activity accelerates decision-making in an invertebrate, the pond snail Lymnaea stagnalis. To investigate decision-making in a novel environment, snails, which normally live in water, were placed on a flat dry surface to simulate the potentially threatening consequence of being in an arid environment. This stimulus initiated two distinct phases in snail behavior: slow circular movements, followed by intense locomotion in a chosen direction. The first phase was prolonged when the test arena was symmetrically lit, compared to one with an apparent gradient of light. However, forced muscular locomotion for two hours prior to the test promoted the transition from random circular motions to a directional crawl, accompanied by an increase in crawling speed but with no effect on the choice of direction. Two hours of intense locomotion produced also strong excitatory effect on the activity of serotonergic neurons in L. stagnalis. Our results suggest that the beneficial effects of physical exercise on cognitive performance in mammals might have deep roots in evolution, granting the opportunity to unravel the origins of such effects at the single neuron and network levels.

The 5-HT3 receptor is essential for exercise-induced hippocampal neurogenesis and antidepressant effects

Exercise has a variety of beneficial effects on brain structure and function, such as hippocampal neurogenesis, mood and memory. Previous studies have shown that exercise enhances hippocampal neurogenesis, induces antidepressant effects and improves learning behavior. Brain serotonin (5-hydroxytryptamine, 5-HT) levels increase following exercise, and the 5-HT system has been suggested to have an important role in these exercise-induced neuronal effects. However, the precise mechanism remains unclear. In this study, analysis of the 5-HT type 3A receptor subunit-deficient (htr3a(-/-)) mice revealed that lack of the 5-HT type 3 (5-HT3) receptor resulted in loss of exercise-induced hippocampal neurogenesis and antidepressant effects, but not of learning enhancement. Furthermore, stimulation of the 5-HT3 receptor promoted neurogenesis. These findings demonstrate that the 5-HT3 receptor is the critical target of 5-HT action in the brain following exercise, and is indispensable for hippocampal neurogenesis and antidepressant effects induced by exercise. This is the first report of a pivotal 5-HT receptor subtype that has a fundamental role in exercise-induced morphological changes and psychological effects.

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.

Control of the Cell Cycle in Adult Neurogenesis and its Relation with Physical Exercise

In the adult brain the neurogenesis is mainly restricted to two neurogenic regions: newly generated neurons arise at the subventricular zone (SVZ) of the lateral ventricle and at the subgranular zone of the hippocampal subregion named the dentate gyrus. The hippocampus is involved in learning and memory paradigms and the generation of new hippocampal neurons has been hypothesized to be a pivotal form of plasticity involved in the process. Moreover the dysregulation of hippocampal adult neurogenesis has been recognized and could anticipate several varieties of brain disease such as Alzheimer disease, epilepsy and depression. Over the last few decades numerous intrinsic, epigenetic and environmental factors have been revealed to deeply influence the process of adult neurogenesis, although the underlying mechanisms remain largely unknown. Growing evidence indicates that physical exercise represents one of the main extrinsic factor able to profoundly increase hippocampal adult neurogenesis, by altering neurochemistry and function of newly generated neurons. The present review surveys how neurogenesis can be modulated by cell cycle kinetics and highlights the putative role of the cell cycle length as a key component of the beneficial effect of running for hippocampal adult neurogenesis, both in physiological conditions and in the presence of defective neurogenesis.

How the Body Talks to the Brain; Peripheral Mediators of Physical Activity-Induced Proliferation in the Adult Hippocampus

In the hippocampal dentate gyrus, stem cells maintain the capacity to produce new neurons into adulthood. These adult-generated neurons become fully functional and are incorporated into the existing hippocampal circuit. The process of adult neurogenesis contributes to hippocampal functioning and is influenced by various environmental, hormonal and disease-related factors. One of the most potent stimuli of neurogenesis is physical activity (PA). While the bodily and peripheral changes of PA are well known, e.g. in relation to diet or cardiovascular conditions, little is known about which of these also exert central effects on the brain. Here, we discuss PA-induced changes in peripheral mediators that can modify hippocampal proliferation, and address changes with age, sex or PA duration/intensity. Of the many peripheral factors known to be triggered by PA, serotonin, FGF-2, IGF-1, VEGF, β-endorphin and adiponectin are best known for their stimulatory effects on hippocampal proliferation. Interestingly, while age negatively affects hippocampal proliferation per se, also the PA-induced response to most of these peripheral mediators is reduced and particularly the response to IGF-1 and NPY strongly declines with age. Sex differences per se have generally little effects on PA-induced neurogenesis. Compared to short term exercise, long term PA may negatively affect proliferation, due to a parallel decline in FGF-2 and the β-endorphin receptor, and an activation of the stress system particularly during conditions of prolonged exercise but this depends on other variables as well and remains a matter of discussion. Taken together, of many possible mediators, serotonin, FGF-2, IGF-1, VEGF, β-endorphin and adiponectin are the ones that most strongly contribute to the central effects of PA on the hippocampus. For a subgroup of these factors, brain sensitivity and responsivity is reduced with age.

Mechanisms of Muscle Denervation in Aging: Insights from a Mouse Model of Amyotrophic Lateral Sclerosis

Muscle denervation at the neuromuscular junction (NMJ) is thought to be a contributing factor in age-related muscle weakness. Therefore, understanding the mechanisms that modulate NMJ innervation is a key to developing therapies to combat age-related muscle weakness affecting the elderly. Two mouse models, one lacking the Cu/Zn superoxide dismutase (SOD1) gene and another harboring the transgenic mutant human SOD1 gene, display progressive changes at the NMJ, including muscle endplate fragmentation, nerve terminal sprouting, and denervation. These changes at the NMJ share many of the common features observed in the NMJs of aged mice. In this review, research findings demonstrating the effects of PGC-1α, IGF-1, GDNF, MyoD, myogenin, and miR-206 on NMJ innervation patterns in the G93A SOD1 mice will be highlighted in the context of age-related muscle denervation.

Sarcopenia and the Common Mental Disorders: a Potential Regulatory Role of Skeletal Muscle on Brain Function?

While it is understood that body composition impacts on physical conditions, such as diabetes and cardiovascular disease, it is only now apparent that body composition might play a role in the genesis of common mental disorders, depression and anxiety. Sarcopenia occurs in ageing and comprises a progressive decline in muscle mass, strength and function, leading to frailty, decreased independence and poorer quality of life. This review presents an emerging body of evidence to support the hypothesis that shared pathophysiological pathways for sarcopenia and the common mental disorders constitute links between skeletal muscle and brain function. Contracting skeletal muscle secretes neurotrophic factors that are known to play a role in mood and anxiety, and have the dual role of nourishing neuronal growth and differentiation, while protecting the size and number of motor units in skeletal muscle. Furthermore, skeletal muscle activity has important immune and redox effects that impact behaviour and reduce muscle catabolism.

Greater aerobic fitness is associated with more efficient inhibition of task-irrelevant information in preadolescent children

A growing number of neuroelectric studies using event-related brain potentials have demonstrated that greater aerobic fitness is associated with superior cognitive functioning across the lifespan. However, empirical data regarding the association between fitness and attentional orienting is scarce, with no evidence in children, and the findings are inconclusive. We designed the present study to examine the relationship between aerobic fitness and involuntary attentional orientation to task-irrelevant information in preadolescent children. Lower-fit and higher-fit children performed a visual oddball task in which irregular (i.e., rule-violating) stimuli appeared as a task-irrelevant dimension, while measures of task performance and the P3a component elicited by the irregular stimuli were assessed. Analyses revealed that higher-fit children exhibited lower miss rates and smaller P3a amplitude relative to lower-fit children. These findings suggest that greater childhood fitness is associated with more efficient inhibition of task-irrelevant information.

Cognitive function and exercise training for chronic renal disease patients: A literature review

OBJECTIVE

Cognitive impairment is very often noted in patients with Chronic Kidney Disease (CKD). Even though, exercise is considered to be a quantifiable activity that improves cognition in animals and humans, it seems that few studies have examined the relationship between cognitive function and CKD from the perspective of physical activity and cognitive performance. Thus, this evidence based review summarizes the present level of knowledge regarding the effects of exercise training on cognitive function in CKD patients.

DATA SOURCES

A comprehensive literature search was conducted in PubMed and Scopus from May 2014 through June 2014, by using the Cochrane and PRISMA guidelines.

REVIEW METHODS

Eligibility of the studies based on titles, abstracts and full-text articles was determined by two reviewers. Studies were selected using inclusion and exclusion criteria. We included only those studies that: assessed cognitive function in humans and animals using validated neuropsychological methods in chronic renal diseases patients; used exercise training protocols; addressed randomized control trials or controlled trials or clinical trials designed to evaluate cognitive impairment; and articles that were written in English. Studies were excluded when they concerned behavioral approaches and underpowered studies.

RESULTS

According to the current review only a few studies have examined the issue of cognitive function in CKD patients. These studies indicate that these patients often exhibit cognitive impairment, which is highly associated with poor outcomes. It has been supported that exercise training can induce positive changes in brain metabolism favoring better scores in cognitive function in Chronic Kidney Disease patients although the physiological mechanisms, which explain the influence of physical activity on cognition, have focused on changes in neurotransmitters, neurotrophins and vasculature.

CONCLUSION

Systematic exercise training seems to improve cognitive function in Chronic Kidney Disease patients but further research is warranted to further clarify the mechanisms involved.

Insulin-like growth factors and related proteins in plasma and cerebrospinal fluids of HIV-positive individuals

Background

Clinically significant dysregulation of the insulin-like growth factor (IGF) family proteins occurs in HIV-infected individuals, but the details including whether the deficiencies in IGFs contribute to CNS dysfunction are unknown.

Methods

We measured the levels of IGF1, IGF2, IGFBP1, IGFBP2, and IGF2 receptor (IGF2R) in matching plasma and cerebrospinal fluid (CSF) samples of 107 HIV+ individuals from CNS HIV Antiretroviral Therapy Effects Research (CHARTER) and analyzed their associations with demographic and disease characteristics, as well as levels of several soluble inflammatory mediators (TNFα, IL-6, IL-10, IL-17, IP-10, MCP-1, and progranulin). We also determined whether IGF1 or IGF2 deficiency is associated with HIV-associated neurocognitive disorder (HAND) and whether the levels of soluble IGF2R (an IGF scavenging receptor, which we also have found to be a cofactor for HIV infection in vitro) correlate with HIV viral load (VL).

Results

There was a positive correlation between the levels of IGF-binding proteins (IGFBPs) and those of inflammatory mediators: between plasma IGFBP1 and IL-17 (β coefficient 0.28, P = 0.009), plasma IGFBP2 and IL-6 (β coefficient 0.209, P = 0.021), CSF IGFBP1 and TNFα (β coefficient 0.394, P < 0.001), and CSF IGFBP2 and TNF-α (β coefficient 0.14, P < 0.001). As IGFBPs limit IGF availability, these results suggest that inflammation is a significant factor that modulates IGF protein expression/availability in the setting of HIV infection. However, there was no significant association between HAND and the reduced levels of plasma IGF1, IGF2, or CSF IGF1, suggesting a limited power of our study. Interestingly, plasma IGF1 was significantly reduced in subjects on non-nucleoside reverse transcriptase inhibitor-based antiretroviral therapy (ART) compared to protease inhibitor-based therapy (174.1 ± 59.8 vs. 202.8 ± 47.3 ng/ml, P = 0.008), suggesting a scenario in which ART regimen-related toxicity can contribute to HAND. Plasma IGF2R levels were positively correlated with plasma VL (β coefficient 0.37, P = 0.021) and inversely correlated with current CD4+ T cell counts (β coefficient −0.04, P = 0.021), supporting our previous findings in vitro.

Conclusions

Together, these results strongly implicate (1) an inverse relationship between inflammation and IGF growth factor availability and the contribution of IGF deficiencies to HAND and (2) the role of IGF2R in HIV infection and as a surrogate biomarker for HIV VL.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0288-6) contains supplementary material, which is available to authorized users.

The effect of exercise on the peripheral nerve in streptozotocin (STZ)-induced diabetic rats

The exact effectiveness of supportive care activities, such as exercise, in diabetes patients has yet to be elucidated in the diabetic peripheral neuropathy (DPN) field. Therefore, this study was designed to investigate the effect of regular exercise on the peripheral nerves of streptozotocin-induced diabetic rats. The animals were divided as follows into six groups according to exercise combination and glucose control: Normal group, normal group with exercise (EXE), diabetic group (DM), DM group with EXE, DM+glucose control with insulin (INS), and DM+INS+EXE. Animals in the exercise groups were made to walk on a treadmill machine everyday for 30 min at a setting of 8 m/min without inclination. After 8 weeks, sensory parameters were evaluated, and after 16 weeks, biochemicals and peripheral nerves were quantified by immunohistochemistry and compared among experimental groups. The resulting data showed that fasting blood glucose levels and HbA1c levels were not influenced significantly by exercise in normal and DM groups. However, the current perception threshold and the von Frey stimulation test revealed higher thresholds in the DM+INS+EXE group than in the DM+INS group (P<0.05). Significantly lower thresholds were observed in untreated DM groups (DM or DM+EXE) compared to the normal and insulin-treated DM groups (P<0.05). Intra-epidermal nerve fiber density was reduced in a lesser degree in the DM+INS+EXE group than in the DM+INS group (9.8±0.4 vs. 9.1±0.5, P<0.05). Exercise alone was not associated with a significant protective effect on the peripheral nerve in the normal or DM groups; however, a beneficial effect from exercise was observed when hyperglycemia was controlled with insulin in the DM group. These findings suggest that exercise has a potential protective effect against DPN based on the preferential effort for glucose control, although exercise alone cannot prevent peripheral nerve damage from hyperglycemia.

Expression of brain-derived neurotrophic factor, IGF-1 and cortisol elicited by regular aerobic exercise in adolescents

[Purpose] This study was conducted on adolescent subjects whose brains are still developing with the purpose of identifying the effect of 8 weeks duration of aerobic exercises on the expression of BDNF, IGF-1 and cortisol, to identify effect of aerobic exercise on the expression of cortisol, BDNF and IGF-1 related to nerve cell growth. [Subjects and Methods] The subjects were 20 junior-high school students with no history of physical illness. The students were divided into an exercise group and a control group. The exercise group performed 3 treadmill exercise times per week for 8 weeks. The exercise time for the consumption of 200 kcal was calculated and the exercises were performed by each individual for 8 weeks. [Results] The exercise group showed statistically significant in increases serum BDNF and IGF-1 after 8 weeks, but cortisol showed no significant change. There were statistically significant differences between the groups in serum BDNF and IGF-1 after 8 weeks, but the difference in cortisol levels was not significant. [Conclusion] We found that long-term regular aerobic exercises has a positive effect on the enhancement of serum BDNF levels at rest and IGF-1 of adolescents who are still undergoing through brain developments.

Effects of voluntary physical exercise, citicoline, and combined treatment on object recognition memory, neurogenesis, and neuroprotection after traumatic brain injury in rats

The biochemical and cellular events that lead to secondary neural damage after traumatic brain injury (TBI) contribute to long-term disabilities, including memory deficits. There is a need to search for single and/or combined treatments aimed at reducing these TBI-related disfunctions. The effects of citicoline and of voluntary physical exercise in a running wheel (3 weeks), alone or in combination, on TBI-related short-term (3 h) and long-term (24 h) object recognition memory (ORM) deficits and on neurogenesis and neuroprotection were examined using a rodent model of TBI (controlled cortical impact injury). Citicoline improved memory deficits at the two times tested, while physical exercise only in the long-term test. Physical exercise had a clear neuroprotective effect as indicated by reduced interhemispheric differences in hippocampal formation and lateral ventricle volumes and in density of mature neurons in the hilus of the dentate gyrus and the perirhinal cortex. Physical exercise also increased cell proliferation and neurogenesis in the granular cell layer of the dentate gyrus. Some degree of neuroprotection of citicoline was suggested by reduced interhemispheric differences in the volume of the hippocampal formation. Contrary to what was expected, the effects of citicoline and physical exercise did not sum up. Further, a negative interference between both treatments was found in several behavioral and histological variables. The promising profiles of both treatments as therapeutic tools in TBI when applied singly underscore the need to perform further works looking for other combined treatment regimens that increase the benefit of each treatment alone.