Treadmill exercise improves spatial learning ability by enhancing brain-derived neurotrophic factor expression in the attention-deficit/hyperactivity disorder rats

Learning and Memory Impairments With Attention-Deficit/Hyperactivity Disorder

ADHD is a common chronic neurodevelopmental disorder and is characterized by persistent inattention, hyperactivity, impulsivity and are often accompanied by learning and memory impairment. Great evidence has shown that learning and memory impairment of ADHD plays an important role in its executive function deficits, which seriously affects the development of academic, cognitive and daily social skills and will cause a serious burden on families and society. With the increasing attention paid to learning and memory impairment in ADHD, relevant research is gradually increasing. In this article, we will present the current research results of learning and memory impairment in ADHD from the following aspects. Firstly, the animal models of ADHD, which display the core symptoms of ADHD as well as with learning and memory impairment. Secondly, the molecular mechanism of has explored, including some neurotransmitters, receptors, RNAs, etc. Thirdly, the susceptibility gene of ADHD related to the learning and impairment in order to have a more comprehensive understanding of the pathogenesis. Key words: Learning and memory, ADHD, Review.

Vinpocetine, a PDE1 modulator, regulates markers of cerebral health, inflammation, and oxidative stress in a rat model of prenatal alcohol-induced experimental attention deficit hyperactivity disorder

Prenatal alcohol exposure (PAE) has been shown to induce symptomatology associated with attention deficit hyperactivity disorder (ADHD) by altering neurodevelopmental trajectories. Phosphodiesterase-1 (PDE1) is expressed centrally and has been used in various experimental brain conditions. We investigated the role of vinpocetine, a PDE1 inhibitor, on behavioral phenotypes and important biochemical deficits associated with a PAE rat model of ADHD. Protein markers of cerebral health (synapsin-IIa, BDNF, and pCREB), inflammation (IL-6, IL-10, and TNF-α), and oxidative stress (TBARS, GSH, and SOD) were analyzed in three brain regions (frontal cortex, striatum, and cerebellum). Hyperactivity, inattention, and anxiety introduced in the offspring due to PAE were assayed using open-field, Y-maze, and elevated plus maze, respectively. Administration of vinpocetine (10 & 20 mg/kg, p.o. [by mouth]) to PAE rat offspring for 4 weeks resulted in improvement of the behavioral profile of the animals. Additionally, levels of protein markers such as synapsin-IIa, BDNF, pCREB, IL-10, SOD, and GSH were found to be significantly increased, with a significant reduction in markers such as TNF-α, IL-6, and TBARS in selected brain regions of vinpocetine-treated animals. Vinpocetine, a selective PDE1 inhibitor, rectified behavioral phenotypes associated with ADHD, possibly by improving cerebral function, reducing brain inflammation, and reducing brain oxidative stress. This study provides preliminary analysis and suggests that the PDE1 enzyme may be an important pharmacological tool to study ADHD as a result of PAE.

Pleiotropic effects of BDNF on the cerebellum and hippocampus: Implications for neurodevelopmental disorders

Brain-derived neurotrophic factor (BDNF) is one of the most studied neurotrophins in the mammalian brain, essential not only to the development of the central nervous system but also to synaptic plasticity. BDNF is present in various brain areas, but highest levels of expression are seen in the cerebellum and hippocampus. After birth, BDNF acts in the cerebellum as a mitogenic and chemotactic factor, stimulating the cerebellar granule cell precursors to proliferate, migrate and maturate, while in the hippocampus BDNF plays a fundamental role in synaptic transmission and plasticity, representing a key regulator for the long-term potentiation, learning and memory. Furthermore, the expression of BDNF is highly regulated and changes of its expression are associated with both physiological and pathological conditions. The purpose of this review is to provide an overview of the current state of knowledge on the BDNF biology and its neurotrophic role in the proper development and functioning of neurons and synapses in two important brain areas of postnatal neurogenesis, the cerebellum and hippocampus. Dysregulation of BDNF expression and signaling, resulting in alterations in neuronal maturation and plasticity in both systems, is a common hallmark of several neurodevelopmental diseases, such as autism spectrum disorder, suggesting that neuronal malfunction present in these disorders is the result of excessive or reduced of BDNF support. We believe that the more the relevance of the pathophysiological actions of BDNF, and its downstream signals, in early postnatal development will be highlighted, the more likely it is that new neuroprotective therapeutic strategies will be identified in the treatment of various neurodevelopmental disorders.

Evaluation of the Relationship Between BDNF Val66Met Gene Polymorphism and Attention Deficit Hyperactivity Disorder: A Meta-Analysis

BACKGROUND

Attention deficit hyperactivity disorder (ADHD) is a common neurobehavioral disorder in childhood. Brain-derived neurotrophic factor (BDNF) is widely distributed in the central nervous system and plays an important role in neural development. Despite several previous studies have examined the association between the Val66Met polymorphism BDNF and ADHD, the results are conflicting.

OBJECTIVE

This study aimed to evaluate the association between Val66Met polymorphism and ADHD in case-control and transmission disequilibrium test (TDT) studies using a meta-analysis.

METHODS

Keywords "rs6265" or "Val66Met" and "Attention deficit hyperactivity disorder" were used to search in the PubMed, Embase, Web of Science, Wanfang, and China National Knowledge Infrastructure databases before April 2021. Genotype data were extracted to calculate odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Fifteen studies, comprising of 8,692 samples (containing 4,364 cases, 4,328 controls) and 1,578 families were included and results demonstrated that rs6265 was not associated with susceptibility to ADHD (OR = 0.95, 95% CI: 0.87-1.04, P = 0.291). Stratified analyses by study design, ethnicity, and sample size further supported that rs6265 was not associated with ADHD.

CONCLUSION

The present study shows that the polymorphism of the BDNF Val66Met gene is not associated with susceptibility to ADHD.

miR-132 and miR-942 Expression Levels in Children with Attention Deficit and Hyperactivity Disorder: A Controlled Study

OBJECTIVE

Although attention deficit hyperactivity disorder (ADHD) is a disease with high genetic transition, our knowledge about the mechanism of the disease is limited. In this study, it was aimed to evaluate the levels of miR-132-3p and miR-942-5p that are associated with the dopamine carrier protein gene (DAT1) and dopamine receptor 5 (DRD5) genes, which have been shown to play a role in the development of ADHD.

METHODS

According to the Diagnostic and Statistical Manual of Mental Disorders 5th edition, 50 children diagnosed with ADHD and 48 healthy controls were included in the study. Affective Disorders and Schizophrenia Interview Schedule-Now and Lifetime Version-Turkish Adaptation was used to evaluate ADHD and the diagnoses accompanying ADHD. Quantitative Real-Time Polymerase Chain Reaction was used to evaluate miR-132-3p and miR-942-5p expression levels.

RESULTS

It was observed that miR-132-3p level (p = 0.001) was significantly higher with children with ADHD compared to the control group, and the level of miR-942-5p (p = 0.181) was higher in ADHD but did not reach statistically significant level.

CONCLUSION

In our study, we found that the increase in the miR-132-3p levels of children with ADHD may be a therapeutic target of the disease.

Therapeutic effects of anodal transcranial direct current stimulation in a rat model of ADHD

Most therapeutic candidates for treating attention-deficit hyperactivity disorder (ADHD) have focused on modulating the dopaminergic neurotransmission system with neurotrophic factors. Regulation of this system by transcranial direct current stimulation (tDCS) could contribute to the recovery of cognitive symptoms observed in patients with ADHD. Here, male spontaneously hypertensive rats (SHR) were subjected to consecutive high-definition tDCS (HD-tDCS) (20 min, 50 μA, current density 63.7 A/m², charge density 76.4 kC/m²) over the prefrontal cortex. This treatment alleviated cognitive deficits, with an increase in tyrosine hydroxylase and vesicular monoamine transporter two and significantly decreased plasma membrane reuptake transporter (DAT). HD-tDCS application increased the expression of several neurotrophic factors, particularly brain-derived neurotrophic factor (BDNF), and activated hippocampal neurogenesis. Our results suggest that anodal HD-tDCS over the prefrontal cortex may ameliorate cognitive dysfunction via regulation of DAT and BDNF in the mesocorticolimbic dopaminergic pathways, and therefore represents a potential adjuvant therapy for ADHD.

Caffeine Consumption plus Physical Exercise Improves Behavioral Impairments and Stimulates Neuroplasticity in Spontaneously Hypertensive Rats (SHR): an Animal Model of Attention Deficit Hyperactivity Disorder

Attention deficit hyperactivity disorder (ADHD) is a prevalent and disabling disorder, mainly characterized by hyperactivity, inattention, and impulsivity, but also by olfactory and memory impairments that frequently persist throughout lifetime. The pathophysiology of ADHD is complex, involving several brain regions and neural pathways including alterations in adenosine neuromodulation. The administration of caffeine (a non-selective adenosine receptor antagonist) and physical exercise have been independently pointed as effective approaches for the management of ADHD symptoms. Here, we evaluated the effects of caffeine consumption (0.3 mg/mL in drinking water) plus physical exercise in running wheels during 6 weeks-starting during either adolescence (30 days old) or adulthood (4-5 months old)-on behavioral performance (including olfactory discrimination, open field, object recognition, and water maze tests) on the brain levels of monoamines (by high-performance liquid chromatography), on proteins related to synaptic plasticity and on brain-derived neurotrophic factor signaling (by Western blot analysis) in spontaneously hypertensive rats (SHRs), a validated animal model of ADHD. SHRs displayed persistent impairments of olfactory and short-term recognition memory from adolescence to adulthood, which were accompanied by lower levels of synaptosomal-associated protein 25 (SNAP-25) in the prefrontal cortex and hippocampus. The association of caffeine plus physical exercise during adolescence or adulthood restored the olfactory discrimination ability and, in an independent manner, improved short-term recognition memory of SHRs. These benefits were not associated to alterations in locomotor activity or in the hypertensive phenotype. The association of caffeine consumption plus physical exercise during adolescence increased the levels of SNAP-25, syntaxin, and serotonin in the hippocampus and prefrontal cortex, and striatal dopamine levels in SHRs. These results provide new evidence of the potential of caffeine and physical exercise, starting at adolescence or adult life, to improve behavioral impairments and stimulate neuroplasticity in ADHD.

Physical exercise in attention deficit hyperactivity disorder - evidence and implications for the treatment of borderline personality disorder

A growing body of literature indicates a potential role for physical exercise in the treatment of attention deficit hyperactivity disorder (ADHD). Suggested effects include the reduction of ADHD core symptoms as well as improvements in executive functions. In the current review, we provide a short overview on the neurophysiological mechanisms assumed to underlie the beneficial effects of exercise. Further, we review the current evidence from experimental studies regarding both acute exercise and long-term interventions in ADHD. While the positive effects observed after acute aerobic exercise are promising, very few well-designed long-term intervention studies have been conducted yet. Moreover, although exercise effects have not yet been studied in borderline personality disorder (BPD), in the end of this paper we derive hypotheses why exercise could also be beneficial for this patient population.

Effect of catalpol on behavior and neurodevelopment in an ADHD rat model

Studies suggest that abnormal neurodevelopment of prefrontal striatal circuits is implicated in the pathogenesis of attention deficit hyperactivity disorder (ADHD). In the present study, we investigated the effect of catalpol, an active ingredient of Rehmanniae radix preparata, which is the most frequently used Chinese medicinal herb for the treatment of ADHD, on behavior and neurodevelopment in spontaneously hypertensive rats (SHR). SHR were divided into SHR group (vehicle, i.g.), methylphenidate (MPH) group (2 mg/kg/day, i.g.), and catalpol group (50 mg/kg/day i.g.), and Wistar-Kyoto (WKY) rats were used as control group (vehicle, i.g.). Open Field Test (OFT) and Morris water maze (MWM) test were performed to assess the effect of catalpol on behavior. Results revealed that both catalpol and MPH treatment decreased average speed, time spent in the central area, rearing times, and central area visits, increased the immobility time of SHR in OFT, and increased number of visits to the annulus, and time spent in target quadrant in the MWM test. Hematoxylin and eosin (H&E) staining showed that catalpol reduced irregular neuronal arrangement, ruptured nuclear membranes, and resulted in disappearance of the nucleolus in the prefrontal cortex (PFC) and striatum of SHR. Moreover, immuno-fluorescent staining of NeuN and myelin basic protein (MBP) indicated that catalpol ameliorated neuronal loss and contributed to myelination. Finally, western blot and immunostaining analysis suggested that several regulatory proteins involved in PFC development were up-regulated by catalpol treatment, such as brain-derived neurotrophic factor (BDNF), cyclin-dependent kinase 5 (Cdk5), p35, fibroblast growth factor (FGF) 21 and its receptor (FGFR)1. Taken together, catalpol can effectively ameliorate hyperactive and impulsive behavior, improve spatial learning and memory in SHR, likely through the neurodevelopmental pathways. Nonetheless, whether catalpol could attenuate inattention in SHR and the pathway by which catalpol reduces neuronal loss remain to be further studied.

Differential Behavioral and Biochemical Responses to Caffeine in Male and Female Rats from a Validated Model of Attention Deficit and Hyperactivity Disorder

Epidemiological studies suggest sex differences in attention deficit and hyperactivity disorder (ADHD) symptomatology. The potential benefits of caffeine have been reported in the management of ADHD, but its effects were not properly addressed with respect to sex differences. The present study examined the effects of caffeine (0.3 g/L) administered since childhood in the behavior and brain-derived neurotrophic factor (BDNF) and its related proteins in both sexes of a rat model of ADHD (spontaneously hypertensive rats-SHR). Hyperlocomotion, recognition, and spatial memory disturbances were observed in adolescent SHR rats from both sexes. However, females showed lack of habituation and worsened spatial memory. Although caffeine was effective against recognition memory impairment in both sexes, spatial memory was recovered only in female SHR rats. Besides, female SHR rats showed exacerbated hyperlocomotion after caffeine treatment. SHR rats from both sexes presented increases in the BDNF, truncated and phospho-TrkB receptors and also phospho-CREB levels in the hippocampus. Caffeine normalized BDNF in males and truncated TrkB receptor at both sexes. These findings provide insight into the potential of caffeine against fully cognitive impairment displayed by females in the ADHD model. Besides, our data revealed that caffeine intake since childhood attenuated behavioral alterations in the ADHD model associated with changes in BDNF and TrkB receptors in the hippocampus.

Serum brain-derived neurotrophic factor levels in treatment-naïve boys with attention-deficit/hyperactivity disorder treated with methylphenidate: an 8-week, observational pretest-posttest study

Brain-derived neurotrophic factor (BDNF) is an important neurotrophin in the brain that modulates dopaminergic neurons. In this study, we aimed to investigate the changes in serum BDNF levels of children with attention-deficit/hyperactivity disorder (ADHD) in response to OROS methylphenidate treatment. We also aimed to determine whether there were any pre-post-differences between ADHD subtypes and comorbid psychiatric disorders in serum BDNF levels. Fifty male children with ADHD and 50 male healthy controls within the age range of 6-12 years were recruited to the study. The psychiatric diagnoses were determined by applying a structured interview with Kiddie schedule for affective disorders and schizophrenia for school-age children-present and lifetime version. The symptom severity of ADHD was measured using the Clinical Global Impression ADHD Severity Scale (CGI-S). Physicians completed Du Paul ADHD questionnaires. The levels of serum BDNF were assessed before and after 8 weeks of treatment with effective dosages of OROS methylphenidate. In the present study, the mean serum BDNF levels of boys with ADHD and of the healthy controls were 2626.33 ± 1528.05 and 2989.11 ± 1420.08 pg/mL, respectively. Although there were no statistically significant difference between the ADHD group and healthy controls at baseline (p = 0.22), the increase of serum BDNF was statistically significant from baseline to endpoint in the ADHD group (p = 0.04). The mean serum BDNF levels at baseline and endpoint of the ADHD group were 2626.33 ± 1528.05 and 3255.80 ± 1908.79 pg/mL, respectively. The serum BDNF levels of ADHD-inattentive subtype were significantly lower at baseline (p = 0.02), whereas BDNF levels post-treatment showed no significant difference. The increase of serum BDNF levels with methylphenidate treatment after 8 weeks was significantly higher in the inattentive group (p = 0.005). The increase of serum BDNF levels with methylphenidate treatment after 8 weeks in boys with ADHD may support the potential role of BDNF in the pathophysiology of ADHD. The role of BDNF in ADHD subtypes in particular should be evaluated with further, larger studies.

Effects of physical exercise and social isolation on anxiety-related behaviors in two inbred rat strains

We investigated the effects of physical exercise (PE) on locomotor activity and anxiety-like behavior in Lewis (LEW) and Spontaneously Hypertensive Rats (SHR) male rats. Rats received either four weeks of forced training, 5days/week, on a treadmill (experiment 1) or were given 21days of free access to running wheels (experiment 2). We also tested the effects of social isolation (SI) (seven days of isolation - experiment 3) on behavior. In experiment 1, 20% of LEW rats and 63% of SHR rats completed the training protocol. PE significantly increased central and peripheral locomotion in the open field (OF) and entries into the open arms in the elevated plus-maze (EPM) in both strains. In experiment 2, the distance traveled by SHR rats on running wheels was significantly higher compared with LEW rats. PE on running wheels also increased the time spent in the center of the OF in SHR rats only. In experiment 3, SI decreased central and peripheral locomotion in the OF in both strains. In summary, forced PE on a treadmill reduced anxiety-like behavior and increased locomotion in male rats of both strains, whereas voluntary PE on running wheels decreased anxiety-like behavior in SHR rats only. SI decreased locomotion in both strains in the OF. This study suggests that spontaneous activity levels are genotype-dependent and the effects of PE depend on the type of exercise performed.

Alterations of Growth Factors in Autism and Attention-Deficit/Hyperactivity Disorder

Growth factors (GFs) are cytokines that regulate the neural development. Recent evidence indicates that alterations in the expression level of GFs during embryogenesis are linked to the pathophysiology and clinical manifestations of attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorders (ASD). In this concise review, we summarize the current evidence that supports the role of brain-derived neurotrophic factor, insulin-like growth factor 2, hepatocyte growth factor (HGF), glial-derived neurotrophic factor, nerve growth factor, neurotrophins 3 and 4, and epidermal growth factor in the pathogenesis of ADHD and ASD. We also highlight the potential use of these GFs as clinical markers for diagnosis and prognosis of these neurodevelopmental disorders.

Treadmill exercise enhances spatial learning ability through suppressing hippocampal apoptosis in Huntington's disease rats

Huntington’s disease is a chronic neurodegenerative disorder inherited in an autosomal dominant fashion, and characterized as involuntary movement. Quinolinic acid has been used to produce an animal model of Huntington’s disease. In the present study, the effect of treadmill exercise on spatial-learning ability and motor coordination focusing on the apoptosis in the hippocampus was investigated using quinolinic acid-induced Huntington’s disease rats. Huntington’s disease was induced by unilateral intrastriatal injection of quinolinic acid (2 μL of 100 nmol) using stereotaxic instrument. The rats in the treadmill exercise groups were subjected to run on a treadmill for 30 min once a day during 14 days. Spatial learning ability and motor coordination were determined by radial 8-arm maze test and rota-rod test. Immunohistochemistry for caspase-3 and western blot for Bax and Bcl-2 were also conducted for the detection of apoptosis. In the present results, spatial learning ability and motor coordination were deteriorated by intrastriatal injection of quinolinic acid. In contrast, treadmill exercise exerted ameliorating effect on quinolinic acid-induced deterioration of spatial learning ability and motor coordination. Bcl-2 expression in the hippocampus was de-creased and expressions of casepase-3 and Bax in the hippocampus were increased in the quinolinic acid-induced Huntington’s disease rats. Treadmill exercise increased Bcl-2 expression and decreased expressions of casepase-3 and Bax in the Huntington’s disease rats. The present results showed that treadmill exercise might ameliorate quinolinic acid-induced loss of spatial learning ability and motor coordination by suppressing apoptosis in the hippocampus.

Treadmill exercise improves short-term memory by enhancing hippocampal cell proliferation in quinolinic acid-induced Huntington's disease rats

Huntington's disease (HD) is an inherited genetic disorder, characterized by cognitive dysfunction and abnormal body movements called chorea. Quinolinic acid (QA) is an endogenous metabolite of tryptophan in the kynurenine pathway. QA-induced alterations are similar to the symptoms of HD patients. Physical exercise has beneficial effects on the brain functions. Exercise increases production of neurotrophic factors in the brain and improves learning ability and memory function. In the present study, we investigated the effects of treadmill exercise short-term memory on QA-induced HD rats in relation with cell proliferation. For the induction of Huntington's animal model, 2 μL of 100 nmol QA was intrastriatal injected into the rats. The rats in the treadmill exercise groups were forced to run on a treadmill for 30 min once a day, five times a week for 2 weeks. Step-down avoidance test was conducted for the determination of short-term memory. Cell proliferation in the hippocampal dentate gyrus was determined by 5-bromo-2'-deoxyuridine (BrdU) and doublecortin (DCX) immunohistochemistry. Western blot for brain-derived neurotrophic factor (BDNF) and tyrosine kinase B (TrkB) were performed. In the present results, treadmill exercise alleviated QA-induced short-term memory impairment in HD rats. Treadmill exercise increased cell proliferation in the hippocampal dentate gyrus through enhancing BDNF expression in the HD rats. These results revealed that treadmill exercise is effective for the symptom improvement in the HD patients.

The Physiology of BDNF and Its Relationship with ADHD

Brain-derived neurotrophic factor (BDNF) is a major neurotrophin in the central nervous system that plays a critical role in the physiological brain functions via its two independent receptors: tropomyosin-related kinase B (TrkB) and p75, especially in the neurodevelopment. Disrupting of BDNF and its downstream signals has been found in many neuropsychological diseases, including attention-deficit hyperactivity disorder (ADHD), a common mental disorder which is prevalent in childhood. Understanding the physiological functions of BDNF during neural development and its potential relationship with ADHD will help us to elucidate the possible mechanisms of ADHD and to develop therapeutic approaches for this disease. In this review, we summarized the important literatures for the physiological functions of BDNF in the neurodevelopment. We also performed an association study on the functional genetic variation of BDNF and ADHD by a case-control study in the Chinese mainland population and revealed the potential correlation between BDNF and ADHD which needs further research to confirm.

Postnatal treadmill exercise alleviates short-term memory impairment by enhancing cell proliferation and suppressing apoptosis in the hippocampus of rat pups born to diabetic rats

During pregnancy, diabetes mellitus exerts detrimental effects on the development of the fetus, especially the central nervous system. In the current study, we evaluated the effects of postnatal treadmill exercise on short-term memory in relation with cell proliferation and apoptosis in the hippocampus of rat pups born to streptozotocin (STZ)-induced diabetic maternal rats. Adult female rats were mated with male rats for 24 h. Two weeks after mating, the pregnant female rats were divided into two groups: control group and STZ injection group. The pregnant rats in the STZ injection group were administered 40 mg/kg of STZ intraperitoneally. After birth, the rat pups were divided into the following four groups: control group, control with postnatal exercise group, maternal STZ-injection group, and maternal STZ-injection with postnatal exercise group. The rat pups in the postnatal exercise groups were made to run on a treadmill for 30 min once a day, 5 times per week for 2 weeks beginning 4 weeks after birth. The rat pups born to diabetic rats were shown to have short-term memory impairment with suppressed cell proliferation and increased apoptosis in the hippocampal dentate gyrus. Postnatal treadmill exercise alleviated short-term memory impairment by increased cell proliferation and suppressed apoptosis in the rat pups born to diabetic rats. These findings indicate that postnatal treadmill exercise may be used as a valuable strategy to ameliorate neurodevelopmental problems in children born to diabetics.