Exercise effects on motor and affective behavior and catecholamine neurochemistry in the MPTP-lesioned mouse

Ndufs4 KO mice: A model to study comorbid mood disorders associated with mitochondrial dysfunction

The Ndufs4 knockout (KO) mouse is a validated and robust preclinical model of mitochondrial diseases (specifically Leigh syndrome), that displays a narrow window of relative phenotypical normality, despite its inherent mitochondrial complex I dysfunction and severe phenotype. Preclinical observations related to psychiatric comorbidities that arise in patients with mitochondrial diseases and indeed in Leigh syndrome are, however, yet to be investigated in this model. Strengthening this narrative is the fact that major depression and bipolar disorder are known to present with deficits in mitochondrial function. We therefore screened the behavioural profile of male and female Ndufs4 KO mice (relative to heterozygous; HET and wildtype; WT mice) between postnatal days 28 and 35 for locomotor, depressive- and anxiety-like alterations and linked it with selected brain biomarkers, viz. serotonin, kynurenine, and redox status in brain areas relevant to psychiatric pathologies (i.e., prefrontal cortex, hippocampus, and striatum). The Ndufs4 KO mice initially displayed depressive-like behaviour in the tail suspension test on PND31 but not on PND35 in the forced swim test. In the mirror box test, increased risk resilience was observed. Serotonin levels of KO mice, compared to HET controls, were increased on PND36, together with increased tryptophan to serotonin and kynurenine turnover. Kynurenine to kynurenic acid turnover was however decreased, while reduced versus oxidized glutathione ratio (GSH/GSSG) was increased. When considering the comorbid psychiatric traits of patients with mitochondrial disorders, this work elaborates on the neuropsychiatric profile of the Ndufs KO mouse. Secondly, despite locomotor differences, Ndufs4 KO mice present with a behavioural profile not unlike rodent models of bipolar disorder, namely variable mood states and risk-taking behaviour. The model may elucidate the bio-energetic mechanisms underlying mood disorders, especially in the presence of mitochondrial disease. Studies are however required to further validate the model's translational relevance.

Investigating affective neuropsychiatric symptoms in rodent models of Parkinson's disease

Affective neuropsychiatric disorders such as depression, anxiety and apathy are among the most frequent non-motor symptoms observed in people with Parkinson's disease (PD). These conditions often emerge during the prodromal phase of the disease and are generally considered to result from neurodegenerative processes in meso-corticolimbic structures, occurring in parallel to the loss of nigrostriatal dopaminergic neurons. Depression, anxiety, and apathy are often treated with conventional medications, including selective serotonin reuptake inhibitors, tricyclic antidepressants, and dopaminergic agonists. The ability of these pharmacological interventions to consistently counteract such neuropsychiatric symptoms in PD is still relatively limited and the development of reliable experimental models represents an important tool to identify more effective treatments. This chapter provides information on rodent models of PD utilized to study these affective neuropsychiatric symptoms. Neurotoxin-based and genetic models are discussed, together with the main behavioral tests utilized to identify depression- and anxiety-like behaviors, anhedonia, and apathy. The ability of various therapeutic approaches to counteract the symptoms observed in the various models is also reviewed.

Exercise as an antidepressant: exploring its therapeutic potential

The COVID-19 pandemic has increased the prevalence of depressive disorders worldwide, requiring alternative treatments beyond medication and psychotherapy. Exercise has positive effects on the brain; therefore, it has emerged as a promising therapeutic option for individuals with depression. Considerable research involving humans and animals offers compelling evidence to support the mental health benefits of physical activity or exercise mediated by the regulation of complex theoretical paradigms. However, challenges such as conducting long-term follow-up assessments and considering individual characteristics remain in human studies despite extensive efforts. While animal studies provide valuable insights into the potential benefits of exercise and its impact on outcomes related to depression and anxiety in rodents exposed to different stress paradigms, translating the findings to humans requires careful evaluation. More research is needed to establish precise exercise prescription guidelines and to better understand the complex relationship between exercise and depressive disorders. Therefore, this concise review explores the evidence supporting exercise intervention as an antidepressant treatment and its underlying mechanisms.

Moderate intensity aerobic exercise in 6-OHDA-lesioned rats alleviates established motor deficits and reduces neurofilament light and glial fibrillary acidic protein serum levels without increased striatal dopamine or tyrosine hydroxylase protein

Background

Alleviation of motor impairment by aerobic exercise (AE) in Parkinson's disease (PD) points to a CNS response that could be targeted by therapeutic approaches, but recovery of striatal dopamine (DA) or tyrosine hydroxylase (TH) has been inconsistent in rodent studies.

Objective

To increase translation of AE, 3 components were implemented into AE design to determine if recovery of established motor impairment, concomitant with >80% striatal DA and TH loss, was possible. We also evaluated if serum levels of neurofilament light (NfL) and glial fibrillary acidic protein (GFAP), blood-based biomarkers of disease severity in human PD, were affected.

Methods

We used a 6-OHDA hemiparkinson rat model featuring progressive nigrostriatal neuron loss over 28 days, with impaired forelimb use 7 days post-lesion, and hypokinesia onset 21 days post-lesion. After establishing forelimb use deficits, moderate intensity AE began 1-3 days later, 3x per week, for 40 min/session. Motor assessments were conducted weekly for 3 wks, followed by determination of striatal DA, TH protein and mRNA, and NfL and GFAP serum levels.

Results

Seven days after 6-OHDA lesion, recovery of depolarization-stimulated extracellular DA and DA tissue content was <10%, representing severity of DA loss in human PD, concomitant with 50% reduction in forelimb use. Despite severe DA loss, recovery of forelimb use deficits and alleviation of hypokinesia progression began after 2 weeks of AE and was maintained. Increased NfLand GFAP levels from lesion were reduced by AE. Despite these AE-driven changes, striatal DA tissue and TH protein levels were unaffected.

Conclusions

This proof-of-concept study shows AE, using exercise parameters within the capabilities most PD patients, promotes recovery of established motor deficits in a rodent PD model, concomitant with reduced levels of blood-based biomarkers associated with PD severity, without commensurate increase in striatal DA or TH protein.

Metformin improves depressive-like behavior in experimental Parkinson's disease by inducing autophagy in the substantia nigra and hippocampus

Parkinson's disease (PD) remains a disease of little known etiology. In addition to the motor symptoms, depression is present in about 40% of patients, contributing to the loss of quality of life. Recently, the involvement of the autophagy mechanism in the pathogenesis of depression has been studied, in addition to its involvement in PD as well. In this study, we tested the effects of metformin, an antidiabetic drug also with antidepressant effects, on depressive-like behavior in a rotenone-induced PD model and on the autophagy process. Mice 8-week-old male C57BL/6 were induced with rotenone for 20 consecutive days (2.5 mg/kg/day) and treated with metformin (200 mg/kg/day) from the 5th day of induction. All the animals were submitted to rotarod, sucrose preference and tail suspension tests. After euthanasia, the substantia nigra and hippocampus were removed for analysis by western blotting or fixed and analyzed by immunofluorescence. The results show that there was an impairment of autophagy in animals induced by rotenone both in nigral and extranigral regions as well as a depressive-like behavior. Metformin was able to inhibit depressive-like behavior and increase signaling pathway proteins, transcription factors and autophagosome-forming proteins, thus inducing autophagy in both the hippocampus and the substantia nigra. In conclusion, we show that metformin has an antidepressant effect in a rotenone-induced PD model, which may result, at least in part, from the induction of the autophagy process.

Application of Neurotoxin-Induced Animal Models in the Study of Parkinson's Disease-Related Depression: Profile and Proposal

Depression can be a non-motor symptom, a risk factor, and even a co-morbidity of Parkinson's disease (PD). In either case, depression seriously affects the quality of life of PD patients. Unfortunately, at present, a large number of clinical and basic studies focused on the pathophysiological mechanism of PD and the prevention and treatment of motor symptoms. Although there has been increasing attention to PD-related depression, it is difficult to achieve early detection and early intervention, because the clinical guidelines mostly refer to depression developed after or accompanied by motor impairments. Why is there such a dilemma? This is because there has been no suitable preclinical animal model for studying the relationship between depression and PD, and the assessment of depressive behavior in PD preclinical models is as well a very challenging task since it is not free from the confounding from the motor impairment. As a common method to simulate PD symptoms, neurotoxin-induced PD models have been widely used. Studies have found that neurotoxin-induced PD model animals could exhibit depression-like behaviors, which sometimes manifested earlier than motor impairments. Therefore, there have been attempts to establish the PD-related depression model by neurotoxin induction. However, due to a lack of unified protocol, the reported results were diverse. For the purpose of further promoting the improvement and optimization of the animal models and the study of PD-related depression, we reviewed the establishment and evaluation strategies of the current animal models of PD-related depression based on both the existing literature and our own research experience, and discussed the possible mechanism and interventions, in order to provide a reference for future research in this area.

Açai Berry Mitigates Parkinson's Disease Progression Showing Dopaminergic Neuroprotection via Nrf2-HO1 Pathways

The current pharmacological treatment for Parkinson's disease (PD) is focused on symptom alleviation rather than disease prevention. In this study, we look at a new strategy to neuroprotection that focuses on nutrition, by a supplementation with Açai berry in an experimental models of PD. Daily orally supplementation with Açai berry dissolved in saline at the dose of 500 mg/kg considerably reduced motor and non-motor symptom and neuronal cell death of the dopaminergic tract induced by 4 injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Furthermore, Açai berry administration reduced α-synuclein aggregation in neurons, enhanced tyrosine hydroxylase and dopamine transporter activities, and avoided dopamine depletion. Moreover, Açai berry administration was able to reduce astrogliosis and microgliosis as well as neuronal death. Its beneficial effects could be due to its bioactive phytochemical components that are able to stimulate nuclear factor erythroid 2-related factor 2 (Nrf2) by counteracting the oxidative stress and neuroinflammation that are the basis of this neurodegenerative disease.

Establishing Equivalent Aerobic Exercise Parameters Between Early-Stage Parkinson's Disease and Pink1 Knockout Rats

BACKGROUND

Rodent Parkinson's disease (PD) models are valuable to interrogate neurobiological mechanisms of exercise that mitigate motor impairment. Translating these mechanisms to human PD must account for physical capabilities of the patient.

OBJECTIVE

To establish cardiovascular parameters as a common metric for cross-species translation of aerobic exercise impact.

METHOD

We evaluated aerobic exercise impact on heart rate (HR) in 21 early-stage PD subjects (Hoehn Yahr ≤1.5) exercising in non-contact boxing training for ≥3 months, ≥3x/week. In 4-month-old Pink1 knockout (KO) rats exercising in a progressively-increased treadmill speed regimen, we determined a specific treadmill speed that increased HR to an extent similar in human subjects.

RESULTS

After completing aerobic exercise for ∼30 min, PD subjects had increased HR∼35% above baseline (∼63% maximum HR). Motor and cognitive test results indicated the exercising subjects completed the timed up and go (TUG) and trail-making test (TMT-A) in significantly less time versus exercise-naïve PD subjects. In KO and age-matched wild-type (WT) rats, treadmill speeds of 8-10 m/min increased HR up to 25% above baseline (∼67% maximum HR), with no further increases up to 16 m/min. Exercised KO, but not WT, rats showed increased locomotor activity compared to an age-matched exercise-naïve cohort at 5 months old.

CONCLUSION

These proof-of-concept results indicate HR is a cross-species translation parameter to evaluate aerobic exercise impact on specific motor or cognitive functions in human subjects and rat PD models. Moreover, a moderate intensity exercise regimen is within the physical abilities of early-stage PD patients and is therefore applicable for interrogating neurobiological mechanisms in rat PD models.

Physical Exercise Exerts Neuroprotective Effect on Memory Impairment by Mitigate the Decline of Striatum Catecholamine and Spine Density in a Vascular Dementia Rat Model

OBJECTIVE

The present study aims to investigate the underlying neurochemical mechanism of physical exercise on striatum synapsis and memory function in vascular dementia model.

METHODS

32 Sprague-Dawley (SD) rats were randomly divided into 4 groups: control group (C group, n = 6), vascular dementia group (Vascular dementia group, n = 7), physical exercise and vascular dementia group (Exe-VD group, n = 6), physical exercise and black group (Exe group, n = 6). 4 weeks of voluntary wheel running were used as pre-exercise training. Vascular dementia model was established by bilateral common carotid arteries occlusion (BCCAo) for 1 week. Passive avoidance test (PAT) were used to test memory function. The level of striatum catecholamine in the microdialysate were detected by enzyme linked immunosorbent assy (ELISA). Golgi staining was used to analyze striatum neuronal spine density.

RESULTS

Behavioral data indicated that 4 weeks of physical exercise ameliorated memory impairment in vascular dementia model. Striatum catecholamine level significantly decreased in VD group when compared with C group (P < .001). But this phenomenon can be rescue by physical exercise (P < .001). In addition, compared with C group, neuronal spine density significantly decreased in VD group (P < .01), but 4 weeks of physical exercise can rescue this phenomenon (P < .05).

CONCLUSION

4 weeks of physical exercise improves memory function by mitigate the decline of striatum catecholamine and spine density in VD model.

Metformin and fluoxetine improve depressive-like behavior in a murine model of Parkinsońs disease through the modulation of neuroinflammation, neurogenesis and neuroplasticity

Thereabout 30-40% of patients with Parkinson's Disease (PD) also have depression contributing to the loss of quality of life. Among the patients who treat depression, about 50% do not show significant improvement due to the limited efficacy of the treatment. So far, there are no effective disease-modifying treatments that can impede its progression. The current clinical approach is based on symptom management. Nonetheless, the reuse of drugs with excellent safety profiles represents an attractive alternative strategy for treating of different clinical aspects of PD. In this study, we evaluated the effects of metformin separately and associated with fluoxetine on depressive like-behavior and motor alterations in experimental Parkinson's disease. C57BL6 mice were induced with rotenone (2.5 mg/kg/day) for 20 days and treated with metformin (200 mg/kg/day) and fluoxetine (10 mg/kg/day) from the 5th day of induction. The animals were submitted to Sucrose Preference, Tail Suspension, and rotarod tests. Hippocampus, prefrontal cortex, and substantia nigra were dissected for molecular and morphological analysis. Metformin and fluoxetine prevented depressive-like behavior and improved motor impairment and increased TH nigral positive cells. Metformin and fluoxetine also reduced IBA-1 and GFAP positive cells in the hippocampus. Moreover, metformin reduced the phospho-NF-kB, IL-1β in the prefrontal cortex and iNOS levels in the hippocampus. Both metformin and fluoxetine increased neurogenesis by increasing KI67, but only the combined treatment increased neuronal survival by NeuN positive cells in the hippocampus. In addition, fluoxetine reduced cell death, decreasing caspase-3 and PARP-1 levels. Lastly, metformin potentiated the effect of fluoxetine on neuroplasticity by increasing BDNF positive cells. Metformin has antidepressant and antiparkinsonian potential due to anti-inflammatory neurogenic, and neuroplasticity-inducing effects when combined with fluoxetine.

Synaptic potentiation of anterior cingulate cortex contributes to chronic pain of Parkinson's disease

Parkinson’s disease (PD) is a multi-system neurodegenerative disorder. Patients with PD often suffer chronic pain. In the present study, we investigated motor, sensory and emotional changes in three different PD mice models. We found that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treatment caused significant changes in all measurements. Mechanical hypersensitivity of PD model induced by MPTP peaked at 3 days and persisted for at least 14 days. Using Fos transgenic mice, we found that neurons in the anterior cingulate cortex (ACC) were activated after MPTP treatment. Inhibiting ACC by bilateral microinjection of muscimol significantly reduced mechanical hypersensitivity and anxiety-like responses. By contrast, MPTP induced motor deficit was not affected, indicating ACC activity is mostly responsible for sensory and emotional changes. We also investigated excitatory synaptic transmission and plasticity using brain slices of MPTP treated animals. While L-LTP was blocked or significantly reduced. E-LTP was not significantly affected in slices of MPTP treated animals. LTD induced by repetitive stimulation was not affected. Furthermore, we found that paired-pulse facilitation and spontaneous release of glutamate were also altered in MPTP treated animals, suggesting presynaptic enhancement of excitatory transmission in PD. Our results suggest that ACC synaptic transmission is enhanced in the animal model of PD, and cortical excitation may play important roles in PD related pain and anxiety.

Gait analysis combined with the expression of TGF-β1, TGF-β3 and CREB during Achilles tendon healing in rat

PURPOSE

To observe the changes of gait behavior and the expression of wound healing factors of transforming growth factor-β1 (TGF-β1), TGF-β3 and cAMP response element binding protein-1 (CREB-1) during the healing of Achilles tendon in a rat model, and to investigate whether gait analysis can be used to evaluate the tendon healing.

METHODS

Achilles tendon of 40 healthy male Sprague-Dawley rats were transected and sutured to establish the Achilles tendon injury (ATI) model. They were randomly divided into 4 groups based on the observational time point at 1, 2, 4 and 6 weeks after injury (n = 10 for each group). Before modeling, 9 rats were randomly selected for CatWalk gait analysis, which contained step cycle, single stance time and average speed. Data were recorded as the normal controls. After then, ATI models were established in the left hind limbs of the all 40 rats (ATI group), while the right hind limbs were only cut and sutured without injury of the Achilles tendon (sham operation group). At 1, 2, 4 and 6 weeks after injury, the gait behavior of the corresponding group of rats (n = 9) as observed and recorded by CatWalk platform. After then, the rats were sacrificed and Achilles tendon of both limbs was harvested. The tendon healing was observed by gross anatomy and histological examination, and the protein and mRNA expression of TGF-β1, TGF-β3, CREB-1 were observed by immunohistochemistry and qPCR. The results of tendon gross grading were analyzed by Wilcoxon rank sum test, and other data were analyzed by one-way analysis of variance among multiple groups.

RESULTS

Compared with normal controls, all gait indexes (step cycle, single stance time and average speed) were greatly affected following ATI, which however improved with time. The step cycle was significantly lower at 1, 2 and 4 weeks after ATI (compared with normal controls, all p < 0.05), but almost returned to the normal level at 6 weeks ((0.694 ± 0.102) vs. (0.503 ± 0.094) s, p > 0.05). The single stance time of the ATI group was significantly shorter at 1 and 2 weeks after operation ((0.078 ± 0.010) s at 1 week, (0.078 ± 0.020) s at 2 weeks, all p < 0.001) and revealed no significant difference at 4 weeks (p = 0.120). The average speed of ATI group at 1, 2, 4, 6 weeks was significantly lower than that in the normal control group (all p < 0.001). Gross observation showed that the grade of local scar adhesion in ATI group increased significantly at 2, 4 and 6 weeks, compared with the sham operation group (all p < 0.001). Extensive adhesion was formed at 6 weeks after ATI. The results of HE staining showed that the number of fibroblast increased gradually and arranged more orderly in ATI group at 1, 2 and 4 weeks (all p < 0.001), and decreased at 6 weeks, but it was still significantly higher than that of the sham operation group (p < 0.001). Immunohistochemistry showed that the positive expression of TGF-β1, TGF-β3, CREB-1 in ATI group was higher than that in the sham operation group at 4 time points (all p < 0.05), which reached the peak at 2 weeks after operation and decreased at 4 weeks (p = 0.002, p < 0.001, p = 0.041, respectively). The results of qPCR suggested that the mRNA expression of TGF-β1, TGF-β3, CREB-1 in ATI group was higher than that in the sham operation group at all-time points (all p < 0.05), which reached the peak at 2 weeks after operation, decreased at 4 weeks, and significantly decreased at 6 weeks (all p < 0.001).

CONCLUSION

Gait behavior indexes are associated with Achilles tendon healing. The study gives an insight of TGF-β1, TGF-β3, CREB-1 changes in the coursing of Achilles tendon healing and these cytokines may be able to be used to regulate the Achilles tendon healing.

The effects of treadmill exercise in animal models of Parkinson's disease: A systematic review

Parkinson's disease (PD) is a progressive disabling brain disorder. Physical exercise has been shown to alleviate the symptoms of PD and, consequently, improve patient quality of life. Exercise mechanisms involved in beneficial effects on PD have been widely investigated. This study aims to systematically review the literature on the use of treadmill exercise in PD animal models. The study was conducted according to Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA). Searches were conducted in MEDLINE, EMBASE, and ISI databases. In total, 78 studies were included. The dopaminergic system, behavior, neuroplasticity, neuroinflammation, mitochondria, and musculoskeletal systems were some of the outcomes evaluated by the selected studies. Based on the systematic review center for laboratory animal experimentation (SYRCLE) RoB tool, the methodologies revealed a high risk of bias and lack of information about study design, which needs attention for data reproducibility. This review can guide future studies that aim to fill existing gaps regarding the effects of treadmill exercise in PD animal models.

Histamine H3 and H4 receptors modulate Parkinson's disease induced brain pathology. Neuroprotective effects of nanowired BF-2649 and clobenpropit with anti-histamine-antibody therapy

Military personnel deployed in combat operations are highly prone to develop Parkinson's disease (PD) in later lives. PD largely involves dopaminergic pathways with hallmarks of increased alpha synuclein (ASNC), and phosphorylated tau (p-tau) in the cerebrospinal fluid (CSF) precipitating brain pathology. However, increased histaminergic nerve fibers in substantia nigra pars Compacta (SNpc), striatum (STr) and caudate putamen (CP) associated with upregulation of Histamine H3 receptors and downregulation of H4 receptors in human cases of PD is observed in postmortem cases. These findings indicate that modulation of histamine H3 and H4 receptors and/or histaminergic transmission may induce neuroprotection in PD induced brain pathology. In this review effects of a potent histaminergic H3 receptor inverse agonist BF-2549 or clobenpropit (CLBPT) partial histamine H4 agonist with H3 receptor antagonist, in association with monoclonal anti-histamine antibodies (AHmAb) in PD brain pathology is discussed based on our own observations. Our investigation shows that chronic administration of conventional or TiO₂ nanowired BF 2649 (1mg/kg, i.p.) or CLBPT (1mg/kg, i.p.) once daily for 1 week together with nanowired delivery of HAmAb (25μL) significantly thwarted ASNC and p-tau levels in the SNpC and STr and reduced PD induced brain pathology. These observations are the first to show the involvement of histamine receptors in PD and opens new avenues for the development of novel drug strategies in clinical strategies for PD, not reported earlier.

Acute MPTP Treatment Impairs Dendritic Spine Density in the Mouse Hippocampus

Among the animal models of Parkinson’s disease (PD), the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned mouse model has shown both dopaminergic (DA) damage and related motor control defects, as observed in patients with PD. Recent studies have suggested that the DA system interacts with the synaptic plasticity of the hippocampus in PD. However, little is known about how alterations in the hippocampal structural plasticity are affected by the DA damage in MPTP-lesioned models. In the present study, we investigated alterations in dendritic complexity and spine density in the mouse hippocampus following acute MPTP treatment (22 mg/kg, intraperitoneally, four times/day, 2-h intervals). We confirmed that acute MPTP treatment significantly decreased initial motor function and persistently reduced the number of tyrosine hydroxylase-positive DA neurons in the substantia nigra. Golgi staining showed that acute MPTP treatment significantly reduced the spine density of neuronal dendrites in the cornu ammonis 1 (CA1) apical/basal and dentate gyrus (DG) subregions of the mouse hippocampus at 8 and 16 days after treatment, although it did not affect dendritic complexity (e.g., number of crossing dendrites, total dendritic length, and branch points per neuron) in both CA1 and DG subregions at all time points after treatment. Therefore, the present study provides anatomical evidence that acute MPTP treatment affects synaptic structure in the hippocampus during the late phase after acute MPTP treatment in mice, independent of any changes in the dendritic arborization of hippocampal neurons. These findings offer data for the ability of the acute MPTP-lesioned mouse model to replicate the non-nigrostriatal lesions of clinical PD.

Neuropsychiatric and Cognitive Deficits in Parkinson's Disease and Their Modeling in Rodents

Parkinson’s disease (PD) is associated with a large burden of non-motor symptoms including olfactory and autonomic dysfunction, as well as neuropsychiatric (depression, anxiety, apathy) and cognitive disorders (executive dysfunctions, memory and learning impairments). Some of these non-motor symptoms may precede the onset of motor symptoms by several years, and they significantly worsen during the course of the disease. The lack of systematic improvement of these non-motor features by dopamine replacement therapy underlines their multifactorial origin, with an involvement of monoaminergic and cholinergic systems, as well as alpha-synuclein pathology in frontal and limbic cortical circuits. Here we describe mood and neuropsychiatric disorders in PD and review their occurrence in rodent models of PD. Altogether, toxin-based rodent models of PD indicate a significant but non-exclusive contribution of mesencephalic dopaminergic loss in anxiety, apathy, and depressive-like behaviors, as well as in learning and memory deficits. Gene-based models display significant deficits in learning and memory, as well as executive functions, highlighting the contribution of alpha-synuclein pathology to these non-motor deficits. Collectively, neuropsychiatric and cognitive deficits are recapitulated to some extent in rodent models, providing partial but nevertheless useful options to understand the pathophysiology of non-motor symptoms and develop therapeutic options for these debilitating symptoms of PD.

Cognitive flexibility deficits in rats with dorsomedial striatal 6-hydroxydopamine lesions tested using a three-choice serial reaction time task with reversal learning

Lesions of the dorsomedial striatum elicit deficits in cognitive flexibility that are an early feature of Parkinson's disease (PD), and presumably reflect alterations in frontostriatal processing. The current study aimed to examine deficits in cognitive flexibility in rats with bilateral 6-hydroxydopamine lesions in the dorsomedial striatum. While deficits in cognitive flexibility have previously been examined in rodent PD models using the cross-maze, T-maze, and a food-digging task, the current study is the first to examine such deficits using a 3-choice serial reaction time task (3-CSRT) with reversal learning (3-CSRT-R). Although the rate of acquisition in 3-CSRT was slower in lesioned compared to control rats, lesioned animals were able to acquire a level of accuracy comparable to that of control animals following 4 weeks of training. In contrast, substantial and persistent deficits were apparent during the reversal learning phase. Our results demonstrate that deficits in cognitive flexibility can be robustly unmasked by reversal learning in the 3-CSRT-R paradigm, which can be a useful test for evaluating effects of dorsomedial striatal deafferentation and interventions.

Dopaminergic afferents from midbrain to dorsolateral bed nucleus of stria terminalis inhibit release and expression of corticotropin-releasing hormone in paraventricular nucleus

Dopaminergic (DAergic) neurons of the midbrain ventral tegmental area (VTA) are known to regulate the hypothalamic-pituitary-adrenal (HPA) axis but have no direct projections to the paraventricular nucleus (PVN) of the hypothalamus. This study investigated whether VTA DAergic afferents modulate glutamatergic transmission-dependent GABAergic neurons in dorsolateral bed nucleus of stria terminalis (dlBNST) to affect the activity of the HPA-axis. Herein, we demonstrate that systemic administration of the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or the VTA-injection of 1-methyl-4-phenylpyridinium ion (MPP+) in male mice (MPTP-mice and MPP+mice) caused a decline of tyrosine hydroxylase positive (TH+) cells in VTA with a reduction in TH+fibers in the dlBNST. MPTP-mice and MPP+mice displayed a clear increase in serum levels of corticosterone (CORT) and adrenocorticotropic hormone, corticotropin-releasing hormone (CRH) expression, and CRH neuron activity in PVN. The presynaptic glutamate release, glutamatergic synaptic transmission and induction of long-term potentiation in dlBNST of MPTP-mice were suppressed, and these effects were rescued by a D1-like DAergic receptor (D1R) agonist and mimicked in control dlBNST by blockade of D1R. MPTP-mice exhibited low expression of glutamic acid decarboxylase and dysfunction of the excitatory-dependent GABAergic circuit in dlBNST, and these effects were recovered by the administration of D1R agonist. Furthermore, either dlBNST-injection of D1R agonist or PVN-injection of GABA_A receptor (GABA_A R) agonist could correct the increased secretion and expression of CRH in MPTP-mice. The results indicate that the DAergic afferents from VTA enhance excitatory-dependent activation of GABAergic neurons in dlBNST, which suppress the activity of the HPA-axis.

Neuropsychiatric Disorders in Parkinson's Disease: What Do We Know About the Role of Dopaminergic and Non-dopaminergic Systems?

Besides the hallmark motor symptoms (rest tremor, hypokinesia, rigidity, and postural instability), patients with Parkinson’s disease (PD) have non-motor symptoms, namely neuropsychiatric disorders. They are frequent and may influence the other symptoms of the disease. They have also a negative impact on the quality of life of patients and their caregivers. In this article, we will describe the clinical manifestations of the main PD-related behavioral disorders (depression, anxiety disorders, apathy, psychosis, and impulse control disorders). We will also provide an overview of the clinical and preclinical literature regarding the underlying mechanisms with a focus on the role of the dopaminergic and non-dopaminergic systems.

Exercise effects on brain and behavior in healthy mice, Alzheimer's disease and Parkinson's disease model-A systematic review and meta-analysis

This systematic review and meta-analysis examines how exercise modifies brain and behavior in healthy mice, dementia (D) and Parkinson disease (PD) models. A search was performed on the Medline and Scopus electronic databases (2008-2019). Search terms were "mice", "brain", "treadmill", "exercise", "physical exercise". In the total, 430 were found but only 103 were included. Animals n = 1,172; exercised 4-8 weeks (Range 24 h to 32 weeks), 60 min/day (Range 8-120 min per day), and 10/12 m/min (Range 0.2 m/min to 36 m/min). Hippocampus, cerebral cortex, striatum and whole brain were more frequently investigated. Exercise improved learning and memory. Meta-analysis showed that exercise increased: cerebral BDNF in health (n = 150; z = 5.8, CI 3.43-12.05; p < 0.001 I2 = 94.3 %), D (n = 124; z = 4.18, CI = 2.22-9.12; p < 0.001; I2 = 93.7 %) and PD (n = 16 z = 4.26, CI 5.03-48.73 p < 0.001 I2 = 94.8 %). TrkB improved in health (n = 84 z = 5.49, CI 3.8-17.73 p < 0.001, I2 = 0.000) and PD (n = 22; z = 3.1, CI = 2.58-67.3, p < 0.002 I2 = 93.8 %). Neurogenesis increased in health (n = 68; z = 7.08, CI 5.65-21.25 p < 0.001; I2 17.58) and D model (n = 116; z = 4.18, CI 2.22-9.12 p < 0.001 I2 93.7 %). Exercise augmented amyloid clearance (n = 166; z = 7.51 CI = 4.86-14.85, p < 0.001 I2 = 58.72) and reduced amyloid plaques in D models (n = 49; z = 4.65, CI = 3.94-15.3 p < 0.001 I2 = 0.000). In conclusion, exercise improved brain and behavior, neurogenesis in healthy and dementia models, reduced toxicity and cerebral amyloid. Evidence regarding inflammation, oxidative stress and energy metabolism were scarce. Studies examining acute vs chronic exercise, extreme training and the durability of exercise benefit were rare. Vascular or glucose metabolism changes were seldom reported.

Exercise-driven restoration of the alcohol-damaged brain

There are vast literatures on the neural effects of alcohol and the neural effects of exercise. Simply put, exercise is associated with brain health, alcohol is not, and the mechanisms by which exercise benefits the brain directly counteract the mechanisms by which alcohol damages it. Although a degree of brain recovery naturally occurs upon cessation of alcohol consumption, effective treatments for alcohol-induced brain damage are badly needed, and exercise is an excellent candidate from a mechanistic standpoint. In this chapter, we cover the small but growing literature on the interactive neural effects of alcohol and exercise, and the capacity of exercise to repair alcohol-induced brain damage. Increasingly, exercise is being used as a component of treatment for alcohol use disorders (AUD), not because it reverses alcohol-induced brain damage, but because it represents a rewarding, alcohol-free activity that could reduce alcohol cravings and improve comorbid conditions such as anxiety and depression. It is important to bear in mind, however, that multiple studies attest to a counterintuitive positive relationship between alcohol intake and exercise. We therefore conclude with cautionary notes regarding the use of exercise to repair the brain after alcohol damage.

Exercise for Parkinson's disease

Parkinson's disease is the second most common neurodegenerative disease with a prevalence rate of 1-2 per 1000 of the population worldwide. Pharmacological management is the mainstay of treatment. Despite optimal medication, motor impairment particularly balance and gait impairment persist leading to various degree of disability and reduced quality-of-life. The present review describes motor impairment including postural impairment, gait dysfunction, reduced muscle strength and aerobic capacity and falls. Physical therapy and complementary exercises have been proven to improve motor performance and functional mobility. Evidence on the efficacy of physical therapy and complementary exercises is presented in this review. These exercises include gait training with cues, gait training with treadmill, Nordic walking, brisk walking, balance training, virtual reality interventions, Tai Chi and dance. All these treatment interventions produce short-term beneficial effects and some interventions demonstrate long-term benefit. Gait training with treadmill enhance walking performance and the effects sustain for 3-6 months. Balance training improves balance, function and reduces fall rate, and these effects carry over to at least 12 months after training ended. Sustained Tai Chi for 6 months, dance therapy for 12 months, progressive resistive training for 24 months alleviates the PD motor symptoms, suggesting that they could slow down PD progression. Based on this evidence, individuals with PD are encouraged to sustain their training in order to improve/maintain their physical ability and to combat the progression of PD.

Recurrent binge ethanol is associated with significant loss of dentate gyrus granule neurons in female rats despite concomitant increase in neurogenesis

Binge drinking is becoming increasingly common among American women and girls. We have previously shown significant cell loss, downregulation of neurotrophins and microgliosis in female rats after a single 4-day ethanol exposure. To determine whether recurrent binge exposure would produce similar effects, we administered ethanol (5 g/kg) or iso-caloric control diet once-weekly for 11 weeks to adult female rats. As we have previously shown exercise neuroprotection against binge-induced damage, half the rats were given access to exercise wheels. Blood ethanol concentration (BEC) did not differ between sedentary and exercised groups, nor did it change across time. Using stereology, we quantified the number and/or size of neurons in the medial prefrontal cortex (mPFC) and hippocampal dentate gyrus (DG), as well as the number and activation state of microglia. Binged sedentary rats had significant cell loss in the dentate gyrus, but exercise eliminated this effect. Compared to sedentary controls, sedentary binged rats and all exercised rats showed increased neurogenesis in the DG. Number and nuclear volume of neurons in the mPFC were not changed. In the hippocampus and mPFC, the number of microglia with morphology indicative of partial activation was increased by recurrent binge ethanol and decreased by exercise. In summary, we show significant binge-induced loss of DG granule neurons despite increased neurogenesis, suggesting an unsuccessful compensatory response. Although exercise eliminated cell loss, our results indicate that infrequent, but recurrent exposure to clinically relevant BEC is neurotoxic.

Exercise as a therapeutic intervention for motor and non-motor symptoms in Parkinson's disease: Evidence from rodent models

Parkinson's disease (PD) is characterised by degeneration of dopaminergic neurons of the nigrostriatal pathway, which leads to the cardinal motor symptoms of the disease - tremor, rigidity and postural instability. A number of non-motor symptoms are also associated with PD, including cognitive impairment, mood disturbances and dysfunction of gastrointestinal and autonomic systems. Current therapies provide symptomatic relief but do not halt the disease process, so there is an urgent need for preventative strategies. Lifestyle interventions such as aerobic exercise have shown potential to lower the risk of developing PD and to alleviate both motor and non-motor symptoms. However, there is a lack of large-scale randomised clinical trials that have employed exercise in PD patients. This review will focus on the evidence from studies on rodent models of PD, for employing exercise as an intervention for both motor and non-motor symptoms.

Depression and adult neurogenesis: Positive effects of the antidepressant fluoxetine and of physical exercise

Of wide interest for health is the relation existing between depression, a very common psychological illness, accompanied by anxiety and reduced ability to concentrate, and adult neurogenesis. We will focus on two neurogenic stimuli, fluoxetine and physical exercise, both endowed with the ability to activate adult neurogenesis in the dentate gyrus of the hippocampus, known to be required for learning and memory, and both able to counteract depression. Fluoxetine belongs to the class of selective serotonin reuptake inhibitor (SSRI) antidepressants, which represent the most used pharmacological therapy; physical exercise has also been shown to effectively counteract depression symptoms in rodents as well as in humans. While there is evidence that the antidepressant effect of fluoxetine requires its pro-neurogenic action, exerted by promoting proliferation, differentiation and survival of progenitor cells of the hippocampus, on the other hand fluoxetine exerts also neurogenesis-independent antidepressant effects by influencing the plasticity of the new neurons generated. Similarly, the antidepressant action of running also correlates with an increase of hippocampal neurogenesis and plasticity, although the gene pathways involved are only partially coincident with those of fluoxetine, such as those involved in serotonin metabolism and synapse formation. We further discuss how extra-neurogenic actions are also suggested by the fact that, unlike running, fluoxetine is unable to stimulate neurogenesis during aging, but still displays antidepressant effects. Moreover, in specific conditions, fluoxetine or running activate not only progenitor but also stem cells, which normally are not stimulated; this fact reveals how stem cells have a long-term, hidden ability to self-renew and, more generally, that neurogenesis is subject to complex controls that may play a role in depression, such as the type of neurogenic stimulus or the state of the local niche. Finally, we discuss how fluoxetine or running are effective in counteracting depression originated from stress or neurodegenerative diseases.

Physical Exercise Modulates L-DOPA-Regulated Molecular Pathways in the MPTP Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is characterized by the degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc), resulting in motor and non-motor dysfunction. Physical exercise improves these symptoms in PD patients. To explore the molecular mechanisms underlying the beneficial effects of physical exercise, we exposed 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrimidine (MPTP)-treated mice to a four-week physical exercise regimen, and subsequently explored their motor performance and the transcriptome of multiple PD-linked brain areas. MPTP reduced the number of DA neurons in the SNpc, whereas physical exercise improved beam walking, rotarod performance, and motor behavior in the open field. Further, enrichment analyses of the RNA-sequencing data revealed that in the MPTP-treated mice physical exercise predominantly modulated signaling cascades that are regulated by the top upstream regulators L-DOPA, RICTOR, CREB1, or bicuculline/dalfampridine, associated with movement disorders, mitochondrial dysfunction, and epilepsy-related processes. To elucidate the molecular pathways underlying these cascades, we integrated the proteins encoded by the exercise-induced differentially expressed mRNAs for each of the upstream regulators into a molecular landscape, for multiple key brain areas. Most notable was the opposite effect of physical exercise compared to previously reported effects of L-DOPA on the expression of mRNAs in the SN and the ventromedial striatum that are involved in-among other processes-circadian rhythm and signaling involving DA, neuropeptides, and endocannabinoids. Altogether, our findings suggest that physical exercise can improve motor function in PD and may, at the same time, counteract L-DOPA-mediated molecular mechanisms. Further, we hypothesize that physical exercise has the potential to improve non-motor symptoms of PD, some of which may be the result of (chronic) L-DOPA use.

The effects of volume versus intensity of long-term voluntary exercise on physiology and behavior in C57/Bl6 mice

Cardiovascular exercise (CVE) is associated with healthy aging and reduced risk of disease in humans, with similar benefits seen in animals. Most rodent studies, however, have used shorter intervention periods of a few weeks to a few months, begging questions as to the effects of longer-term, or even life-long, exercise. Additionally, most animal studies have utilized a single exercise treatment group - usually unlimited running wheel access - resulting in large volumes of exercise that are not clinically relevant. It is therefore incumbent to determine the physiological and cognitive/behavioral effects of a range of exercise intensities and volumes over a long-term period that model a lifelong commitment to CVE. In the current study, C57/Bl6 mice remained sedentary or were allowed either 1, 3, or 12 h of access to a running wheel per day, 5 days/weeks, beginning at 3.5-4 months of age. Following an eight-month intervention period, animals underwent a battery of behavioral testing, then euthanized and blood and tissue were collected. Longer access to a running wheel resulted in greater volume and higher running speed, but more breaks in running. All exercise groups showed similarly reduced body weight, increased muscle mass, improved motor function on the rotarod, and reduced anxiety in the open field. While all exercise groups showed increased food intake, this was greatest in the 12 h group but did not differ between 1 h and 3 h mice. While exercise dose-dependently increased working memory performance in the y-maze, the 1 h and 12 h groups showed the largest changes in the mass of many organs, as well as alterations in several behaviors including social interaction, novel object recognition, and Barnes maze performance. These findings suggest that long-term exercise has widespread effects on physiology, behavior, and cognition, which vary by "dose" and measure, and that even relatively small amounts of daily exercise can provide benefits.

Corticosterone level and central dopaminergic activity involved in agile and exploratory behaviours in formosan wood mice (Apodemus semotus)

The native Formosan wood mouse (Apodemus semotus) is the dominant rodent in Taiwan. In their natural environment, Formosan wood mice exhibit high locomotor activity, including searching and exploratory behaviours, which is observed similarly in the laboratory environment. How the behavioural responses of Formosan wood mice exhibit in elevated plus maze and marble burying tests remains unclear. How corticosterone levels and central dopaminergic activities are related to the behaviours in these tests is also unclear. This study compared the behaviours of Formosan wood mice with that of C57BL/6J mice using the elevated plus maze and marble burying tests, and measured the corticosterone levels and central dopaminergic activities. Formosan wood mice showed greater locomotor and exploratory activity than the C57BL/6J mice. Similarly, the marble burying and rearing numbers were higher for Formosan wood mice. High locomotor and exploratory behaviours were strongly correlated with corticosterone levels after acute mild restraint stress in Formosan wood mice. The anxiolytic, diazepam, reduced the high exploratory activity, corticosterone levels and central dopaminergic activities. The high locomotor and exploratory behaviours of Formosan wood mice are related to the corticosterone levels and central dopaminergic activities. These data may explain Formosan wood mice dominance in the intermediate altitude of Taiwan.

Voluntary Physical Exercise Improves Subsequent Motor and Cognitive Impairments in a Rat Model of Parkinson's Disease

Background: Parkinson’s disease (PD) is typically characterized by impairment of motor function. Gait disturbances similar to those observed in patients with PD can be observed in animals after injection of neurotoxin 6-hydroxydopamine (6-OHDA) to induce unilateral nigrostriatal dopamine depletion. Exercise has been shown to be a promising non-pharmacological approach to reduce the risk of neurodegenerative disease. Methods: In this study, we investigated the long-term effects of voluntary running wheel exercise on gait phenotypes, depression, cognitive, rotational behaviors as well as histology in a 6-OHDA-lesioned rat model of PD. Results: We observed that, when compared with the non-exercise controls, five-week voluntary exercise alleviated and postponed the 6-OHDA-induced gait deficits, including a significantly improved walking speed, step/stride length, base of support and print length. In addition, we found that the non-motor functions, such as novel object recognition and forced swim test, were also ameliorated by voluntary exercise. However, the rotational behavior of the exercise group did not show significant differences when compared with the non-exercise group. Conclusions: We first analyzed the detailed spatiotemporal changes of gait pattern to investigate the potential benefits after long-term exercise in the rat model of PD, which could be useful for future objective assessment of locomotor function in PD or other neurological animal models. Furthermore, these results suggest that short-term voluntary exercise is sufficient to alleviate cognition deficits and depressive behavior in 6-OHDA lesioned rats and long-term treatment reduces the progression of motor symptoms and elevates tyrosine hydroxylase (TH), Brain-derived neurotrophic factor (BDNF), bone marrow tyrosine kinase in chromosome X (BMX) protein expression level without affecting dopaminergic (DA) neuron loss in this PD rat model.

Neuroprotective effects of voluntary running on cognitive dysfunction in an α-synuclein rat model of Parkinson's disease

Parkinson's disease (PD) is no longer primarily classified as a motor disorder due to increasing recognition of the impact on patients of several nonmotor PD symptoms, including cognitive dysfunction. These nonmotor symptoms are highly prevalent and greatly affect the quality of life of patients with PD, and so, therapeutic interventions to alleviate these symptoms are urgently needed. The aim of this study was to investigate the potential neuroprotective effects of voluntary running on cognitive dysfunction in an adeno-associated virus-α-synuclein rat model of PD. Bilateral intranigral administration of adeno-associated virus-α-synuclein was found to induce motor dysfunction and a significant loss of nigral dopaminergic neurons, neither of which were rescued by voluntary running. Overexpression of α-synuclein also resulted in significant impairment on hippocampal neurogenesis-dependent pattern separation, a cognitive task; this was rescued by voluntary running. This was substantiated by an effect of running on neurogenesis levels in the dorsal dentate gyrus, suggesting that the functional effects of running on pattern separation were mediated via increased neurogenesis.

Running wheel exercise reduces α-synuclein aggregation and improves motor and cognitive function in a transgenic mouse model of Parkinson's disease

Exercise has been recommended to improve motor function in Parkinson patients, but its value in altering progression of disease is unknown. In this study, we examined the neuroprotective effects of running wheel exercise in mice. In adult wild-type mice, one week of running wheel activity led to significantly increased DJ-1 protein concentrations in muscle and plasma. In DJ-1 knockout mice, running wheel performance was much slower and Rotarod performance was reduced, suggesting that DJ-1 protein is required for normal motor activity. To see if exercise can prevent abnormal protein deposition and behavioral decline in transgenic animals expressing a mutant human form of α-synuclein in all neurons, we set up running wheels in the cages of pre-symptomatic animals at 12 months old. Activity was monitored for a 3-month period. After 3 months, motor and cognitive performance on the Rotarod and Morris Water Maze were significantly better in running animals compared to control transgenic animals with locked running wheels. Biochemical analysis revealed that running mice had significantly higher DJ-1, Hsp70 and BDNF concentrations and had significantly less α-synuclein aggregation in brain compared to control mice. By contrast, plasma concentrations of α-synuclein were significantly higher in exercising mice compared to control mice. Our results suggest that exercise may slow the progression of Parkinson's disease by preventing abnormal protein aggregation in brain.

Exercise-Induced Neuroprotection of the Nigrostriatal Dopamine System in Parkinson's Disease

Epidemiological studies indicate that physical activity and exercise may reduce the risk of developing Parkinson's disease (PD), and clinical observations suggest that physical exercise can reduce the motor symptoms in PD patients. In experimental animals, a profound observation is that exercise of appropriate timing, duration, and intensity can reduce toxin-induced lesion of the nigrostriatal dopamine (DA) system in animal PD models, although negative results have also been reported, potentially due to inappropriate timing and intensity of the exercise regimen. Exercise may also minimize DA denervation-induced medium spiny neuron (MSN) dendritic atrophy and other abnormalities such as enlarged corticostriatal synapse and abnormal MSN excitability and spiking activity. Taken together, epidemiological studies, clinical observations, and animal research indicate that appropriately dosed physical activity and exercise may not only reduce the risk of developing PD in vulnerable populations but also benefit PD patients by potentially protecting the residual DA neurons or directly restoring the dysfunctional cortico-basal ganglia motor control circuit, and these benefits may be mediated by exercise-triggered production of endogenous neuroprotective molecules such as neurotrophic factors. Thus, exercise is a universally available, side effect-free medicine that should be prescribed to vulnerable populations as a preventive measure and to PD patients as a component of treatment. Future research needs to establish standardized exercise protocols that can reliably induce DA neuron protection, enabling the delineation of the underlying cellular and molecular mechanisms that in turn can maximize exercise-induced neuroprotection and neurorestoration in animal PD models and eventually in PD patients.

Mouse models of neurodegenerative disease: preclinical imaging and neurovascular component

Neurodegenerative diseases represent great challenges for basic science and clinical medicine because of their prevalence, pathologies, lack of mechanism-based treatments, and impacts on individuals. Translational research might contribute to the study of neurodegenerative diseases. The mouse has become a key model for studying disease mechanisms that might recapitulate in part some aspects of the corresponding human diseases. Neurodegenerative disorders are very complicated and multifactorial. This has to be taken in account when testing drugs. Most of the drugs screening in mice are very difficult to be interpretated and often useless. Mouse models could be condiderated a 'pathway models', rather than as models for the whole complicated construct that makes a human disease. Non-invasive in vivo imaging in mice has gained increasing interest in preclinical research in the last years thanks to the availability of high-resolution single-photon emission computed tomography (SPECT), positron emission tomography (PET), high field Magnetic resonance, Optical Imaging scanners and of highly specific contrast agents. Behavioral test are useful tool to characterize different animal models of neurodegenerative pathology. Furthermore, many authors have observed vascular pathological features associated to the different neurodegenerative disorders. Aim of this review is to focus on the different existing animal models of neurodegenerative disorders, describe behavioral tests and preclinical imaging techniques used for diagnose and describe the vascular pathological features associated to these diseases.

Physical exercise-induced fatigue: the role of serotonergic and dopaminergic systems

Brain serotonin and dopamine are neurotransmitters related to fatigue, a feeling that leads to reduced intensity or interruption of physical exercises, thereby regulating performance. The present review aims to present advances on the understanding of fatigue, which has recently been proposed as a defense mechanism instead of a “physiological failure” in the context of prolonged (aerobic) exercises. We also present recent advances on the association between serotonin, dopamine and fatigue. Experiments with rodents, which allow direct manipulation of brain serotonin and dopamine during exercise, clearly indicate that increased serotoninergic activity reduces performance, while increased dopaminergic activity is associated with increased performance. Nevertheless, experiments with humans, particularly those involving nutritional supplementation or pharmacological manipulations, have yielded conflicting results on the relationship between serotonin, dopamine and fatigue. The only clear and reproducible effect observed in humans is increased performance in hot environments after treatment with inhibitors of dopamine reuptake. Because the serotonergic and dopaminergic systems interact with each other, the serotonin-to-dopamine ratio seems to be more relevant for determining fatigue than analyzing or manipulating only one of the two transmitters. Finally, physical training protocols induce neuroplasticity, thus modulating the action of these neurotransmitters in order to improve physical performance.

Methyl-4-phenylpyridinium (MPP+) differentially affects monoamine release and re-uptake in murine embryonic stem cell-derived dopaminergic and serotonergic neurons

1-Methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) is known to selectively damage dopaminergic (DA) cells in the substantia nigra and to produce symptoms which are alike to those observed in Parkinson's disease (PD). Based on the similarity between MPTP-induced neurotoxicity and PD-related neuropathology, application of MPTP or its metabolite methyl-4-phenylpyridinium (MPP+) was successfully established in experimental rodent models to study PD-related neurodegenerative events. MPP+ is taken up by the dopamine transporter (DAT) into DA neurons where it exerts its neurotoxic action on mitochondria by affecting complex I of the respiratory chain. MPP+ is also a high affinity substrate for the serotonin transporter (SERT), however little is known about possible toxic effects of MPP+ on serotonergic (5-HT) neurons. In order to compare cell type-specific effects of MPP+ treatment, we have differentiated mouse embryonic stem (ES) cells into DA and 5-HT neurons and studied the impact of MPP+ treatment on both types of monoaminergic neurons in vitro. MPP+ treatment impacts on mitochondrial membrane potential in DA as well as 5-HT ES cell-derived neurons. Although mitochondria metabolisms are similarly affected, synaptic vesicle cycling is only impaired in DA ES cell-derived neurons. Most importantly we show that MPP+ induces DAT externalization in DA neurons, but internalization of SERT in 5-HT neurons. This diverse MPP+-induced transporter trafficking is reflected by elevated substrate uptake in DA neurons, and diminished substrate uptake in 5-HT neurons. In summary, our experimental data point toward differential effects of MPP+ intoxication on neurotransmitter release and re-uptake in different types of monoaminergic neurons.

Environmental Factors Promoting Neural Plasticity: Insights from Animal and Human Studies

We do not all grow older in the same way. Some individuals have a cognitive decline earlier and faster than others who are older in years but cerebrally younger. This is particularly easy to verify in people who have maintained regular physical activity and healthy and cognitively stimulating lifestyle and even in the clinical field. There are patients with advanced neurodegeneration, such as Alzheimer's disease (AD), that, despite this, have mild cognitive impairment. What determines this interindividual difference? Certainly, it cannot be the result of only genetic factors. We are made in a certain manner and what we do acts on our brain. In fact, our genetic basis can be modulated, modified, and changed by our experiences such as education and life events; daily, by sleep schedules and habits; or also by dietary elements. And this can be seen as true even if our experiences are indirectly driven by our genetic basis. In this paper, we will review some current scientific research on how our experiences are able to modulate the structural organization of the brain and how a healthy lifestyle (regular physical activity, correct sleep hygiene, and healthy diet) appears to positively affect cognitive reserve.

Treadmill exercise delays the onset of non-motor behaviors and striatal pathology in the CAG140 knock-in mouse model of Huntington's disease

Depression, cognitive impairments, and other neuropsychiatric disturbances are common during the prodromal phase of Huntington's disease (HD) well before the onset of classical motor symptoms of this degenerative disorder. The purpose of this study was to examine the potential impact of physical activity in the form of exercise on a motorized treadmill on non-motor behavioral features including depression-like behavior and cognition in the CAG₁₄₀ knock-in (KI) mouse model of HD. The CAG₁₄₀ KI mouse model has a long lifespan compared to other HD rodent models with HD motor deficits emerging after 12months of age and thus provides the opportunity to investigate early life interventions such as exercise on disease progression. Motorized treadmill running was initiated at 4weeks of age (1h per session, 3 times per week) and continued for 6months. Non-motor behaviors were assessed up to 6months of age and included analysis of depression-like behavior (using the tail-suspension and forced-swim tests) and cognition (using the T-maze and object recognition tests). At both 4 and 6months of age, CAG₁₄₀ KI mice displayed significant depression-like behavior in the forced swim and tail suspension tests and cognitive impairment by deficits in reversal relearning in the T-maze test. These deficits were not evident in mice engaged in treadmill running. In addition, exercise restored striatal dopamine D2 receptor expression and dopamine neurotransmitter levels both reduced in sedentary HD mice. Finally, we examined the pattern of striatal expression of mutant huntingtin (mHTT) protein and showed that the number and intensity of immunohistochemical staining patterns of intranuclear aggregates were significantly reduced with exercise. Altogether these findings begin to address the potential impact of lifestyle and early intervention such as exercise on modifying HD progression.

The effects of physical exercise on nonmotor symptoms and on neuroimmune RAGE network in experimental parkinsonism

Parkinson's disease (PD) prodromal stages comprise neuropsychiatric perturbations that critically compromise a patient's quality of life. These nonmotor symptoms (NMS) are associated with exacerbated innate immunity, a hallmark of overt PD. Physical exercise (PE) has the potential to improve neuropsychiatric deficits and to modulate immune network including receptor for advanced glycation end products (RAGE) and Toll-like receptors (TLRs) in distinct pathological settings. Accordingly, the present study aimed to test the hypothesis that PE 1) alleviates PD NMS and 2) modulates neuroimmune RAGE network in experimental PD. Adult Wistar rats subjected to long-term mild treadmill were administered intranasally with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and probed for PD NMS before the onset of motor abnormalities. Twelve days after MPTP, neuroimmune RAGE network transcriptomics (real-time quantitative PCR) was analyzed in frontal cortex, hippocampus, and striatum. Untrained MPTP animals displayed habit-learning and motivational deficits without gross motor impairments (cued version of water-maze, splash, and open-field tests, respectively). A suppression of RAGE and neuroimmune-related genes was observed in frontal cortex on chemical and physical stressors (untrained MPTP: RAGE, TLR5 and -7, and p22 NADPH oxidase; saline-trained animals: RAGE, TLR1 and -5 to -11, TNF-α, IL-1β, and p22 NADPH oxidase), suggesting the recruitment of compensatory mechanisms to restrain innate inflammation. Notably, trained MPTP animals displayed normal cognitive/motivational performances. Additionally, these animals showed normal RAGE expression and neuroprotective PD-related DJ-1 gene upregulation in frontal cortex when compared with untrained MPTP animals. These findings corroborate PE efficacy in improving PD NMS and newly identify RAGE network as a neural substrate for exercise intervention. Additional research is warranted to unveil functional consequences of PE-induced modulation of RAGE/DJ-1 transcriptomics in PD premotor stages.NEW & NOTEWORTHY This study newly shows that physical exercise (PE) corrects nonmotor symptoms of the intranasal 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of experimental parkinsonism. Additionally, we show that suppression of neuroimmune receptor for advanced glycation end products (RAGE) network occurs in frontal cortex on chemical (MPTP) and physical (PE) interventions. Finally, PE normalizes frontal cortical RAGE transcriptomics and upregulates the neuroprotective DJ-1 gene in the intranasal MPTP model of experimental parkinsonism.

Motor learning in animal models of Parkinson's disease: Aberrant synaptic plasticity in the motor cortex

In Parkinson's disease (PD), dopamine depletion causes major changes in the brain, resulting in the typical cardinal motor features of the disease. PD neuropathology has been restricted to postmortem examinations, which are limited to only a single time of PD progression. Models of PD in which dopamine tone in the brain is chemically or physically disrupted are valuable tools in understanding the mechanisms of the disease. The basal ganglia have been well studied in the context of PD, and circuit changes in response to dopamine loss have been linked to the motor dysfunctions in PD. However, the etiology of the cognitive dysfunctions that are comorbid in PD patients has remained unclear until now. In this article, we review recent studies exploring how dopamine depletion affects the motor cortex at the synaptic level. In particular, we highlight our recent findings on abnormal spine dynamics in the motor cortex of PD mouse models through in vivo time-lapse imaging and motor skill behavior assays. In combination with previous studies, a role of the motor cortex in skill learning and the impairment of this ability with the loss of dopamine are becoming more apparent. Taken together, we conclude with a discussion on the potential role for the motor cortex in PD, with the possibility of targeting the motor cortex for future PD therapeutics. © 2017 International Parkinson and Movement Disorder Society.

The exercise-glucocorticoid paradox: How exercise is beneficial to cognition, mood, and the brain while increasing glucocorticoid levels

Exercise is known to have beneficial effects on cognition, mood, and the brain. However, exercise also activates the hypothalamic-pituitary-adrenal axis and increases levels of the glucocorticoid cortisol (CORT). CORT, also known as the "stress hormone," is considered a mediator between chronic stress and depression and to link various cognitive deficits. Here, we review the evidence that shows that while both chronic stress and exercise elevate basal CORT levels leading to increased secretion of CORT, the former is detrimental to cognition/memory, mood/stress coping, and brain plasticity, while the latter is beneficial. We propose three preliminary answers to the exercise-CORT paradox. Importantly, the elevated CORT, through glucocorticoid receptors, functions to elevate dopamine in the medial prefrontal cortex under chronic exercise but not chronic stress, and the medial prefrontal dopamine is essential for active coping. Future inquiries may provide further insights to promote our understanding of this paradox.

MPTP Impairs Dopamine D1 Receptor-Mediated Survival of Newborn Neurons in Ventral Hippocampus to Cause Depressive-Like Behaviors in Adult Mice

Parkinson’s disease (PD) is characterized by motor symptoms with depression. We evaluated the influence of dopaminergic depletion on hippocampal neurogenesis process to explore mechanisms of depression production. Five consecutive days of 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injection in mice (MPTP-mice) reduced dopaminergic fibers in hippocampal dentate gyrus (DG). MPTP-mice exhibited depressive-like behaviors later for 2–3 weeks. BrdU was injected 4 h after last-injection of MPTP. BrdU-positive (BrdU⁺) cells in dorsal (d-DG) and ventral (v-DG) DG were examined on day 1 (D1), 7 (D7), 14 (D14) and 21 (D21) after BrdU injection. Fewer D7-, D14- and D21-BrdU⁺ cells or BrdU⁺/NeuN⁺ cells, but not D1-BrdU⁺ cells, were found in v-DG of MPTP-mice than in controls. However, the number of BrdU⁺ cells in d-DG did not differ between the both. Loss of doublecortin-positive (DCX⁺) cells was observed in v-DG of MPTP-mice. Protein kinase A (PKA) and Ca²⁺/cAMP-response element binding protein (CREB) phosphorylation were reduced in v-DG of MPTP-mice, which were reversed by D1-like receptor (D1R) agonist SKF38393, but not D2R agonist quinpirole. The treatment of MPTP-mice with SKF38393 on days 2–7 after BrdU-injection reduced the loss of D7- and D21-BrdU⁺ cells in v-DG and improved the depressive-like behaviors; these changes were sensitive to PKA inhibitor H89. Moreover, the v-DG injection of SKF38393 in MPTP-mice could reduce the loss of D21-BrdU⁺ cells and relieve the depressive-like behaviors. In control mice, the blockade of D1R by SCH23390 caused the reduction of D21-BrdU⁺ cells in v-DG and the depressive-like behaviors. Our results indicate that MPTP-reduced dopaminergic depletion impairs the D1R-mediated early survival of newborn neurons in v-DG, producing depressive-like behaviors.

MPP+-Lesioned Mice: an Experimental Model of Motor, Emotional, Memory/Learning, and Striatal Neurochemical Dysfunctions

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces motor and nonmotor dysfunctions resembling Parkinson's disease (PD); however, studies investigating the effects of 1-methyl-4-phenylpyridinium (MPP⁺), an active oxidative product of MPTP, are scarce. This study investigated the behavioral and striatal neurochemical changes (related to oxidative damage, glial markers, and neurotrophic factors) 24 h after intracerebroventricular administration of MPP⁺ (1.8-18 μg/mouse) in C57BL6 mice. MPP⁺ administration at high dose (18 μg/mouse) altered motor parameters, since it increased the latency to leave the first quadrant and reduced crossing, rearing, and grooming responses in the open-field test and decreased rotarod latency time. MPP⁺ administration at low dose (1.8 μg/mouse) caused specific nonmotor dysfunctions as it produced a depressive-like effect in the forced swim test and tail suspension test, loss of motivational and self-care behavior in the splash test, anxiety-like effect in the elevated plus maze test, and short-term memory deficit in the step-down inhibitory avoidance task, without altering ambulation. MPP⁺ at doses of 1.8-18 μg/mouse increased tyrosine hydroxylase (TH) immunocontent and at 18 μg/mouse increased α-synuclein and decreased parkin immunocontent. The astrocytic calcium-binding protein S100B and glial fibrillary acidic protein (GFAP)/S100B ratio was decreased following MPP⁺ administration (18 μg/mouse). At this highest dose, MPP⁺ increased the ionized calcium-binding adapter molecule 1 (Iba-1) immunocontent, suggesting microglial activation. Also, MPP⁺ at a dose of 18 μg/mouse increased thiobarbituric acid reactive substances (TBARS) and glutathione (GSH) levels and increased glutathione peroxidase (GPx) and hemeoxygenase-1 (HO-1) immunocontent, suggesting a significant role for oxidative stress in the MPP⁺-induced striatal damage. MPP⁺ (18 μg/mouse) also increased striatal fibroblast growth factor 2 (FGF-2) and brain-derived neurotrophic factor (BDNF) levels. Moreover, MPP⁺ decreased tropomyosin receptor kinase B (TrkB) immunocontent. Finally, MPP⁺ (1.8-18 μg/mouse) increased serum corticosterone levels and did not alter acetylcholinesterase (AChE) activity in the striatum but increased it in cerebral cortex and hippocampus. Collectively, these results indicate that MPP⁺ administration at low doses may be used as a model of emotional and memory/learning behavioral deficit related to PD and that MPP⁺ administration at high dose could be useful for analysis of striatal dysfunctions associated with motor deficits in PD.

Voluntary wheel-running attenuates insulin and weight gain and affects anxiety-like behaviors in C57BL6/J mice exposed to a high-fat diet

It is widely accepted that lifestyle plays a crucial role on the quality of life in individuals, particularly in western societies where poor diet is correlated to alterations in behavior and the increased possibility of developing type-2 diabetes. While exercising is known to produce improvements to overall health, there is conflicting evidence on how much of an effect exercise has staving off the development of type-2 diabetes or counteracting the effects of diet on anxiety. Thus, this study investigated the effects of voluntary wheel-running access on the progression of diabetes-like symptoms and open field and light-dark box behaviors in C57BL/6J mice fed a high-fat diet. C57BL/6J mice were placed into either running-wheel cages or cages without a running-wheel, given either regular chow or a high-fat diet, and their body mass, food consumption, glucose tolerance, insulin and c-peptide levels were measured. Mice were also exposed to the open field and light-dark box tests for anxiety-like behaviors. Access to a running-wheel partially attenuated the obesity and hyperinsulinemia associated with high-fat diet consumption in these mice, but did not affect glucose tolerance or c-peptide levels. Wheel-running strongly increased anxiety-like and decreased explorative-like behaviors in the open field and light-dark box, while high-fat diet consumption produced smaller increases in anxiety. These results suggest that voluntary wheel-running can assuage some, but not all, of the physiological problems associated with high-fat diet consumption, and can modify anxiety-like behaviors regardless of diet consumed.