Abstract
Background
Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterised by the degeneration of dopaminergic neurons in the substantia nigra pars compacta, resulting in motor symptoms such as tremor, rigidity and bradykinesia, along with cognitive impairments. While conventional research has largely focused on pathological degeneration, recent advances highlight the role of neuroplasticity—the brain’s ability to reorganise and adapt neural circuits—as a potential mechanism for functional recovery and disease modification.
Summary
This review examines therapeutic strategies that enhance neuroplasticity in chronic Parkinson’s disease mouse models. Key approaches discussed include neurotrophic factor (NTF) administration, deep brain stimulation (DBS), stem cell–based therapies and physical exercise. Evidence from experimental studies suggests that NTFs support dopaminergic neuron survival and synaptic repair, DBS modulates dysfunctional neural circuits and promotes adaptive plasticity, stem cell therapies offer both neuronal replacement and neurotrophic support, and physical exercise stimulates endogenous neuroplastic processes such as neurogenesis and synaptic reorganisation. Despite promising findings, variations in experimental design, disease severity and outcome measures across studies limit direct comparison and translation of results.
Key Message
Neuroplasticity-based interventions represent a promising avenue for slowing disease progression and improving functional outcomes in Parkinson’s disease. Integrating pharmacological, neuromodulatory and behavioural approaches may enhance therapeutic efficacy, though further research is required to standardise protocols and facilitate clinical translation.
Introduction
Parkinson’s Disease and Neuroplasticity in Chronic Mouse Models
Parkinson’s disease (PD) is an age-related progressive neurodegenerative disorder, essentially caused by loss or impairment of dopaminergic neurons within the substantia nigra pars compacta. It results in symptoms such as rest tremor, rigidity, bradykinesia, and, at later stages, postural instability and gait disturbance. 1 Clinical diagnosis is based largely on presentation of symptoms and levodopa responsiveness. Though the G is not established, PD is thought to be a product of intricate genetic and environmental interactions. 2
Neuroplasticity and PD
Neuroplasticity, the process of adaptation and reorganisation of the brain, is present at molecular, cellular, and cortical levels. It is affected by age, health, genetic makeup, and lifestyle. In PD, increased neuroplasticity can aid in replacing deficient neuronal functions by making new or reinforcing existing neural connections. 3 Remaining dopaminergic neurons exhibit adaptive modification, such as changed protein expression and increased dopamine synthesis. 4
Chronic Mouse Models of PD
As an ongoing process, one of the chronic MPTP regimens established in mice to recapitulate the progressive character of human PD with a high degree of fidelity. In addition, the processes of oxidative stress, mitochondrial pathology, and neuroinflammation can be modelled in these mice. 5 Transgenic animals can provide information about molecular mechanisms and allow us to test possible therapies. 6
Mechanisms of Neuroplasticity
Major mechanisms are: Synaptic plasticity: Changes connections between neurons through activities of LTP and LTD in learning and recovery. Neurogenesis: Primarily occurs in the hippocampus, which constructs memory and repairs. Reorganisation of circuits: Recovers from damage by synaptic changes and reassignments in function.
All these mechanisms highlight the possibility of brain recovery, thereby offering a basis for the development of therapies for PD and other neurodegenerative disorders.
Therapeutic Strategies
Administration of Neurotrophic Factor
Neuroplasticity is the lifelong ability of the brain to change and adapt. Neurotrophic factors (NTFs), especially brain-derived neurotrophic factor (BDNF), are crucial mediators of survival, synaptic function, axon growth, and adult neurogenesis. 7 The fine-tuned secretion of BDNF controlled by exercise and other factors allows it to be a prime target for therapies. 8 It is thought that BDNF, GDNF, and VEGF undergo upregulation after exercise, affording neuroprotective effects on MPTP-, 6-OHDA-, or LPS-treated animals in models of PD. The disadvantage systemic NTF administration has is seldom blocked by the blood-brain barrier, which has led to recent evaluation of delivery via viral vectors.
Deep Brain Stimulation
With implants that convey electric stimulation to brain structures, such as the subthalamic nucleus, deep brain stimulation (DBS) modifies neural circuits and fosters adaptive plasticity. 9 It has also been shown to cause synaptic reorganisation, neurogenesis, and increased interconnectivity in PD mouse models. 10 While it alleviates the patients’ motor and cognitive symptoms, the downside of DBS is its surgical invasiveness, dependence on the variation from one individual to another, and the modulatory effects determined by stimulation parameters.
Stem Cell Therapies
Stem cell therapies aim to restore dopaminergic neurons lost and stimulate neuroplasticity. Embryonic stem cells, iPSCs, and mesenchymal stem cells have all been promising for the treatment of PD models by differentiating into dopaminergic neurons and secreting NTFs. 11 Neural stem cell-transplanted animals exhibit improved motor function and connectivity; yet some major pitfalls remain, namely, immune rejection, tumour formation, and ethical issues. Advances in scaffold technology and gene editing are being investigated to optimise therapeutic outcomes. 12
Physical Exercise
Exercise acts as an inexpensive, non-invasive option to enhance neuroplasticity by means of BDNF enhancement, neurogenesis induction, and the facilitation of synaptic plasticity. 13 Animal studies in PD show direct evidence of the diminution of dopaminergic neuronal loss, neuroinflammation, and oxidative stress by exercise, while it improves motor function and cognition. 14 Therefore, concurrent exercise with other therapeutic interventions such as DBS or NTFs may exhibit a synergistic impact on brain repair and functional recovery.
Method
The review followed a rigid approach to identify and include experimental studies concerning neuroplasticity-enhancing therapies in chronic PD mouse models. A thorough literature search was undertaken in databases such as PubMed, Scopus, and Google Scholar. Search keywords consisted of ‘Parkinson’s disease’, ‘neuroplasticity’, ‘chronic mouse models’, ‘neurotrophic factors’, ‘deep brain stimulation’, ‘stem cell therapy’, and ‘exercise’. Peer-reviewed original research articles that focused on chronic models, essentially toxin-induced models (such as MPTP and 6-OHDA) or genetically modified models, and those that had been written in the English language were selected. The analysis focused on interventions promoting synaptic reorganisation, neurogenesis, or remodelling of circuits. Exclusion criteria comprised acute PD models, non-mouse species, and studies without neuroplasticity-related endpoints. Data concerning the type of intervention, mechanism of action, functional outcomes, and limitations were extracted. Based on the collected information, the studies were categorised thematically and synthesised to analyse the trends, mechanisms, and translational potential. Such a process ensured a systematic.
Result
The key studies that informed the therapeutic strategies discussed in this review are summarised in Table 1.
Papers Used as References in Defining the Therapeutic Strategies.
Discussion
Therapeutic Combinations
Bundling these therapeutic strategies would maximise neuroplasticity and possibly even overcome the complex nature of PD. For instance, delivery of NTFs together with exercise may synergise the effects of both treatment modalities by promoting neurogenesis and synaptic reorganisation simultaneously. In a similar manner, the combination of DBS with stem cell treatments can offer short-term symptomatic benefit with long-term regenerative impacts. More research is needed to optimise these combinations and to evaluate their safety and effectiveness in chronic PD models prior to applying them to the clinic.
Critical Analysis
The paragraphs summarise the given text:
Neurotrophic factors: It appears BDNF and GDNF NTFs maintain the survival of dopaminergic neurons and synaptic reorganisation in PD. They thus cause axonal sprouting and synaptic reinnervation for functional recuperation.
Their therapeutic applications are limited by poor diffusion within brain tissue, short half-life, and the requirement of invasive delivery techniques. To overcome these, new studies are investigating newer delivery techniques such as encapsulated cell bio-delivery and nanoparticles.
Deep brain stimulation: DBS is a common and beneficial method of modulating abnormal neural circuits of PD by providing electrical stimulation to areas like the subthalamic nucleus or globus pallidus interna. It strengthens synaptic plasticity and reorganisation of motor pathways, thus lessening motor manifestations. However, controversy persists over the neurological risks of DBS, as well as over the accuracy of electrode placement; individual patient variables are of concern, as are some hardware-related issues. This problem is constantly being revised as targeting approaches and closed-loop designs improve.
Stem cell-based therapies: Potentially, iPSCs and MSCs in stem cell therapy offer the alluring espoir for long-term neuroregeneration of PD. The cells have the capacity to replace dying dopaminergic neurons and provide neurotrophic support while integrating into host neural networks. Some major challenges still remain, such as immune rejection, the threats of incomplete differentiation and tumorigenesis, and continued functional integration into appropriate neural circuits. Genetic engineering and biomaterial scaffold technologies are being explored to boost therapeutic efficacy.
Physical exercise: For PD, physical training induces endogenous neuroplasticity as a non-surgical therapy. Aerobic and strength exercises are considered neurogenesis promoters, synaptic plasticity, and BDNF levels, while also enhancing motor and cognitive abilities. Exercise also improves general health and prevents the development of comorbidities. However, the benefits remain small and require constant and indefinite implementation. Customisation and partnering the exercise intervention with other adjunct therapies would probably maximise the benefits.
Limitations of Animal Studies
Even though chronic mouse models have proven to be exceedingly useful in elucidating the mechanisms of PD pathology and therapeutics, they are of necessity limited in their ability to recapitulate the complexity of human disease. Frequently, these models utilise toxin-induced or genetic means of modelling dopaminergic loss, which do not exactly reflect the progressive and multifactorial nature of PD in humans. 22 For instance, the motor-independent symptoms, such as depression and cognitive impairment, have failed to be reproduced well, which would restrict the therapeutic assessment ability. In addition, the structures of the brain, size, and complexity of circuits of a mouse are far different from those of humans, which at times leads to overestimation of therapeutic efficiency. 23 Motor recovery behaviour in mice might not reflect improvement in the quality of life of humans.
Obstacles to Scaling Interventions for Clinical Application
Many barriers must be overcome in order to implement a pipeline from animals to humans. Delivery strategies remain the most complex, particularly concerning NTFs and stem cell-based therapies, in terms of targeted and sustained delivery to damaged brain regions. The invasiveness of some interventions, such as DBS and stem cell transplant, is a concern for safety, even more so in susceptible PD populations. For bodily exercise, inter-individual heterogeneity of adherence and responsiveness renders it hard to standardise as treatment. Finally, the high expense and resource usage involved in some therapies, especially stem cells and DBS, restrict their availability. Prohibitive regulation and moral considerations complicate the use of stem cells, especially embryonic or gene-modified forms.
There are two issues of prime importance in human PD; they are heterogeneity, namely, in man, the environmental, genetic, and lifestyle factors result in variant presentation of the disease and therapy. 24 This heterogeneity necessitates individualisation approaches that are difficult to replicate in preclinical standardised models.
Conclusion
Enhancement of neuroplasticity offers a new avenue that can be aimed at to eradicate the progressive and debilitating consequences linked with PD. These therapeutics comprise NTFs treatment, DBS, stem cell therapy, and exercise, which can assist in maintaining neuronal function, enhancing neural repair, and result in improved motor and cognitive functions in chronic mouse models of PD. Each of these therapies has its strength, from the very specific neuroprotective effects of NTFs to the regenerative effects of stem cell therapy, and even the least expensive treatment, that is, physical exercise. In the clinical realm, the various treatment methods are challenging, as aforesaid limitations. The multifaceted pathology and heterogeneity of human PD underscore the limitations of translatability from animal models to human disease. Delivery challenges, invasiveness, costs, and unpredictability are all issues that landscapes highlight the need for innovative approaches that make these therapies more efficient and, importantly, more accessible to the common man. The heterogeneity of PD also means that intervention is tailor-made to the individual, necessitating further studies and fine-tuning.
Future research directions must be aimed at combining these approaches in order to take advantage of their complementary activities, maximise delivery systems for target-specific and long-lasting efficacy, and refine preclinical models to more accurately mimic human PD. With these challenges overcome, we can pave the way for therapeutic progress, not only slowing the development of the disease but additionally maximising the quality of life for those afflicted with this disease.
Footnotes
Authors’ Contribution
Saranya TS contributed to the conceptualisation, supervision, and overall review framework. Gayathri Raj assisted in the literature search and synthesis of data. Kevimeno Kiso contributed to the writing and formatting of the manuscript and integration of critical discussions.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.
Funding
The authors received no financial support for the research, authorship and/or publication of this article.
ICMJE Statement
All authors meet the ICMJE criteria for authorship. All authors have reviewed and approved the final version of the manuscript.
Patient Consent
Not applicable. No patient data or human participants were involved in this study.
Statement of Ethics
Not applicable.
