Restoration of the striatal circuitry: from developmental aspects toward clinical applications

In the basal ganglia circuitry, the striatum is a highly complex structure coordinating motor and cognitive functions and it is severely affected in Huntington's disease (HD) patients. Transplantation of fetal ganglionic eminence (GE) derived precursor cells aims to restore neural circuitry in the degenerated striatum of HD patients. Pre-clinical transplantation in genetic and lesion HD animal models has increased our knowledge of graft vs. host interactions, and clinical studies have been shown to successfully reduce motor and cognitive effects caused by the disease. Investigating the molecular mechanisms of striatal neurogenesis is a key research target, since novel strategies aim on generating striatal neurons by differentiating embryonic stem cells or by reprogramming somatic cells as alternative cell source for neural transplantation

Environmental housing and duration of exposure affect striatal graft morphology in a rodent model of Huntington's disease

Clinical trials of cell replacement therapy in Huntington's disease have shown its safety, feasibility, and potentially long-lasting effects. However, more needs to be known regarding the conditions that stimulate plasticity and compensation achieved by neural grafts to maximize posttransplantation recovery of such neurorehabilitative therapies. The effects of enriched environment (EE), behavioral experience, and transplantation can each separately influence neuronal plasticity and recovery of function after brain damage, and the mechanisms by which these factors interact to modify the survival, integration, or function of grafted tissues are at present unknown. To investigate the effects of variable housing conditions and duration on morphological and cellular changes within embryonic striatal transplants, rats received unilateral excitotoxic lesions of the striatum, followed by E15 whole-ganglionic eminence suspension grafts. The rats were divided into three groups according to housing: full-time EE, 1 h/day exposure to EE, or standard laboratory cages. The experimental design included “early” (7 weeks postgrafting) and “late” (13 weeks postgrafting) survival time points to explore the effects of exposure lengths to the three housing conditions. The morphological and cellular effects on the grafts were analyzed using immunohistochemistry, cell morphology, image analysis, and enzyme-linked immunoassay. Both the duration of the exposure and the housing conditions were seen to influence multiple parameters of grafted cell morphology. The factors acted either independently (e.g., on graft size), complementarily (e.g., on spine density), or had no distinctive effect (e.g., on lesion size) on graft development. Features of embryonic striatal grafts and their trophic milieu were influenced both by the complexity of the environmental conditions and by the length of exposure to them. The data suggest that neurorehabilitation should be a feature of clinical trials of cell transplantation in order to exploit the underlying mechanisms that promote anatomical integration of the grafted cells and maximize transplant-mediated functional recovery

Continuous High-Frequency Stimulation of the Subthalamic Nucleus Improves Cell Survival and Functional Recovery Following Dopaminergic Cell Transplantation in Rodents

Subthalamic nucleus (STN) high-frequency stimulation (HFS) is a routine treatment in Parkinson’s disease (PD), with confirmed long-term benefits. An alternative, but still experimental, treatment is cell replacement and restorative therapy based on transplanted dopaminergic neurons. The current experiment evaluated the potential synergy between neuromodulation and grafting by studying the effect of continuous STN-HFS on the survival, integration, and functional efficacy of ventral mesencephalic dopaminergic precursors transplanted into a unilateral 6-hydroxydopamine medial forebrain bundle lesioned rodent PD model. One group received continuous HFS of the ipsilateral STN starting a week prior to intrastriatal dopaminergic neuron transplantation, whereas the sham-stimulated group did not receive STN-HFS but only dopaminergic grafts. A control group was neither lesioned nor transplanted. Over the following 7 weeks, the animals were probed on a series of behavioral tasks to evaluate possible graft and/or stimulation-induced functional effects. Behavioral and histological data suggest that STN-HFS significantly increased graft cell survival, graft–host integration, and functional recovery. These findings might open an unexplored road toward combining neuromodulative and neuroregenerative strategies to treat severe neurologic conditions

Morphological and cellular changes within embryonic striatal grafts associated with enriched environment and involuntary exercise

Environmental enrichment (EE) and exercise have been implicated in influencing behaviour and altering neuronal processes associated with cellular morphology in both ‘normal’ and injured states of the CNS. Using a rodent model of Huntington's disease, we investigated whether prolonged EE or involuntary exercise can induce morphological and cellular changes within embryonic striatal transplants. Adult rats were trained on the Staircase test – requiring fine motor control to reach and collect reward pellets – prior to being lesioned unilaterally in the dorsal neostriatum with quinolinic acid. The lesioned animals received E15 whole ganglionic eminence cell suspension grafts followed by housing in EE or standard cages. Half of the animals in standard cages received daily forced exercise on a treadmill. The grafted animals showed significant functional recovery on both the Staircase test and in drug-induced rotation. Neither the housing conditions nor the training had an impact on the behaviour, with the exception of the treadmill reducing the ipsilateral drug-induced rotation observed amongst the lesioned animals. However, the animals housed in the EE had significantly increased striatal brain-derived neurotrophic factor (BDNF) levels, and graft neurons in these animals exhibited both greater spine densities and larger cell volumes. Animals on forced exercise regime had reduced BDNF levels and grafted cells with sparser spines. The study suggests that the context of the animal can affect the plasticity of transplanted cells. Appropriately exploiting the underlying, and yet unknown, mechanisms could lead the way to improved anatomical and potentially functional integration of the graft

The corridor task: Striatal lesion effects and graft-mediated recovery in a model of Huntington's disease

Experimental validation of cell replacement therapy as a treatment of neurodegenerative diseases requires the demonstration of graft-mediated behavioural recovery. The Corridor task proved to be simple and efficient to conduct with a robust ipsilateral retrieval bias in our rodent Huntington's disease model. The Corridor task is a viable behavioural option, particularly to non-specialised laboratories, for the evaluation of lateralised striatal damage and the probing of alternative therapeutic strategies, including transplantation

Chapter Transplantation of Foetal Ventral Mesencephalic Grafts in Parkinson’s Disease: A Still Evolving Concept with New Regulatory Challenges

Physiological & neuro-psychology, biopsycholog

Chapter Transplantation of Foetal Ventral Mesencephalic Grafts in Parkinson’s Disease: A Still Evolving Concept with New Regulatory Challenges

Physiological & neuro-psychology, biopsycholog

Roscovitine, an experimental CDK5 inhibitor, causes delayed suppression of microglial, but not astroglial recruitment around intracerebral dopaminergic grafts.

Inhibitors of cell cycle proteins are known to reduce glial activation and to be neuroprotective in a number of settings. In the context of intracerebral grafting, glial activation is documented to correlate with graft rejection. However, the effects of modification of glial reactivity following grafting in the CNS are poorly understood. Moreover, it is not completely clear if the glial cells themselves trigger the rejection process, or are they secondarily activated. The present study investigated the effect of microglial inhibition by the cyclin-dependant kinase 5 (CDK5) inhibitor roscovitine following intracerebral transplantation in the rodent model of Parkinson's disease. Single cell suspension of rat E14 ventral mesencephalic tissue was transplanted to the dopamine-depleted striatum of unilaterally 6-hydroxydopamine (6-OHDA) lesioned male Sprague-Dawley rats. Experimental animals received injections of roscovitine (20 mg/kg) or a vehicle solution three times following the procedure. Immunohistochemistry was carried out on Day 7 and Day 28 to quantitatively describe the glial reaction adjacent to grafts. The data confirm that systemic roscovitine treatment significantly reduced microglial recruitment adjacent to the grafts on Day 28, without exhibiting significant effects on astroglia. However, this was not found to correlate with elevated numbers of neurons in the grafts. Moreover, microglial reaction surrounding grafts was less pronounced compared to control animals, subjected to the mechanical influence only, even without roscovitine treatment. Our results are the first to show the effect of cell cycle inhibition in the context of neuronal transplantation. The findings suggest that microglial activation around intracerebral grafts can be modified pharmacologically. However, the results do not confirm direct neuroprotective effects of cell cycle inhibition after intracerebral transplantation. Reducing microglial recruitment around grafts could be beneficial by reducing inflammation-related degenerative processes. Sparing astrocytes in the same time provides transplanted cells with essential trophics and support. We consider microglial inhibition to be a possible approach for reducing later graft-related complications

Feasibility and Safety of Continuous and Chronic Bilateral Deep Brain Stimulation of the Medial Forebrain Bundle in the Naïve Sprague-Dawley Rat

Objective. Deep brain stimulation (DBS) of the superolateral branch of the medial forebrain bundle (MFB) has provided rapid and dramatic reduction of depressive symptoms in a clinical trial. Early intracranial self-stimulation experiments of the MFB suggested detrimental side effects on the animals’ health; therefore, the current study looked at the viability of chronic and continuous MFB-DBS in rodents, with particular attention given to welfare issues and identification of stimulated pathways. Methods. Sprague-Dawley female rats were submitted to stereotactic microelectrode implantation into the MFB. Chronic continuous DBS was applied for 3–6 weeks. Welfare monitoring and behavior changes were assessed. Postmortem histological analysis of c-fos protein expression was carried out. Results. MFB-DBS resulted in mild and temporary weight loss in the animals, which was regained even with continuing stimulation. MFB-DBS led to increased and long-lasting c-fos expression in target regions of the mesolimbic/mesocortical system. Conclusions. Bilateral continuous chronic MFB-DBS is feasible, safe, and without impact on the rodent’s health. MFB-DBS results in temporary increase in exploration, which could explain the initial weight loss, and does not produce any apparent behavioral abnormalities. This platform represents a powerful tool for further preclinical investigation of the MFB stimulation in the treatment of depression