Ablation of the subthalamic nucleus protects dopaminergic phenotype but not cell survival in a rat model of Parkinson's disease

Therapeutic Viewpoint on Rat Models of Locomotion Abnormalities and Neurobiological Indicators in Parkinson's Disease

BACKGROUND

Locomotion problems in Parkinson's syndrome are still a research and treatment difficulty. With the recent introduction of brain stimulation or neuromodulation equipment that is sufficient to monitor activity in the brain using electrodes placed on the scalp, new locomotion investigations in patients having the capacity to move freely have sprung up.

OBJECTIVE

This study aimed to find rat models and locomotion-connected neuronal indicators and use them all over a closed-loop system to enhance the future and present treatment options available for Parkinson's disease.

METHODS

Various publications on locomotor abnormalities, Parkinson's disease, animal models, and other topics have been searched using several search engines, such as Google Scholar, Web of Science, Research Gate, and PubMed.

RESULTS

Based on the literature, we can conclude that animal models are used for further investigating the locomotion connectivity deficiencies of many biological measuring devices and attempting to address unanswered concerns from clinical and non-clinical research. However, translational validity is required for rat models to contribute to the improvement of upcoming neurostimulation-based medicines. This review discusses the most successful methods for modelling Parkinson's locomotion in rats.

CONCLUSION

This review article has examined how scientific clinical experiments lead to localised central nervous system injuries in rats, as well as how the associated motor deficits and connection oscillations reflect this. This evolutionary process of therapeutic interventions may help to improve locomotion- based treatment and management of Parkinson's syndrome in the upcoming years.

Recovery of motor function is associated with rescue of glutamate biomarkers in the striatum and motor cortex following treatment with Mucuna pruriens in a murine model of Parkinsons disease

There is growing interest in the use of natural products for the treatment of Parkinson's disease (PD). Mucuna pruriens has been used in the treatment of humans with PD. The goal of this study was to determine if daily oral treatment with an extract of Mucuna pruriens, starting after the MPTP-induced loss of nigrostriatal dopamine in male mice, would result in recovery/restoration of motor function, tyrosine hydroxylase (TH) protein expression in the nigrostriatal pathway, or glutamate biomarkers in both the striatum and motor cortex. Following MPTP administration, resulting in an 80 % loss of striatal TH, treatment with Mucuna pruriens failed to rescue either striatal TH or the dopamine transporter back to the control levels, but there was restoration of gait/motor function. There was an MPTP-induced loss of TH-labeled neurons in the substantia nigra pars compacta and in the number of striatal dendritic spines, both of which failed to be recovered following treatment with Mucuna pruriens. This Mucuna pruriens-induced locomotor recovery following MPTP was associated with restoration of two striatal glutamate transporter proteins, GLAST (EAAT1) and EAAC1 (EAAT3), and the vesicular glutamate transporter 2 (Vglut2) within the motor cortex. Post-MPTP treatment with Mucuna pruriens, results in locomotor improvement that is associated with recovery of striatal and motor cortex glutamate transporters but is independent of nigrostriatal TH restoration.

Subthalamic nucleus deep brain stimulation induces nigrostriatal dopaminergic plasticity in a stable rat model of Parkinson's disease

OBJECTIVE

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been a highly effective treatment option for middle to late stage Parkinson's disease for decades. Though, the underlying mechanisms of action, particularly effects on the cellular level, remain in part unclear. In the context of identifying disease-modifying effects of STN-DBS by prompting cellular plasticity in midbrain dopaminergic systems, we analyzed neuronal tyrosine hydroxylase and c-Fos expression in the substantia nigra pars compacta (SNpc) and ventral tegmental area (VTA).

METHODS

We applied 1 week of continuous unilateral STN-DBS in a group of stable 6-hydroxydopamine (6-OHDA) hemiparkinsonian rats (STNSTIM) in comparison to a 6-OHDA control group (STNSHAM). Immunohistochemistry identified NeuN+, tyrosine hydroxylase+ and c-Fos+ cells within the SNpc and VTA.

RESULTS

After 1 week, rats in the STNSTIM group had 3.5-fold more tyrosine hydroxylase+ neurons within the SNpc (P = 0.010) but not in the VTA compared to sham controls. There was no difference in basal cell activity as indicated by c-Fos expression in both midbrain dopaminergic systems.

CONCLUSION

Our data support a neurorestorative effect of STN-DBS in the nigrostriatal dopaminergic system already after 7 days of continuous STN-DBS in the stable Parkinson's disease rat model without affecting basal cell activity.

Deep brain stimulation-induced neuroprotection: A critical appraisal

Over the last two decades deep brain stimulation (DBS) has become a widely used therapeutic alternative for a variety of neurological and psychiatric diseases. The extensive experience in the field of movement disorders has provided valuable knowledge and has led the path to its application to other hard-to-treat conditions. Despite the recognised symptomatic beneficial effects, its capacity to modify the course of a disease has been in constant debate. The ability to demonstrate neuroprotection relies on a thorough understanding of the functioning of both normal and pathological neural structures, as well as their stimulation induced alterations, all of which to this date remain incomplete. Consequently, there is no consensus over the definition of neuroprotection nor its means of quantification or evaluation. Additionally, neuroprotection has been indirectly addressed in most of the literature, challenging the efforts to narrow its interpretation. As such, a broad spectrum of evidence has been considered to demonstrate disease modifying interventions. This paper aims to provide a critical appraisal of the current evidence on potential neuroprotective effects of DBS in neurodegenerative brain disorders.

Subthalamic nucleus deep brain stimulation induces sustained neurorestoration in the mesolimbic dopaminergic system in a Parkinson's disease model

BACKGROUND

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is an established therapeutic principle in Parkinson's disease, but the underlying mechanisms, particularly mediating non-motor actions, remain largely enigmatic.

OBJECTIVE/HYPOTHESIS

The delayed onset of neuropsychiatric actions in conjunction with first experimental evidence that STN-DBS causes disease-modifying effects prompted our investigation on how cellular plasticity in midbrain dopaminergic systems is affected by STN-DBS.

METHODS

We applied unilateral or bilateral STN-DBS in two independent cohorts of 6-hydroxydopamine hemiparkinsonian rats four to eight weeks after dopaminergic lesioning to allow for the development of a stable dopaminergic dysfunction prior to DBS electrode implantation.

RESULTS

After 5 weeks of STN-DBS, stimulated animals had significantly more TH⁺ dopaminergic neurons and fibres in both the nigrostriatal and the mesolimbic systems compared to sham controls with large effect sizes of g_Hedges = 1.9-3.4. DBS of the entopeduncular nucleus as the homologue of the human Globus pallidus internus did not alter the dopaminergic systems. STN-DBS effects on mesolimbic dopaminergic neurons were largely confirmed in an independent animal cohort with unilateral STN stimulation for 6 weeks or for 3 weeks followed by a 3 weeks washout period. The latter subgroup even demonstrated persistent mesolimbic dopaminergic plasticity after washout. Pilot behavioural testing showed that augmentative dopaminergic effects on the mesolimbic system by STN-DBS might translate into improvement of sensorimotor neglect.

CONCLUSIONS

Our data support sustained neurorestorative effects of STN-DBS not only in the nigrostriatal but also in the mesolimbic system as a potential factor mediating long-latency neuropsychiatric effects of STN-DBS in Parkinson's disease.

Loss of Collapsin Response Mediator Protein 4 Attenuates 6-Hydroxydopamine-Induced Impairments in a Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is a chronic neurodegenerative disorder characterized by impaired motor symptoms induced by the degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNc). Many factors are speculated to operate in the mechanism of PD, including oxidative stress, mitochondrial dysfunction, abnormal protein handling, and PD induced apoptosis. Besides, researchers have recently shown that inflammatory secretions may engage neighboring cells such as astrocytes, which then induce autocrine and paracrine responses that amplify the inflammation, leading to neurodegeneration. In the present study, we analyzed the neuroprotective and anti-inflammatory effects of collapsin response mediator protein 4 (CRMP4) deletion in 6-hydroxydopamine (6-OHDA)-injected male mice, as well as its effects on motor impairments. Our findings indicated that the deletion of CRMP4 could maintain the TH-positive fibers in the striatum and the TH-positive cells in SNc, attenuate the inflammatory responses, and improve motor coordination and rotational behavior. Furthermore, based on our findings at the early time points, we hypothesized that primary differences between the Crmp4+/+ and Crmp4-/- mice may occur in microglia instead of neurons. Although further work should be carried out to clarify the specific role of CRMP4 in the pathogenesis of PD, our findings suggest that it could be a possible target for the treatment of PD.

A Computational Model of Loss of Dopaminergic Cells in Parkinson's Disease Due to Glutamate-Induced Excitotoxicity

Parkinson's disease (PD) is a neurodegenerative disease associated with progressive and inexorable loss of dopaminergic cells in Substantia Nigra pars compacta (SNc). Although many mechanisms have been suggested, a decisive root cause of this cell loss is unknown. A couple of the proposed mechanisms, however, show potential for the development of a novel line of PD therapeutics. One of these mechanisms is the peculiar metabolic vulnerability of SNc cells compared to other dopaminergic clusters; the other is the SubThalamic Nucleus (STN)-induced excitotoxicity in SNc. To investigate the latter hypothesis computationally, we developed a spiking neuron network-model of SNc-STN-GPe system. In the model, prolonged stimulation of SNc cells by an overactive STN leads to an increase in ‘stress' variable; when the stress in a SNc neuron exceeds a stress threshold, the neuron dies. The model shows that the interaction between SNc and STN involves a positive-feedback due to which, an initial loss of SNc cells that crosses a threshold causes a runaway-effect, leading to an inexorable loss of SNc cells, strongly resembling the process of neurodegeneration. The model further suggests a link between the two aforementioned mechanisms of SNc cell loss. Our simulation results show that the excitotoxic cause of SNc cell loss might initiate by weak-excitotoxicity mediated by energy deficit, followed by strong-excitotoxicity, mediated by a disinhibited STN. A variety of conventional therapies were simulated to test their efficacy in slowing down SNc cell loss. Among them, glutamate inhibition, dopamine restoration, subthalamotomy and deep brain stimulation showed superior neuroprotective-effects in the proposed model.

Subthalamic nucleus deep brain stimulation is neuroprotective in the A53T α-synuclein Parkinson's disease rat model

Objective

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a highly effective symptomatic therapy for motor deficits in Parkinson's disease (PD). An additional, disease‐modifying effect has been suspected from studies in toxin‐based PD animal models, but these models do not reflect the molecular pathology and progressive nature of PD that would be required to evaluate a disease‐modifying action. Defining a disease‐modifying effect could radically change the way in which DBS is used in PD.

Methods

We applied STN‐DBS in an adeno‐associated virus (AAV) 1/2‐driven human mutated A53T α‐synuclein (aSyn)‐overexpressing PD rat model (AAV1/2‐A53T‐aSyn). Rats were injected unilaterally, in the substantia nigra (SN), with AAV1/2‐A53T‐aSyn or control vector. Three weeks later, after behavioral and nigrostriatal dopaminergic deficits had developed, rats underwent STN‐DBS electrode implantation ipsilateral to the vector‐injected SN. Stimulation lasted for 3 weeks. Control groups remained OFF stimulation. Animals were sacrificed at 6 weeks.

Results

Motor performance in the single pellet reaching task was impaired in the AAV1/2‐A53T‐aSyn–injected stim‐OFF group, 6 weeks after AAV1/2‐A53T‐aSyn injection, compared to preoperative levels (–82%; p < 0.01). Deficits were reversed in AAV1/2‐A53T‐aSyn, stim‐ON rats after 3 weeks of active stimulation, compared to the AAV1/2‐A53T‐aSyn stim‐OFF rats (an increase of ∼400%; p < 0.05), demonstrating a beneficial effect of DBS. This motor improvement was maintained when the stimulation was turned off and was accompanied by a higher number of tyrosine hydroxylase⁺ SN neurons (increase of ∼29%), compared to AAV1/2‐A53T‐aSyn stim‐OFF rats (p < 0.05).

Interpretation

Our data support the putative neuroprotective and disease‐modifying effect of STN‐DBS in a mechanistically relevant model of PD. Ann Neurol 2017;81:825–836

Ceftriaxone prevents the neurodegeneration and decreased neurogenesis seen in a Parkinson's disease rat model: An immunohistochemical and MRI study

Manganese-enhanced magnetic resonance imaging (MEMRI) is a widely used technique for detecting neuronal activity in the brain of a living animal. Ceftriaxone (CEF) has been shown to have neuroprotective effects in neurodegenerative diseases. The present study was aimed at clarifying whether, in an 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease (PD) rat model, the known CEF-induced neuronal protection was accompanied by neurogenesis and decreased loss of neuronal activity. After MPTP lesioning (day 0), the rats were treated with CEF (100mg/kg/day, i.p.) or saline for 15 days. They were then injected with MnCl2 (40mg/kg, i.p.) on day 13 and underwent a brain MRI scan on day 14, then the brain was taken for histological evaluation on day 15. The results showed that MPTP lesioning resulted in decreased neuronal activity and density in the nigrostriatal dopaminergic (DAergic) system and the hippocampal CA1, CA3, and dentate gyrus (DG) areas and reduced neurogenesis in the DG, but in hyperactivity in the subthalamic nucleus (STN). These neuronal changes were prevented by CEF treatment. Positive correlations between MEMRI R1 values and neuronal density in the hippocampus were evidenced. Neuronal densities in the hippocampus and SNc were positively correlated. In addition, the R1 value of the STN showed a positive correlation with its neuronal activity but showed a negative correlation with the density of DAergic neurons in the SNc. Therefore, MEMRI R1 value may serve as a good indicator for PD severity and the effect of treatment. To our knowledge, this is the first study showing that CEF prevents loss of neuronal activity and neurogenesis in the brain of PD rats. CEF may therefore have clinical potential in the treatment of PD.

Intervention with exercise restores motor deficits but not nigrostriatal loss in a progressive MPTP mouse model of Parkinson's disease

Many studies have investigated exercise therapy in Parkinson's disease (PD) and have shown benefits in improving motor deficits. However, exercise does not slow down the progression of the disease or induce the revival of lost nigrostriatal neurons. To examine the dichotomy of behavioral improvement without the slowing or recovery of dopaminergic cell or terminal loss, we tested exercise therapy in an intervention paradigm where voluntary running wheels were installed half-way through our progressive PD mouse model. In our model, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is administered over 4 weeks with increased doses each week (8, 16, 24, 32-kg/mg). We found that after 4 weeks of MPTP treatment, mice that volunteered to exercise had behavioral recovery in several measures despite the loss of 73% and 53% tyrosine hydroxylase (TH) within the dorsolateral (DL) striatum and the substantia nigra (SN), respectively which was equivalent to the loss seen in the mice that did not exercise but were also administered MPTP for 4 weeks. Mice treated with 4 weeks of MPTP showed a 41% loss of vesicular monoamine transporter II (VMAT2), a 71% increase in the ratio of glycosylated/non-glycosylated dopamine transporter (DAT), and significant increases in glutamate transporters including VGLUT1, GLT-1, and excitatory amino acid carrier 1. MPTP mice that exercised showed recovery of all these biomarkers back to the levels seen in the vehicle group and showed less inflammation compared to the mice treated with MPTP for 4 weeks. Even though we did not measure tissue dopamine (DA) concentration, our data suggest that exercise does not alleviate motor deficits by sparing nigrostriatal neurons, but perhaps by stabilizing the extraneuronal neurotransmitters, as evident by a recovery of DA and glutamate transporters. However, suppressing inflammation could be another mechanism of this locomotor recovery. Although exercise will not be a successful treatment alone, it could supplement other pharmaceutical approaches to PD therapy.

Neuroprotection by 6-(methylsulfinyl)hexyl isothiocyanate in a 6-hydroxydopamine mouse model of Parkinson׳s disease

A number of pathogenic factors have been implicated in the progression of Parkinson׳s disease (PD), including oxidative stress, mitochondrial dysfunction, inflammation, excitotoxicity, and signals mediating apoptosis cascade. 6-(methylsulfinyl)hexyl isothiocyanate (6-MSITC) is a major component in wasabi, a very popular spice in Japan and a member of the Brassica family of vegetables. This study was designed to investigate the neuroprotective effects of 6-MSITC in a PD mouse model. Mice were treated with 6-MSITC (5mg/kg twice a week) for four weeks after the unilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA). On the 28th day, 6-OHDA-injected mice showed behavioral impairments, a significant decrease in tyrosine hydroxylase (TH) and an increase in apoptosis. In addition, lesioned mice showed reduced glutathione levels and glutathione-S-transferase and glutathione reductase activities. Notably, 6-MSITC demonstrated neuroprotective effects in our experimental model strongly related to the preservation of functional nigral dopaminergic neurons, which contributed to the reduction of motor dysfunction induced by 6-OHDA. Furthermore, this study provides evidence that the beneficial effects of 6-MSITC could be attributed to the decrease of apoptotic cell death and to the activation of glutathione-dependent antioxidant systems. These findings may render 6-MSITC as a promising molecule for further pharmacological studies on the investigation for disease-modifying treatment in PD.

Indirect application of near infrared light induces neuroprotection in a mouse model of parkinsonism - an abscopal neuroprotective effect

We have previously shown near infrared light (NIr), directed transcranially, mitigates the loss of dopaminergic cells in MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-treated mice, a model of parkinsonism. These findings complement others suggesting NIr treatment protects against damage from various insults. However one puzzling feature of NIr treatment is that unilateral exposure can lead to a bilateral healing response, suggesting NIr may have 'indirect' protective effects. We investigated whether remote NIr treatment is neuroprotective by administering different MPTP doses (50-, 75-, 100-mg/kg) to mice and treating with 670-nm light directed specifically at either the head or body. Our results show that, despite no direct irradiation of the damaged tissue, remote NIr treatment produces a significant rescue of tyrosine hydroxylase-positive cells in the substantia nigra pars compacta at the milder MPTP dose of 50-mg/kg (∼30% increase vs sham-treated MPTP mice, p<0.05). However this protection did not appear as robust as that achieved by direct irradiation of the head (∼50% increase vs sham-treated MPTP mice, p<0.001). There was no quantifiable protective effect of NIr at higher MPTP doses, irrespective of the delivery mode. Astrocyte and microglia cell numbers in substantia nigra pars compacta were not influenced by either mode of NIr treatment. In summary, the findings suggest that treatment of a remote tissue with NIr is sufficient to induce protection of the brain, reminiscent of the 'abscopal effect' sometimes observed in radiation treatment of metastatic cancer. This discovery has implications for the clinical translation of light-based therapies, providing an improved mode of delivery over transcranial irradiation.

Subthalamotomy in the treatment of Parkinson's disease: clinical aspects and mechanisms of action

Parkinson's disease (PD) is a neurodegenerative condition that can be pharmacologically treated with levodopa. However, important motor and nonmotor symptoms appear with its long-term use. The subthalamic nucleus (STN) is known to be involved in the pathophysiology of PD and to contribute to levodopa-induced complications. Surgery is considered in patients who have advanced PD that is refractory to pharmacotherapy and who display disabling dyskinesia. Deep brain stimulation of the STN is currently the main surgical procedure for PD, but lesioning is still performed. This review covers the clinical aspects and complications of subthalamotomy as one of the lesion-based options for PD patients with levodopa-induced dyskinesias. Moreover, the authors discuss the possible effects of subthalamic lesioning.

High frequency stimulation of the subthalamic nucleus leads to presynaptic GABA(B)-dependent depression of subthalamo-nigral afferents

Patients with akinesia benefit from chronic high frequency stimulation (HFS) of the subthalamic nucleus (STN). Among the mechanisms contributing to the therapeutic success of HFS-STN might be a suppression of activity in the output region of the basal ganglia. Indeed, recordings in the substantia nigra pars reticulata (SNr) of fully adult mice revealed that HFS-STN consistently produced a reduction of compound glutamatergic excitatory postsynaptic currents at a time when the tetrodotoxin-sensitive components of the local field potentials had already recovered after the high frequency activation. These observations suggest that HFS-STN not only alters action potential conduction on the way towards the SNr but also modifies synaptic transmission within the SNr. A classical conditioning-test paradigm was then designed to better separate the causes from the indicators of synaptic depression. A bipolar platinum-iridium macroelectrode delivered conditioning HFS trains to a larger group of fibers in the STN, while a separate high-ohmic glass micropipette in the rostral SNr provided test stimuli at minimal intensity to single fibers. The conditioning-test interval was set to 100 ms, i.e. the time required to recover the excitability of subthalamo-nigral axons after HFS-STN. The continuity of STN axons passing from the conditioning to the test sites was examined by an action potential occlusion test. About two thirds of the subthalamo-nigral afferents were occlusion-negative, i.e. they were not among the fibers directly activated by the conditioning STN stimulation. Nonetheless, occlusion-negative afferents exhibited signs of presynaptic depression that could be eliminated by blocking GABA(B) receptors with CGP55845 (1 µM). Further analysis of single fiber-activated responses supported the proposal that the heterosynaptic depression of synaptic glutamate release during and after HFS-STN is mainly caused by the tonic release of GABA from co-activated striato-nigral afferents to the SNr. This mechanism would be consistent with a gain-of-function hypothesis of DBS.

Neuroprotective effect of sulforaphane in 6-hydroxydopamine-lesioned mouse model of Parkinson's disease

Parkinson's disease (PD) is characterized by the selective loss of dopaminergic nigrostriatal neurons, which leads to disabling motor disturbances. Sulforaphane (SFN), found in cruciferous vegetables, is a potent indirect antioxidant and recent advances have shown its neuroprotective activity in various experimental models of neurodegeneration. This study was undertaken to examine the effects of SFN on behavioral changes and dopaminergic neurotoxicity in mice exposed to 6-hydroxydopamine (6-OHDA). For this purpose, mice were treated with SFN (5mg/kg twice a week) for four weeks after the unilateral intrastriatal injection of 6-OHDA. The increase in 6-OHDA-induced rotations and deficits in motor coordination were ameliorated significantly by SFN treatment. In addition, SFN protected 6-OHDA-induced apoptosis via blocking DNA fragmentation and caspase-3 activation. These results were further supported by immunohistochemical findings in the substantia nigra that showed that SFN protected neurons from neurotoxic effects of 6-OHDA. The neuroprotective effect of SFN may be attributed to its ability to enhance glutathione levels and its dependent enzymes (glutathione-S-transferase and glutathione reductase) and to modulate neuronal survival pathways, such as ERK1/2, in the brain of mice. These results suggest that SFN may potentially be effective in slowing down the progression of idiopathic PD by the modulation of oxidative stress and apoptotic machinery.

The impact of subthalamic deep brain stimulation on nigral neuroprotection-myth or reality?

OBJECTIVE

  In the present review article we summarize available clinical and preclinical evidence, if modulation of the subthalamic nucleus (STN) could be a target for neuroprotection in Parkinson's disease (PD).

BACKGROUND

  Chronic deep brain stimulation (DBS) of the STN has emerged as a powerful therapeutic alternative for the treatment of PD, ensuring stable symptom control for up to five years despite the progressive nature PD.

MATERIALS AND METHODS

  Comparative review of literature in PuBMed available up to December 2008.

RESULTS

  The assessment of neuroprotection has been proven difficult in the clinical situation, as medical or surgical therapeutic options that improve PD symptoms could be erroneously considered to be neuroprotective because of the difficulty of differentiating between symptomatic effects and potential neuromodulative disease-related effects of various treatment options applied in PD. The methodological limitations of clinical trials underline the importance of putative neuroprotective compounds to be tested in clinically driven preclinical studies. Thus, animal models, mimicking progressive nigrostriatal cell death, are indispensable to further advance the important issue of neuroprotection or neuromodulation following DBS.

CONCLUSION

  Clear clinical evidence for STN-DBS-related neuroprotection in PD is missing. However, numerous preclinical studies show (and are discussed) that silencing of the STN via lesion or DBS may exert neuromodulative effects on nigral dopamine neurons.

Lessons learned from the transgenic Huntington's disease rats

Huntington's disease (HD) is a fatal inherited disorder leading to selective neurodegeneration and neuropsychiatric symptoms. Currently, there is no treatment to slow down or to stop the disease. There is also no therapy to effectively reduce the symptoms. In the investigation of novel therapies, different animal models of Huntington's disease, varying from insects to nonhuman primates, have been created and used. Few years ago, the first transgenic rat model of HD, carrying a truncated huntingtin cDNA fragment with 51 CAG repeats under control of the native rat huntingtin promoter, was introduced. We have been using this animal model in our research and review here our experience with the behavioural, neurophysiological, and histopathological phenotype of the transgenic Huntington's disease rats with relevant literature.

Glial cell-line derived neurotrophic factor is essential for electroconvulsive shock-induced neuroprotection in an animal model of Parkinson's disease

Sustained motor improvement in human patients with idiopathic Parkinson's disease has been described following electroconvulsive shock (ECS) treatment. In rats, ECS stimulates the expression of various trophic factors (TFs), some of which have been proposed to exert neuroprotective actions. We previously reported that ECS protects the integrity of the rat nigrostriatal dopaminergic system against 6-hydroxydopamine (6-OHDA)-induced toxicity; in order to shed light into its neuroprotective mechanism, we studied glial cell-line derived neurotrophic factor (GDNF) levels (the most efficient TF for dopaminergic neurons) in the substantia nigra (SN) and striatum of 6-OHDA-injected animals with or without ECS treatment. 6-OHDA injection decreased GDNF levels in the SN control animals, but not in those receiving chronic ECS, suggesting that changes in GDNF expression may participate in the ECS neuroprotective mechanism. To evaluate this possibility, we inhibit GDNF by infusion of GDNF function blocking antibodies in the SN of 6-OHDA-injected animals treated with ECS (or sham ECS). Animals were sacrificed 7 days after 6-OHDA infusion, and the integrity of the nigrostriatal system was studied by tyrosine hydroxylase immunohistochemistry and Cresyl Violet staining. Neuroprotection observed in ECS-treated animals was inhibited by GDNF antibodies in the SN. These results robustly demonstrate that GDNF is essential for the ECS neuroprotective effect observed in 6-OHDA-injected animals.

Generation of a model of L-DOPA-induced dyskinesia in two different mouse strains

Prolonged use of the dopamine precursor L-DOPA for the treatment of Parkinson's disease commonly results in abnormal involuntary movements, which are termed L-DOPA-induced dyskinesia (LID). Over-activity at corticostriatal synapses onto neurons of the direct and indirect striatal output pathways has been implicated in the development of dyskinesia, but it has proved difficult to investigate the pathways separately due to their morphological similarities. The recent development of bacterial artificial chromosome mice that express green fluorescent protein in either the direct or indirect pathway allows visual identification of the output neurons in each pathway. Here we describe the use of two different strains of these transgenic mice (pure FVB and FVB crossed with C57BL6) in the development of mouse models of L-DOPA-induced dyskinesia. This model will allow the direct and indirect pathways to be studied individually to delineate the cellular and molecular mechanisms underlying dyskinesias. These studies demonstrate that mouse strain impacts on behavioural responses and L-DOPA sensitivity. Therefore, when generating mouse models of LID, strain must be taken into consideration when choosing the L-DOPA dosing regimen.

Neuroprotection of midbrain dopaminergic cells in MPTP-treated mice after near-infrared light treatment

This study explores whether near-infrared (NIr) light treatment neuroprotects dopaminergic cells in the substantia nigra pars compacta (SNc) and the zona incerta-hypothalamus (ZI-Hyp) from degeneration in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice. BALB/c albino mice were divided into four groups: 1) Saline, 2) Saline-NIr, 3) MPTP, 4) MPTP-NIr. The injections were intraperitoneal and they were followed immediately by NIr light treatment (or not). Two doses of MPTP, mild (50 mg/kg) and strong (100 mg/kg), were used. Mice were perfused transcardially with aldehyde fixative 6 days after their MPTP treatment. Brains were processed for tyrosine hydroxylase (TH) immunochemistry. The number of TH(+) cells was estimated using the optical fractionator method. Our major finding was that in the SNc there were significantly more dopaminergic cells in the MPTP-NIr compared to the MPTP group (35%-45%). By contrast, in the ZI-Hyp there was no significant difference in the numbers of cells in these two groups. In addition, our results indicated that survival in the two regions after MPTP insult was dose-dependent. In the stronger MPTP regime, the magnitude of loss was similar in the two regions ( approximately 60%), while in the milder regime cell loss was greater in the SNc (45%) than ZI-Hyp ( approximately 30%). In summary, our results indicate that NIr light treatment offers neuroprotection against MPTP toxicity for dopaminergic cells in the SNc, but not in the ZI-Hyp.

C-terminal mechano growth factor protects dopamine neurons: a novel peptide that induces heme oxygenase-1

To assess potential efficacy of mechano growth factor (MGF) for chronic neurodegenerative disorders, we studied whether MGF protects dopamine (DA) neurons subjected to neurotoxic stress. We show that a short 24-amino acid C-terminal peptide of MGF (MGF24) upregulates heme oxygenase-1 (HO-1) expression and protects SH-SY5Y cells against apoptosis and cell loss induced by three DA cell-specific neurotoxins: 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenylpyridinium (MPP(+)), and rotenone. MGF24 maintains the mitochondrial membrane potential and blocks the release of mitochondrial apoptotic-inducing factor into the cytoplasm induced by 6-OHDA, MPP(+), and rotenone. Chemical inhibition of HO-1 with zinc protoporphyrin-IX prevents neuroprotection by MGF24 against the three neurotoxins. MGF24 does not activate Akt signaling nor does Akt inhibition block MGF24 protection of SH-SY5Y cells. In 6-OHDA-lesioned rats, central or peripheral MGF24 administration protects against the development of contralateral forelimb under-utilization, reduces ipsilateral nigral DA cell body loss, and attenuates tyrosine hydroxylase fiber loss in the ipsilateral striatum, independent of IGF-1 receptor activation. Peripheral MGF24 administration upregulates HO-1 expression in striatal and midbrain tissue. This report is the first to demonstrate that a small peptide, MGF24, upregulates HO-1, an important cell defense mediator, and protects DA cells, suggesting new strategies for neuroprotection in Parkinson's disease.

Enriched environment protects the nigrostriatal dopaminergic system and induces astroglial reaction in the 6-OHDA rat model of Parkinson's disease

Enriched environment (EE) is neuroprotective in several animal models of neurodegeneration. It stimulates the expression of trophic factors and modifies the astrocyte cell population which has been said to exert neuroprotective effects. We have investigated the effects of EE on 6-hydroxydopamine (6-OHDA)-induced neuronal death after unilateral administration to the medial forebrain bundle, which reaches 85-95% of dopaminergic neurons in the substantia nigra after 3 weeks. Continuous exposure to EE 3 weeks before and after 6-OHDA injection prevents neuronal death (assessed by tyrosine hydroxylase staining), protects the nigrostriatal pathway (assessed by Fluorogold retrograde labeling) and reduces motor impairment. Four days after 6-OHDA injection, EE was associated with a marked increase in glial fibrillary acidic protein staining and prevented neuronal death (assessed by Fluoro Jade-B) but not partial loss of tyrosine hydroxylase staining in the anterior substantia nigra. These results robustly demonstrate that EE preserves the entire nigrostriatal system against 6-OHDA-induced toxicity, and suggests that an early post-lesion astrocytic reaction may participate in the neuroprotective mechanism.

Deep brain stimulation of the subthalamic nucleus for the treatment of Parkinson's disease

High-frequency deep brain stimulation (DBS) of the subthalamic nucleus (STN-HFS) is the preferred surgical treatment for advanced Parkinson's disease. In the 15 years since its introduction into clinical practice, many studies have reported on its benefits, drawbacks, and insufficiencies. Despite limited evidence-based data, STN-HFS has been shown to be surgically safe, and improvements in dopaminergic drug-sensitive symptoms and reductions in subsequent drug dose and dyskinesias are well documented. However, the procedure is associated with adverse effects, mainly neurocognitive, and with side-effects created by spread of stimulation to surrounding structures, depending on the precise location of electrodes. Quality of life improves substantially, inducing sudden global changes in patients' lives, often requiring societal readaptation. STN-HFS is a powerful method that is currently unchallenged in the management of Parkinson's disease, but its long-term effects must be thoroughly assessed. Further improvements, through basic research and methodological innovations, should make it applicable to earlier stages of the disease and increase its availability to patients in developing countries.

Continuous intraventricular infusion of erythropoietin exerts neuroprotective/rescue effects upon Parkinson's disease model of rats with enhanced neurogenesis

Parkinson's disease (PD) is characterized by degeneration of nigrostriatal dopaminergic neuronal systems. Several therapeutic tools for PD include medication using L-DOPA and surgeries such as deep brain stimulation are established. However, the therapies are considered as symptomatic therapy, but not basic remedy for PD and a new regenerative therapy would be desired to explore. In this study, the neuroprotective/rescue effects of erythropoietin (EPO), a well known hematopoietic hormone, on dopaminergic neurons were explored with neurogeneic potencies of EPO. EPO (100 IU/day) was continuously administered with micro-osmotic pump for a week to PD model of rats induced by intrastriatal 6-hydroxydopamine (6-OHDA) injection with subsequent behavioral and immunohistochemical investigations. The number of amphetamine-induced rotations of EPO-treated rats significantly decreased, compared to the control rats. The preservation of dopaminergic neurons of EPO-treated rats were confirmed by tyrosine hydroxylase staining and Fluoro-Gold staining. The number of bromodeoxyuridine (BrdU)/polysialic acid-neural cell adhesion molecule (PSA-NCAM) double positive cells in the subventricular zone of EPO treated rats significantly increased with migratory potencies to the damaged striatum,compared to the control rats. Furthermore, TUNEL staining and phosphorylated Akt staining revealed that the neuroprotective/rescue effects of EPO might be mediated by anti-apoptotic effects through the increase of phosphorylated Akt. These results suggest that continuous low dose infusion of EPO exerts neuroprotective/rescue effects with neurogeneic potentials. EPO might be a strong tool for PD therapy, although the further experiments should be added.

Patterns of FOS expression in the spinal cord and periaqueductal grey matter of 6OHDA-lesioned rats

A less well-known feature of Parkinson disease is that up to 40% of patients experience distinct sensory disturbances, including hyperalgesia and chronic pain. There is a limited understanding of the neural mechanisms that generate these symptoms, however. This study explores the patterns of Fos expression (a well-known marker for changes in cell activity) in the spinal cord and periaqueductal grey matter (PaG), two major sensory (nociceptive) centers, of hemiParkinsonian rats. The medial forebrain bundle (mfb; major tract carrying dopaminergic nigrostriatal axons) was injected with either 6OHDA or saline (controls). A week later, some rats were subjected to mechanical stimulation (pinching) of the hindpaw for 2 h, whereas others received no stimulation. Thereafter, brains were processed using routine tyrosine hydroxylase (marker for dopaminergic cells) or Fos immunocytochemistry. In the PaG, there were many more Fos(+) cells in the 6OHDA-lesioned than in the Control group, in both the stimulation and, in particular, the non-stimulation cases. In the spinal cord, there were also more Fos(+) cells in the 6OHDA-lesioned than in the Control group, but in the stimulation cases only. Overall, the results show distinct changes in Fos expression in the spinal cord and PaG of 6OHDA-lesioned rats, suggesting a substrate for some of the abnormal sensory (nociceptive) circuits that may be evident in parkinsonian cases.

Frontiers in the surgical treatment of Parkinson's disease

Despite the continued refinement of medical and surgical therapies, the treatment of Parkinson's disease (PD) remains challenging. Current treatment strategies are largely focused on managing the motor symptoms of the disease, either by dopamine-based medications or, in advanced stages, by the application of deep brain stimulation to more stably alter the function of the basal ganglia. Important advances have been made in the last decade, but unfortunately a number of the motor symptoms of late-stage PD remain poorly treated, and while currently available therapies address the symptoms of the disease, they fail to alter the course of the disease itself. This has spurred basic and clinical exploration on a number of fronts. Several centers have examined novel stimulation targets to treat refractory symptoms of gait difficulty and axial imbalance. Basic and clinical researchers are examining whether the use of deep brain stimulation might slow the progress of the disease and thus be a useful neuroprotective therapy if initiated earlier in the progression of the disease. An expanded understanding of the genetic and cellular events that underlie PD has led some researchers to explore the use of neurotrophic factors or genetic restoration to preserve threatened neuronal populations. Finally, there has been much research on the use of fetal mesencephalic or stem cell populations to restore dopaminergic function. In this report, we will examine each of these potential new surgical therapies and the promise they may hold for the future treatment of PD.

PI3 kinase/Akt activation mediates estrogen and IGF-1 nigral DA neuronal neuroprotection against a unilateral rat model of Parkinson's disease

Recently, using the medial forebrain bundle (MFB) 6-hydroxydopmaine (6-OHDA) lesion rat model of Parkinson's disease (PD), we have demonstrated that blockade of central IGF-1 receptors (IGF-1R) attenuated estrogen neuroprotection of substantia nigra pars compacta (SNpc) DA neurons, but exacerbated 6-OHDA lesions in IGF-1 only treated rats (Quesada and Micevych [2004]: J Neurosci Res 75:107-116). This suggested that the IGF-1 system is a central mechanism through which estrogen acts to protect the nigrostriatal DA system. Moreover, these results also suggest that IGF-1R-induced intracellular signaling pathways are involved in the estrogen mechanism that promotes neuronal survival. In vitro, two convergent intracellular signaling pathways used by estrogen and IGF-1, the mitogen-activated protein kinase (MAPK/ERK), and phosphatidyl-inositol-3-kinase/Akt (PI3K/Akt), have been demonstrated to be neuroprotective. Continuous central infusions of MAPK/ERK and PI3K/Akt inhibitors were used to test the hypothesis that one or both of these signal transduction pathways mediates estrogen and/or IGF-1 neuroprotection of SNpc DA neurons after a unilateral administration of 6-OHDA into the MFB of rats. Motor behavior tests and tyrosine hydroxylase immunoreactivity revealed that the inhibitor of the PI3K/Akt pathway (LY294002) blocked the survival effects of both estrogen and IGF-1, while an inhibitor of the MAPK/ERK signaling (PD98059) was ineffective. Western blot analyses showed that estrogen and IGF-1 treatments increased PI3K/Akt activation in the SN; however, MAPK/ERK activation was decreased in the SN. Indeed, continuous infusions of inhibitors blocked phosphorylation of PI3K/Akt and MAPK/ERK. These findings indicate that estrogen and IGF-1-mediated SNpc DA neuronal protection is dependent on PI3K/Akt signaling, but not on the MAPK/ERK pathway.

Protection of dopaminergic neurons by electroconvulsive shock in an animal model of Parkinson’s disease

Electroconvulsive shock (ECS) improves motor function in Parkinson's disease. In rats, ECS stimulates the expression of various factors some of which have been proposed to exert neuroprotective actions. We have investigated the effects of ECS on 6-hydroxydopamine (6-OHDA)-injected rats. Three weeks after a unilateral administration of 6-OHDA, 85-95% nigral dopaminergic neurons are lost. Chronic ECS prevented this cell loss, protect the nigrostriatal pathway (assessed by FloroGold retrograde labeling) and reduce motor impairment in 6-OHDA-treated animals. Injection of 6-OHDA caused loss of expression of glial cell-line derived neurotrophic factor (GDNF) in the substantia nigra. Chronic ECS completely prevented this loss of GDNF expression in 6-OHDA-treated animals. We also found that protected dopaminergic neurons co-express GDNF receptor proteins. These results strongly suggest that endogenous changes in GDNF expression may participate in the neuroprotective mechanism of ECS against 6-OHDA induced toxicity.

Systemic administration of an mGluR5 antagonist, but not unilateral subthalamic lesion, counteracts l-DOPA-induced dyskinesias in a rodent model of Parkinson's disease

Altered glutamatergic neurotransmission is central to the expression of Parkinson's disease (PD) symptoms and may underlie l-DOPA-induced dyskinesias. Drugs acting on glutamate metabotropic receptors (mGluR) of group I can modulate subthalamic nucleus (STN) overactivity, which plays a pivotal role in these phenomena, and may counteract dyskinesias. To address these issues, we investigated the effects of a 3-week treatment with mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP), or of a subthalamic lesion, on abnormal involuntary movements (AIMs) and associated striatal expression of transcription factor FosB/Delta FosB caused by chronic l-DOPA administration, in rats with a nigrostriatal lesion. MPEP virtually abolished AIMs and reduced, dramatically, striatal expression of FosB/Delta FosB. Reduced FosB/Delta FosB expression, coupled with nonsignificant reduction of AIMs, was also observed in STN-lesioned rats. Our data confirm the role of glutamatergic neurotransmission in the pathogenesis of dyskinesias and the potential of mGluR5 antagonists in the treatment of l-DOPA-induced dyskinesias.

Human neural progenitor cell transplants into the subthalamic nucleus lead to functional recovery in a rat model of Parkinson’s disease

Despite the success of foetal nigral transplantation for the treatment of Parkinson's disease, supply limitations of tissue means that alternative sources must be found. Transplantation of human neural progenitor cells (HNPCs) may offer a solution, however few studies have shown functional recovery in animal models of PD without cell modification. Here we show that unmodified HNPC grafted into the subthalamic nucleus (STN) show excellent survival of up to 5 months and induce significant functional recovery following amphetamine-induced rotations within 4 weeks. For the first time we also show that HNPCs, which remain in an immature nestin-positive state, produce VEGF in vivo allowing further modification of the host brain. This suggests that even in the absence of cell replacement strategies utilising immature progenitor cells could be of real therapeutic value.

Lesions of dopaminergic neurons in the substantia nigra pars compacta and in the ventral tegmental area enhance depressive-like behavior in rats

Depression is the most common psychiatric complication in Parkinson's disease (PD). The pathophysiological events leading to PD-associated depression, however, remain largely unknown. The present study tested the differential implication of dopaminergic systems in depressive-like behavior in rats and its response to l-Dopa and the selective serotonin reuptake inhibitor citalopram. The learned helplessness model was used as a behavioral paradigm. Rats were lesioned in the substantia nigra pars compacta (SNc) and the ventral tegmental area (VTA) and assigned to subgroups with respect to the stereologically verified extent of the nigral and/or VTA degeneration. Both lesions increased depressive-like behavior in rats, which was reduced by both citalopram and l-Dopa treatment. We conclude that dopaminergic lesions of either the SNc or the VTA contribute to the manifestation of depressive-like behavior in rats. The effects of citalopram administration on depressive behavior induced by lesions of dopaminergic brain regions furthermore suggest an involvement of serotonergic pathways in dopaminergic cell loss-induced depression.

SPECT imaging, immunohistochemical and behavioural correlations in the primate models of Parkinson's disease

Dopamine active transporter (DAT) single photon emission computerised tomography (SPECT) is considered a useful and practical technique for early diagnosis of Parkinson's disease (PD) and assessment of its progression. The application of this technique, particularly as a surrogate marker for therapeutic and neuroprotective trials in Parkinsonism, however, is dependent on pathological validation. In the absence of human studies, we used 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) primate models of Parkinsonism to verify correlation between the SPECT, immunohistochemical and behavioural data. The DAT SPECT data correlated strongly and significantly with the substantia nigra pars compacta tyrosine hydroxylase and Nissl cell counts as well as the behavioural scores. Within the limitations of small numbers inherent to such studies, this data provides the first attempt at pathological validation of SPECT in primates.