Behavioral improvement and dopamine release in a Parkinsonian rat model

Botulinum Neurotoxin-A Injected Intrastriatally into Hemiparkinsonian Rats Improves the Initiation Time for Left and Right Forelimbs in Both Forehand and Backhand Directions

Forelimb stepping is a widely used test for the assessment of forelimb akinesia in hemiparkinsonian (hemi-PD) rats. The initiation time (IT) is considered the most sensitive parameter in the stepping test procedure. Here we propose a novel, reliable, and simple method for the measurement of IT of both forelimbs in both forehand and backhand directions in rats. Evaluating the same videos taken for quantifying adjusting steps, IT measurements were done without additional experiments. This is in contrast to the classical approach introduced by Olsson et al. (1995), in which separate experiments are necessary. We successfully applied our approach to hemi-PD rats intrastriatally treated with botulinum neurotoxin-A (BoNT-A). In naïve rats, an IT of about 0.62 s was found, and in right-sided hemi-PD rats the IT of the left forepaw increased to about 3.62 s. These hemi-PD rats showed, however, reduced ITs of the impaired left forepaws 1 month and the second time 7 months after induction of hemi-PD via the injection of 1 ng BoNT-A into the ipsilateral striatum, depending on post BoNT-A survival time. The method described offers the possibility of a precise and animal-friendly evaluation of IT in rats, including the beneficial effect of BoNT-A treatment in hemi-PD rats.

Motor activity affects dopaminergic and noradrenergic systems of the dorsal horn of the rat lumbar spinal cord

Dopamine (DA) and noradrenaline (NA) modulate responses to nociceptive stimuli, within the dorsal horn of the spinal cord. Both neurotransmitters may play a role in supraspinal regulation in response to proprioceptive afferences to the dorsal horn. However, direct evidence of changes in neurotransmitter release within the dorsal horn due to non-noxious stimuli is lacking. The present study was designed to determine, whether non-nociceptive exercise produces changes in release of DA and NA within the dorsal horn, and whether these changes are associated with long-lasting inhibition after the exercise stops. Microdialysis probes, implanted in layers 2-5 of Rexed, in combination with high-performance liquid chromatography coupled to electrochemical detection (HPLC-EC) were used to measure concentrations of DA and NA metabolite (MHPG) in lumbar spinal cords of rats. Microdialysate was sampled before, during, and after a treadmill exercise of one hour. Results indicate that DA and NA releases are inhibited during non-nociceptive motor activity. At rest, DA concentration was 204 ± 10.5 pg/10 μl and was significantly decreased during exercise to -11.4% (P ≤ 0.05). Greater decrease occurred after 30 min of exercise and was of -31.4% (P ≤ 0.05). Similarly, MHPG was significantly decreased of -18% during exercise (P ≤ 0.05). When exercise stopped, both systems showed long-lasting inhibition. Exercise post-release lasted 30 min for DA and 90 min for MHPG. MHPG greatest decrease of -47.8% occurred 30 min after stopping the exercise (P ≤ 0.001). Thus, DA and NA systems seem to respond to exercise-induced proprioceptive afferent stimuli to the dorsal horn.

Neurturin protects against 6-hydroxydopamine-induced reductions in evoked dopamine overflow in rat striatum

Neurturin (NTN), a member of the glial cell line-derived neurotrophic factor (GDNF) family, has substantial effects on normal and lesioned nigrostriatal dopamine systems. However, its ability to protect against toxin-induced loss of striatal dopamine release has not been previously reported. The goal of the present study was to determine if NTN could protect against 6-hydroxydopamine (6-OHDA)-induced reductions in striatal dopamine overflow and tissue levels of dopamine and to compare the effects of NTN with those of GDNF. Male Fischer-344 rats were given a single injection of vehicle, or 5 microg NTN or GDNF, into the right striatum. The following day the animals were given a single injection of 12 microg 6-OHDA into the striatum at the same site where the trophic factor was injected. Microdialysis experiments conducted three weeks later indicated that the 6-OHDA decreased basal levels of dopamine and metabolites in the lesioned striatum compared to the contralateral striatum, and NTN was able to partially protect against the 6-OHDA-induced reductions. Injection of NTN one day prior to 6-OHDA also led to significant protection against loss of both potassium- and amphetamine-evoked overflow of dopamine. The NTN treatments partially protected against 6-OHDA-induced reductions in striatal tissue levels of dopamine and completely protected against loss of nigral dopamine content. The protective effects of NTN were similar in magnitude to those of GDNF. These results support that within the experimental parameters used in this study, NTN is as effective as GDNF in protecting against the dopamine-depleting effects of intrastriatal 6-OHDA.

In vivo microdialysis in Parkinson's research

Parkinson's disease (PD) is a progressive neurodegenerative disorder that is primarily characterized by the degeneration of dopamine (DA) neurons in the nigrostriatal system, which in turn produces profound neurochemical changes within the basal ganglia, representing the neural substrate for parkinsonian motor symptoms. The pathogenesis of the disease is still not completely understood, but environmental and genetic factors are thought to play important roles. Research into the pathogenesis and the development of new therapeutic intervention strategies that will slow or stop the progression of the disease in human has rapidly advanced by the use of neurotoxins that specifically target DA neurons. Over the years, a broad variety of experimental models of the disease has been developed and applied in diverse animal species. The two most common toxin models used employ 6-hydroxydopamine (6-OHDA) and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/1-methyl-4-phenilpyridinium ion (MPTP/MPP+), either given systemically or locally applied into the nigrostriatal pathway, to resemble PD features in animals. Both neurotoxins selectively and rapidly destroy catecolaminergic neurons, although with different mechanisms. Since in vivo microdialysis coupled to high-performance liquid chromatography is an established technique for studying physiological, pharmacological, and pathological changes of a wide range of low molecular weight substances in the brain extracellular fluid, here we review the most prominent animal and human data obtained by the use of this technique in PD research.

Human interleukin-10 gene transfer is protective in a rat model of Parkinson's disease

In Parkinson's disease (PD) chronic inflammation occurs in the substantia nigra (SNc) concurrently with dopaminergic neurodegeneration. In models of PD, microglial activation precedes neurodegeneration in the SNc, suggesting that the underlying pathogenesis involves a complex response in the nigrostriatal pathway, and that the innate immune system plays a significant role. We have investigated the neuroprotective effect of an adeno-associated viral type-2 (AAV2) vector containing the complementary DNA (cDNA) for human interleukin-10 (hIL-10) in the unilateral 6-hydroxydopamine (6-OHDA) rat model of PD. AAV2-hIL-10 reduced the 6-OHDA-induced loss of tyrosine hydroxylase (TH)-positive neurons in the SNc, and also reduced loss of striatal dopamine (DA). Pretreatment with AAV2-hIL-10 reduced glial activation in the SNc but did not attenuate striatal release of the inflammatory cytokine IL-1beta. Assessment of rotational behavior in response to apomorphine challenge showed absence of asymmetry, confirming protection of dopaminergic innervation of the lesioned striatum. At baseline, 6-OHDA-lesioned animals displayed a deficit in contralateral forelimb use, but pretreatment with AAV2-hIL-10 reduced this forelimb akinesia. Transcriptional analyses revealed alteration of a few genes by AAV2-hIL-10; these alterations may contribute to neuroprotection. This study supports the need for further investigations relating to gene therapies aimed at reducing neuroinflammation in early PD.

Preclinical development of gene therapy for Parkinson's disease

Multiple targets and pathways may be amenable to the development of gene therapy approaches for Parkinson's disease. This article discusses some of the cellular and brain circuit pathways relevant to Parkinson's disease that would be clinically amenable to gene therapy. Approaches could be classified according to two main categories, i.e. symptomatic vs. neuroprotective/neurorestorative strategies. Examples of the different possibilities currently in development are given and feature both dopaminergic and non-dopaminergic symptomatic treatments of parkinsonian symptoms and/or L-DOPA-induced side effects, anti-apoptotic neuroprotective strategies and growth-factor delivery for neuroprotection/neurorestoration. While gene therapy has been mostly used so far for enhancing the expression of the target gene, the use of dominant negative or siRNA opens new possibilities. This, combined with the key feature of gene delivery that offers access to intracellular signalling pathways, is likely to further expand the number of proposed targets to be studied.

THE DOPAMINERGIC NIGROSTRIATAL SYSTEMAND PARKINSON'S DISEASE

For several decades, the clinical study of Parkinson's disease has driven an increasingly sophisticated understanding of the dopaminergic system and its complex role in modulating motor behavior. This article reviews salient areas of research in this field, commencing with the molecular biology of the development of the mesencephalic dopaminergic system. We then discuss events thought to be crucial in the cellular and molecular pathology of Parkinson's disease, proposed mechanisms of cell death, and relevant toxin models. These advancements are used as a template to review emerging therapeutic techniques, including neuroprotection strategies, surgical treatment of trophic factors, gene therapy, and neural transplantation.

Improvements in motor behavioral tests during deep brain stimulation of the subthalamic nucleus in rats with different degrees of unilateral parkinsonism

Deep brain stimulation (DBS) improves motor performance in Parkinson's disease (PD) patients. To evaluate the effects of subthalamic nucleus (STN)-DBS on impaired motor behavior, we studied improvements in motor performance after delivery of unilateral stimulation to the STN in rats with mild and severe lesions of the nigrostriatal dopamine system caused by injecting 6-hydroxydopamine into the striatum. The rats were trained and performed motor behavioral tests including rotational behavior test, stepping test, and rotarod test before and after receiving DBS. We demonstrated that stimulation at a current strength of 200 microA, which stopped most of the D-amphetamine-induced rotational behaviors in these two groups, improved movement impairments in both the mild and severe groups and that the improvements in the mild group were significantly better than those in the severe group. More experimental and clinical studies are needed to evaluate the efficiency of STN-DBS for different stages of PD.

The stepping test and its learning process in different degrees of unilateral striatal lesions by 6-hydroxydopamine in rats

Four different levels of the nigrostriatal dopamine system lesions were produced by injections of 6-hydroxydopamine at one-, two-, three-, or four-sites in the striatum and drug-induced rotational movement and stepping test were performed to evaluate behavioral impairments in the rat model of Parkinson's disease. A dose-dependent progressive loss of tyrosine hydroxylase-positive cells in the substance nigra pars compacta was observed in rats with striatal lesion from one- to four-sites. Though the differences in the rotational behavior and stepping test between the lesioned and control rats were highly significant, there were no differences in those behaviors among four groups of lesioned rats. During observation of these behavioral tests, the authors found that the times of trials required for acquisition of the stepping test on the first day of training, which reflected learning acuity, increased in a dose-dependent manner in the lesioned rats as compared with the controls. On the contrary, the times of trials on the next day and in the next week, which reflected retention of the acquired memories, were not different among the groups. In conclusion, the rotational movement and stepping test were not sensitive enough to distinguish severity of the striatal lesions, and learning acuity, but not retention of memories, was disturbed by the striatal lesions.

Delivery of sonic hedgehog or glial derived neurotrophic factor to dopamine-rich grafts in a rat model of Parkinson's disease using adenoviral vectors Increased yield of dopamine cells is dependent on embryonic donor age

The poor survival of dopamine grafts in Parkinson's disease is one of the main obstacles to the widespread application of this therapy. One hypothesis is that implanted neurons, once removed from the embryonic environment, lack the differentiation factors needed to develop the dopaminergic phenotype. In an effort to improve the numbers of dopamine neurons surviving in the grafts, we have investigated the potential of adenoviral vectors to deliver the differentiation factor sonic hedgehog or the glial cell line-derived neurotrophic factor GDNF to dopamine-rich grafts in a rat model of Parkinson's disease. Adenoviral vectors containing sonic hedgehog, GDNF, or the marker gene LacZ were injected into the dopamine depleted striatum of hemiparkinsonian rats. Two weeks later, ventral mesencephalic cell suspensions were prepared from embryos of donor ages E12, E13, E14 or E15 and implanted into the vector-transduced striatum. Pre-treatment with the sonic hedgehog vector produced a three-fold increase in the numbers of tyrosine hydroxylase-positive (presumed dopaminergic) cells in grafts derived from E12 donors, but had no effect on E13-E15 grafts. By contrast, pre-treatment with the GDNF vector increased yields of dopamine cells in grafts derived from E14 and E15 donors but had no effect on grafts from younger donors. The results indicate that provision of both trophic and differentiation factors can enhance the yields of dopamine neurons in ventral mesencephalic grafts, but that the two factors differ in the age and stage of embryonic development at which they have maximal effects.

Effect of AdGDNF on dopaminergic neurotransmission in the striatum of 6-OHDA-treated rats

We have previously observed that the delivery of an adenoviral vector encoding for glial cell line-derived neurotrophic factor (AdGDNF) into the substantia nigra (SN) 7 days after intrastriatal administration of 6-hydroxydopamine (6-OHDA) protects dopamine (DA)-dependent behaviors, tyrosine hydroxylase immunoreactive (TH+) cells in SN, and amphetamine-induced c-fos induction in striatum. In the present study, we sought to determine if the behavioral protection observed in 6-OHDA-treated rats receiving AdGDNF was associated with an increase in DA availability in the striatum as measured by microdialysis. Rats received intrastriatal 6-OHDA (16 microg/2.8 microl) or vehicle followed 7 days later by intranigral AdGDNF (3.2x10(7) pfu/2 microl), AdLacZ (3.2 x 10(7) pfu/2 microl), or phosphate buffered saline (PBS). Three weeks later, microdialysis samples were collected from the same striatal region under basal conditions, following KCl (100 mM) or amphetamine (250 microM) administered via the striatal microdialysis probe, or amphetamine administered systemically (6.8 mg/kg i.p). Animals given 6-OHDA followed by either PBS or AdLacZ showed a decrease in basal extracellular striatal DA levels to 24% of control. In contrast, basal extracellular DA in 6-OHDA-lesioned rats with a nigral injection of AdGDNF was almost 3-fold higher than 6-OHDA-vehicle treated animals, 65% of control DA levels. Moreover, although KCl and amphetamine produced no increase in striatal DA release in 6-OHDA-treated rats that subsequently were given either PBS or AdLacZ, these manipulations increased DA levels significantly in 6-OHDA-treated rats later given AdGDNF. Thus, DA neurotransmission within the striatum of 6-OHDA treated rats appears to be enhanced by increased expression of GDNF in the nigra.

Delayed gene therapy of glial cell line-derived neurotrophic factor is efficacious in a rat model of Parkinson's disease

Gene transfer of glial cell line-derived neurotrophic factor (GDNF) in rodent models of Parkinson's disease (PD) has been shown to protect against neurodegeneration either prior to or immediately after neurotoxin-induced lesions; however, the nigrostriatal pathway was largely intact when gene delivery was completed in these models, which may not accurately reflect the clinical situation encountered with Parkinson's patients. In this study, replication-incompetent adenoviral vectors encoding the rat GDNF gene were administered into the striatum 4 weeks following 6-hydroxydopamine (6-OHDA) injection in the unilateral striatum, more closely resembling fully developed PD. Apomorphine-induced rotational behavior testing was performed every week following 6-OHDA injection. At the 10th week after gene transfer, the striatal dopamine concentrations were measured by HPLC with an electrochemical detector and the number of tyrosine hydroxylase (TH)-positive dopamine neurons in the substantia nigra (SN) was determined by immunohistochemistry. Injection of 6-OHDA into the striatum produced stable increases in rotation, which reached a plateau between 4 and 5 weeks post-injection. The number of TH-positive neuron in the SN and dopamine levels in the striatum was significantly lower in the 6-OHDA group compared to the normal group. Gene transfer of GDNF, but not beta-galactosidase, significantly increased the number of TH-positive neurons and dopamine levels, with a subsequent behavioral recovery between 5 and 10 weeks following GDNF transduction. These findings demonstrate that adenovirus-mediated gene transfer of GDNF is efficacious even in the late stages of 6-OHDA-induced PD rats. They also provide further evidence on the effectiveness of GDNF-based gene therapy for experimental Parkinson's disease.

Gene therapy in Parkinson?s disease

Gene therapy in Parkinson's disease appears to be at the brink of the clinical study phase. Future gene therapy protocols will be based on a substantial amount of preclinical data regarding the use of ex vivo and in vivo genetic modifications with the help of viral or non-viral vectors. To date, the supplementation of neurotrophic factors and substitution for the dopaminergic deficit have formed the focus of trials to achieve relief in animal models of Parkinson's disease. Newer approaches include attempts to influence detrimental cell signalling pathways and to inhibit overactive basal ganglia structures. Nevertheless, current models of Parkinson's disease do not mirror all aspects of the human disease, and important issues with respect to long-term protein expression, choice of target structures and transgenes and safety remain to be solved. Here, we thoroughly review available animal data of gene transfer in models of Parkinson's disease.

Metabolic engineering: advances in modeling and intervention in health and disease

The field of metabolic engineering encompasses a powerful set of tools that can be divided into (a) methods to model complex metabolic pathways and (b) techniques to manipulate these pathways for a desired metabolic outcome. These tools have recently seen increased utility in the medical arena, and this paper aims to review significant accomplishments made using these approaches. The modeling of metabolic pathways has been applied to better understand disease-state physiology in a variety of cellar, subcellular, and organ systems, including the liver, heart, mitochondria, and cancerous cells. Metabolic pathway engineering has been used to generate cells with novel biochemical functions for therapeutic use, and specific examples are provided in the areas of glycosylation engineering and dopamine-replacement therapy. In order to document the potential of applying both metabolic modeling and pathway manipulation, we describe pertinent advances in the field of diabetes research. Undoubtedly, as the field of metabolic engineering matures and is applied to a wider array of problems, new advances and therapeutic strategies will follow.

Future and current surgical therapies in Parkinson's disease

PURPOSE OF REVIEW

The mainstay of treatment for Parkinson's disease remains medical therapy. With improved surgical precision and decreased morbidity, stereotactic lesioning and deep brain stimulation have become more popular. New therapies currently in clinical trials include gene therapy and direct drug delivery to the brain. The present review discusses surgical therapies for the treatment of Parkinson's disease and the status of experimental strategies currently in preclinical and clinical testing.

RECENT FINDINGS

Both stereotactic ablation and deep brain stimulation of the thalamus, globus pallidus interna, and subthalamic nucleus are discussed and compared in the current literature. New therapies such as drug infusions into the brain, gene therapy, and neural transplantation are in clinical trials and have been tested extensively in animals. Safety and efficacy of such therapies are discussed in recent literature.

SUMMARY

Although medication remains the first and main line of treatment and the mainstay for Parkinson's disease, advances in techniques and safety of operations have made surgical interventions more popular. Thalamic surgery remains helpful only in a limited subset of patients with predominent tremor that is unresponsive to medication. Bilateral subthalamic nucleus DBS holds the most promising results for patients with tremor, severe motor fluctuations and dyskinesias from L-dopa, with the best improvements seen in daily activities and quality of life. Newer therapies currently in clinical trial include gene therapy to replace lost gamma-aminobutyric acid inputs to the subthalamic nucleus and globus pallidus interna/substantia nigra pars reticulata, and infusion of recombinant glial derived neurotrophic factor to support at-risk nigrostriatal neurons. Further developments in these areas, along with evolution in stem cell science that hopefully will permit replacement of lost neurons, may alter the nature of surgical practice in Parkinson's disease patients in the not too distant future.