Animal models of parkinsonism

Gray Matter Atrophy in a 6-OHDA-induced Model of Parkinson's Disease

INTRODUCTION

Magnetic resonance imaging (MRI) based brain morphometric changes in unilateral 6-hydroxydopamine (6-OHDA) induced Parkinson's disease (PD) model can be elucidated using voxel-based morphometry (VBM), study of alterations in gray matter volume and Machine Learning (ML) based analyses.

METHODS

We investigated gray matter atrophy in 6-OHDA induced PD model as compared to sham control using statistical and ML based analysis. VBM and atlas-based volumetric analysis was carried out at regional level. Support vector machine (SVM)-based algorithms wherein features (volume) extracted from (a) each of the 150 brain regions (b) statistically significant features (only) and (c) volumes of each cluster identified after application of VBM (VBM_Vol) were used for training the decision model. The lesion of the 6-OHDA model was validated by estimating the net contralateral rotational behaviour by the injection of apomorphine drug and motor impairment was assessed by rotarod and open field test.

RESULTS AND DISCUSSION

In PD, gray matter volume (GMV) atrophy was noted in bilateral cortical and subcortical brain regions, especially in the internal capsule, substantia nigra, midbrain, primary motor cortex and basal ganglia-thalamocortical circuits in comparison with sham control. Behavioural results revealed an impairment in motor performance. SVM analysis showed 100% classification accuracy, sensitivity and specificity at both 3 and 7 weeks using VBM_Vol.

CONCLUSION

Unilateral 6-OHDA induced GMV changes in both hemispheres at 7th week may be associated with progression of the disease in the PD model. SVM based approaches provide an increased classification accuracy to elucidate GMV atrophy.

Reserpine-induced rat model for depression: Behavioral, physiological and PET-based dopamine receptor availability validation

BACKGROUND

Reserpine (RES), a Vesicular Monoamine Transporter 2 (VMAT2) inhibitor agent, has been used in preclinical research for many years to create animal models for depression and to test experimental antidepressant strategies. Nevertheless, evidence of the potential use and validity of RES as a chronic pharmacological model for depression is lacking, and there are no comprehensive studies of the behavioral effects in conjunction with molecular outcomes.

METHODS

Experiment 1. Following baseline behavior testing sensitive to depression-like phenotype and locomotion (Phase 1), 27 Sprague-Dawley (SD) rats received i.p. either vehicle solution (0.0 mg/kg), low (0.2 mg/kg) or high (0.8 mg/kg) RES dose for 20 days using a pre-determined schedule and reassessed for behavioral phenotypes (Phase 2). After 10 days washout period, and a final behavioral assessment (Phase 3), the brains were collected 16 days after the last injection for mRNA-expression assessment. Experiment 2. In a similar timetable as in Experiment 1 but without the behavioral testing, 12 SD rats underwent repetitive dopamine D2/3 receptor PET scanning with [18F]DMFP following each Phase. The binding potential (BPND) of [18F]DMFP was quantified by kinetic analysis as a marker of striatal D2/3R availability. Weight and welfare were monitored throughout the study.

RESULTS

Significant, dose-dependent weight loss and behavioral deficits including both motor (hypo-locomotion) and non-motor behavior (anhedonia, mild anxiety and reduced exploration) were found for both the low and high dose groups with significant decrease in D2R mRNA expression in the accumbal region for the low RES group after Phase 3. Both RES treated groups showed substantial increase in [18F]DMFP BPND (in line with dopamine depletion) during Phase 2 and 3 compared to baseline and Controls.

CONCLUSIONS

The longitudinal design of the study demonstrated that chronic RES administration induced striatal dopamine depletion that persisted even after the wash-out period. However, the behavior phenotype observed were transient. The data suggest that RES administration can induce a rodent model for depression with mild face validity.

Evidence of Neuroplastic Changes after Transcranial Magnetic, Electric, and Deep Brain Stimulation

Electric and magnetic stimulation of the human brain can be used to excite or inhibit neurons. Numerous methods have been designed over the years for this purpose with various advantages and disadvantages that are the topic of this review. Deep brain stimulation (DBS) is the most direct and focal application of electric impulses to brain tissue. Electrodes are placed in the brain in order to modulate neural activity and to correct parameters of pathological oscillation in brain circuits such as their amplitude or frequency. Transcranial magnetic stimulation (TMS) is a non-invasive alternative with the stimulator generating a magnetic field in a coil over the scalp that induces an electric field in the brain which, in turn, interacts with ongoing brain activity. Depending upon stimulation parameters, excitation and inhibition can be achieved. Transcranial electric stimulation (tES) applies electric fields to the scalp that spread along the skull in order to reach the brain, thus, limiting current strength to avoid skin sensations and cranial muscle pain. Therefore, tES can only modulate brain activity and is considered subthreshold, i.e., it does not directly elicit neuronal action potentials. In this review, we collect hints for neuroplastic changes such as modulation of behavior, the electric activity of the brain, or the evolution of clinical signs and symptoms in response to stimulation. Possible mechanisms are discussed, and future paradigms are suggested.

Beneficial Effects of Citrus-Derived Polymethoxylated Flavones for Central Nervous System Disorders

The number of patients with central nervous system disorders is increasing. Despite diligent laboratory and clinical research over the past 30 years, most pharmacologic options for the prevention and long-term treatment of central nervous system disorders and neurodegenerative disorders have been unsuccessful. Therefore, the development of drugs and/or functional foods to prevent the onset of neurodegenerative disorders is highly expected. Several reports have shown that polymethoxylated flavones (PMFs) derived from citrus fruit, such as nobiletin, tangeretin, and 3,3',4',5,6,7,8-heptamethoxyflavone, are promising molecules for the prevention of neurodegenerative and neurological disorders. In various animal models, PMFs have been shown to have a neuroprotective effect and improve cognitive dysfunction with regard to neurological disorders by exerting favorable effects against their pathological features, including oxidative stress, neuroinflammation, neurodegeneration, and synaptic dysfunction as well as its related mechanisms. In this review, we describe the profitable and ameliorating effects of citrus-derived PMFs on cognitive impairment and neural dysfunction in various rat and murine models or in several models of central nervous system disorders and identify their mechanisms of action.

Generation of Pluripotent Stem Cells Using Somatic Cell Nuclear Transfer and Induced Pluripotent Somatic Cells from African Green Monkeys

Patient-specific stem cells derived from somatic cell nuclear transfer (SCNT) embryos or from induced pluripotent stem cells (iPSCs) could be used to treat various diseases with minimal immune rejection. Many studies using these cells have been conducted in rats and mice; however, there exist numerous dissimilarities between the rodents and humans limiting the clinical predictive power and experimental utility of rodent experiments alone. Nonhuman primates (NHPs) share greater homology to human than rodents in all respects, including genomics, physiology, biochemistry, and the immune system. Thus, experimental data obtained from monkey studies would be more predictive for designing an effective cell replacement therapy in humans. Unfortunately, there are few iPSC lines and even fewer SCNT lines that have been derived in NHPs, hampering broader studies in regenerative medicine. One promising potential therapy would be the replacement of dopamine neurons that are lost in Parkinson's disease. After dopamine depletion by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), the African green monkey (Chlorocebus sabaeus) shows the most complete model of Parkinsonism compared with other species and brain pathology and behavioral changes are almost identical to those in humans after accidental exposure to MPTP. Therefore, we have developed a SCNT procedure to generate multiple pluripotent stem cell lines in this species for studies of possible treatment of Parkinsonism and for comparing with cells derived from iPSCs. Using 24 female monkeys as egg donors and 7 somatic cell donor monkeys, we have derived 11 SCNT embryonic stem cell lines that expressed typical stemness genes and formed all three germ layer derivatives. We also derived two iPSC lines using an episome-mediated reprogramming factor delivery system. This report describes the process for deriving these cell lines and proving their pluripotency for differentiation into various potentially therapeutic cells.

Effects of Heating-needle Stimulation in Restoration of Weakened Descending Inhibition of Nociception in a Rat Model of Parkinson's Disease

Here we investigated variations of endogenous descending modulation of nociception and therapeutic effects of intramuscular (i.m.) heating-needle stimulation in early stage of Parkinson's disease (PD) induced by unilateral microinjection of 3.5 μl of 2.5 μg/μl 6-hydroxydopamine into the rat striatum. Paw withdrawal reflexes to noxious mechanical and heat stimuli in PD rats with and without exposure to i.m. 5.8% saline induced muscle nociception were evaluated. Experimental PD had no influence on mechanical or heat sensitivity in the baseline condition, whereas descending facilitation was stronger and descending inhibition was weaker in PD rats than vehicle-treated or naive rats during muscle nociception (P < 0.05). Striatal administration of 5 μg of dopamine failed to reverse the PD-associated changes in descending facilitation or inhibition, whereas dopamine in the thalamic mediodorsal (MD) nucleus and ventromedial (VM) nucleus significantly decreased the increase in descending facilitation and reversed the attenuation in descending inhibition, respectively (P < 0.05). I.m. 43 °C of heating-needle stimulation had no effects on the enhanced descending facilitation in PD rats, but it markedly increased descending inhibition and reversed the increase in the number of apomorphine-induced body rotations (P < 0.05), which effects were dose-dependently attenuated by raclopride, a dopamine 2 receptor antagonist, in the thalamic VM nucleus (P < 0.05). The results indicate that the early-stage PD is associated with enhanced descending facilitation and weakened descending inhibition. From clinical perspective, 43 °C heat therapeutic regime promises to selectively enhance descending inhibition that is accompanied by improvement of motor dysfunction in PD.

Validation of a New Scoring Scale for Behavioral Assessment of L-Dopa-Induced Dyskinesia in the Rat: A New Tool for Early Decision-Making in Drug Development

The 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated nonhuman primate (NHP) has been described as the most translatable model for experimental reproduction of L-dopa-induced dyskinesia (LID). However, from a drug discovery perspective, the risk associated with investment in this type of model is high due to the time and cost. The 6-hydroxydopamine (6-OHDA) rat dyskinesia model is recommended for testing compounds but relies on onerous, and nonstandard behavioral rating scales. We sought to develop a simplified and sensitive method aiming at assessing LID in the rat. The purpose was to validate a reliable tool providing earlier insight into the antidyskinetic potential of compounds in a time/cost-effective manner before further investigation in NHP models. Unilaterally 6-OHDA-lesioned rats were administered L-dopa (20 mg/kg) and benserazide (5 mg/kg) daily for 3 weeks starting 4 weeks postlesion, then coadministered with amantadine (20-30-40 mg/kg). An adapted rating scale was used to score LID frequency and a severity coefficient was applied depending on the features of the observed behavior. A gradual increase (about 3-fold) in LID score was observed over the 3 weeks of L-dopa treatment. The rating scale was sensitive enough to highlight a dose-dependent amantadine-mediated decrease (about 2.2-fold) in LID score. We validated a simplified method, able to reflect different levels of severity in the assessment of LID and, thus, provide a reliable tool for drug discovery.

Optogenetic approaches to evaluate striatal function in animal models of Parkinson disease

Optogenetics refers to the ability to control cells that have been genetically modified to express light-sensitive ion channels. The introduction of optogenetic approaches has facilitated the dissection of neural circuits. Optogenetics allows for the precise stimulation and inhibition of specific sets of neurons and their projections with fine temporal specificity. These techniques are ideally suited to investigating neural circuitry underlying motor and cognitive dysfunction in animal models of human disease. Here, we focus on how optogenetics has been used over the last decade to probe striatal circuits that are involved in Parkinson disease, a neurodegenerative condition involving motor and cognitive abnormalities resulting from degeneration of midbrain dopaminergic neurons. The precise mechanisms underlying the striatal contribution to both cognitive and motor dysfunction in Parkinson disease are unknown. Although optogenetic approaches are somewhat removed from clinical use, insight from these studies can help identify novel therapeutic targets and may inspire new treatments for Parkinson disease. Elucidating how neuronal and behavioral functions are influenced and potentially rescued by optogenetic manipulation in animal models could prove to be translatable to humans. These insights can be used to guide future brain-stimulation approaches for motor and cognitive abnormalities in Parkinson disease and other neuropsychiatric diseases.

Behavioral pharmacology of pain

Behavioral methods are extensively used in pain research. Rodent modeling tends to rely on evoked responses but there is a growing interest in behavioral readouts that may capture elements of ongoing pain and disability, reflecting the major clinical signs and symptoms. Clinically, analgesics show greater efficacy in acute pain after standard surgery than in chronic conditions but are never completely effective on a population basis. In contrast, experimental pharmacological studies in rodents often demonstrate full efficacy, but there is variability in sensitivity between models and readouts. Full efficacy is rarely seen when more complex or multiple readouts are used to quantify behavior, especially after acute surgery or in studies of clinical pain in animals. Models with excellent sensitivity for a particular drug class exist and are suitable for screening mechanistically similar drugs. However, if used to compare drugs with different modes of action or to predict magnitude of clinical efficacy, these models will be misleading. Effective use of behavioral pharmacology in pain research is thus dependent on selection and validation of the best models for the purpose.

Neuroprotective activity of Stereospermum suaveolens DC against 6-OHDA induced Parkinson's disease model

OBJECTIVES

To evaluate the neuroprotective effect of Stereospermum suaveolens DC on 6-hydroxy dopamine induced Parkinson's disease model.

MATERIALS AND METHODS

The study was conducted on Sprague-Dawley rats where parkinson's disease was induced by producing the striatal 6-hydroxy dopamine lesions. The test animals received methanolic extract of Stereospermum suaveolens at dose of 125, 250 and 500 mg/kg for 42 days. Behavioral assessment, spontaneous locomotor activity and muscular coordination were studied. Antioxidant levels, striatal infraction area were assessed and histopathological studies were carried out.

RESULTS

The Stereospermum suaveolens DC methanolic extract showed significant dose dependent increase in behavioral activity, improved muscular coordination. Significant reduction of lipid peroxidation (LPO), increased antioxidant enzymes like superoxide dismutase (SOD), catalase (CAT) and non-enzymatic activity of glutathione (GSH) and total thiol levels in extract treated groups was observed in test groups as compared to control group. Striatal infarction area was significantly reduced in extract treated groups as compared to control group.

CONCLUSION

The methanolic extract of Stereospermum suaveolens DC showed neuroprotective activity against 6-hydroxy dopamine induced Parkinson's disease in rats.

Nonhuman primates as animal models for toxicology research

There is a long history for the use of nonhuman primates in toxicological research. This unit reviews applications in reproductive toxicology and teratology, neural toxicology and neurobehavioral toxicology, immunotoxicology, respiratory (lung) toxicology, and chemical carcinogenesis.

Aged monkeys as a partial model for Parkinson's disease

Parkinson's Disease (PD) and the natural aging process share a number of biochemical mechanisms, including reduced function of dopaminergic systems. The present study aims to determine the extent that motor and behavioral changes in aged monkeys resemble parkinsonism induced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The behavioral and physiological changes in PD are believed to result largely from selective depletion of dopamine in the nigrostriatal system. In the present study, ten aged female monkeys were compared with three groups: 9 untreated young adult female monkeys, 10 young adult male monkeys and 13 older male monkeys that had been exposed to MPTP. Trained observers, blind as to age and drug condition and without knowledge of the hypotheses, scored the monkeys using the Parkinson's factor score (Parkscore), which has been validated by a high correlation with post mortem striatal dopamine (DA) concentrations. The aged animals had higher scores on the Parkscore compared with the young adults, with most of its component behavioral items showing significance (tremor, Eating Problems, Delayed initiation of movement, and Poverty of Movement). L-Dopa and DA-agonists did not clearly reverse the principal measure of parkinsonism. DA concentrations post mortem were 63% lower in 3 aged monkeys in the ventral putamen compared with 4 young adults, with greater reductions in putamen than in caudate (45%). We conclude that aged monkeys, unexposed to MPTP, show a similar profile of parkinsonism to that seen after the neurotoxin exposure to MPTP in young adult monkeys. The pattern of greater DA depletion in putamen than in caudate in aged monkeys is the same as in human Parkinson's disease and contrasts with the greater depletion in caudate seen after MPTP. Aged monkeys of this species reflect many facets of Parkinson's disease, but like older humans do not improve with standard dopamine replacement pharmacotherapies.

The timing of administration, dose dependence and efficacy of dopa decarboxylase inhibitors on the reversal of motor disability produced by L-DOPA in the MPTP-treated common marmoset

Dopa decarboxylase inhibitors are routinely used to potentiate the effects of L-DOPA in the treatment of Parkinson's disease. However, neither in clinical use nor in experimental models of Parkinson's disease have the timing and dose of dopa decarboxylase inhibitors been thoroughly explored. We now report on the choice of dopa decarboxylase inhibitors, dose and the time of dosing relationships of carbidopa, benserazide and L-alpha-methyl dopa (L-AMD) in potentiating the effects of L-DOPA in the 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP)-treated common marmoset. Pre-treatment with benserazide for up to 3h did not alter the motor response to L-DOPA compared to simultaneous administration with L-DOPA. There was some evidence of a relationship between carbidopa and benserazide dose and increased locomotor activity and the reversal of motor disability. But in general, commonly used dose levels of dopa decarboxylase inhibitors appeared to produce a maximal motor response to L-DOPA. In contrast, dyskinesia intensity and duration continued to increase with both carbidopa and benserazide dose. The novel dopa decarboxylase inhibitor, L-AMD, increased locomotor activity and improved motor disability to the same extent as carbidopa or benserazide but importantly this was accompanied by significantly less dyskinesia. This study shows that currently, dopa decarboxylase inhibitors may be routinely employed in the MPTP-treated primate at doses which are higher than those necessary to produce a maximal potentiation of the anti-parkinsonian effect of L-DOPA. This may lead to excessive expression of dyskinesia in this model of Parkinson's disease and attention should be given to the dose regimens currently employed.

The application of Russell and Burch 3R principle in rodent models of neurodegenerative disease: the case of Parkinson's disease

Currently, the accepted ethical standards for the regulation of animal experimentation are provided by the 3R principle (Replacement, Reduction and Refinement). The development of alternative methods to the use of animals (Replacement), the design of adequate experimental protocols to reduce the number of animals (Reduction), the application of refinement practices (Refinement) are all aspects to be considered to ensure ethical and scientific validity to animal experimentation. This review intends to address these issues, using experimental research on Parkinson's disease (PD) as a paradigmatic example of the use of animal models to improve knowledge on a devastating human pathology. In particular, current rodent models of PD and their validity are reviewed and discussed, and methodologies that may ultimately reduce animal's suffering emphasized. Although procedures referring to with 3R principle can be traced in the literature reviewed, they are not considered yet an important part of the methodological information. The formal inclusion in scientific papers of a section devoted to 3Rs may increase knowledge and eventually adherence to this principle by scientists.

Increased host neuronal survival and motor function in BMT Parkinsonian mice: Involvement of immunosuppression

We examined the potential of bone marrow transplantation (BMT) to rescue dopaminergic neurons in a mouse model of Parkinson's disease (PD). A BMT from mice transgenic for green fluorescent protein (GFP(+)) given either before or after administration of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) led to the accumulation of transplanted adult GFP(+) bone-marrow-derived cells (BMDC) in the substantia nigra, where dopaminergic neurodegeneration occurs in PD. Post-BMT, mice exposed to MPTP had substantially greater numbers of endogenous tyrosine hydroxylase-positive neuronal cell bodies in the substantia nigra and increased dopamine transporter-positive projections into the striatum compared to controls. Moreover, motor function was restored to normal within 1 month post-MPTP in BMT-treated mice assayed by a rotarod behavioral test. The effect of BMT on PD was indirect, as no evidence of BMDC fusion with or transdifferentiation into dopaminergic neurons was observed. BMDC activated by BMT or associated factors could play a trophic role in rescuing damaged cells. Alternatively, the beneficial effects of BMT are due to immunosuppression reflected by a reduction in the proportion of T-cells and a reduction of T-cell proliferation in BMT mice. These findings highlight that when immunosuppression is required for transplantation studies, the amelioration of symptoms may not be due to the transplant itself. Further, they suggest that the immune system plays a role in the development of characteristics typical of PD.

Auditory and vestibular defects and behavioral alterations after neonatal administration of streptomycin to Lewis rats: Similarities and differences to the circling (ci2/ci2) Lewis rat mutant

The clinical usefulness of aminoglycoside antibiotics is limited by their ototoxicity. In rodents, damage to the inner ear is often associated with rotational behavior and locomotor hyperactivity reminiscent of such behaviors resulting from an imbalance of forebrain dopamine systems. Based on previous observations in the circling (ci2/ci2) Lewis (LEW) rat mutant, a spontaneous mutation leading to hair cell loss, deafness, impairment of vestibular functions, lateralized circling, hyperactivity and alterations in the nigrostriatal dopamine system, we have recently hypothesized that vestibular defects during postnatal development, independent of whether induced or inherited, lead to secondary changes in the dopaminergic system within the basal ganglia, which would be a likely explanation for the typical behavioral phenotype seen in such models. In the present study, we directly compared the phenotype induced by streptomycin in LEW rats with that of the ci2 LEW rat mutant. For this purpose, we treated neonatal LEW rats over 3 weeks by streptomycin, which induced bilateral degeneration of cochlear and vestibular hair cells. Following this treatment period, the behavioral syndrome of the streptomycin-treated animals, including the lateralized rotational behavior, was almost indistinguishable from that of ci2 mutant rats. However, in contrast to the ci2 mutant rat, all alterations, except the hearing loss, were only transient, disappearing between 7 and 24 weeks following treatment. In conclusion, in line with our hypothesis, vestibular defects induced in normal LEW rats led to the same phenotypic behavior as the inherited vestibular defect of ci2 mutant rats. However, with increasing time for recovery, adaptation to the vestibular impairment developed in streptomycin-treated rats, while all deficits persisted in the mutant animals. At least in part, the transient nature of the abnormal behaviors resulting from treatment with streptomycin could be explained by adaptation to the vestibular impairment by the use of visual cues, which is not possible in ci2 rats because of progressive retinal degeneration in these mutants. Although further experiments are needed to prove this hypothesis, the present study shows that direct comparisons between these two models serve to understand the mechanisms underlying the complex behavioral phenotype in rodents with vestibular defects and how these defects are compensated.

Sustained improvement of motor function in hemiparkinsonian rats chronically treated with low doses of caffeine or trihexyphenidyl

The effects of chronic oral treatment with low doses of caffeine (1-3 mg/kg) and trihexyphenidyl (0.1-0.2 mg/kg) were tested on hemiparkinsonian rats, which received the following treatments in a counterbalanced order: vehicle, caffeine, trihexyphenidyl, and caffeine plus trihexyphenidyl. Three preclinical models were used: the stepping test, the cylinder test, and the staircase test. Compared to pre-lesion values, the forepaw contralateral to the dopamine-denervated side showed impaired stepping, fewer wall contacts in the cylinder test, and fewer pellets retrieved in the staircase test. In the stepping test both doses of caffeine produced a complete recovery of motor function (100%), whereas the effect of trihexyphenidyl was less intense (77-80%). In this same test the maximal effect of drugs did not develop tolerance during 2-3 weeks, and was completely reversible after drug cessation. In the cylinder test only the wall contacts performed simultaneously with both forepaws were significantly increased by caffeine (3 mg/kg) and trihexyphenidyl (0.2 mg/kg), and this effect was also reversible. In the staircase test none of the treatments improved food pellet retrieval with the contralateral forepaw. Altogether, these results show that chronic treatment with caffeine, at doses similar to daily human consumption, produces a sustained improvement in the use of the contralateral forelimb in unilaterally 6-hydroxydopamine denervated rats, without the development of tolerance. Although the combined administration of caffeine plus trihexyphenidyl showed no synergism in these models, the results suggest that low doses of caffeine (1-3 mg/kg/day) could be of therapeutic value for the reversal of motor symptoms in parkinsonian patients.

Comparison of bilaterally 6-OHDA- and MPTP-lesioned rats as models of the early phase of Parkinson's disease: Histological, neurochemical, motor and memory alterations

This study compares histological, neurochemical, behavioral, motor and cognitive alterations as well as mortality of two models of Parkinson's disease in which 100 microg 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or 6 microg 6-hydroxydopamine (6-OHDA) was bilaterally infused into the central region of the substantia nigra, compact part, of adult male Wistar rats. Both neurotoxins caused a significant loss of nigral tyrosine hydroxylase-immunostained cells and striatal dopamine depletion, but 6-OHDA caused more widespread and intense cell loss, more intense body weight loss and more mortality than MPTP. Both 6-OHDA- and MPTP-lesioned rats presented similar deficits in performing a working memory and a cued version of the Morris water maze task and few exploratory/motor alterations in the open field and catalepsy tests. However, rats presented a significant and transitory increase in locomotor activity after the MPTP lesion and a hypolocomotor behavior tended to be present after the 6-OHDA lesion. The picture of mild motor effects and robust impairment of habit learning and spatial working memory observed in MPTP-lesioned rats models the early phase of Parkinson's disease.

Method of construction of a MRI-based tabular database of 3D stereotaxic co-ordinates for individual structures in the basal ganglia of Macaca mulatta

Primate models are commonly used in Parkinson's disease research to study stereotaxic strategies that demand accurate localization of the structures in basal ganglia. We demonstrate a method to construct an extensive tabular database of 3D stereotaxic co-ordinates of various basal ganglia structures from high-quality magnetic resonance (MR) images of 47 adult female 3-5 kg rhesus monkeys. For each animal, the structures in the basal ganglia were traced as they appeared on the axial MR images. Their maximal outlines were projected in the axial plane to create a stack of images and X, Y, Z co-ordinates were calculated for margins of each structure. These co-ordinates and the outlines of the individual nuclei help delineate a "common area," which was further narrowed down to a point that represents the 'most reliable target point' (MRTP) in subthalamic nucleus, globus pallidum, caudate and putamen on both sides. Common area and MRTP represent the region that can most definitely be associated with a structure and hence the most definite target for a given structure. The goal of this study is to demonstrate the method of construction, discuss the feasibility and usefulness of such a tabular database that could potentially add to accuracy of localization while using atlas-based stereotaxy. Though use of MRI remains a standard practice and advances in imaging have made targeting for functional surgery more accurate, in developing countries that implies prohibitive costs per procedure. Population based human databases similar to the monkey database described here, when used along with less expensive imaging modalities can reduce the costs considerably as well as add to the accuracy of targeting.

Neuroprotective effects of the antiparkinson drugMucuna pruriens

Mucuna pruriens possesses significantly higher antiparkinson activity compared with levodopa in the 6-hydroxydopamine (6-OHDA) lesioned rat model of Parkinson's disease. The present study evaluated the neurorestorative effect of Mucuna pruriens cotyledon powder on the nigrostriatal tract of 6-OHDA lesioned rats. Mucuna pruriens cotyledon powder significantly increased the brain mitochondrial complex-I activity but did not affect the total monoamine oxidase activity (in vitro). Unlike synthetic levodopa treatment, Mucuna pruriens cotyledon powder treatment significantly restored the endogenous levodopa, dopamine, norepinephrine and serotonin content in the substantia nigra. Nicotine adenine dinucleotide (NADH) and coenzyme Q-10, that are shown to have a therapeutic benefit in Parkinson's disease, were present in the Mucuna pruriens cotyledon powder. Earlier studies showed that Mucuna pruriens treatment controls the symptoms of Parkinson's disease. This additional finding of a neurorestorative benefit by Mucuna pruriens cotyledon powder on the degenerating dopaminergic neurons in the substantia nigra may be due to increased complex-I activity and the presence of NADH and coenzyme Q-10.

Antiparkinsonian activity of Ro 25-6981, a NR2B subunit specific NMDA receptor antagonist, in animal models of Parkinson's disease

N-methyl-D-aspartate (NMDA) receptor antagonists have antiakinetic and antidyskinetic effects in animals models of Parkinson's disease (PD). However, non-selective inhibition of NMDA receptors throughout the central nervous system may result in undesired effects such as ataxia and psychosis. We therefore studied Ro 25-6981, an activity-dependent antagonist of NMDA receptors containing the NR2B subunit which are predominantly expressed in the striatum. Ro 25-6981 induced contraversive rotations in 6-hydroxydopamine (6-OHDA)-lesioned rats without stimulating locomotion in normal rats and reversed parkinsonian symptoms in 1-methyl-4-phenyl-1,2,3,6,-tetrahydropyridine (MPTP)-treated common marmosets. Due to the small number of marmosets, there were no significant differences between Ro 25-6981 and vehicle though there was a significant trend toward differences, as shown by the Page test. Furthermore, Ro 25-6981 potentiated the action of levodopa in both species and attenuated the maximal levodopa response in 6-OHDA-lesioned rats chronically treated with levodopa without reducing the overall response. Ro 25-6981 also potentiated the action of the dopamine receptor agonists apomorphine, A68930 and quinpirole in 6-OHDA-lesioned rats. The present observations suggest a therapeutic potential of NR2B-selective NMDA receptor antagonists in the management of PD.

Neurobehavioral assessment in the information age

The elucidation of the human and mouse genomes provides new opportunities for exploring the genetic underpinnings of complex mammalian behaviors. This information also provides new windows into the pathophysiology and treatment of neuropsychiatric diseases. Optimal use of the rapidly escalating numbers of mouse lines engineered for these purposes is hindered, however, by practical and theoretical limitations of common behavioral analyses. New strategies combining automated behavioral monitoring and information technologies are currently under development in both academic and industrial settings. These hold promise, both for improving the throughput of mouse behavioral assessment and for providing new insights into the neurobiology of mammalian behavioral regulation.

Effects of electrolytic and 6-hydroxydopamine lesions of rat nigrostriatal pathway on nitric oxide synthase and nicotinamide adenine dinucleotide phosphate diaphorase

The aim of the present study was to assess degenerative changes in the nitric oxide (NO) system of basal ganglia in animals with experimentally induced Parkinson's disease. In one procedure, rats were stereotaxically injected with 6-hydroxydopamine (6-OHDA) in the right medial forebrain bundle; in a second procedure, electrodes were implanted in the right substantia nigra pars compacta (SNc). After 15 and 30 days animals were tested for rotational asymmetry induced by apomorphine. Apomorphine induced rotation in lesioned animals, towards the ipsilateral side after electrolytic lesion and towards contralateral side in 6-OHDA animals. Structural deficits in basal ganglia were quantified by nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and by nitric oxide synthase (NOS) immunoreactivity. 6-OHDA and electrolytic lesions induced a significant decrease in the number of NADPH-d/NOS positive cells in the lesion ipsilateral to SNc, in contrast with cell number increase in the ipsilateral dorsal striatum. By contrast, 6-OHDA-treated animals showed a decrease in the number of NOS immunoreactive cells in the contralateral nucleus accumbens. We conclude that populations of NO-synthesizing neurons are differentially regulated in Parkinson's disease induced by different experimental procedures.

Degeneration of the nigrostriatal pathway and induction of motor deficit by tetrahydrobiopterin: an in vivo model relevant to Parkinson's disease

We determined whether the preferential toxicity of tetrahydrobiopterin (BH4) on dopamine-producing cells, which we have previously observed in vitro, might also occur in vivo and generate characteristics associated with Parkinson's disease. Intrastriatal BH4 injection caused a loss of tyrosine hydroxylase immunoreactivity and decreased dopamine content. The dopaminergic cell bodies topologically corresponding to the lesioned terminals were selectively degenerated. This was accompanied by a dose-dependent and asymmetric movement deficit in the contralateral forepaw. Direct injection of BH4 into the substantia nigra caused a loss of tyrosine hydroxylase immunoreactivity, but injection into the dorsal raphe was without effect on the GTP cyclohydrolase-immunoreactive serotonergic neurons, demonstrating selectivity for the dopaminergic system. BH4 exhibited a range of potency comparable to that of 6-hydroxydopamine. Thus, this animal model generated by the administration of BH4, the molecule endogenously present in the monoaminergic neurons, exhibited morphological, biochemical, and behavioral characteristics associated with Parkinson's disease and may be useful for studies in dopaminergic degeneration.

Asymmetrical development of the monoamine systems in 2,4-dichlorophenoxyacetic acid treated rats

The purpose of this study was to determine whether the regional brain biogenic amine levels in adult rats were altered by pre- and post-natal exposure to 2,4-dichlorophenoxyacetic acid (2,4-D). Pregnant rats were daily orally exposed to 70 mg/kg per day of 2,4-D from gestation day (GD) 16 to post-partum day (PPD) 23. After weaning, the pups were assigned to one of two subgroups: T1 fed with untreated diet up to post-natal day (PND) 90 and T2 (maintained with 2,4-D diet up to PND 90). In addition, we wanted to know the effect of 2,4-D on lateralization in the monoamine systems of the basal ganglia of these adult rats and whether there was any correlation with the behavioral developmental pattern previously reported by us. In this study the content of noradrenaline (NA) was significantly increased in substantia nigra (SN) while it decreased in cerebellum in male and female rats of T2 group. The decreased dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovallinic acid (HVA) contents in cerebellum, midbrain, ventral tegmental area (VTA) and prefrontal cortex (PFc) showed an alteration in the mesocorticolimbic system. However, an increase of DA in SN and of DOPAC and HVA in nucleus accumbens (NAc) in both sexes and of DA and DOPAC (only in females) in striatum was detected. The contents of serotonin (5-hydroxytryptamine, 5-HT) were significantly increased in both sexes in PFc, striatum (St), midbrain, SN and cerebellum. Variations of any monoamine levels in NAc and VTA were determined. T1 rats were irreversibly altered: a diminution in DA and/or DOPAC levels in PFc, midbrain, VTA and cerebellum was determined. Indolamines of these rats were increased in both sexes in PFc and St. There was also a large increase in 5-HT levels in midbrain of male rats. Although no changes in the dopaminergic system with respect to their control values in any side of these brain structures were observed, DA and DOPAC levels were found to be decreased in the right side with respect to the left side in striata and accumbens nuclei in T2 female rats supporting the behavioral rotation previously registered by us in these rats. In addition, the increased 5-HT content detected in both the right and left striata observed in this study could be the answer to the behaviors observed and to the early alterations in dopamine in basal ganglia by 2,4-D in neonatal exposed rats, mediated by a serotonergic modulation on the dopaminergic system.

A novel black-hooded mutant rat (ci3) with spontaneous circling behavior but normal auditory and vestibular functions

Abnormal circling behavior in rodents is usually attributed to vestibular dysfunction. In rats, all circling mutants described previously have inner ear defects resulting in auditory and vestibular dysfunctions. Here, we describe a new mutant rat with abnormal spontaneous circling behavior but normal auditory and vestibular functions. The new circling mutant rat was discovered in progeny of an apparently normal black-hooded (BH) rat inbred line [BH.7A(LEW)/Won] and was termed ci3, because we recently found two other mutant circling rats (ci1 and ci2) in a Lewis (LEW) inbred rat strain. The ci3 mutant is characterized by circling behavior and locomotor hyperactivity, which occur in phases or bursts either spontaneously or in response to stress, e.g., when rats are transferred to a new environment. Video monitoring of undisturbed rats in their home cage during the light and dark periods showed that circling behavior is much more intense during the dark period, i.e., during the active phase of the animals. Most ci3 rats show a lateral preference in their rotational behavior, i.e., they either rotate to the left or to the right. Brainstem auditory evoked potential testing and different tests of vestibular function did not disclose any auditory or marked vestibular defects in ci3 rats. Furthermore, no morphological abnormalities were seen during histological examination of the cochlear and vestibular nuclei in the brainstem. Neurochemical determination of dopamine and dopamine metabolite levels in striatum, nucleus accumbens and substantia nigra showed that ci3 rats have a significant asymmetry in striatal dopamine in that dopamine levels were significantly lower in the hemisphere contralateral to the preferred direction of turning. Consistent with this finding, immunohistological examination of dopaminergic neurons in substantia nigra and ventral tegmental area yielded a significant laterality in the medial part of substantia nigra pars compacta with a lower density of tyrosine hydroxylase-positive neurons in the contralateral hemisphere of mutant circling rats, while no laterality was seen in unaffected rats of the background strain [BH.7A(LEW)/Won].Thus, the novel mutant ci3 rat exhibits several features which clearly differ from previously described circling rat or mouse mutants. The behavioral phenotype occurs in the absence of auditory or obvious vestibular defects and is most likely a consequence of lateralized abnormalities found in the nigrostriatal circuit. Apart from the use of ci3 rats for studying the functional lateralization of brain functions, the ci3 mutant may serve as a new model for movement disorders with abnormal lateralization.

Novel observations with FDOPA-PET imaging after early nigrostriatal damage

Striatal 6-[18F]fluoro-L-DOPA (FDOPA) kinetic rate constants were measured by positron emission tomography (PET) in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated squirrel monkeys. After scanning, stereological counts of dopaminergic neurons were done in substantia nigra, and dopamine (DA) and metabolite concentrations were determined in the caudate, putamen, and substantia nigra. Graded doses of MPTP produced animals with mild to moderate reductions (10-35%) in dopaminergic neurons, where the percent of cell loss was proportional to the amount of MPTP given. Striatal DA and metabolite concentrations were relatively unchanged in animals given 1.0 and 1.5 mg/kg of MPTP, but were significantly reduced after 2.0 mg/kg of MPTP. All animals injected with a single dose of MPTP showed no overt signs of parkinsonism. In contrast, DA and metabolite concentrations in the substantia nigra were significantly reduced for all MPTP-treated animals. Reduction of dopaminergic indices in the substantia nigra did not parallel reductions in the striatum, indicating differential sensitivity of the nigrostriatal pathway to the neurotoxic effects of MPTP. The percent change in FDOPA uptake (Ki) and decarboyxlation (k3) after MPTP showed significant positive correlations to striatal DA levels, but not to the number of dopaminergic neurons. This suggests that FDOPA is a good index of striatal DA levels.

Central nervous system stimulatory action from the root extract of Plumbago zeylanica in rats

The effects of a 50% ethanol extract of the root of Plumbago zeylanica (P. zeylanica) were investigated on locomotor behaviour and central dopaminergic activity in rats. The effects on the ambulatory behaviour were assessed along with the levels of dopamine (DA) and its metabolite homovanillic acid (HVA) in the striatum after a single oral dose (100, 200 and 300 mg/kg body weight) of the extract. The extract significantly increased the spontaneous motility in animals. The ambulatory and rotatory behaviour in the treated groups were higher than in the control group (p < 0.05). There were marked differences in the ambulatory behaviour between 100 and 300 mg/kg, indicating that the responses were stimulatory and dose-dependent. The stereotypic behaviour which is characteristic of a dopamine agonist showed biphasic effects. However, there was no significant difference between the groups (p > 0.05). The results showed that the extract of the root of P. zeylanica specifically enhanced the spontaneous ambulatory activity without inducing stereotypic behaviour. The neurochemical estimations revealed elevated levels of DA and HVA in striatum compared with the control rats (p < 0.01). The levels were higher for the 100 mg/kg treated group than the other groups. The levels declined by increasing the dosage of the extract to 200 mg/kg and 300 mg/kg, however, these levels remained higher than the control group. The relationship between motor activity and levels of dopamine are not parallel. These behavioural and biochemical results indicated stimulatory properties of the extract of the root of P. zeylanica, which may be mediated by dopaminergic mechanisms in the rat brain.

Temporal changes of dopaminergic and glutamatergic receptors in 6-hydroxydopamine-treated rat brain

Quantitative receptor autoradiography was used to examine the sequential patterns of changes in dopaminergic and glutamatergic receptors in the brain of rats lesioned with 6-hydroxydopamine. The animals were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks of postlesion. Degeneration of the nigrostriatal pathway caused a significant increase in dopamine D(2) receptors in the ipsilateral striatum from 1 to 8 weeks of postlesion. In the ipsilateral substantia nigra (SN), a significant decrease in dopamine D(2) receptors was also observed from 1 to 8 weeks of postlesion. On the other hand, dopamine D(1) receptors were increased in the ipsilateral ventromedial striatum from 2 to 4 weeks of postlesion. In the ipsilateral SN, a transient increase in dopamine D(1) receptors was observed only 1 week after lesioning. However, other regions in both ipsilateral and contralateral sides showed no significant change in dopamine D(1) and D(2) receptors during postlesion except for a transient change in a few regions. N-Methyl-D-aspartate (NMDA) receptors showed no significant changes in all brain regions studied during the postlesion. In contrast, a transient increase in excitatory amino acid transport sites was observed only in the frontal cortex and ventromedial striatum of the ipsilateral side at 2 weeks of postlesion. However, glycine receptors showed a significant change in any brain areas of both ipsilateral and contralateral sides after lesioning. The change in the brain areas of contralateral side was more pronounced than that of ipsilateral side for glycine receptors. In addition, dopamine uptake sites showed a severe damage in the ipsilateral striatum from 1 to 8 weeks after lesioning. In the contralateral side, in contrast, no significant change in dopamine uptake sites was found in the striatum during the postlesion. These results indicate that unilateral injection of 6-hydroxydopamine in the medial forebrain bundle can cause a significant increase in dopamine D(1) and D(2) receptors in the striatum. The increase in dopamine D(2) receptors was more pronounced than that in dopamine D(1) receptors in the striatum after 6-hydroxydopamine treatment. In contrast, dopamine uptake sites showed a severe damage in the striatum during the postlesion. Furthermore, our results support the existence of dopamine D(2) receptors on the neurons of SN, but not dopamine D(1) receptors. For glutamatergic receptor system, the present study suggests that the changes in glycine receptors may be more susceptible to degeneration of nigrostriatal pathway than NMDA receptors and excitatory amino acid transport sites. Thus, our findings are of interest in relation of degeneration of the nigrostriatal pathway that occurs in Parkinson's disease

A behavioural study of the effect of pentadecapeptide BPC 157 in Parkinson's disease models in mice and gastric lesions induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydrophyridine

The effect of a stomach pentadecapeptide, BPC 157, on Parkinson's disease in mice was investigated, along with its salutary activity on stomach lesions induced by parkinsongenic agents. Parkinsongenic agents, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30.0 mg x kg(-1)b.w. i.p. once daily for 6d, and after 4d once 50.0 mg x kg(-1)b.w. i.p.) or reserpine (5.0 mg x kg(-1)b.w. i.p.) were applied i.p. BPC 157 (1.50 microg or 15.0 ng x kg(-1)b.w. i.p.) was applied 15 min before or alternatively 15 min after each MPTP administration. In reserpine studies, BPC 157 (10.0 microg or 10.0 ng x kg(-1)b.w. i.p.) was given either 15 min before reserpine or in the already established complete catalepsy 24 h thereafter. BPC 157 strongly improved the MPTP-impaired somatosensory orientation and reduced the MPTP-induced hyperactivity, and most importantly, MPTP-motor abnormalities (tremor, akinesia, catalepsy -otherwise very prominent in saline control), leading to almost complete abolition of otherwise regularly lethal course of MPTP treatment in controls. Likewise, in reserpine experiments, BPC 157 strongly prevented the development of otherwise very prominent catalepsy and when applied 24 h thereafter reversed the established catalepsy. In addition, a reduction of reserpine-hypothermy (BPC 157 pre-treatment) and reversal of further prominent temperature fall (BPC 157 post-treatment) have been consistently observed. Taking together these data, as the two most suitable animal models were consistently used and since the high effectiveness was demonstrated in pre- and post-treatment, microg and ng regimens, BPC 157 as an organoprotector should be further therapeutically investigated. Additionally, given in either regimen, pentadecapeptide BPC 157 strongly attenuated the stomach lesions in mice that otherwise consistently appeared in mice treated with the parkinsogenic neurotoxin MPTP.

Alterations of second messenger systems in the rat brain after 6-hydroxydopamine lesions of the medial forebrain bundle

We studied the sequential changes in second messenger systems in the striatum and substantia nigra (SN) after 6-hydroxydopamine lesions of the medial forebrain bundle in rats. The animals were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks postlesion. [3H]Phorbol-12, 13-dibutyrate (PDBu), [3H]forskolin and [3H]rolipram were used to label protein kinase C (PKC), adenylyl cyclase and calcium/calmodulin-independent cyclic-AMP phosphodiesterase, respectively. The degeneration of nigrostriatal pathway produced a significant increase in [3H]PDBu binding in the ventromedial part of the ipsilateral striatum from 2 to 8 weeks postlesion. In the contralateral side, [3H]PDBu binding showed a transient increase in the SN only 4 weeks after lesioning. [3H]Forskolin binding showed a significant increase in the ipsilateral and contralateral striatum from 2 to 4 weeks postlesion. In the ipsilateral SN, a significant increase in [3H]forskolin binding was observed at 4 weeks after lesioning. However, no significant change in [3H]forskolin binding was observed in the contralateral SN during postlesion. On the other hand, [(3)H]rolipram binding showed no conspicuous alteration in the brain during postlesion. These results demonstrate that rats made hemiparkinsonism by unilateral 6-hydroxydopamine injection have a significant increase in [3H]PDBu and [3H]forskolin binding in the striatum and/or SN, whereas no significant change in [3H]rolipram binding is observed in these areas during postlesion. Our findings also suggest that the increase in [3H]forskolin binding is more pronounced than that in [3H]PDBu binding in the brain after unilateral 6-hydroxydopamine injection. Thus, our studies may provide valuable information concerning degeneration of the nigrostriatal pathway such as Parkinson's disease.

Immunohistochemical and neurochemical studies on nigral and striatal functions in the circling (ci) rat, a genetic animal model with spontaneous rotational behavior

Asymmetrical spontaneous turning behavior or circling phenomena are often related to components of the dopaminergic system, particularly to an imbalance of nigrostriatal function. When a rotational preference is observed, it is typically in a direction away from the brain hemisphere with higher striatal dopaminergic transmission. We have recently described a rat mutant (ci) with spontaneous circling behavior and other signs of functional brain asymmetry. Neurochemical determinations showed that mutants of both genders have significantly lower concentrations of dopamine and dopamine metabolites in the striatum ipsilateral to the preferred direction of rotation. In the present study, we used immunohistochemical, neurochemical, and autoradiographic techniques to characterize the dopaminergic abnormalities of the ci rat mutant in more detail. Age-matched non-affected controls of the same strain were used for comparison. Immunohistochemical labeling of dopaminergic neurons and fibers in substantia nigra pars compacta, ventral tegmental area, and striatum did not indicate any significant neurodegeneration or asymmetry that could explain the lateralization in dopamine levels in striatum of ci rats. Neurochemical determinations substantiated that ci rats of both genders have a significant imbalance in striatal dopamine metabolism, but a similar significant lateralization was also seen in non-affected female controls. Comparison of dopamine, serotonin, noradrenaline and several monoamine metabolite levels in substantia nigra, striatum, nucleus accumbens and frontal cortex of ci rats and controls did not disclose any marked difference between affected and non-affected animals which was consistently found in both genders. Quantitative autoradiographic determination of binding densities of dopamine transporter and D1 and D2 receptors in several parts of the striatum and substantia nigra indicated that ci rats have a significantly higher binding density of dopamine transporter and receptors than controls. Taken together, ci mutant rats of both genders exhibit an asymmetry in striatal dopamine and metabolite levels and an enhanced dopamine transporter and receptor binding, but the link of these differences in dopaminergic parameters with the rotational behavior of the animals is not clear yet. The lack of any significant dopaminergic cell loss in the substantia nigra and the locomotor hyperactivity observed in the mutants clearly suggest that the ci rat is not suited as a model of Parkinsonism but rather constitutes a model of a hyperkinetic motor syndrome.

Sequential changes of dopaminergic receptors in the rat brain after 6-hydroxydopamine lesions of the medial forebrain bundle

We investigated the sequential patterns of changes in dopamine uptake sites, D1 and D2 receptors in the brain of animals lesioned with 6-hydroxydopamine using quantitative receptor autoradiography. The rats were unilaterally lesioned in the medial forebrain bundle and the brains were analyzed at 1, 2, 4 and 8 weeks postlesion. Degeneration of the nigrostriatal pathway caused a significant loss of dopamine uptake sites in the ipsilateral striatum, substantia nigra (SN) and ventral tegmental area (VTA) in the lesioned animals. Dopamine D1 receptors were significantly increased in the ventromedial part of striatum of the ipsilateral side from 2 to 4 weeks postlesion. In the ipsilateral SN, a transient increase in dopamine D1 receptors was observed only 1 week after lesioning. However, the frontal cortex, parietal cortex and dorsolateral part of the striatum showed no significant change in dopamine D1 receptors throughout the experiments. On the other hand, dopamine D2 receptors were decreased increased in the ipsilateral SN and VTA from 1 week to 8 weeks postlesion. In the ipsilateral striatum, dopamine D2 receptors were increased in the dorsolateral part from 2 weeks to 8 weeks and in the ventromedial part from 2 weeks to 4 weeks. However, the frontal cortex and parietal cortex showed no significant change in dopamine D2 receptors during postlesion. In the contralateral side, most of regions examined showed no significant change in dopamine uptake sites, dopamine D1 receptors and dopamine D2 receptors during postlesion except for a transient change in a few regions. These results demonstrate that 6-hydroxydopamine can cause a severe functional damage in dopamine uptake sites in the striatum, SN and VTA. Our findings also suggest that the up-regulation in dopamine D2 receptors is more pronounced than that in dopamine D1 receptors in the brain after 6-hydroxydopamine treatment. Furthermore, our results support the existence of dopamine D2 receptors on the neurons of SN and VTA. Thus, our findings provide insights into the pathogenesis of Parkinson's disease.

Pathology of idiopathic dystonia: findings from genetic animal models

Dystonia is a common movement disorder which is thought to represent a disease of the basal ganglia. However, the pathogenesis of the idiopathic dystonias, i.e. the neuroanatomic and neurochemical basis, is still a mystery. Research in dystonia is complicated by the existence of various phenotypic and genotypic subtypes of idiopathic dystonia, probably related to heterogeneous dysfunctions. In neurological diseases in which no obvious neuronal degeneration can be found, such as in idiopathic dystonia, the identification of a primary defect is difficult, because of the large number of chemically distinct, but functionally interrelated, neurotransmitter systems in the brain. The variable response to pharmacological agents in patients with idiopathic dystonia supports the notion that the underlying biochemical dysfunctions vary in the subtypes of idiopathic dystonia. Hence, in basic research it is important to clearly define the involved type of dystonia. Animal models of dystonias were described as limited. However, over the last years, there has been considerable progress in the evaluation of animal models for different types of dystonia. Apart from animal models of symptomatic dystonia, genetic animal models with inherited dystonia which occurs in the absence of pathomorphological alterations in brain and spinal cord are describe. This review will focus mainly on genetic animal models of different idiopathic dystonias and pathophysiological findings. In particular, in the case of the mutant dystonic (dt) rat, a model of generalized dystonia, and in the case of the genetically dystonic hamster (dt(sz)), a model of paroxysmal dystonic choreoathetosis has been used, as these show great promise in contributing to the identification of underlying mechanisms in idiopathic dystonias, although even a proper animal model will probably never be equivalent to a human disease. Several pathophysiological findings from animal models are in line with clinical observations in dystonic patients, indicating abnormalities not only in the basal ganglia and thalamic nuclei, but also in the cerebellum and brainstem. Through clinical studies and neurochemical data several similarities were found in the genetic animal models, although the current data indicates different defects in dystonic animals which is consistent with the notion that dystonia is a heterogenous disorder. Different supraspinal dysfunctions appear to lead to manifestation of dystonic movements and postures. In addition to increasing our understanding of the pathophysiology of idiopathic dystonia, animal models may help to improve therapeutic strategies for this movement disorder.

Distribution of zinc in the substantia nigra of rats treated with 6-hydroxydopamine

To study the relationship between tissue accumulation of Zinc (Zn) and neurodegeneration in the nigrostriatal dopaminergic pathway, 65Zn distribution in this pathway was examined after unilateral injection of 6-hydroxydopamine (6-OHDA) into the substantia nigra of rats. When 65ZnCl2 was intravenously injected 4 days after treatment with 6-OHDA, 65Zn was concentrated in the ipsilateral substantia nigra 6 days after 65Zn injection. On the other hand, 19 d after treatment with 6-OHDA, 65Zn distribution in the ipsilateral substantia nigra was decreased to the level of the contralateral one. When NH4(99)TcO4, which cannot go through the blood-brain barrier, was injected into rats 4 d after treatment with 6-OHDA, 99Tc was concentrated in the ipsilateral substantia nigra 30 min after 99Tc injection, but no longer detectable 6 d after injection. These results suggest that Zn is necessary for a repair process called replacement gliosis after the death of neurons and that excess Zn does not accumulate in the lesion after completion of the gliosis.

Hemispheric asymmetries in spontaneous firing characteristics of substantia nigra pars reticulata neurons following a unilateral 6-hydroxydopamine lesion of the rat nigrostriatal pathway

Single unit activity of substantia nigra pars reticulata (SNR) neurons was recorded bilaterally in rats subjected to unilateral 6-hydroxydopamine lesions of the ascending mesostriatal dopaminergic pathway, resulting in an almost complete loss of dopaminergic neurons in the ipsilateral SN pars compacta. Firing rate and firing pattern of SNR neurons in lesioned rats were compared with respective data from sham-lesioned rats and naive controls. In lesioned rats, the mean firing rate of SNR neurons at the lesioned side was significantly reduced and there was an increase in the occurrence of bursting activity. In contrast, firing rate in the contralateral SNR was significantly increased without change in the frequency of bursting neurons. This asymmetrical change in spontaneous firing characteristics of SNR neurons following the lesion could be involved in the complex behavioral changes seen in this model of Parkinson's disease.

The spontaneous release of acetylcholinesterase in rat substantia nigra is altered by local changes in extracellular levels of dopamine

Acetylcholinesterase release in the guinea-pig substantia nigra has been previously investigated 'on-line', using a sensitive chemiluminescent system. Since histological observations suggest that there is a difference in acetylcholinesterase distribution in the rat substantia nigra compared to that of the guinea-pig, the first aim of the present study was to use this chemiluminescent method to characterise acetylcholinesterase release in this brain region of the freely moving rat, and the second was explore the relationship between acetylcholinesterase release and dopamine systems in this region. Accordingly, acetylcholinesterase release in the rat substantia nigra was studied under basal conditions of spontaneous release and following the local administration of (a) elevated potassium ions (30, 45, 60'mM), (b) a stimulator of dopamine/acetylcholinesterase release-D-amphetamine (10(-7), 10(-6) and 10(-5) M), (c) an inhibitor of dopamine uptake-GBR12909 (10(-7), 10(-6) and 10(-5) M). Spontaneous release of acetylcholinesterase in this brain region of the rat appears to be comparable with that observed in the guinea-pig, despite the smaller number of acetylcholinesterase-containing neurones. Furthermore, not only elevated potassium ions, but D-amphetamine as well as GBR12909, all produced significant increases in the percentage spontaneous release of acetylcholinesterase. Thus, the release of acetylcholinesterase in this region may be triggered by levels of dopamine outside of the neurone.

Behavioral and neurochemical dysfunction in the circling (ci) rat: a novel genetic animal model of a movement disorder

One of the crucial breakthroughs in research on parkinsonism was the observation of circling behaviour in rodents after unilateral intranigral injection of 6-hydroxydopamine. This Ungerstedt model remains one of the basic animal models of Parkinson's disease. We report here the first mutant rat strain with abnormal circling behaviour and several other features reminiscent of the Ungerstedt Parkinson model. The neurological disorder in the novel mutant rat strain is determined monogenetically by a recessive autosomal gene termed circling (ci). Mutant rats of both genders exhibit an intense asymmetric circling in an open-field or rotometer, which is enhanced by treatment with amphetamine. Neurochemical determinations show that mutants of both genders have significantly lower concentrations of dopamine and dopamine metabolites in the striatum ipsilateral to the preferred direction of rotation. Furthermore, in a forelimb-reaching test for assessing the skilled motor capacities of rats, ci rats show a marked deficit on the side contralateral to the preferred direction of turning, which is analogous to motor deficits previously described for rats subjected to unilateral 6-hydroxydopamine lesions. The new mutant rat strain thus exhibits remarkable similarities to the Ungerstedt model and could be used to study the endogenous processes, particularly the genetic components, that might eventually lead to progressive motor dysfunctions.

Differential release of acetylcholinesterase in vivo, from the guinea pig substantia nigra compared to the caudate putamen following dopamine depletion

In the substantia nigra acetylcholinesterase may have a novel role unrelated to acetylcholine but linked instead to dopamine. Using a sensitive chemiluminescent system, we have investigated the effects of dopamine depletion on the vivo release of acetylcholinesterase in both the substantia nigra and the caudate putamen. Dopamine levels in the caudate putamen were significantly depleted compared to the non-lesioned side, using either of two different toxins for dopaminergic nigrostriatal cells: 6-hydroxydopamine ( 1 or 3 weeks prior to study) or N-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (1 week prior to study). Spontaneous release of acetylcholinesterase from the substantia nigra was significantly reduced following all three pretreatments; however, in the caudate putamen a significant reduction in the spontaneous release of acetylcholinesterase, compared to controls, was only seen in animals studied 1 week after the administration of 6-hydroxydopamine. In all control groups, application of potassium ions (60 mM) evoked a significant release of acetylcholinesterase in the substantia nigra (p < 0.05) and this effect persisted in the surviving neurones following a partial lesion by neurotoxin pre-treatment. The results from this study are discussed in the light of a regulatory mechanism for acetylcholinesterase release from the striatum, which may come into operation depending on the extent of destruction of dopaminergic nigrostriatal neurones.

Parkinson's disease, trophic factors, and adrenal medullary chromaffin cell grafting: basic and clinical studies

Neural transplantation is one of the promising approaches for the treatment of Parkinson's disease. Although the strategy of using adrenal medulla as donor tissue, rather than fetal nigra tissue, started as an alternative method, recent experimental studies demonstrated the efficacy of adrenal medulla grafting as a neurotrophic source. Many methods to increase the survival of grafted chromaffin cells have been developed, some of which have already been applied clinically with encouraging results. This review summarizes the advancements of adrenal medulla grafting in basic and clinical studies. Special attention is focused on the relationship with neurotrophic factors and how we can enhance the survival of grafted chromaffin cells.

Dose-dependent lesions of the dopaminergic nigrostriatal pathway induced by intrastriatal injection of 6-hydroxydopamine

Animal models with partial lesions of the dopaminergic nigrostriatal pathway may be useful for developing neuroprotective and neurotrophic therapies for Parkinson's disease. To develop such a model, different doses of 6-hydroxydopamine (0.0, 0.625, 1.25, 2.5 and 5.0 micrograms/microliters in 3.5 microliters of saline) were unilaterally injected into the striatum of rats. Animals that received 1.25 to 5.0 micrograms/microliters 6-hydroxydopamine displayed dose-dependent amphetamine and apomorphine-induced circling. 6-Hydroxydopamine also caused dose-dependent reductions in [3H]mazindol-labeled dopamine uptake sites in the lesioned striatum and ipsilateral substantia nigra pars compacta (up to 93% versus contralateral binding), with smaller losses in the nucleus accumbens, olfactory tubercle and ventral tegmental area. In the substantia nigra pars compacta and the ventral tegmental area, the number of Nissl-stained neurons decreases in parallel with the reduction in [3H]mazindol binding. The reduction in [3H]mazindol binding in the striatum and the nucleus accumbens, and the reduction in [3H]mazindol binding and in the number of Nissl-stained neurons in the substantia nigra pars compacta and the ventral tegmental area is stable for up to 12 weeks after the lesion. Macroscopically, forebrain coronal sections showed normal morphology, except for rats receiving 5.0 micrograms/microliters 6-hydroxydopamine in which striatal cross-sectional area was reduced, suggesting that this high dose non-specifically damages intrinsic striatal neurons. Nissl-stained sections revealed an area of neuronal loss and intense gliosis centered around the needle track, which increased in size with the dose of neurotoxin. Striatal [3H]sulpiride binding was increased by 2.5 micrograms/microliters and 5.0 micrograms/microliters 6-hydroxydopamine, suggesting up-regulation of dopamine D2 receptors. Striatal binding of [3H]CGS 21680-labeled adenosine A2a receptors, but not of [3H]SCH 23390-labeled dopamine D1 receptors, was reduced at the highest dose, suggesting preservation of the striatal intrinsic neurons with the lower doses. This study indicates that intrastriatal injection of different doses of 6-hydroxydopamine can be used to cause increasing amounts of dopamine denervation, which could model Parkinson's disease of varying degrees of severity. Injecting 3.5 microliters of 2.5 micrograms/microliters 6-hydroxydopamine appears to be particularly useful as a general model of early Parkinson's disease, since it induces a lesion characterized by robust drug-induced rotation, changes in binding consistent with approximately 70% dopamine denervation, approximately 19% dopamine D22 receptor up-regulation, negligible intrinsic striatal damage and stability for at least 12 weeks. This study outlines a technique for inducing partial lesions of the nigrostriatal dopamine pathway in rats.(ABSTRACT TRUNCATED AT 400 WORDS)

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) disrupts social memory/recognition processes in the male mouse

Male mice treated with MPTP or vehicle were tested for their ability to demonstrate a memory-recognition response as evaluated in a habituation-dishabituation task. Treatment with MPTP severely disrupted the male's habituation-dishabituation response profile compared to vehicle treated animals. Administration of L-DOPA at 45 min prior to behavioral testing in MPTP animals restored their performance on the habituation-dishabituation test to levels observed in vehicle treated animals. There was also a tendency for L-DOPA to produce enhanced responsiveness in vehicle treated animals. Mice treated with MPTP had significantly reduced concentrations of norepinephrine within the olfactory bulb and hippocampus. Vehicle treated mice administered L-DOPA had significantly increased dopamine concentrations within the corpus striatum. These results suggest that, in addition to its putative effects upon the nigrostriatal dopaminergic system and motor behavior, MPTP is also exerting substantial effects upon other systems. In particular, the noradrenergic system and its potential involvement with memory/recognition processes in the CD-1 mouse appears to be very sensitive to the neurotoxic effects of MPTP.