Metabolic activity of the basal ganglia in parkinsonian syndromes in human and non-human primates: a cytochrome oxidase histochemistry study

Microarrays, Enzymatic Assays, and MALDI-MS for Determining Specific Alterations to Mitochondrial Electron Transport Chain Activity, ROS Formation, and Lipid Composition in a Monkey Model of Parkinson’s Disease

Multiple evidences suggest that mitochondrial dysfunction is implicated in the pathogenesis of Parkinson’s disease via the selective cell death of dopaminergic neurons, such as that which occurs after prolonged exposure to the mitochondrial electron transport chain (ETC) complex I inhibitor, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrine (MPTP). However, the effects of chronic MPTP on the ETC complexes and on enzymes of lipid metabolism have not yet been thoroughly determined. To face these questions, the enzymatic activities of ETC complexes and the lipidomic profile of MPTP-treated non-human primate samples were determined using cell membrane microarrays from different brain areas and tissues. MPTP treatment induced an increase in complex II activity in the olfactory bulb, putamen, caudate, and substantia nigra, where a decrease in complex IV activity was observed. The lipidomic profile was also altered in these areas, with a reduction in the phosphatidylserine (38:1) content being especially relevant. Thus, MPTP treatment not only modulates ETC enzymes, but also seems to alter other mitochondrial enzymes that regulate the lipid metabolism. Moreover, these results show that a combination of cell membrane microarrays, enzymatic assays, and MALDI-MS provides a powerful tool for identifying and validating new therapeutic targets that might accelerate the drug discovery process.

Evidence of Neurobiological Changes in the Presymptomatic PINK1 Knockout Rat

BACKGROUND

Genetic models of Parkinson's disease (PD) coupled with advanced imaging techniques can elucidate neurobiological disease progression, and can help identify early biomarkers before clinical signs emerge. PTEN-induced putative kinase 1 (PINK1) helps protect neurons from mitochondrial dysfunction, and a mutation in the associated gene is a risk factor for recessive familial PD. The PINK1 knockout (KO) rat is a novel model for familial PD that has not been neuroradiologically characterized for alterations in brain structure/function, alongside behavior, prior to 4 months of age.

OBJECTIVE

To identify biomarkers of presymptomatic PD in the PINK1 -/- rat at 3 months using magnetic resonance imaging techniques.

METHODS

At postnatal weeks 12-13; one month earlier than previously reported signs of motor and cognitive dysfunction, this study combined imaging modalities, including assessment of quantitative anisotropy across 171 individual brain areas using an annotated MRI rat brain atlas to identify sites of gray matter alteration between wild-type and PINK1 -/- rats.

RESULTS

The olfactory system, hypothalamus, thalamus, nucleus accumbens, and cerebellum showed differences in anisotropy between experimental groups. Molecular analyses revealed reduced levels of glutathione, ATP, and elevated oxidative stress in the substantia nigra, striatum and deep cerebellar nuclei. Mitochondrial genes encoding proteins in Complex IV, along with mRNA levels associated with mitochondrial function and genes involved in glutathione synthesis were reduced. Differences in brain structure did not align with any cognitive or motor impairment.

CONCLUSIONS

These data reveal early markers, and highlight novel brain regions involved in the pathology of PD in the PINK1 -/- rat before behavioral dysfunction occurs.

Permeability of blood-brain barrier in macaque model of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinson disease

Brain bioavailability of drugs developed to address central nervous system diseases is classically documented through cerebrospinal fluid collected in normal animals, i.e., through an approximation as there are fundamental differences between cerebrospinal fluid and tissue contents. The fact that disease might affect brain availability of drugs is almost never considered at this stage although several conditions are associated with blood-brain barrier damage. Building upon our expertise in Parkinson's disease translational research, the present study addressed this gap comparing plasma and cerebrospinal fluid bioavailability of l-3,4-dihydroxyphenylalanine, carbamazepine, quinidine, lovastatin, and simvastatin, in healthy and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated macaques, the gold standard model of Parkinson's disease. The drugs were selected based upon their differential transport across the blood-brain barrier. Interestingly, brain bioavailability of quinidine was decreased while others were unaffected. Pharmacokinetics and pharmacodynamics experiments of drugs addressing Parkinson's disease might thus be performed in healthy animals unless the drugs are known to interact with the organic cation transporter.

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

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

Ceftriaxone prevents and reverses behavioral and neuronal deficits in an MPTP-induced animal model of Parkinson's disease dementia

Glutamatergic hyperactivity plays an important role in the pathophysiology of Parkinson's disease (PD). Ceftriaxone increases expression of glutamate transporter 1 (GLT-1) and affords neuroprotection. This study was aimed at clarifying whether ceftriaxone prevented, or reversed, behavioral and neuronal deficits in an 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD rat model. Male Wistar rats were injected daily with either ceftriaxone starting 5 days before or 3 days after MPTP lesioning (day 0) or saline and underwent a bar-test on days 1-7, a T-maze test on days 9-11, and an object recognition test on days 12-14, then the brains were taken for histological evaluation on day 15. Dopaminergic degeneration in the substantia nigra pars compacta and striatum was observed on days 3 and 15. Motor dysfunction in the bar test was observed on day 1, but disappeared by day 7. In addition, lesioning resulted in deficits in working memory in the T-maze test and in object recognition in the object recognition task, but these were not observed in rats treated pre- or post-lesioning with ceftriaxone. Lesioning also caused neurodegeneration in the hippocampal CA1 area and induced glutamatergic hyperactivity in the subthalamic nucleus, and both changes were suppressed by ceftriaxone. Increased GLT-1 expression and its co-localization with astrocytes were observed in the striatum and hippocampus in the ceftriaxone-treated animals. To our knowledge, this is the first study showing a relationship between ceftriaxone-induced GLT-1 expression, neuroprotection, and improved cognition in a PD rat model. Ceftriaxone may have clinical potential for the prevention and treatment of dementia associated with PD.

NMDA receptor antagonism potentiates the L-DOPA-induced extracellular dopamine release in the subthalamic nucleus of hemi-parkinson rats

Long term treatment with L-3,4-dihydroxyphenylalanine (L-DOPA) is associated with several motor complications. Clinical improvement of this treatment is therefore needed. Lesions or high frequency stimulation of the hyperactive subthalamic nucleus (STN) in Parkinson's disease (PD), alleviate the motor symptoms and reduce dyskinesia, either directly and/or by allowing the reduction of the L-DOPA dose. N-methyl-D-aspartate (NMDA) receptor antagonists might have similar actions. However it remains elusive how the neurochemistry changes in the STN after a separate or combined administration of L-DOPA and a NMDA receptor antagonist. By means of in vivo microdialysis, the effect of L-DOPA and/or MK 801, on the extracellular dopamine (DA) and glutamate (GLU) levels was investigated for the first time in the STN of sham and 6-hydroxydopamine-lesioned rats. The L-DOPA-induced DA increase in the STN was significantly higher in DA-depleted rats compared to shams. MK 801 did not influence the L-DOPA-induced DA release in shams. However, MK 801 enhanced the L-DOPA-induced DA release in hemi-parkinson rats. Interestingly, the extracellular STN GLU levels remained unchanged after nigral degeneration. Furthermore, administration of MK 801 alone or combined with L-DOPA did not alter the STN GLU levels in both sham and DA-depleted rats. The present study does not support the hypothesis that DA-ergic degeneration influences the STN GLU levels neither that MK 801 alters the GLU levels in lesioned and non-lesioned rats. However, NMDA receptor antagonists could be used as a beneficial adjuvant treatment for PD by enhancing the therapeutic efficacy of l-DOPA at least in part in the STN.

Animal models of Parkinson's disease: a source of novel treatments and clues to the cause of the disease

Animal models of Parkinson's disease (PD) have proved highly effective in the discovery of novel treatments for motor symptoms of PD and in the search for clues to the underlying cause of the illness. Models based on specific pathogenic mechanisms may subsequently lead to the development of neuroprotective agents for PD that stop or slow disease progression. The array of available rodent models is large and ranges from acute pharmacological models, such as the reserpine- or haloperidol-treated rats that display one or more parkinsonian signs, to models exhibiting destruction of the dopaminergic nigro-striatal pathway, such as the classical 6-hydroxydopamine (6-OHDA) rat and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse models. All of these have provided test beds in which new molecules for treating the motor symptoms of PD can be assessed. In addition, the emergence of abnormal involuntary movements (AIMs) with repeated treatment of 6-OHDA-lesioned rats with L-DOPA has allowed for examination of the mechanisms responsible for treatment-related dyskinesia in PD, and the detection of molecules able to prevent or reverse their appearance. Other toxin-based models of nigro-striatal tract degeneration include the systemic administration of the pesticides rotenone and paraquat, but whilst providing clues to disease pathogenesis, these are not so commonly used for drug development. The MPTP-treated primate model of PD, which closely mimics the clinical features of PD and in which all currently used anti-parkinsonian medications have been shown to be effective, is undoubtedly the most clinically-relevant of all available models. The MPTP-treated primate develops clear dyskinesia when repeatedly exposed to L-DOPA, and these parkinsonian animals have shown responses to novel dopaminergic agents that are highly predictive of their effect in man. Whether non-dopaminergic drugs show the same degree of predictability of response is a matter of debate. As our understanding of the pathogenesis of PD has improved, so new rodent models produced by agents mimicking these mechanisms, including proteasome inhibitors such as PSI, lactacystin and epoximycin or inflammogens like lipopolysaccharide (LPS) have been developed. A further generation of models aimed at mimicking the genetic causes of PD has also sprung up. Whilst these newer models have provided further clues to the disease pathology, they have so far been less commonly used for drug development. There is little doubt that the availability of experimental animal models of PD has dramatically altered dopaminergic drug treatment of the illness and the prevention and reversal of drug-related side effects that emerge with disease progression and chronic medication. However, so far, we have made little progress in moving into other pharmacological areas for the treatment of PD, and we have not developed models that reflect the progressive nature of the illness and its complexity in terms of the extent of pathology and biochemical change. Only when this occurs are we likely to make progress in developing agents to stop or slow the disease progression. The overarching question that draws all of these models together in the quest for better drug treatments for PD is how well do they recapitulate the human condition and how predictive are they of successful translation of drugs into the clinic? This article aims to clarify the current position and highlight the strengths and weaknesses of available models.

Knockdown of GAD67 protein levels normalizes neuronal activity in a rat model of Parkinson's disease

BACKGROUND

Dopamine depletion of the striatum is one of the hallmarks of Parkinson's disease. The loss of dopamine upregulates GAD67 expression in the striatal projection neurons and causes other changes in the activity of the basal ganglia circuit.

METHODS

To normalize the GAD67 expression in the striatum after dopamine depletion, we developed several lentiviral vectors that express RNA interference (RNAi) directed against GAD67 mitochondrial RNA. The vectors were injected into the striatum of hemiparkinsonian rats and the level of GAD67 protein as well as a marker of neuronal activity, mtCO1, was analyzed using western blots.

RESULTS

Unilateral lesions of the dopamine neurons in substantia nigra resulted in an increased level of GAD67 protein in the ipsilateral striatum. Furthermore, we detected significantly higher levels of mtCO1, after dopamine depletion in the striatum. Using a lentiviral vectors with a synthetic miRNA scaffold to deliver RNAi, we were able to normalize the GAD67 protein levels in the parkinsonian rat striatum. In addition, we were able to normalize the increased neural activity, which resulted from the loss of dopamine as measured by the marker mtCO1.

CONCLUSIONS

We conclude that RNAi directed against GAD67 may be a valid approach to correct the dysregulation of the basal ganglia circuit in a rat model of Parkinson's disease. The possibility to correct for a loss of dopamine using nondopamimetic tools is interesting because it may be more directed towards the casual mechanisms of the motor symptoms.

The DYT1 carrier state increases energy demand in the olivocerebellar network

DYT1 dystonia is caused by a GAG deletion in TOR1A, the gene which encodes torsinA. Gene expression studies in rodents and functional imaging studies in humans suggest that DYT1 dystonia may be a network disorder of neurodevelopmental origin. To generate high resolution metabolic maps of DYT1 dystonia and pinpoint dysregulated network elements, we performed 2-deoxyglucose autoradiography and cytochrome oxidase (CO) histochemistry in transgenic mice expressing human mutant (hMT1) torsinA and wild-type littermates. In comparison with controls, hMT1 mice showed increased glucose utilization (GU) in the inferior olive (IO) medial nucleus (IOM), IO dorsal accessory nucleus and substantia nigra compacta, and decreased GU in the medial globus pallidus (MGP) and lateral globus pallidus. The hMT1 mice showed increased CO activity in the IOM and Purkinje cell layer of cerebellar cortex, and decreased CO activity in the caudal caudate-putamen, substantia nigra reticulata and MGP. These findings suggest that (1) the DYT1 carrier state increases energy demand in the olivocerebellar network and (2) the IO may be a pivotal node for abnormal basal ganglia-cerebellar interactions in dystonia.

Basal Ganglia circuits underlying the pathophysiology of levodopa-induced dyskinesia

Involuntary movements or dyskinesia, represent a debilitating complication of levodopa therapy for Parkinson's disease. Dyskinesia is, ultimately, experienced by the vast majority of the patients. Despite the importance of this problem, little was known about the cause of dyskinesia, a situation that has dramatically evolved in the last few years with a focus upon the molecular and signaling changes induced by chronic levodopa treatment. Departing from this, we here review the progress made in functional anatomy and neuroimaging that have had a tremendous impact on our understanding of the anatomo-functional organization of the basal ganglia in Parkinsonism and dyskinetic states, notably the demonstration that dyskinesia are linked to a pathological processing of limbic and cognitive information.

Altered expression of neuronal nitric oxide synthase in weaver mutant mice

The weaver mouse represents the only genetic animal model of gradual nigrostriatal dopaminergic neurodegeneration which is proposed as a pathophysiological phenotype of Parkinson's disease. The aim of the present study was to analyze the nitric oxide and dopaminergic systems in selected brain regions of homozygous weaver mice at different postnatal ages corresponding to specific stages of the dopamine loss. Structural deficits were evaluated by quantification of tyrosine hydroxylase and neuronal nitric oxide synthase-immunostaining in the cortex, striatum, accumbens nuclei, subthalamic nuclei, ventral tegmental area, and substantia nigra compacta of 10-day, 1- and 2-month-old wild-type and weaver mutant mice. The results confirmed the progressive loss of dopamine during the postnatal development in the adult weaver mainly affecting the substantia nigra pars compacta, striatum, and subthalamic nucleus and slightly affecting the accumbens nuclei and ventral tegmental area. A general decrease in neuronal nitric oxide synthase-immunostaining with age was revealed in both the weaver and wild-type mice, with the decrease being most pronounced in the weaver. In contrast, there was an increase in the substantia nigra pars compacta nitric oxide synthase-immunostaining and a decrease mainly in the subthalamic and accumbens nuclei of the 2-month-old weaver mutant. The decrease in the expression of nNOS may bear functional significance related to the process of aging. DA neurons from the substantia nigra directly modulate the activity of subthalamic nucleus neurons, and their loss may contribute to the abnormal activity of subthalamic nucleus neurons. Although the functional significance of these changes is not clear, it may represent plastic compensating adjustments resulting from the loss of dopamine innervation, highlighting a possible role of nitric oxide in this process.

The duration of the motor response to apomorphine boluses is conditioned by the length of a prior infusion in Parkinson's disease

"Pulsatile" administration of levodopa has been invocated a relevant factor for motor fluctuations in Parkinson's disease (PD). We studied dopaminergic sensitivity to apomorphine in 10 parkinsonian patients with motor fluctuations. Patients were tested as follows: the minimal effective dose of apomorphine (MED-1) was administered in the morning to induce an on response. Fifteen minutes after this motor response had disappeared, an apomorphine infusion was initiated and maintained to ensure on periods of three different durations on different days. Infusion lasted for approximately 30, 60 and 90 minutes. Subsequently, the infusion was stopped, and after 15 minutes in the off state, a second bolus of apomorphine (MED-2) was given. The mean infusion doses were 49.2 +/- 5.4, 108.4 +/- 10.3, and 150 +/- 8.2 mg. These elicited on periods of 48.2 +/- 4.1, 110 +/- 4.5, and 195 +/- 3.8 minutes. The MED-2 elicited on responses with a duration of 30 +/- 4.5, 18.4 +/- 3.2, and 11.2 +/- 4.1 minutes. The duration of the on response induced by the apomorphine infusions correlated inversely (P < 0.01) with the on induced by the MED-2 of apomorphine. Our findings indicate that a continuous dopaminergic stimulus may induce pharmacodynamic changes associated with tolerance in PD patients.

Subcortical elevation of metabolism in Parkinson's disease--a critical reappraisal in the context of global mean normalization

In a recent issue of NeuroImage, we presented evidence that biased global mean (GM) normalization of brain PET data can generate the appearance of subcortical foci with relative hypermetabolism in patients with Parkinson's disease (PD), and other degenerative disorders. In a commentary to our article, Ma and colleagues presented a study seeking to establish that a pattern of widespread hypermetabolism, known as the Parkinson's disease related pattern (PDRP) is a genuine metabolic feature of PD. In the present paper, we respond to the arguments presented by Ma et al., and we provide a critical reappraisal of the evidence for the existence of the PDRP. To this end, we present new analyses of PET data sets, which demonstrate that very similar patterns of relative subcortical increases are seen in PD, Alzheimer's disease, hepatic encephalopathy, healthy aging, and simulation data. Furthermore, longitudinal studies of PD previously reported relative hypermetabolism in very small anatomical structures such as the subthalamic nucleus. We now demonstrate how focal hypermetabolism attributed to small nuclei can similarly arise as a consequence of GM normalization. Finally, we give a comprehensive summary of the entire deoxyglucose autoradiography literature on acquired parkinsonism in experimental animals. Based on this evidence, we conclude that (1) there is no quantitative evidence for widespread subcortical hypermetabolism in PD, (2) very similar patterns of subcortical hyperactivity are evident in various other brain disorders whenever GM normalization is utilized, and (3) the PDRP is not evident in animal models of PD. In the absence of quantitative evidence for the PDRP, our alternative interpretation of normalization bias seems the more parsimonious explanation for the reports of relative hypermetabolism in PD.

Molecular mechanisms of L-DOPA-induced dyskinesia

L-DOPA (L-3,4-dihydroxyphenylalanine) remains the most effective drug for the treatment of Parkinson's disease. However, chronic use causes dyskinesia, a complex motor phenomenon that consists of two components: the execution of involuntary movements in response to drug administration, and the 'priming' phenomenon that underlies these movements' establishment and persistence. A reinterpretation of recent data suggests that priming for dyskinesia results from nigral denervation and the loss of striatal dopamine input, which alters glutamatergic synaptic connectivity in the striatum. The subsequent response of the abnormal basal ganglia to dopaminergic drugs determines the manner and timing of dyskinesia expression. The combination of nigral denervation and drug treatment establishes inappropriate signalling between the motor cortex and the striatum, leading to persistent dyskinesia.

The firing activity of presumed cholinergic and non-cholinergic neurons of the pedunculopontine nucleus in 6-hydroxydopamine-lesioned rats: an in vivo electrophysiological study

Several studies have shown that the neuronal activity of the pedunculopontine nucleus is increased in Parkinson's disease. In the present study, the changes were examined in the firing rate and firing pattern of presumed cholinergic and non-cholinergic neurons in the pedunculopontine nucleus of 6-hydroxydopamine-lesioned rats by using extracellular recording. In the lesioned rats, the mean firing rate of both presumed cholinergic and non-cholinergic neurons in the pedunculopontine nucleus increased significantly compared to normal rats. With regard to firing pattern, the majority of presumed cholinergic and non-cholinergic neurons fired regularly in normal rats. After substantia nigra pars compacta-lesion, the percentage of presumed non-cholinergic neurons exhibiting irregular pattern increased significantly compared to normal rats, while having no significant change in the firing pattern of presumed cholinergic neurons. Collectively, these results indicate that the presumed cholinergic and non-cholinergic neurons in the pedunculopontine nucleus are overactive in 6-hydroxydopamine-lesioned rats, particularly, presumed non-cholinergic neuron firing is more irregular, which suggests that the firing activity of presumed cholinergic and non-cholinergic neurons is affected by the different afferents from the basal ganglia and related structures.

Increased mRNA expression of cytochrome oxidase in dorsal raphe nucleus of depressive suicide victims

Suicidal behavior is a problem with important social repercussions. Some groups of the population show a higher risk of suicide; for example, depression, alcoholism, psychosis or drug abuse frequently precedes suicidal behavior. However, the relationship between metabolic alterations in the brain and premorbid clinical symptoms of suicide remains uncertain. The serotonergic and noradrenergic systems have frequently been, implicated in suicidal behavior and the amount of serotonin in the brain and CSF of suicide victims has been found to be low compared with normal subjects. However, there are contradictory results regarding the role of noradrenergic neurons in the mediation of suicide attempts, possibly reflecting the heterogeneity of conditions that lead to a common outcome. In the present work we focus on the subgroup of suicide victims that share a common diagnosis of major depression. Based on post-mortem studies analyzing mRNA expression by in situ hybridization, serotonergic neurons from the dorsal raphe nucleus (DRN) from depressive suicide victims are seen to over-express cytochrome oxidase mRNA. However, no corresponding changes were found in the expression of tyrosine hydroxylase (TH) mRNA in the noradrenergic neurons of the Locus Coeruleus (LC). These results suggest that, despite of the low levels of serotonin described in suicide victims, the activity of DRN neurons could increase in the suicidally depressed, probably due to the over activation of serotonin re-uptake. No alteration was found in noradrenergic neurons, suggesting that they play no crucial role in the suicidal behavior of depressive patients.

Macromolecule biosynthesis: a key function of sleep

The function(s) of sleep remains a major unanswered question in biology. We assessed changes in gene expression in the mouse cerebral cortex and hypothalamus following different durations of sleep and periods of sleep deprivation. There were significant differences in gene expression between behavioral states; we identified 3,988 genes in the cerebral cortex and 823 genes in the hypothalamus with altered expression patterns between sleep and sleep deprivation. Changes in the steady-state level of transcripts for various genes are remarkably common during sleep, as 2,090 genes in the cerebral cortex and 409 genes in the hypothalamus were defined as sleep specific and changed (increased or decreased) their expression during sleep. The largest categories of overrepresented genes increasing expression with sleep were those involved in biosynthesis and transport. In both the cerebral cortex and hypothalamus, during sleep there was upregulation of multiple genes encoding various enzymes involved in cholesterol synthesis, as well as proteins for lipid transport. There was also upregulation during sleep of genes involved in synthesis of proteins, heme, and maintenance of vesicle pools, as well as antioxidant enzymes and genes encoding proteins of energy-regulating pathways. We postulate that during sleep there is a rebuilding of multiple key cellular components in preparation for subsequent wakefulness.

Impact of chronic subthalamic high-frequency stimulation on metabolic basal ganglia activity: a 2-deoxyglucose uptake and cytochrome oxidase mRNA study in a macaque model of Parkinson's disease

The mechanisms of action of high-frequency stimulation (HFS) of the subthalamic nucleus (STN) remain only partially understood. Hitherto, experimental studies have suggested that STN-HFS reduces the activity of STN neurons. However, some recent reports have challenged this view, showing that STN-HFS might also increase the activity of globus pallidus internalis (GPi) neurons that are under strong excitatory drive of the STN. In addition, most results emanate from studies applying acute STN-HFS, while parkinsonian patients receive chronic stimulation. Thus, the present study was designed to assess the effect of chronic (10 days) STN-HFS in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated nonhuman primate. For this purpose, 2-deoxyglucose (2-DG) uptake, a measure of global synaptic activity, was assessed in the basal ganglia and the motor thalamus after chronic unilateral STN-HFS. Cytochrome oxidase subunit 1 (COI) mRNA expression, a marker of efferent metabolic activity, was additionally assessed in the globus pallidus. Chronic STN-HFS (i) reversed abnormally decreased 2-DG uptake in the STN of parkinsonian nonhuman primates, (ii) reversed abnormally increased 2-DG accumulation in the GPi while COI mRNA expression was increased, suggesting global activation of GPi neurons, and (iii) reversed abnormally increased 2-DG uptake in the ventrolateral motor thalamus nucleus. The simultaneous decrease in 2-DG uptake and increase in COI mRNA expression are difficult to reconcile with the current model of basal ganglia function and suggest that the mechanisms by which STN-HFS exerts its clinical benefits are more complex than a simple reversal of abnormal activity in the STN and its targets.

Decreased expression of l-dopa-induced dyskinesia by switching to ropinirole in MPTP-treated common marmosets

Current concepts suggest that pulsatile stimulation of dopamine receptors following L-dopa administration leads to priming for dyskinesia in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine hydrochloride (MPTP)-treated primates, while continuous dopaminergic stimulation with long-acting dopamine agonists does not. We investigated whether L-dopa-induced dyskinesia is reduced by switching to a dopamine agonist. MPTP-treated marmosets received chronic treatment with L-dopa or ropinirole in doses producing equivalent motor activity and reversal of motor deficits. Administration of L-dopa led to the rapid onset of moderate to severe dyskinesia, whereas ropinirole produced only mild dyskinesia. Animals initially treated with L-dopa were switched to an equivalent dose of ropinirole and those treated with ropinirole were switched to an equivalent dose of L-dopa for 56 days. L-dopa-primed animals that were switched to ropinirole showed a trend towards a reduction of dyskinesia intensity, whereas animals initially treated with ropinirole and switched to L-dopa showed a trend toward increased dyskinesia intensity. A subsequent, acute L-dopa challenge reversed motor deficits and induced intense dyskinesia in both groups. This suggests that L-dopa leads to the priming and expression of dyskinesia, but that expression is not maintained when switching to a long-acting dopamine agonist. In contrast, dopamine agonists may prime for dyskinesia, but do not lead to its full expression.

Globus pallidus external segment

The external segment of the pallidum (GP(e)) is a relatively large nucleus located caudomedial to the neostriatum (Str). The GP(e) receives major inputs from two major basal ganglia input nuclei, the Str and the subthalamic nucleus (STN), and sends its output to many basal ganglia nuclei including the STN, the Str, the internal pallidal segment (GP(i)), and the substantia nigra (SN). Thus, the GPe can be placed at the center of the basal ganglia connection diagram (Fig. 1(A)). From the viewpoint that emphasizes the direct and indirect pathways of the basal ganglia, the GP(e) is a component of the indirect pathway that relays Str inputs to the STN. The indirect pathway can be traced in Fig. 1(A), although it comprises only a part of multiple indirect pathways. This chapter begins with a brief description of the anatomical organization of the GP(e) followed by physiological and pharmacological characterizations of GABAergic responses in the GP(e).

Time-course of nigrostriatal damage, basal ganglia metabolic changes and behavioural alterations following intrastriatal injection of 6-hydroxydopamine in the rat: new clues from an old model

Despite the progressive development of innovative animal models for Parkinson's disease, the intracerebral infusion of neurotoxin 6-hydroxydopamine (6-OHDA) remains the most widely used means to induce an experimental lesion of the nigrostriatal pathway in the animal, due to its relatively low complexity and cost, coupled with the high reproducibility of the lesion obtained. To gain new information from such a classic model, we studied the time-course of the nigrostriatal damage, metabolic changes in the basal ganglia nuclei (cytochrome oxidase activity) and behavioural modifications (rotational response to apomorphine) following unilateral injection of 6-OHDA into the corpus striatum of rat, over a 4-week period. Striatal infusion of 6-OHDA caused early damage of dopaminergic terminals, followed by a slowly evolving loss of dopaminergic cell bodies in the substantia nigra pars compacta, which became apparent during the second week post-injection and peaked at the 28th day post-infusion; the rotational response to apomorphine was already present at the first time point considered (Day 1), and remained substantially stable throughout the 4-week period of observation. The evolution of the nigrostriatal lesion was accompanied by complex changes in the metabolic activity of the other basal ganglia nuclei investigated (substantia nigra pars reticulata, entopeduncular nucleus, globus pallidus and subthalamic nucleus), which led, ultimately, to a generalized, metabolic hyperactivity, ipsilaterally to the lesion. However, peculiar patterns of metabolic activation, or inhibition, characterized the post-lesional responses of each nucleus, in the early and intermediate phases, with peculiar response profiles that varied closely related to the functional position occupied within the basal ganglia circuitry.

Lesion of the pedunculopontine nucleus reverses hyperactivity of the subthalamic nucleus and substantia nigra pars reticulata in a 6-hydroxydopamine rat model

The pedunculopontine nucleus (PPN) and the subthalamic nucleus (STN) are reciprocally connected by excitatory projections. In the 6-hydroxydopamine (6-OHDA) rat model the PPN was found to be hyperactive. Similarly, the STN and the substantia nigra pars reticulata (SNr) showed increased activity in Parkinson's disease (PD) animal models. A lesion of the STN was shown to restore increased activity levels in the SNr of 6-OHDA-treated rats. As the STN and the PPN were reciprocally connected by excitatory projections and both structures were shown to be hyperactive in PD animal models, the present study was performed in order to investigate the changes in neuronal activity of the STN and SNr under urethane anesthesia after unilateral ibotenic acid lesioning of the PPN in animals with previous unilateral 6-OHDA lesions of the substantia nigra pars compacta (SNc). The firing rate of STN neurons significantly increased from 10.3 +/- 0.6 spikes/s (mean +/- SEM) to 17.8 +/- 1.8 spikes/s after SNc lesion and returned to normal levels of 10.8 +/- 0.7 spikes/s after additional lesion of the PPN. Similarly, the firing rate of SNr neurons significantly increased from 19.0 +/- 1.1 to 25.9 +/- 1.4 spikes/s after SNc lesion, the hyperactivity being reversed after additional PPN lesion to 16.8 +/- 1.2 spikes/s. The reversal of STN and SNr hyperactivity of 6-OHDA-treated rats by additional PPN lesion suggests an important modulatory influence of the PPN on STN activity. Moreover, these findings could indicate a new therapeutic strategy in PD by interventional modulation of the PPN.

Regional brain variations of cytochrome oxidase activity and motor coordination in Girk2Wv (Weaver) mutant mice

The Girk2(Wv) (weaver) phenotype, caused by a mutated inward rectifying potassium channel, is characterized by degeneration of cerebellar granule cell population as well as midbrain dopamine-containing cells of the nigrostriatal pathway. To investigate the regional brain metabolic consequences of this combined pathology, cytochrome oxidase (CO) activity was measured by histochemistry from brain regions of wild-type and homozygous Girk2(Wv) mutant mice and correlated with motor performances. CO activity of Girk2(Wv) mutants was abnormal in cerebellar cortex, dentate nucleus, and brainstem regions (medial and lateral vestibular nuclei, prepositus, superior colliculus, lateral cuneiform nucleus, and reticular nuclei) implicated in the gaze system. CO activity increased in midbrain dopaminergic regions after correcting for tissue density, regions with severe depletion of tyrosine hydroxylase activity. Forebrain regions were relatively spared in term of CO activity, except for subthalamic nucleus, lateral geniculate nucleus, and cortical eye field. Similarly to the Rora(sg) cerebellar mutant, metabolic alterations in cerebellar and vestibular regions were linearly correlated with poor motor coordination, underlining the sensitivity of these tests to cerebellar dysfunction.

Changes in the neuronal activity in the pedunculopontine nucleus in chronic MPTP-treated primates: an in situ hybridization study of cytochrome oxidase subunit I, choline acetyl transferase and substance P mRNA expression

The pedunculopontine nucleus is a mesencephalic nucleus that has widespread and reciprocal connections with the basal ganglia. It has been implicated in the physiopathology of akinesia, rigidity, gait failure and sleep disorders associated with Parkinson's disease. In this study, in situ hybridization was used to examine the changes in neuronal metabolic activity (measuring cytochrome oxidase subunit I) and in the level of acetylcholine and Substance P synthesis in the pedunculopontine nucleus of monkeys chronically treated with MPTP. Significant reductions were observed in cytochrome oxidase subunit I (p = 0.001), choline acetyl transferase (p = 0.003) and substance P (p = 0.006) mRNA expression in parkinsonian animals compared with controls, indicating that pedunculopontine cholinergic neurons activity decreases with parkinsonism.

Consequences of unilateral nigrostriatal denervation on the thalamostriatal pathway in rats

The position of the caudal intralaminar nuclei within basal ganglia circuitry has largely been neglected in most studies dealing with basal ganglia function. During the past few years, there has been a growing body of evidence suggesting that the thalamic parafascicular nucleus in rodents (PF) exerts a multifaceted modulation of basal ganglia nuclei, at different levels. Our aim was to study the activity of the thalamostriatal pathway in rats with unilateral dopaminergic depletion. The experimental approach comprised first unilateral delivery of 6-OHDA in the medial forebrain bundle. Thirty days post-lesioning, animals showing a clear asymmetry were then subjected to bilateral injection of Fluoro-Gold (FG) within the striatum. Subsequently, expression of the mRNA encoding the vesicular glutamate transporter 2 (vGLUT2) was detected within thalamostriatal-projecting neurons (FG-labeled) by in situ hybridization and the results were confirmed by laser-guided capture microdissection microscopy followed by real-time PCR. The data showed that there was a marked neuronal loss restricted to PF neurons projecting to the dopamine-depleted striatum. Moreover, PF neurons innervating the dopamine-depleted striatum were intensely hyperactive. These neurons showed a marked increase on the expression of vGLUT2 mRNA as well as for the mRNA encoding the subunit I of cytochrome oxidase as compared with those neurons projecting to the striatum with normal dopamine content. Thus, the selective neurodegeneration of PF neurons innervating the striatum together with the increased activity of the thalamostriatal pathway coexist after nigrostriatal denervation.

Prolonged blockade of NMDA or mGluR5 glutamate receptors reduces nigrostriatal degeneration while inducing selective metabolic changes in the basal ganglia circuitry in a rodent model of Parkinson's disease

We compared the neuroprotective and metabolic effects of chronic treatment with ionotropic or metabotropic glutamate receptor antagonists, in rats bearing a unilateral nigrostriatal lesion induced by 6-hydroxydopamine (6-OHDA). The ionotropic, N-methyl-D-aspartate receptor antagonist MK-801 increased cell survival in the substantia nigra pars compacta (SNc) and corrected the metabolic hyperactivity (increased cytochrome oxidase activity) of the ipsilateral substantia nigra pars reticulata (SNr) associated with the lesion, but showed no effects on the 6-OHDA-induced hyperactivity of the subthalamic nucleus (STN). Significant-although less pronounced-protection of SNc neurons was also observed following treatment with the metabotropic glutamate receptor (mGluR5) antagonist 2-methyl-6-(phenylehtynyl)-pyridine (MPEP). As opposed to MK-801, MPEP abolished the STN metabolic hyperactivity associated with the nigrostriatal lesion, without affecting SNr activity. Specific modulation of STN hyperactivity obtained with mGluR5 blockade may, therefore, open interesting perspectives for the use of this class of compounds in the treatment of Parkinson's disease.

Subthalamic nucleus lesioning inhibits expression and phosphorylation of c-Jun in nigral neurons in the rat's 6-OHDA model of Parkinson's disease

Parkinson's Disease (PD) is characterized by a loss of nigral dopamine (DA) neurons, followed by a striatal DA deficit. Inhibition of the subthalamic nucleus (STN) reverses L-DOPA sensitive motor symptoms and improves efficacy of pharmacotherapy in PD-patients. The underlying mechanism of these effects, however, remains largely unknown. Previously, we could show in the rat's 6-hydroxyDA (6-OHDA) model of PD that ablative STN-lesioning exerts functionally neuroprotective effects on the DAergic nigrostriatal pathway against 6-OHDA toxicity, in terms of elevating the number of tyrosine hydroxylase (TH)-expressing neurons rather than enhancing the total number of cells surviving 2 and 6 weeks post lesioning, as assessed via fluorogold staining. These data were correlated with increased functional recovery of 6-OHDA-lesioned rats with preceding STN-lesioning. Here, we extend the previous study design to observation periods of up to 12 weeks to assess long-term effects. Furthermore, to elucidate cellular mechanisms underlying potential neuroprotective effects, we explore the regulation of cellular markers involved in neurodegenerative cascades via immunocytochemistry. We show that preceding STN-lesioning significantly inhibits 6-OHDA induced expression/phosphorylation of the transcription factor c-Jun in surviving nigral neurons in comparison with controls. However, we also demonstrate that functionally neuroprotective effects of preceding STN-lesioning subside after 12 weeks, as assessed with TH immunostaining. We therefore conclude that c-Jun induction/phosphorylation is involved in 6-OHDA toxicity and that STN-lesioning transiently preserves of dopaminergic phenotype of nigral neurons partially via delaying the induction and attenuating the expression and phosphorylation of c-Jun.

Unilateral lesion of the pedunculopontine nucleus induces hyperactivity in the subthalamic nucleus and substantia nigra in the rat

Recent data suggest a role for the pedunculopontine nucleus (PPN) in the pathophysiology of Parkinson's disease. Although there is anatomical evidence that the PPN and the basal ganglia are reciprocally connected, the functional importance of these connections is poorly understood. Lesioning of the PPN was shown to induce akinesia in primates, whereas in the 6-hydroxydopamine rat model the PPN was found to be hyperactive. As both nigrostriatal dopamine depletion and lesioning of the PPN were shown to induce akinesia and parkinsonism, the present study was performed in order to investigate the changes in neuronal activity of the subthalamic nucleus (STN) and the substantia nigra pars reticulata (SNr) after unilateral ibotenic acid lesioning of the PPN and after unilateral 6-hydroxydopamine lesioning of the substantia nigra pars compacta (SNc). The firing rate of STN neurones significantly increased from 10.2 +/- 6.2 (mean +/- SD) to 14.6 +/- 11.7 spikes/s after lesion of the PPN and to 18.6 +/- 14.5 spikes/s after lesion of the SNc. The activity of the SNr significantly increased from 19.6 +/- 10.5 to 28.7 +/- 13.4 spikes/s after PPN lesioning and to 23.5 +/- 10.8 spikes/s after SNc lesioning. Furthermore, PPN lesion decreased the number of spontaneously firing dopaminergic SNc cells, while having no effect on their firing rate. The results of our study show that lesion of the PPN leads to hyperactivity of the STN and SNr, similar to the changes induced by lesion of the SNc. Moreover, the decreased activity of SNc cells observed after PPN lesion might be at the origin of activity changes in the STN and SNr.

A role for endocannabinoids in viral-induced dyskinetic and convulsive phenomena

Dyskinesias and seizures are both medically refractory disorders for which cannabinoid-based treatments have shown early promise as primary or adjunctive therapy. Using the Borna disease (BD) virus rat, an animal model of viral encephalopathy with spontaneous hyperkinetic movements and seizure susceptibility, we identified a key role for endocannabinoids in the maintenance of a balanced tone of activity in extrapyramidal and limbic circuits. BD rats showed significant elevations of the endocannabinoid anandamide in subthalamic nucleus, a relay nucleus compromised in hyperkinetic disorders. While direct and indirect cannabinoid agonists had limited motor effects in BD rats, abrupt reductions of endocannabinoid tone by the CB1 antagonist SR141716A (0.3 mg/kg, i.p.) caused seizures characterized by myoclonic jerks time-locked to periodic spike/sharp wave discharges on hippocampal electroencephalography. The general opiate antagonist naloxone (NLX) (1 mg/kg, s.c.), another pharmacologic treatment with potential efficacy in dyskinesias or L-DOPA motor complications, produced similar seizures. No changes in anandamide levels in hippocampus and amygdala were found in convulsing NLX-treated BD rats. In contrast, NLX significantly increased anandamide levels in the same areas of normal uninfected animals, possibly protecting against seizures. Pretreatment with the anandamide transport blocker AM404 (20 mg/kg, i.p.) prevented NLX-induced seizures. These findings are consistent with an anticonvulsant role for endocannabinoids, counteracting aberrant firing produced by convulsive agents, and with a functional or reciprocal relation between opioid and cannabinoid tone with respect to limbic convulsive phenomena.

Changes in cytoskeletal gene expression linked to MPTP-treatment in Mice

Parkinson's disease is a neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra and a marked reduction of dopamine (DA) levels in the striatum. Binding to its specific receptors, DA switches on a complex program of intracellular signaling that regulates gene expression. We evaluated the changes in striatal gene expression in a mouse model of Parkinson's disease, using differential display analysis. The mRNA for the cytoskeleton family proteins, radixin, cofilin and centractin/ARP-1, was abnormally expressed in the striatum of these MPTP-treated mice. Moreover, we also found that radixin mRNA and its protein levels are under DA control through specific D1-dopaminergic receptors in a dose- and time-dependent manner in the GT1-7 neural cell line. These findings suggest a role for DA for regulation of cytoskeletal proteins involved in the integrity and function of synapsis.

Activation of group III metabotropic glutamate receptors presynaptically reduces both GABAergic and glutamatergic transmission in the rat globus pallidus

To investigate the role of group III metabotropic glutamate receptors (mGluRs) in the globus pallidus (GP), whole-cell recordings were performed using rat brain slice preparations. Application of the group III mGluRs specific agonist L(+)-2-amino-4-phosphonobutyric acid (L-AP4) suppressed the amplitude of striatal stimulation-induced IPSCs and internal capsule stimulation-induced EPSCs in most of the GP neurons that were capable of generating repetitive firing without spike accommodation. The suppression of IPSCs and EPSCs was accompanied by an increase in the paired-pulse ratio. The L-AP4 effects were antagonized by (R,S)-alpha-cyclopropyl-4-phosphophenylglycine, a blocker for group II/III mGluRs. L-AP4 reduced the frequency of mIPSCs and mEPSCs without changing their amplitude distribution. L-AP4 failed to change iontophoretic glutamate induced responses. These results suggest that the subthalamo-pallidal glutamatergic input might homo- and hetero-synaptically control GABAergic and glutamatergic transmission in the GP.

Cytochrome oxidase activity in the monkey globus pallidus and subthalamic nucleus after ablation of striatal interneurons expressing substance P receptors

To understand functional roles of striatal interneurons in primate basal ganglia circuitry, we ablated interneurons expressing substance P (SP) receptors (SPR) in the putamen with SP-saporin, a SPR selective neurotoxin. The effect of SP-saporin injection into the putamen was evaluated by examining the loss of cholinergic interneurons and NADPHd-positive (nicotinamide adenine dinucleotide phosphate diaphorase positive) interneurons. We then analyzed regional metabolic changes using cytochrome oxidase (CO) histochemistry. CO activity in some regions of the internal and external segments of the globus pallidus (GP) in the lesioned hemisphere was lower than that in the contralateral or surrounding GP regions. CO activity in the subthalamic nucleus, however, showed no significant change. The present findings suggest that striatopallidal projection neurons exert enhanced inhibitory influence on the GP without modulatory control by the striatal SPR-expressing interneurons.

Conditional ablation of striatal neuronal types containing dopamine D2 receptor disturbs coordination of basal ganglia function

Dopamine (DA) exerts synaptic organization of basal ganglia circuitry through a variety of neuronal populations in the striatum. We performed conditional ablation of striatal neuronal types containing DA D2 receptor (D2R) by using immunotoxin-mediated cell targeting. Mutant mice were generated that express the human interleukin-2 receptor alpha-subunit under the control of the D2R gene. Intrastriatal immunotoxin treatment of the mutants eliminated the majority of the striatopallidal medium spiny neurons and cholinergic interneurons. The elimination of these neurons caused hyperactivity of spontaneous movement and reduced motor activation in response to DA stimulation. The elimination also induced upregulation of GAD gene expression in the globus pallidus (GP) and downregulation of cytochrome oxidase activity in the subthalamic nucleus (STN), whereas it attenuated DA-induced expression of the immediate-early genes (IEGs) in the striatonigral neurons. In addition, chemical lesion of cholinergic interneurons did not alter spontaneous movement but caused a moderate enhancement in DA-induced motor activation. This enhancement of the behavior was accompanied by an increase in the IEG expression in the striatonigral neurons. These data suggest that ablation of the striatopallidal neurons causes spontaneous hyperactivity through modulation of the GP and STN activity and that the ablation leads to the reduction in DA-induced behavior at least partly through attenuation of the striatonigral activity as opposed to the influence of cholinergic cell lesion. We propose a possible model in which the striatopallidal neurons dually regulate motor behavior dependent on the state of DA transmission through coordination of the basal ganglia circuitry.

Dual effects of intermittent or continuous L-DOPA administration on gene expression in the globus pallidus and subthalamic nucleus of adult rats with a unilateral 6-OHDA lesion

Intermittent oral doses of levodopa (L-DOPA) are routinely used to treat Parkinson's disease, but with prolonged use can result in adverse motor complications, such as dyskinesia. Continuous administration of L-DOPA achieves therapeutic efficacy without producing this effect, yet the molecular mechanisms are unclear. This study examined, by in situ hybridization histochemistry, the effects of continuous or intermittent L-DOPA administration on gene expression in the globus pallidus and subthalamic nucleus of adult rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion of the nigrostriatal pathway. Results were compared to 6-OHDA-treated rats receiving vehicle. Our results provide original evidence that continuous L-DOPA normalizes the 6-OHDA-lesion-induced increase in mRNA levels encoding for the 67 kDa isoform of glutamate decarboxylase in neurons of the globus pallidus and cytochrome oxidase subunit I mRNA levels in the subthalamic nucleus. The extent of normalization did not differ between the continuous and intermittent groups. In addition, intermittent L-DOPA induced an increase in the mRNA levels encoding for the 65 kDa isoform of glutamate decarboxylase in globus pallidus neurons ipsilateral to the lesion and a bilateral increase in c-fos mRNA expression in the subthalamic nucleus. These results suggest that continuous L-DOPA tends to normalize the 6-OHDA-lesion-induced alterations in cell signaling in the pallido-subthalamic loop. On the other hand, we propose that chronic intermittent L-DOPA exerts a dual effect by normalizing cell signaling in a subpopulation of neurons in the globus pallidus and subthalamic nucleus while inducing abnormal signaling in another subpopulation.

A multiple target neural transplantation strategy for Parkinson's disease

Intracerebral transplantation of embryonic ventral mesencephalic tissue is a potential treatment for patients with Parkinson's disease for whom medical management is unsatisfactory. Neural transplantation for parkinsonism has been studied experimentally in animal models of Parkinson's disease for more than two decades. These animal studies have shown significant graft survival, synapse formation, graft induced-dopamine release, and behavioural recovery in transplanted animals. Encouraged by these results, clinical programs have been initiated over the past 15 years; more than 250 patients worldwide have undergone neural transplantation. Both animal and clinical studies indicate that neural transplantation has the potential to become a valuable treatment option for Parkinson's disease. However, while many transplant recipients obtain clinically useful symptom relief, in all cases functional recovery is incomplete. Certain symptoms do not respond well to transplant therapy, and those symptoms that do typically do not resolve completely. This has spurred efforts to optimize the transplant procedure. One important approach is exploring novel methods such as multiple site transplantation. This transplantation strategy results in a more complete reinnervation of the dopaminergic circuitry that is affected in Parkinson's disease. In principle, multiple site transplantation should provide a more satisfactory resolution of symptoms. Here we review the progress made in multiple site neural transplantation for Parkinson's disease. The effects of intrastriatal, intranigral, intrasubthalamic nucleus, and intrapallidal grafts in animal models of Parkinson's disease are analysed. The current data suggest that intrastriatal grafts alone are inadequate to promote complete functional recovery. A multiple target strategy may restore dopaminergic input to affected basal ganglia nuclei and improve outcomes of neural transplantation in Parkinson's disease.

Systemic administration of dizocilpine maleate (MK-801) or L-dopa reverses the increases in GAD65 and GAD67 mRNA expression in the globus pallidus in a rat hemiparkinsonian model

This study examined the consequences of systemic treatment with either L-dopa or MK-801 on the levels of mRNAs encoding the 65 and 67 kDa isoforms of glutamate decarboxylase (GAD65 and GAD67) in the striatum and globus pallidus (GP) of rats rendered hemiparkinsonian by intranigral 6-hydroxydopamine injection. GADs mRNA levels were assessed by means of in situ hybridization histochemistry. In the striatum, dopamine denervation resulted in increased GAD67 mRNA levels at the rostral and caudal levels, whereas GAD65 showed selective increase at the caudal level. L-dopa and MK-801 treatments showed differential effects on the two GAD isoform levels in rats with 6-hydroxydopamine lesion. The lesion-induced increases in GAD67 transcripts were potentiated by L-dopa but unaffected by MK-801, whereas the increases in GAD65 were suppressed by MK-801 but unaffected by L-dopa. These data suggest a heterogeneity of glutamate-dopamine interaction in the anteroposterior extent of the striatum and show that NMDA-mediated mechanisms are involved in the 6-hydroxydopamine lesion-induced transcriptional changes in striatal GAD65 but not GAD67. In GP, the 6-OHDA lesion elicited increases in both GAD65 and GAD67 mRNA levels. L-dopa or MK-801 treatment suppressed the lesion-induced augmentations in the two GADs mRNA levels. These results indicate that dopamine denervation-induced changes in the functional activity of GP neurons involve both dopamine and glutamate NMDA receptor-mediated mechanisms. Comparison between the effects of L-dopa and MK-801 treatments on markers of the activity of striatal and pallidal GABA neurons further suggest that the impact of these treatments at the GP level do not depend solely on the striatopallidal input.

Environmental enrichment: effects on stereotyped behavior and regional neuronal metabolic activity

The present study evaluated whether environmental enrichment-related effects on the development of stereotyped behavior in deer mice were associated with alterations in neuronal metabolic activity. Deer mice were reared under either enriched or standard housing conditions for 60 days following weaning. All mice were then placed in automated photocell detectors and classified as either stereotypic or non-stereotypic. Neuronal metabolic activity was then assessed using cytochrome oxidase (CO) histochemistry. The results demonstrated that environmental enrichment significantly increased neuronal metabolic activity in the motor cortex. Furthermore, non-stereotypic mice exhibited significantly more CO activity than stereotypic mice in the cortex, striatum, nucleus accumbens, thalamus, hippocampus and amygdala. This latter effect was due to the enriched mice as evidenced by a significant interaction between housing condition and behavioral status in the cortex, striatum, nucleus accumbens, thalamus and hippocampus. Thus, the observed increase in CO activity reflected increased neuronal metabolic activity in non-stereotypic enriched mice relative to stereotypic enriched mice. These results suggest that, in a developmental model of spontaneous stereotypy, the enrichment-related prevention of stereotyped behavior is associated with increased CO activity.

Intraoperative microrecordings of the subthalamic nucleus in Parkinson's disease

Microelectrode recordings of single unit neuronal activity were used during stereotactic surgery to define the subthalamic nucleus for chronic deep brain stimulation in the treatment of Parkinson's disease. By using five parallel trajectories, often two to three microelectrodes allow us to recognize subthalamic nucleus (STN) neuronal activity. STN neurons were easily distinguished from cells of the overlying zona incerta and the underlying substantia nigra. During a typical exploratory track, we can observe a very low background noise in the zona incerta and almost complete absence of single cell recording. Penetration of the electrode tip into the STN is characterized by a sudden increase in background activity and single cell activity of spontaneously active neurons. The exit of electrode tip out of the STN corresponds to a decrease in background noise and a loss of single cell activity. Spontaneous neuronal activity increases again when the electrode tips enters the substantia nigra pars reticulata (SNr); however, the activity is less rich than in the STN, indicating a more cell-sparse nucleus. STN neurons are characterized by a mean firing rate of 42.30 +/- 22.00 spikes/sec (mean +/- SD). The STN cells exhibited irregular or bursty discharge pattern. The pattern of single cell activity in the SNr is a more regular tonic activity that can easily be distinguished from the bursting pattern in the STN. The most useful criteria to select a trajectory are (1) the length of an individual trajectory displaying typical STN activity, (2) the bursting pattern of activity, and (3) motor responses typical of the sensorimotor part of the nucleus. In conclusion, microelectrode recording of the subthalamic area improves the accuracy of targeting the STN.

Characterisation of striatal NMDA receptors involved in the generation of parkinsonian symptoms: intrastriatal microinjection studies in the 6-OHDA-lesioned rat

Treatments for Parkinson's disease based on replacement of lost dopamine have several problems. Following loss of dopamine, enhanced N-methyl-D-aspartate (NMDA) receptor-mediated transmission in the striatum is thought to be part of the cascade of events leading to the generation of parkinsonian symptoms. We determined the localisation and pharmacological characteristics of NMDA receptors that play a role in generating parkinsonian symptoms within the striatum. Rats were lesioned unilaterally with 6-hydroxydopamine (6-OHDA), and cannulae implanted bilaterally to allow injection of a range of NMDA receptor antagonists at different striatal sites. When injected rostrally into the dopamine-depleted striatum, the glycine site partial agonist, (+)-HA-966 (44-400 nmol) caused a dose-dependent contraversive rotational response consistent with an antiparkinsonian action. (+)-HA-966 (400 nmol) had no effect when infused into more caudal regions of the dopamine-depleted striatum, or following injection into any striatal region on the dopamine-intact side. To determine the pharmacological profile of NMDA receptors involved in inducing parkinsonism in 6-OHDA-lesioned rats, a range of NMDA receptor antagonists was infused directly into the rostral striatum. Ifenprodil (100 nmol) and 7-chlorokynurenate (37 nmol), but not MK-801 (15 nmol) or D-APV (25 nmol) elicited a dramatic rotational response when injected into the dopamine-depleted striatum. This pharmacological profile is not consistent with an effect mediated via blocking NR2B-containing NMDA receptors. The effect of intrastriatal injection of ifenprodil was increased in animals previously treated with levodopa (L-dopa) methyl ester. This was seen as an increase in on-time and in peak rotational response. We propose that stimulation of NR2B-containing NMDA receptors in the rostral striatum underlies the generation of parkinsonian symptoms. These studies are in line with previous findings suggesting that administration of NR2B-selective NMDA receptor antagonists may be therapeutically beneficial for parkinsonian patients, when given de novo and following L-dopa treatment.

Unilateral lesion of the nigrostriatal pathway induces an increase of neuronal activity of the pedunculopontine nucleus, which is reversed by the lesion of the subthalamic nucleus in the rat

The role of the pedunculopontine nucleus (PPN) in the pathophysiology of Parkinson's disease is still unclear. Using microrecordings, we investigated the changes occurring in PPN neurons after lesions of the substantia nigra compacta (SNc) and the role of the subthalamic nucleus (STN) in these changes. In normal rats the firing rate of PPN neurons was 10.6 +/- 1.4 spikes/s, the majority of neurons (91%) having a regular firing pattern, 6% irregular and 3% in bursts. In rats with 6-hydroxydopamine lesions of the SNc, the firing rate increased significantly to 18.3 +/- 3.0 spikes/s compared with normal rats. In addition, the firing pattern changed significantly: 70% of the neurons discharged regularly, 27% irregularly and 3% in bursts. In rats with ibotenic acid lesions of the STN, the firing rate decreased significantly to 7.2 +/- 0.9 spikes/s and the firing pattern changed significantly: 50% of the neurons discharged regularly, 43% irregularly and 7% in bursts. The rats with combined SNc and STN lesions showed no change in the firing rate (8.5 +/- 1.0 spikes/s) compared to normal rats. The firing pattern changed significantly: 69% of the cells discharged regularly, 26% irregularly and 5% in bursts. These findings demonstrate that PPN neurons are overactive and more irregular in the 6-hydroxydopamine-lesioned rats, suggesting the implication of this nucleus in the pathophysiology of parkinsonism. Moreover, the fact that STN lesions induced a reduction in the firing rate of the PPN in normal rats and a normalization of the firing rate in rats with 6-hydroxydopamine lesions suggests that this nucleus is under major control of the STN.

Blockade of NMDA receptors by MK-801 reverses the changes in striatal glutamate immunolabeling in 6-OHDA-lesioned rats

A lesion of the dopamine (DA)-containing nigrostriatal pathway with 6-hydroxydopamine (6-OHDA) results in an increase in the density of nerve terminal glutamate immunolabeling and in the mean percentage of asymmetrical synapses containing a discontinuous postsynaptic density [Meshul et al. (1999) Neuroscience 88:1-16]. Similar alterations in striatal glutamate synapses have been reported following blockade of striatal DA D-2 receptors with subchronic haloperidol treatment [Meshul et al. (1994) Brain Res 648:181-195]. The haloperidol-induced change in glutamate synapses was blocked by coadministration of the N-methyl-D-aspartate (NMDA) noncompetitive receptor antagonist MK-801. In order to determine if blockade of NMDA receptors could alter the density of nerve terminal glutamate immunolabeling following a 6-OHDA lesion of the nigrostriatal pathway, MK-801 was administered to lesioned animals for 14 days. In addition, the number of apomorphine-induced contralateral rotations was determined prior to and following the administration of MK-801. MK-801 administration reversed the increase in the density of nerve terminal glutamate immunolabeling due to a 6-OHDA lesion. There was a small but significant decrease in the number of apomorphine-induced contralateral rotations following administration of MK-801 compared to the number of rotations prior to treatment with the NMDA antagonist. These results demonstrate that blockade of postsynaptic NMDA receptors affects the density of presynaptic glutamate immunolabeling and that this change in nerve terminal glutamate density is associated with a decreased behavioral response to direct DA receptor stimulation. Whether the effect of MK-801 is directly on the striatum or acts through other excitatory pathways of the basal ganglia remains unclear.

The motor circuit of the human basal ganglia reconsidered

The standard model of human basal ganglia organization was introduced in the 1980s on the basis of animal experiments and clinical experience of various human motor disorders. This paper reviews evidence from various sources which suggests that this standard model only incompletely accounts for aspects of basal ganglia function, and thus requires modification.

Functional mapping of the human globus pallidus: contrasting effect of stimulation in the internal and external pallidum in Parkinson's disease

Our objective was to elaborate a functional map of the globus pallidus by correlating the intrapallidal localization of quadripolar electrodes implanted in parkinsonian patients with the clinical effect of the stimulation of each contact. Five patients with L-DOPA-responsive Parkinson's disease presenting severe motor fluctuations and L-DOPA-induced dyskinesias were treated by continuous bilateral high-frequency stimulation of the globus pallidus. The effects of stimulation on parkinsonian disability were tested through each of the four stimulating contacts of each electrode. The anatomical localization of each of the stimulating contacts was determined by confronting the pre- and post-operative magnetic resonance imaging with the anatomical atlas of Schaltenbrand and Wharen.(34) The registration procedure comprised digitization of the atlas, the use of deformation tools to fit atlas sections with magnetic resonance imaging sections, and three-dimensional reconstruction of both the atlas and the magnetic resonance imaging sections. Analysis of the 32 stimulating contacts tested did not reveal a somatotopic organization in the pallidal region investigated but demonstrated that high-frequency stimulation had contrasting effects depending on whether it was applied to the external or the internal pallidum. Akinesia was improved by stimulation of the external pallidum but worsened by stimulation of the internal pallidum. In contrast, parkinsonian rigidity was improved by stimulation of either part of the pallidum. The areas in the internal pallidum where stimulation worsened akinesia were those in which stimulation reduced or suppressed L-DOPA-induced dyskinesias. Conversely, stimulation applied to the external pallidum induced dyskinesias. The fact that rigidity was improved by stimulation of the internal and external pallidum suggests that the neuronal bases of parkinsonian rigidity are different from those of akinesia and dyskinesias. The effect on akinesia and dyskinesias is in agreement with the current model of basal ganglia circuitry(10) if high-frequency stimulation activates rather than inhibits pallidal neurons, a possibility which is very likely since there are marked anatomical, biochemical and electrophysiological differences between the globus pallidus and the subthalamic nucleus. This study demonstrates that high-frequency stimulation of the globus pallidus in parkinsonian patients has contrasting effects depending on whether it is applied to the external or the internal part of this nucleus. The effect on akinesia and dyskinesias suggests that stimulation activates pallidal neurons, a result which challenges the generally accepted concept that high-frequency stimulation inactivates neurons in the region stimulated.

The indirect basal ganglia pathway in dopamine D(2) receptor-deficient mice

Recent pathophysiological models of basal ganglia function in Parkinson's disease predict that specific neurochemical changes in the indirect pathway would follow the lack of stimulation of D(2) dopamine receptors. Post mortem studies of the basal ganglia in genetically modified mice lacking functional copies of the D(2) dopamine receptor gene allowed us to test these predictions. When compared with their congenic N(5) wild-type siblings, mice lacking D(2) receptors show an increased expression of enkephalin messenger RNA in the striatum, and an increased activity and expression of cytochrome oxidase I in the subthalamic nucleus, as expected. In addition, D(2) receptor-deficient mice display a reduced expression of glutamate decarboxylase-67 messenger RNA in the globus pallidus, as the basal ganglia model predicts. This reduction contrasts with the lack of change or increase in glutamate decarboxylase-67 messenger RNA expression found in animals depleted of dopamine after lesions of the mesostriatal dopaminergic system. Furthermore, D(2) receptor-deficient mice show a significant decrease in substance P messenger RNA expression in the striatonigral neurons which form the direct pathway. Finally, glutamate decarboxylase-67 messenger RNA expression in the basal ganglia output nuclei was not affected by mutations in the D(2) receptor gene, a fact that could probably be related to the absence of a parkinsonian locomotor phenotype in D(2) receptor-deficient mice. In summary, these findings provide compelling evidence demonstrating that the lack of endogenous stimulation of D(2) receptors is sufficient to produce subthalamic nucleus hyperactivity, as assessed by cytochrome oxidase I histochemistry and messenger RNA expression, and strongly suggest the existence of interactions between the basal ganglia direct and indirect pathways.

Exercise increases metabolic capacity in the motor cortex and striatum, but not in the hippocampus

Acute bouts of exercise have been shown to produce transient increases in regional cerebral glucose utilization, oxygen uptake, and cerebral blood flow in motor cortex, striatum, and hippocampus. The purpose of this study was to determine whether or not chronic exercise will cause long-term metabolic plasticity in brain structures activated during physical activity. The activity of cytochrome oxidase (COX), is coupled to the production of ATP, and reflects long-term plasticity in metabolic capacity. The present study examined whether or not 6 months of voluntary exercise would increase COX activity in the striatum, sensorimotor cortex, and three hippocampal subfields. Five-month-old, female Long-Evans hooded rats were randomly assigned to a control or exercise condition. Exercising rats had running wheels attached to their home cages. After the training period, fresh brains were rapidly frozen and sectioned with a cryostat. COX activity was measured using COX histochemical methods and optical densitometry. Rats in the exercise condition had significantly higher optical density in the hindlimb and forelimb motor cortices (18%, P<0.01) and dorsolateral caudate putamen (17%, P<0.01), but not in the ventrolateral caudate putamen or any subfield of the hippocampus. Although exercise is believed to increase neuronal activity in the hippocampus, motor cortex and striatum, only limb representations in the motor cortex and striatum increase bioenergetic capacity after regular exercise.

The subthalamic nucleus, hemiballismus and Parkinson's disease: reappraisal of a neurosurgical dogma

The subthalamic nucleus (STN) currently is considered to play a key role in the pathophysiological origin of the parkinsonian state and is therefore the main target for surgical treatment of Parkinson's disease. The authors review the incidence of hemichorea/ballism (HCB) as a complication of thalamotomy, pallidotomy or campotomy procedures before the introduction of levodopa therapy, including the few reported cases accompanied by a neuropathological study. The literature shows that only a small number of parkinsonian patients with HCB had a lesion of the STN. Preliminary data in Parkinson's disease patients submitted to a subthalamotomy with current functional stereotaxy also indicate that HCB is a very rare complication. To explain this observation, we suggest that the parkinsonian state is characterized by an increased threshold for the induction of dyskinesia following STN lesioning. This arises as a consequence of reduced activity in the 'direct' GABA projection to the globus pallidus medialis (GPm) which accompanies dopamine depletion. Lesioning of the STN reduces excitation of the GPm, and theoretically this should induce dyskinesias. However, an STN lesion also, simultaneously, further reduces the hypoactivity in the globus pallidus lateralis (GPl) that is a feature of Parkinson's disease, and hence may compensate for GPm hypoactivity, thus self-stabilizing basal ganglia output activity and reducing the risk of HCB. We conclude that lesioning of the STN in Parkinson's disease is a feasible approach in some circumstances.