L-DOPA reverses the hypokinetic behaviour and rigidity in rotenone-treated rats

Peripherally and locally administered rotenone (an inhibitor of mitochondrial complex I) has been proposed as a model of Parkinson's disease (PD) as it induces nigrostriatal degeneration associated with alpha-synuclein inclusions. If rotenone-induced symptoms represent a model of PD, than they should be counteracted by L-DOPA. To answer this question, rats were treated with rotenone 2.5 mg/kg over 48 days. Behavioural data showed a strong increase in catalepsy, a decrease in locomotor activity and biochemical data showed a significant depletion of dopamine levels in the striatum (Cpu) and substantia nigra in rotenone treated animals compared to vehicle. To examine the effectiveness of L-DOPA in reversing the motor deficit in rats, a dose of L-DOPA (10 mg/kg) in combination with the peripheral amino acid decarboxylase inhibitor benserazide were daily administrated intraperitonially for a period of 10 days in the rotenone-treated rats. This treatment counteracted catalepsy and increased locomotor activity and number of rearings but decreased inactive sitting. In this animal model (rotenone model), catalepsy tests and motor activities showed that the clinically used anti-parkinsonian drug L-DOPA substitutes rotenone-induced dopamine (DA) deficiency.     

Controversies on new animal models of Parkinson's disease pro and con: the rotenone model of Parkinson's disease (PD)

A general complex I deficit has been hypothesized to contribute to neurodegeneration in Parkinson's disease (PD) and all toxins used to destroy dopaminergic neurons are complex I inhibitors. With MPTP or 6-OHdopamine, this hypothesis can not be tested since these toxins selectively accumulate in the dopaminergic neurons. However with rotenone, which penetrates all cells, the hypothesis can be tested. Thus, the proof of the hypothesis is whether or not rotenone-induced neurodegeneration mimics the degenerative processes underlying PD. Low doses of rotenone (1.5 or 2.5 mg/kg in oil i.p.) were administered to Sprague Dawley rats on a daily basis. After about 20 days of treatment, signs of parkinsonism occurred and the concentrations of NO and peroxidase products rose in the brain, especially in the striatum. After 60 days of treatment, rotenone had destroyed dopaminergic neurons. Behaviourally, catalepsy was evident, a hunchback posture and reduced locomotion. Other transmitter systems were not, or much less affected. L-DOPA-methylester (10 mg/kg plus decarboxylase inhibition) potently reversed the parkinsonism in rats. Also when infused directly into the dopaminergic neurons, rotenone produced parkinsonism which was antagonized by L-DOPA. Some peripheral symptoms of PD are mimiced by rotenone too, for example a low testosterone concentration in the serum and a loss of dopaminergic amacrine cells in the retina. These results support the hypothesis of an involvement of complex I in PD and render the rotenone model as a suitable experimental model. The slow onset of degeneration make it suitable also to study neuroprotective strategies. Evidence that rotenone-induced neurodegeneration spreads beyond the dopaminergic system is not contradictory given that, according to the new staging studies, also degeneration in PD is not confined to dopamine neurons.     

Dietary restriction and 2-deoxyglucose administration improve behavioral outcome and reduce degeneration of dopaminergic neurons in models of Parkinson's disease.

Parkinson's disease (PD) is an age-related disorder characterized by progressive degeneration of dopaminergic neurons in the substantia nigra (SN) and corresponding motor deficits. Oxidative stress and mitochondrial dysfunction are implicated in the neurodegenerative process in PD. Although dietary restriction (DR) extends lifespan and reduces levels of cellular oxidative stress in several different organ systems, the impact of DR on age-related neurodegenerative disorders is unknown. We report that DR in adult mice results in resistance of dopaminergic neurons in the SN to the toxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP-induced loss of dopaminergic neurons and deficits in motor function were ameliorated in DR rats. To mimic the beneficial effect of DR on dopaminergic neurons, we administered 2-deoxy-D-glucose (2-DG; a nonmetabolizable analogue of glucose) to mice fed ad libitum. Mice receiving 2-DG exhibited reduced damage to dopaminergic neurons in the SN and improved behavioral outcome following MPTP treatment. The 2-DG treatment suppressed oxidative stress, preserved mitochondrial function, and attenuated cell death in cultured dopaminergic cells exposed to the complex I inhibitor rotenone or Fe2+. 2-DG and DR induced expression of the stress proteins heat-shock protein 70 and glucose-regulated protein 78 in dopaminergic cells, suggesting involvement of these cytoprotective proteins in the neuroprotective actions of 2-DG and DR. The striking beneficial effects of DR and 2-DG in models of PD, when considered in light of recent epidemiological data, suggest that DR may prove beneficial in reducing the incidence of PD in humans.     

Chronic Administration with Rotenone does not Enhance MPTP Neurotoxicity in C57BL/6 Mice

Systematic administration of rotenone as one of pesticides is known to produce degeneration of nigral dopaminergic neurons and motor deficits in experimental animals. Here, we investigated to determine whether systematic administration of rotenone causes the increased susceptibility in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice. Rotenone was injected into MPTP-treated mice over a period of 4 weeks. Thereafter, we evaluated the effect of rotenone 1, 3, and 6 weeks after the cessation of treatment with rotenone. In the present study with HPLC analysis, rotenone did not enhance MPTP-induced dopaminergic neurotoxicity in mice. Furthermore, MPTP + rotenone (9 mg/kg)-treated mice exhibit a significant loss of motor activity 1 day after the cessation of treatment with rotenone, However, no significant change of motor activity was found in MPTP-treated and MPTP + rotenone (9 mg/kg)-treated animals 6 weeks after the cessation of treatment with 0.5% carboxymethyl cellulose or rotenone. Our Western blot analysis study demonstrated that the change of tyrosine hydroxylase and glial fibrillary acidic protein protein levels in MPTP-treated mice was similar than that in MPTP + rotenone-treated animals. These results suggest that rotenone did not enhance MPTP neurotoxicity in mice. Our findings suggest that rotenone is not a reliable model for PD. Thus, our findings provide further valuable information for the pathogenesis of PD for exposure to agricultural pesticides.     

Rotenone destroys dopaminergic neurons and induces parkinsonian symptoms in rats

Rotenone (an inhibitor of mitochondrial NADH dehydrogenase, a naturally occurring toxin and a commonly used pesticide) appears to reproduce the neurochemical, neuropathological and behavioural feature of Parkinson's disease (PD) in the rat. In this study, rotenone was administrated on a daily basis systemically by intraperitoneal injection of two different doses: 1.5 mg/kg (low dose) and 2.5 mg/kg (moderate dose), over a period of 2 months. This treatment caused depletion of dopamine in the posterior striatum (CPu) and prefrontal cortex and also reduced tyrosine hydroxylase-immunoreactivity in CPu. Behavioural experiments showed dose-dependent catalepsy in the two treatment groups of rats. Data from this study indicate that in rats rotenone is capable of causing degeneration of dopaminergic neurons and induction of parkinsonian symptoms. It is concluded that the causal mechanisms of neuronal degeneration implicate a complex I deficiency in the aetiology of rotenone-induced and perhaps in some cases of sporadic PD.     

Dose-dependent loss of motor function after unilateral medial forebrain bundle rotenone lesion in rats: a cautionary note

The organic pesticide rotenone is a neurotoxin suspected to cause Parkinson's disease (PD) symptoms by selectively targeting and compromising the survival of dopaminergic neurons. Rotenone in rodent models reproduces key features of human PD by impairing the mitochondrial electron transport chain, leading to intracellular alpha-synuclein aggregates and functional impairments typical for PD. The present study characterized the dose-response relationship of standard rotenone concentrations in motor impairments in a rat model. Rats received a single medial forebrain bundle injection of 4, 8, or 12 μg of rotenone. Animals were assessed in skilled limb use, skilled and non-skilled walking and exploratory activity as well as drug-induced rotation. The results revealed rotational bias and stable impairments in skilled walking and gross motor function up to five weeks post injection. However, transient motor deficits facilitated rapid improvement of skilled reaching success. Mainly the temporal aspects of skilled and non-skilled motor performance were responsive to different rotenone concentrations. By contrast, drug-induced rotation and nigral TH+ cell loss were not influenced by different rotenone doses. Rats infused with 8 μg and 12 μg seemed to have reached a ceiling effect in motor deficits as they were not distinguishable in behavioral measures. Most strikingly, the stereological and morphological analyses revealed non-specific toxicity of vehicle and rotenone infusions that caused macroscopic lesions beyond nigral boundaries. These findings suggest that sensitivity of comprehensive motor tests to subtle modulation of dopamine function is independent of dopamine cell loss per se. Furthermore, caution is advised concerning non-specific toxicity of rotenone and vehicle substances in experimental animal models.     

GDNF reverses priming for dyskinesia in MPTP-treated, L-DOPA-primed common marmosets

Parkinson's disease (PD) is associated with a progressive loss of dopamine neurons in the substantia nigra and degeneration of dopaminergic terminals in the striatum. Although L-DOPA treatment provides the most effective symptomatic relief for PD it does not prevent the progression of the disease, and its long-term use is associated with the onset of dyskinesia. In rodent and primate studies, glial cell line-derived neurotrophic factor (GDNF) may prevent 6-OHDA- or MPTP-induced nigral degeneration and so may be beneficial in the treatment of PD. In this study, we investigate the effects of GDNF on the expression of dyskinesia in L-DOPA-primed MPTP-treated common marmosets, exhibiting dyskinesia. GDNF or saline was administered by two intraventricular injections, 4 weeks apart, to MPTP-treated, L-DOPA-treated common marmosets primed to exhibit dyskinesia. Prior to GDNF or saline administration, all animals displayed marked dyskinesia when treated with L-DOPA. GDNF administration produced a significant improvement in motor disability and, following the second injection of GDNF, a significant improvement in the locomotor activity was observed. Following the administration of L-DOPA there was a greater reversal of disability and a reduction in the intensity of L-DOPA-induced dyskinesia in GDNF-treated animals compared to saline-treated controls. However, there was no significant difference in L-DOPA's ability to increase locomotor activity between GDNF-treated and saline-treated animals. GDNF treatment caused a significant increase in the number of tyrosine hydroxylase-positive neurons in the substantia nigra, but no change in [(3)H]mazindol binding to dopamine terminals was found in the striatum of GDNF-treated animals compared to saline-treated controls. In GDNF-treated animals a small but significant reduction in enkephalin mRNA was observed in the caudate nucleus but not in the putamen or the nucleus accumbens. Substance P mRNA expression was equally reduced in the caudate nucleus and the putamen of the GDNF-treated animals but not in the nucleus accumbens. Intraventricular administration of GDNF improved MPTP-induced disability and reversed dopamine cell loss in the substantia nigra. GDNF also diminished L-DOPA-induced dyskinesia, which may relate to its ability to partly restore nigral dopaminergic transmission or to modify the activity of striatal output pathways.     

Acute intranigral infusion of rotenone in rats causes progressive biochemical lesions in the striatum similar to Parkinson's disease

We examined in Sprague-Dawley rats whether intranigral administration of complex-I inhibitor, rotenone, produces biochemical lesions in the striatum similar to those observed in Parkinson's disease (PD). Unilateral stereotaxic infusion of rotenone (2-12 mug in 1 mul) into substantia nigra (SN) pars compacta caused significant inhibition of complex-I activity and increased production of hydroxyl radicals in vivo as measured employing spectrophotometric and HPLC-electrochemical procedures, respectively. It also caused a significant time- and dose-dependent reduction of dopamine level, but not serotonin, in the ipsilateral striatum when assayed using an HPLC electrochemical method. This effect was found to be progressive for 90 days. A dose-dependent decrease in nigral glutathione level, as measured fluorimetrically, was also observed to be progressive till 90th day. A significant decrease in tyrosine hydroxylase immunoreactivity in the striatum (73 +/- 8.4% as assessed by densitometric studies) or in SN ipsilateral to the side of infusion suggested nigrostriatal neuronal degeneration. A dose of rotenone (6 microg in 1 microl) that caused 55% striatal dopamine depletion when infused into the SN failed to affect serotonin levels in the terminal regions when infused into the nucleus raphe dorsalis, indicating rotenone's specificity of action towards dopaminergic neurons. Our findings suggest that unilateral infusion of rotenone reproduces neurochemical and neuropathological features of hemiparkinsonism in rats and indicate an active involvement of oxidative stress in rotenone-induced nigrostriatal neurodegeneration. The present study also demonstrates more sensitivity of dopaminergic neurons towards rotenone and establishes mitochondrial complex-I damage as one of the major contributory components of neurodegeneration in PD. The progressive nature of pathology in this model closely mimics idiopathic PD, and absence of mortality warrants the use of this model in drug discovery programs.     

Some central effects of CGP 37849 and CGP 39551, the competitive NMDA receptor antagonists: potential antiparkinsonian activity

Summary Two new competitive NMDA receptor antagonists with oral activity CGP 37849 (D,L-E-amino-methyl-phosphono-3-pentenoic acid) and its ethyl ester CGP 39551 were studied in rats. CGP 37849 did not change the locomotor activity or increased it. The hyperactivity induced by CGP 37849 was antagonized by haloperidol but not idazoxan or prazosin. CGP 39551 decreased the locomotor activity. The studied compounds did not increase the locomotion in monoamine-depleted (pretreated with reserpine and -methyl-p-tyrosine) rats. Clonidine induced antiakinetic effect in monoamine-depleted rats. This effect was more pronounced after joint administration of clonidine and CGP 37849 or CGP 39551. The locomotor hyperactivity induced by joint dministration of CGP 37849 and clonidine was inhibited by haloperidol but not prazosin or idazoxan. CGP 37849 but not CGP 39551 also enhanced antiakinetic effect of L-DOPA (given together with benserazide) in monoamine-depleted rats. CGP 37849 antagonized the spiperone- and fluphenazine-induced catalepsy; CGP 39551 had considerably weaker antagonistic effect. The reserpine-induced catalepsy was attenuated by CGP 37849. MK-801, a non-competitive NMDA antagonist inhibited spiperone- but not reserpine-induced catalepsy. The obtained results indicate that CGP 37849 administered alone or in combination with L-DOPA or clonidine may be a potential antiparkinsonian drug.     

An update on the rotenone models of Parkinson's disease: Their ability to reproduce the features of clinical disease and model gene–environment interactions

Parkinson's disease (PD) is the second most common neurodegenerative disorder that is characterized by two major neuropathological hallmarks: the degeneration of dopaminergic neurons in the substantia nigra (SN) and the presence of Lewy bodies in the surviving SN neurons, as well as other regions of the central and peripheral nervous system. Animal models have been invaluable tools for investigating the underlying mechanisms of the pathogenesis of PD and testing new potential symptomatic, neuroprotective and neurorestorative therapies. However, the usefulness of these models is dependent on how precisely they replicate the features of clinical PD with some studies now employing combined gene–environment models to replicate more of the affected pathways. The rotenone model of PD has become of great interest following the seminal paper by the Greenamyre group in 2000 (Betarbet et al., 2000). This paper reported for the first time that systemic rotenone was able to reproduce the two pathological hallmarks of PD as well as certain parkinsonian motor deficits. Since 2000, many research groups have actively used the rotenone model worldwide. This paper will review rotenone models, focusing upon their ability to reproduce the two pathological hallmarks of PD, motor deficits, extranigral pathology and non-motor symptoms. We will also summarize the recent advances in neuroprotective therapies, focusing on those that investigated non-motor symptoms and review rotenone models used in combination with PD genetic models to investigate gene–environment interactions.     

Localization and functional significance of striatal neurons immunoreactive to aromatic L-amino acid decarboxylase or tyrosine hydroxylase in rat Parkinsonian models

Striatal neurons which are immunoreactive (ir) to aromatic L-amino-acid decarboxylase (AADC) or tyrosine hydrodroxylase (TH) may play a role in the decarboxylation of L-DOPA to dopamine (DA) in advanced stages of Parkinson's disease (PD). However, the functional significance of these neurons and the mechanisms responsible for their induction remain to be clarified. In this study, rats were subjected to different types of dopaminergic or serotonergic denervation and L-DOPA injection to study the effects on these neurons. AADC-ir neurons were found in both normal and DA-denervated striata, and no significant differences in their number and distribution were induced following different types of denervation or L-DOPA administration. TH-ir neurons were only found in DA-denervated striata. However, TH-ir neurons did not appear in those areas with maximal DA depletion, but rather were observed near spared or partially lesioned DA terminals. The population of AADC-ir neurons may make a significant contribution to the effects of exogenous L-DOPA in advanced stages of PD. In addition, TH-ir neurons may contribute to these effects, since we have detected AADC-ir in TH-ir neurons using confocal laser scanning microscopy. Finally, neither L-DOPA therapy nor serotonergic denervation induces significant changes in the number or distribution of these neurons.     

Neuroprotective Effects of Metallothionein Against Rotenone-Induced Myenteric Neurodegeneration in Parkinsonian Mice

Parkinson’s disease (PD) is a neurodegenerative disease with motor symptoms as well as non-motor symptoms that precede the onset of motor symptoms. Mitochondrial complex I inhibitor, rotenone, has been widely used to reproduce PD pathology in the central nervous system (CNS) and enteric nervous system (ENS). We reported previously that metallothioneins (MTs) released from astrocytes can protect dopaminergic neurons against oxidative stress. The present study examined the changes in MT expression by chronic systemic rotenone administration in the striatum and colonic myenteric plexus of C57BL mice. In addition, we investigated the effects of MT depletion on rotenone-induced neurodegeneration in CNS and ENS using MT-1 and MT-2 knockout (MT KO) mice, or using primary cultured neurons from MT KO mice. In normal C57BL mice, subcutaneous administration of rotenone for 6 weeks caused neurodegeneration, increased MT expression with astrocytes activation in the striatum and myenteric plexus. MT KO mice showed more severe myenteric neuronal damage by rotenone administration after 4 weeks than wild-type mice, accompanied by reduced astroglial activation. In primary cultured mesencephalic neurons from MT KO mice, rotenone exposure induced neurotoxicity in dopaminergic neurons, which was complemented by addition of recombinant protein. The present results suggest that MT seems to provide protection against neurodegeneration in ENS of rotenone-induced PD model mice.     

Calpain as a potential therapeutic target in Parkinson's disease

Pathophysiology of idiopathic Parkinson's disease (PD) is associated with degeneration of dopaminergic neurons and inflammatory responses in the mid-brain substantia nigra (SN). However, central dopaminergic replenishment therapeutic strategy with L-3,4-dihydroxyphenylalanine (L-DOPA), the precursor for dopamine synthesis, does not fully rescue these cells in SN or improve motor function. Besides, prolonged use of L-DOPA worsens the clinical symptoms in PD patients. Thus, there is a possibility that other areas of central nervous system may also be affected in this disease. Spinal cord, the final coordinator of movement in the central nervous system, may be one such site that is critically affected during pathogenesis of this complex movement disorder. In this review, we summarize the evidence in support of involvement of calpain, a Ca(2+)-activated non-lysosomal protease, in spinal cord degeneration in two models of experimental parkinsonism induced by the neurotoxin 1-methyl-4-phenyl 1,2,3,6-tetrahydropyridine and also the environmental toxin rotenone. The key focus of this review is to discuss the role that calpain plays in disrupting the structural and functional integrity of the spinal cord in these experimental models of parkinsonism. A similar disruptive role of calpain has been reported earlier in SN of PD patients as well as in experimental PD animals. Studies in rodent and cell culture models of PD suggest that treatment with calpain inhibitors (e.g., calpeptin, MDL-28170) can prevent neuronal death and restore functions. Furthermore, the degradation of calpain substrates in both brain and spinal cord during pathogenesis of PD suggested a putative role of calpain, and calpain inhibition as a therapeutic strategy in PD.     

Chronic rotenone treatment induces behavioral effects but no pathological signs of parkinsonism in mice

It has been hypothesized that exposures to neurotoxic pesticides together with aging and genetic factors increase the risk for developing Parkinson's disease (PD) which is characterized by a progressive degeneration of the nigrostriatal dopaminergic pathway. Chronic treatment with the pesticide rotenone has been reported to induce parkinsonism in rats. Although transgenic mice (but not transgenic rats) are available to investigate the importance of environmental factors in genetically predisposed animals, the effects of chronic rotenone exposure have so far not been examined in intact mice. Therefore, we investigated the effects of chronic exposure to rotenone (2.5 or 4.0-5.0 mg/kg s.c. for 30-45 days) in mice aged 2.5, 5, or 12 months. During the treatment period, the effects on vitality and motor behavior were investigated. Furthermore, the toxicity of rotenone on dopaminergic nigrostriatal neurons and peripheral tissues was examined. In comparison with control mice, rotenone-treated mice had a decreased spontaneous motor activity, but the density of nigral dopaminergic neurons failed to show any significant changes, except for a tendency to decrease in old mice treated with 4 mg/kg. At the tested doses, rotenone caused a moderate hepatic fatty degeneration. The data indicate that rotenone is not able to cause the neuropathological characteristics of PD in mice under these testing paradigms, which were similar to those of the rotenone rat model. Further studies will have to clarify whether genetic mouse models of PD might be more sensitive to the neurotoxic effects of rotenone.     

A modified MPTP treatment regime produces reproducible partial nigrostriatal lesions in common marmosets

Standard MPTP treatment regimens in primates result in > 85% destruction of nigral dopaminergic neurons and the onset of marked motor deficits that respond to known symptomatic treatments for Parkinson's disease (PD). The extent of nigral degeneration reflects the late stages of PD rather than events occurring at its onset. We report on a modified MPTP treatment regimen that causes nigral dopaminergic degeneration in common marmosets equivalent to that occurring at the time of initiation of motor symptoms in man. Subcutaneous administration of MPTP 1 mg/kg for 3 consecutive days caused a reproducible 60% loss of nigral tyrosine hydroxylase (TH)-positive cells, which occurred mainly in the calbindin-D(28k)-poor nigrosomes with a similar loss of TH-immunoreactivity (TH-ir) in the caudate nucleus and the putamen. The animals showed obvious motor abnormalities with reduced bursts of activity and the onset of motor disability. However, the loss of striatal terminals did not reflect early PD because a greater loss of TH-ir occurred in the caudate nucleus than in the putamen and a marked reduction in TH-ir occurred in striatal patches compared to the matrix. Examination of striatal fibres following a partial MPTP lesion showed a conspicuous increase in the number and the diameter of large branching fibres in the putaminal and to some extent caudatal matrix, pointing to a possible compensatory sprouting of dopaminergic terminals. In addition, these partially lesioned animals did not respond to acute treatment with L-DOPA. This primate partial lesions model may be useful for examining potential neuroprotective or neurorestorative agents for PD.     

A30P α-synuclein impairs dopaminergic fiber regeneration and interacts with L-DOPA replacement in MPTP-treated mice

Parkinson's disease (PD) is the most common neurodegenerative movement disorder and is characterized by the loss of dopaminergic neurons from the substantia nigra pars compacta (SNpc). α-synuclein (αsyn) has been linked to the pathophysiology of PD, because of its mutations causing familial PD and its accumulation in brains of patients with familial and sporadic PD. Dopamine (DA) replacement is the most effective therapy for ameliorating the motor symptoms of PD; however, it remains controversial whether DA-replacement boosts regeneration in the dopaminergic system or accelerates disease progression and enhances neuronal loss. Here, we studied the effect of chronic L-DOPA treatment on dopaminergic neurons in wild-type (WT) and A30P αsyn transgenic mice after MPTP treatment. Acute MPTP intoxication induced degeneration of dopaminergic neurons in both WT and A30P αsyn transgenic mice. A strong regeneration of dopaminergic fibers at 90 days after MPTP was observed in WT mice. In contrast, regeneration was less pronounced in A30P αsyn mice. Chronic L-DOPA treatment after MPTP intoxication did not only reduce the regeneration of nigrostriatal fibers but also led to an increased apoptotic gene-expression profile in the SNpc and to a decline of TH-positive neurons in A30P αsyn. Our findings reveal that the presence of A30P αsyn inhibits the regeneration of nigrostriatal dopaminergic fibers, and that L-DOPA treatment might interact with the pathogenesis in PD.     

Antiparkinsonian activity of L-propyl-L-leucyl-glycinamide or melanocyte-inhibiting factor in MPTP-treated common marmosets.

The neuropeptide melanocyte-inhibiting factor (MIF) or L-propyl-L-leucyl-glycinamide (PLG) has been reported in some studies to improve the motor signs of Parkinson's disease (PD) and in rodent models of PD. In this study of oral and intravenous MIF in N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets, a wide range of doses of MIF administered alone (0.25, 1, 2, 5, 10, 20 mg/kg orally) did not increase locomotor activity, relieve motor disability, or induce dyskinesias. When MIF (1.0 and 5.0 mg/kg orally or 10 and 20 mg/kg intravenously) was administered concomitantly with levodopa/benserazide, no significant differences in motor function or dyskinesias were observed compared with levodopa/benserazide alone. The results of this first study of MIF in the marmoset MPTP model provide no encouragement for the reinvestigation of MIF in the clinical management of the motor signs of PD.     

Effect of locus coeruleus denervation on levodopa-induced motor fluctuations in hemiparkinsonian rats

Parkinson's disease (PD) is characterized not only by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta (SNc) but also by a degeneration of locus coeruleus (LC) noradrenergic neurons. It has been suggested that deficient LC noradrenergic mechanisms might play a critical role in symptomatology and in the progression of PD. However, the effect of LC depletion on levodopa-induced motor complications, such as the motor fluctuations, is still unknown. Male Sprague-Dawley rats received 50 mg/kg intraperitoneal (i.p.) of [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine] (DSP-4) or saline 7 days before the day of 6-hydroxydopamine (6-OHDA, 8 mug) administration in the medial forebrain bundle. Four weeks later, animals were treated with levodopa (25 mg/kg with benserazide, twice at day, i.p.) for 22 days. Rotational behavior was measured on days 1 and 22 of levodopa administration. Tyrosine hydroxylase (TH) immunohistochemistry was performed to evaluate the neurodegeneration in the SNc and LC. Striatal dopamine transporter (DAT) immunohistochemistry was performed to evaluate DA depletion. As expected, levodopa administration decreased the duration of the motor response in the vehicle-pretreated group (P < 0.01). A potentiation of levodopa-induced shortening in the duration of motor response was not achieved after LC depletion since no significant differences were observed in the duration of rotational behavior between these two groups on day 22. In addition, LC depletion did not potentiate either the total number of rotations or the maximal peak of rotation induced by levodopa treatment. These results suggest that LC depletion might not be involved in the pathophysiology of levodopa-induced motor fluctuations.     

Behavioral and immunohistochemical effects of chronic intravenous and subcutaneous infusions of varying doses of rotenone

Mitochondrial toxins such as the complex 1 inhibitor rotenone are widely used as pesticides and may be present in military environments. Administration of rotenone can induce biochemical and histological alterations similar to those of Parkinson's disease in rats. However, only a subset of animals show these effects and it is unclear whether more subtle alterations are caused by chronic administration of rotenone in those animals that appear resistant to its toxic effects on dopaminergic nerve terminals. To address this question, vehicle or rotenone (2.0, 2.5, or 3.5 mg/kg/day) was administered intravenously or subcutaneously for 21 days to adult rats, and rotenone effects on survival, motor behavior, and striatal tyrosine hydroxylase immunoreactivity (TH-IR) were examined. Both intravenous and subcutaneous rotenone induced a dose-dependent decrease in survival rates. Surviving animals showed a decrease in spontaneous rearing. Locomotor activity and movement initiation time were also altered in some of the experimental groups. Confirming previous results, TH-IR in the striatum was markedly decreased in rats that fell ill early in the study and in a few of the surviving rats with high rotenone doses. However, none of the surviving rats receiving 2.0 mg/kg/day showed TH-IR loss reminiscent of Parkinson's disease, and loss of striatal TH-IR across doses was not correlated with motor behavior in individual rats. Thus, chronic administration of low doses of rotenone induces motor anomalies even in animals that do not develop histological signs of Parkinson's disease, indicating a pervasive neurological effect of moderate mitochondrial dysfunction in vivo.     

Behavioural and neurochemical effects of Ro 40-7592, a new COMT inhibitor with a potential therapeutic activity in Parkinson's disease

Summary Behavioural and some neurochemical effects of Ro 40-7592 (3,4-dihydroxy-4-methyl-5-nitrobenzophenone), a new COMT inhibitor, were studied in rats and mice. Ro 40-7592 increased the effect of L-DOPA (plus benserazide) on locomotor activity, reserpine-induced hypothermia, and catalepsy induced by pimozide, haloperidol and fluphenazine. Locomotor hyperactivity induced by amphetamine or nomifensine, as well as stereotypy induced by amphetamine (but not apomorphine), were also increased by Ro 40-7592. The drug stimulated exploratory activity in the open field test. It decreased the levels of HVA and 3-MT, increased the level of DOPAC but did not change the levels of dopamine in the striatum, nucleus accumbens and frontal cortex. These results indicate that Ro 40-7592 may improve the therapy with L-DOPA (plus decarboxylase inhibitor) of Parkinson's disease.