Effect of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine on the regional distribution of brain monoamines in the rhesus monkey

Adrenergic receptors in Alzheimer's disease brain: selective increases in the cerebella of aggressive patients

In this study, the distribution and concentration of beta1, beta2, and alpha2 adrenergic receptors were examined in the frontal cortex, hypothalamus, and cerebellum of Alzheimer's disease (AD) and age-matched control human brains by receptor autoradiography. The purpose of this study was to detect changes in adrenergic receptor concentrations in key areas of the brain known to affect behavior. For these studies, [125I]iodopindolol ([125I]IPIN) was used to visualize total beta adrenergic sites (with ICI-89,406 and ICI-118, 551 as subtype-selective antagonists to visualize beta2 and beta1 receptors, respectively). [3H]UK-14,304 was used to localize the alpha2 sites. Essentially no significant difference in adrenergic receptor concentration was found between total AD cases taken together and control patients. It was found, however, that there were important distinctions within the AD group when cases were subdivided according to the presence or absence of aggression, agitation, and disruptive behavior. Aggressive AD patients had markedly increased (by approximately 70%) concentrations of alpha2 receptors in the cerebellar cortex compared with nonaggressive patients with similar levels of cognitive deficit. The levels of cerebellar alpha2 receptors in aggressive AD patients were slightly above the healthy elderly controls, suggesting that these receptors are preserved and perhaps increased in this subgroup of AD. beta1 And beta2 adrenergic receptors of the cerebellar cortex showed smaller but significant ( approximately 25%) increases in concentration in aggressive AD subjects versus both nonaggressive AD patients and controls. No significant differences were found in adrenergic receptor concentrations within the frontal cortex or hypothalamus. These results point out the importance of distinguishing behavioral subgroups of AD when looking for specific neurochemical changes. These autoradiographic results may reflect the importance of the cerebellum in behavioral control.

Animal models of Parkinson's disease: an empirical comparison with the phenomenology of the disease in man

Animal models are an important aid in experimental medical science because they enable one to study the pathogenetic mechanisms and the therapeutic principles of treating the functional disturbances (symptoms) of human diseases. Once the causative mechanism is understood, animal models are also helpful in the development of therapeutic approaches exploiting this understanding. On the basis of experimental and clinical findings. Parkinson's disease (PD) became the first neurological disease to be treated palliatively by neurotransmitter replacement therapy. The pathological hallmark of PD is a specific degeneration of nigral and other pigmented brainstem nuclei, with a characteristic inclusion, the Lewy body, in remaining nerve cells. There is now a lot of evidence that degeneration of the dopaminergic nigral neurones and the resulting striatal dopamine-deficiency syndrome are responsible for its classic motor symptoms akinesia and bradykinesia. PD is one of many human diseases which do not appear to have spontaneously arisen in animals. The characteristic features of the disease can however be more or less faithfully imitated in animals through the administration of various neurotoxic agents and drugs disturbing the dopaminergic neurotransmission. The cause of chronic nigral cell death in PD and the underlying mechanisms remain elusive. The partial elucidation of the processes underlie the selective action of neurotoxic substances such as 6-hydroxydopamine (6-OHDA) or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), has however revealed possible molecular mechanisms that give rise to neuronal death. Accordingly, hypotheses concerning the mechanisms of these neurotoxines have been related to the pathogenesis of nigral cell death in PD. The present contribution starts out by describing some of the clinical, pathological and neurochemical phenomena of PD. The currently most important animal models (e.g. the reserpine model, neuroleptic-induced catalepsy, tremor models, experimentally-induced degeneration of nigrostriatal dopaminergic neurons with 6-OHDA, methamphetamine, MPTP, MPP+, tetrahydroisoquinolines, beta-carbolines, and iron) critically reviewed next, and are compared with the characteristic features of the disease in man.

Subsets of midbrain dopaminergic neurons in monkeys are distinguished by different levels of mRNA for the dopamine transporter: comparison with the mRNA for the D2 receptor, tyrosine hydroxylase and calbindin immunoreactivity

The midbrain dopamine system can be divided into two groups of cells based on chemical characteristics and connectivity. The dorsal tier neurons, which include the dorsal pars compacta and the ventral tegmental area, are calbindin-positive, and project to the shell of the nucleus accumbens. The ventral tier neurons are calbindin-negative and project to the sensorimotor striatum. This study examined the distribution of the mRNAs for the dopamine transporter molecule (DAT) and the D2 receptor in the midbrain of monkeys by using in situ hybridization. The distribution patterns were compared to that of tyrosine hydroxylase and calbindin immunohistochemistry. The results show that high levels of hybridization for DAT and the D2 receptor mRNA are found in the ventral tier, calbindin-negative neurons and relatively low levels are found in the dorsal, calbindin-positive tier. Within the dorsal tier, the dorsal substantia nigra pars compacta has the least amount of both messages. These results show that in monkeys, the ventral tegmental area and the dorsal pars compacta form a dorsal continuum of dopamine neurons which express lower levels of mRNA for DAT and D2 receptor than the ventral tier. DAT has been shown to be involved in the selective neurotoxicity of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Different levels of DAT mRNA and calbindin may explain the differential effects of MPTP neurotoxicity.

Cognitive deficits precede motor deficits in a slowly progressing model of parkinsonism in the monkey

Five adult Macaca fascicularis monkeys were trained to perform tests of cognitive and motor functioning that included a complex visual pattern discrimination task, an object retrieval task, a test of task persistence, and a timed motor task. Once stable baseline performance was achieved, monkeys were administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at doses of 0.05 to 0.075 mg/kg, 2 to 3 times per week for a total of 24 weeks. Animals were assessed weekly for performance on the previously learned tasks. All monkeys developed performance deficits in a predictable pattern with behavioural and cognitive deficits (i.e. deficits in task persistence and the cognitive component of object retrieval) appearing in advance of measurable motor deficits. Deficits in visual pattern discrimination never appeared. These results show that specific cognitive dysfunction pre-dates motor dysfunction in a chronic, slowly progressing parkinson model in monkeys and support the contention that cognitive deficits in Parkinson's disease may precede the motor signs of the disorder and may not be caused by them.

Effects of nigrostriatal denervation and L-dopa therapy on the GABAergic neurons in the striatum in MPTP-treated monkeys and Parkinson's disease: an in situ hybridization study of GAD67 mRNA

The effects of nigrostriatal denervation and L-dopa therapy on GABAergic neurons were analysed in patients with Parkinson's disease and in monkeys rendered parkinsonian by MPTP intoxication. The expression of the messenger RNA coding for the 67 kDa isoform of glutamic acid decarboxylase (GAD67 mRNA), studied by quantitative in situ hybridization, was used as an index of the GABAergic activity of the striatal neurons. A significant increase in GAD67 mRNA expression, generalized to all GABAergic neurons, was observed in MPTP-treated monkeys compared to control monkeys in the putamen and caudate nucleus (+44 and +67% respectively), but not in the ventral striatum. L-Dopa therapy significantly reduced GAD67 mRNA expression in the putamen and caudate nucleus to levels similar to those found in control monkeys. However, the return to normal of GAD67 mRNA expression was not homogeneous across all neurons since it was followed by an increase of labelling in one subpopulation of GABAergic neurons and a decrease in another. These data suggest that in MPTP-treated monkeys the degeneration of nigrostriatal dopaminergic neurons results in a generalized increase in GABAergic activity in all the GABAergic neurons of the striatum, which is partially reversed by L-dopa therapy. As the expression of GAD67 mRNA is less intense in the ventral than in the dorsal striatum, this increase in striatal GABAergic activity may be related to the severity of nigrostriatal denervation. In parkinsonian patients who had been chronically treated with L-dopa, GAD67 mRNA expression was significantly decreased in all GABAergic neurons, in the caudate nucleus (by 44%), putamen (by 43.5%) and ventral striatum (by 26%). The opposite variation of GAD67 mRNA in patients with Parkinson's disease, compared with MPTP-treated monkeys, might be explained by the combination of chronic nigrostriatal denervation and long-term L-dopa therapy.

Alterations in dopamine uptake sites and D1 and D2 receptors in cats symptomatic for and recovered from experimental parkinsonism

The administration of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to adult cats severely disrupts the dopaminergic innervation of the striatum. Animals display a parkinson-like syndrome, consisting of akinesia, bradykinesia, postural instability, and rigidity, which spontaneously recovers by 4-6 weeks after the last administration of MPTP. In this study we used quantitative receptor autoradiography to examine changes in DA uptake sites and DA receptors in the basal ganglia of normal, and symptomatic and recovered MPTP-treated cats. Consistent with the destruction of the nigrostriatal DA pathway, there was a severe loss of DA uptake sites, labeled with [3H]-mazindol, in the caudate nucleus (64-82%), nucleus accumbens (44%), putamen (63%), and substantia nigra pars compacta (SNc, 53%) of symptomatic cats. Following behavioral recovery, there were no significant changes in DA uptake site density. Significant increases of [3H]-SCH 23390 binding to D1 DA receptors were observed in the dorsal caudate (> 24%; P < 0.05) of symptomatic cats and in all regions of the caudate-putamen (> 30%; P < 0.05) of recovered animals. [3H]-SCH 23390 binding in the substantia nigra pars reticulata was half of that in the striatum and showed no changes in symptomatic or recovered animals. No alterations in the binding of [125I]-epidepride to D2 receptors was observed in any region of the striatum in either symptomatic or recovered animals. [125I]-Epidepride binding in the SNc was decreased by > 36% (P < 0.05) following MPTP treatment. These data show that cats made parkinsonian by MPTP exposure have a significant decrease in the number of DA reuptake sites throughout the striatum and that recovery of sensorimotor function in these animals is not correlated with an increase in the number of striatal reuptake sites. Behavioral recovery, however, does seem to be correlated with a general elevation of D1 receptors throughout the striatal complex. The present data also show that direct correlations between changes in DA receptor regulation after a large DA depleting lesion and behavioral deficits or recovery from those deficits are difficult and that the relationships between DA receptors/transporters and behavior require further study.

Chronic MPTP treatment reproduces in baboons the differential vulnerability of mesencephalic dopaminergic neurons observed in Parkinson's disease

Chronic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to baboons was shown previously to result in a motor syndrome and a pattern of striatal dopaminergic fibre loss similar to those observed in idiopathic Parkinson's disease. In the present study, tyrosine hydroxylase-immunoreactive neurons were quantified in the mesencephalon of control (n = 4) and chronically MPTP-treated (n = 3) baboons. MPTP induced a significant reduction in neuronal cell density in the substantia nigra (63.8% reduction) and the ventral tegmental area (53.1%). Within the substantia nigra, obvious mediolateral and dorsoventral gradients of neuronal cell loss were observed. First, the pars lateralis was more affected than the lateral divisions of the pars compacta (89.6% vs 73.8% cell loss), which in turn were more depleted than the medial divisions (60.1% reduction). Second, the ventral regions of the pars compacta were more degenerated than the dorsal parts (82.4 vs 51.5% decrease). This regional pattern is strikingly similar to that observed in Parkinson's disease and indicates that two subpopulations of dopaminergic neurons are distinguishable on the basis of their differential vulnerability to MPTP. Finally, the present study confirms that chronic mitochondrial complex I inhibition using MPTP in primates is sufficient to reproduce the typical dopaminergic cell loss and striatal fibre depletion observed in Parkinson's disease.

MPTP-induced parkinsonism in primates: pattern of striatal dopamine loss following acute and chronic administration

We analyzed the effect of two different schedules of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment on dopaminergic systems in the striatum of cynomolgus monkeys. Acute MPTP treatment produced a marked dopamine (DA) depletion, more severe in the caudate nucleus than in the putamen. Chronic MPTP induced a more pronounced reduction in DA levels, the putamen being slightly more affected than the caudate nucleus, in accord with immunohistochemical findings that showed a higher loss of tyrosine-hydroxylase positive neurons in ventral subpopulations of the substantia nigra pars compacta. A striking increment in the quotient DOPAC+HVA/DA was also observed in chronically but not in acutely treated monkeys, especially in the putamen. In chronically treated animals there was a nearly complete loss of DA in all subdivisions of the putamen. In the caudate nucleus, a rostrocaudal gradient of DA depletion was found, with a greater decrease in DA concentration in the rostral parts, especially in the dorsolateral portions. The pattern of striatal DA loss characteristic of Parkinson's disease can be reproduced to a certain extent in MPTP-intoxicated primates.

Cortical glucose metabolism in Parkinson's disease without dementia

There have been several reports of decreased regional cerebral metabolic rates for glucose (rCMRglc) in Parkinson's disease (PD), although others find no differences between PD patients and controls. Differences in the cognitive status of the PD patients may account for some of these inconsistencies. We report the results of a PET study using 18F-fluorodeoxyglucose (FDG) to measure rCMRglc in eight nondemented PD patients, six of whom were receiving dopaminergic medications, and eight age-matched control subjects. We scanned one tomographic level through the temporal lobes that included both temporal neocortex and mesial temporal cortex, and one tomographic level through the basal ganglia that included frontal and parietal cortex. Previously determined rate constants and an operational equation were used to determine rCMRglc. On average, rCMRglc values were 23% below control values for all regions studied, with the greatest differences in posterior brain regions (visual association cortex, primary visual cortex, and parietal cortex) and thalamus. These results indicate that PD patients may show neocortical hypometabolism, especially in posterior brain regions, in the absence of any demonstrable cognitive deficits.

Does neuromelanin contribute to the vulnerability of catecholaminergic neurons in monkeys intoxicated with MPTP?

The question has been raised as to whether neuromelanin, a by-product of catecholamine metabolism which accumulates during aging in primate midbrain neurons, contributes to the selective vulnerability of subgroups of dopaminergic neurons in Parkinson's disease. 1-Methyl-4-phenylpyridinium (MPP+) a metabolite of 1-methyl, 4-phenyl, 1,2,3,6-tetrahydropyridine (MPTP) is toxic to dopaminergic neurons, particularly in primates, producing a motor syndrome similar to that observed in Parkinson's disease. To test whether this neurotoxin preferentially affects melanized neurons, the survival of melanized and non-melanized catecholaminergic neurons was analysed after MPTP intoxication in the midbrain of the cynomolgus monkey (Macaca fascicularis). Experiments were performed on six animals chronically treated with MPTP (two were severely disabled, four moderately affected) and two age-matched control monkeys. Two populations of neurons were examined on regularly spaced sections throughout the midbrain: catecholaminergic neurons, identified by tyrosine hydroxylase immunohistochemistry and neuromelanin-containing neurons, visualized by Masson's method. The total number of neurons of each type was estimated in the different midbrain catecholaminergic cell groups using computer assisted image analysis. In the midbrains of control animals not all catecholaminergic neurons contained neuromelanin. The percentage of melanized neurons compared to the total population of tyrosine hydroxylase-positive neurons was high in the substantia nigra pars compacta (81.5%) and in the locus coeruleus (98%), intermediate in the substantia nigra pars lateralis (70%), in the catecholaminergic cell group A8 (50%), and in the ventral tegmental area (41.5%) and almost nil in the central gray substance. In MPTP-treated monkeys, the severity of the loss of catecholaminergic neurons was variable within the different midbrain cell groups, though of similar intensity in severely and mildly disabled monkeys. A relationship was found between the loss of dopaminergic neurons in the different mesencephalic cell groups of MPTP-intoxicated animals and the percentage of melanized neurons they normally contain (r = 0.98; P = 0.04). The percentage loss of catecholaminergic neurons in the locus coeruleus, the only noradrenergic cell group studied, was lower than expected from the correlation curve obtained for dopaminergic cell groups. Altogether, these findings indicate: (i) that dopaminergic neurons are more vulnerable to MPTP-toxicity than noradrenergic neurons; and (ii) that among dopaminergic neurons, those containing neuromelanin are more susceptible, indicating a possible role of neuromelanin in MPTP-toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Serotonergic sprouting in primate MTP-induced hemiparkinsonism

Immunocytochemistry to serotonin, dopamine beta hydroxylase (DBH), and tyrosine hydroxylase (TH) was studied in the brains of 2 cebus monkeys that had developed permanent hemiparkinsonism after intracarotid injection of 1.2 mg N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and were sacrificed after 10-12 months. A pronounced depletion of TH-immunoreactive neurons was found in the substantia nigra, caudate nucleus, and putamen, ipsilaterally to the injected side. In these dopamine-denervated structures, the number of serotonergic fibers was increased in the ipsilateral compared with the contralateral side, or with an untreated control monkey. Serotonergic neurons in the brainstem appeared to be unaffected. Topography and number of DBH-positive fibers in the control and the MPTP-injected sides were comparable.

N-methyl-4-phenylpyridinium (MPP+) potentiates the killing of cultured hepatocytes by catecholamines

The role of catecholamines in the toxicity of MPTP (N-methyl-4-phenyl- 1,2,3,6-tetrahydropyridine) was explored. The killing of cultured hepatocytes by dopamine and 6-hydroxydopamine was enhanced following inhibition of glutathione reductase by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), a manipulation known to sensitize such cells to an oxidative stress. The participation of activated oxygen species in the cell injury under such circumstances was shown by the ability of catalase and the ferric iron chelator deferoxamine to protect the hepatocytes. The toxicity of catecholamines was also potentiated by the mitochondrial site I (NADH dehydrogenase) inhibitor rotenone. MPP+ (N-methyl-4-phenyl-pyridinium), the putative toxic metabolite of MPTP is also a site I inhibitor. Incubation of hepatocytes with MPP+ similarly potentiated the toxicity of 6-hydroxydopamine, dopamine, and norepinephrine under conditions where MPP+ alone or catecholamines alone did not kill cells. Hepatocytes that had accumulated dopamine from the medium were killed by a subsequent exposure to MPP+ in the absence of a catecholamine in the medium. Hepatocytes that had not been pretreated with dopamine were not affected by the subsequent exposure to MPP+. These data indicated that catecholamines render hepatocytes more susceptible to the toxicity of MPP+ and suggest that the presence of catecholamines in specific neurons in the brain may be related to the selective neurotoxicity of MPTP.

Chronic administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine to monkeys: behavioural, morphological and biochemical correlates

The behavioural, biochemical and morphological effects of a chronic administration of low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) were studied in the common marmoset. Monkeys received the toxin (1 mg/kg i.p.) twice a week for four months. Group A monkeys were studied one week after the last injection of MPTP; group B monkeys were studied eight months after the last toxic injection. The monkey behaviour was observed throughout the experiment; the biochemical and morphological correlates were studied post mortem in the neostriatum and in the substantia nigra, respectively. Data collected from MPTP-treated marmosets were compared to those obtained from sham-injected control monkeys. The results can be summarized as follows. (1) In all MPTP-treated marmosets a progressive Parkinsonism occurred. In group B monkeys, a gradual behavioural recovery was observed after MPTP was discontinued. (2) Biochemical analysis of group A marmosets showed a depletion of dopamine, of 3,4-hydroxyphenylacetic acid and of homovanillic acid, and no variations in dopamine turnover in the neostriatum of MPTP-treated marmosets. In group B, biochemical analysis showed no differences between controls and MPTP-treated animals. (3) Morphological analysis showed that the density of midbrain dopaminergic neurons located in the substantia nigra was unchanged in group A monkeys, but was reduced by 6.8% in MPTP-treated monkeys of group B. The measurement of cross-sectional area showed that midbrain dopaminergic neurons were swollen in MPTP-treated monkeys of group A, with a 11.0% increase of cell size as compared to controls. In group A the nuclei were also swollen, being 304.8% larger in MPTP-treated monkeys, with a nucleus-to-cytoplasm ratio of 65.9% (as compared to 34.0% of controls). In group B monkeys cell size was increased by 18.4% in MPTP-treated marmosets, but the nuclei were of comparable size. The present data show that a chronic administration of low doses of MPTP brings about biochemical and morphological abnormalities. The first occur acutely in terminals and are reverted early after discontinuance of exposure to the toxin; the latter occur in dopaminergic perikarya, last longer than biochemical abnormalities and, at variance with them, increase in severity after MPTP is discontinued. Morphological abnormalities include early events, such as a transient swelling of nuclei or a long-lasting swelling of neurons, and late events, such as a decrease in the number of tyrosine hydroxylase-positive perikarya.(ABSTRACT TRUNCATED AT 400 WORDS)

Serotoninergic terminal transporters are differentially affected in Parkinson's disease and progressive supranuclear palsy: an autoradiographic study with [3H]citalopram

Receptor autoradiography with [3H]citalopram as ligand was used to study the distribution of serotonin uptake binding sites in post mortem brain tissues from patients with Parkinson's disease, progressive supranuclear palsy and from age-matched controls. Significant decreases in [3H]citalopram binding sites were found in the cerebral cortex of patients with Parkinson's disease and progressive supranuclear palsy. Densities of [3H]citalopram binding sites were significantly reduced in all components of the basal ganglia of Parkinson's disease but only in the head of caudate nucleus of progressive supranuclear palsy patients. The density of [3H]citalopram binding sites in the raphe nuclei of Parkinson's disease was comparable to control values. Our results suggest that serotoninergic terminals are differentially affected in Parkinson's disease and in progressive supranuclear palsy.

The biology and behaviour of intracerebral adrenal transplants in animals and man

The catecholamine containing chromaffin cells of the adrenal medulla have recently been employed as intracerebral grafts in man and animals with lesions of the nigrostriatal dopaminergic system. This review outlines the basic biology of the chromaffin cell with reference to its efficacy as a source of dopamine in the grafted state. This is followed by an evaluation of the use of these grafts in experimentally lesioned animals and in patients with Parkinson's disease.

Stable parkinsonian syndrome and uneven loss of striatal dopamine fibres following chronic MPTP administration in baboons

The progressive degeneration of dopamine neurons observed in idiopathic Parkinson's disease was mimicked by injecting low doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to baboons, on a chronic basis. Five Papio papio baboons were treated on two different regimens (chronic intravenous administration at weekly intervals for 20-21 months or, daily MPTP treatment for five days followed five to six months later by chronic weekly injections for 5-21.5 months). All animals were assessed for motor symptoms during and after neurotoxic treatment. Both regimens invariably resulted in the appearance of a progressive and irreversible syndrome characterized by action and resting tremor, cogwheel rigidity, postural impairments, hypokinesia and bradykinesia. In some animals, symptoms of resting tremor and rigidity initially restricted to one side of the body became bilateral within a few months of treatment. Subtle abnormalities that may be found in idiopathic Parkinson's disease such as alterations of the blink reflex response were also noted. Neuropathological examination of caudate nucleus, putamen, substantia nigra and ventral tegmental area in brain sections stained for tyrosine hydroxylase showed a typical uneven striatal dopamine fibre loss and a neuronal depletion in the dopaminergic mesencephalic cell groups that reproduce those observed in idiopathic Parkinson's disease. Immunocytochemical observations and behavioural data show that chronic rather than acute MPTP injection regimens can replicate most of the neuropathological and the clinical features typical of idiopathic Parkinson's disease, possibly by increasing the ability of this neurotoxin to target specific subpopulations of mesencephalic dopaminergic neurons.

Calbindin D-28K in the dopaminergic mesocortical projection of a monkey (Aotus trivirgatus)

Injections of fluorescent dyes were made in the prefrontal and motor cortex of owl monkeys and retrogradely labeled neurons in the mesencephalon were analyzed for tyrosine hydroxylase and calbindin-D28K immunostaining. Numbers of mesocortical dopaminergic neurons in the dorsal substantia nigra compacta and in the ventral tegmental area also contain calbindin-D28K. This cortically projecting calbindin-D28K containing subpopulation of the dopaminergic mesencephalic cells may be characterized by different electrophysiological properties and a lesser vulnerability to cell death.

Age-related effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment of common marmosets

The effect of treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on juvenile (6-8 months), young adult (2-4 years) and aged (8-10 years) common marmosets were compared. Juvenile marmosets were more resistant to the actions of MPTP and required a greater cumulative dose over a longer period to induce the same degree of motor disability observed in older animals. Young adult and aged marmosets showed an equivalent motor recovery in the 4-5 weeks following cessation of MPTP treatment, but juvenile animals were less able to compensate for the motor impairments. Losses of putamen [3H]dopamine uptake and caudate nucleus dopamine content were equivalent in young adult and aged animals. However, juvenile animals showed a more marked degree of dopamine depletion and reduction in [3H]dopamine uptake. Histological analysis showed cell loss in the substantia nigra to be most prominent in juvenile animals although it was evident in all groups. No loss of cells in the locus coeruleus was apparent in any of the groups studied, and no intraneuronal eosinophilic inclusions were seen. Greater nigral cell loss and dopamine depletion were required in juvenile animals to impair motor function. The degree of behavioural recovery was less in juvenile animals than in young adult and aged marmosets. The extent of behavioural recovery appeared linked to the severity of cell loss and was not reduced in old age.

Changes in brain catecholamines and dopamine uptake sites at different stages of MPTP parkinsonism in monkeys

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to produce parkinsonism in primates. We have studied the changes in brain catecholamines and the distribution of desipramine insensitive mazindol binding sites in MPTP parkinsonian primates at different levels of parkinsonism. Thirty-seven monkeys (Macaca fascicularis) were utilized in this study. Twelve naive animals received no treatment and served as controls. Twenty-five animals were rendered parkinsonian with serial injections of MPTP. All animals were given scored neurologic examinations throughout the study. Their movement was quantitated in an activity box. The animals were sacrificed 30-360 days after their last MPTP injection. The clinical exam of the MPTP parkinsonian monkeys demonstrated mildly to severely affected animals. There was an exponential decrease in brain catecholamine levels with increased clinical parkinsonism. The MPTP parkinsonian animals showed the greatest decrease (67-99.8%) in tissue dopamine levels in the caudate nucleus. The putamen followed closely in severity (48-99.8%) and the nucleus accumbens was much less affected (0-40%). The percent reduction of norepinephrine in the anterior pole of the frontal cortex (0-48%) was similar in degree to the decreased dopamine levels in the nucleus accumbens. Mazindol binding was decreased 30-98% in the caudate nucleus, 20-97% in the putamen, 0-26% in the nucleus accumbens, 80-96% in the substantia nigra pars compacta and 49-94% in the ventral tegmental area. In the striatum, the decreased mazindol binding was more pronounced laterally and posteriorly. In each animal, there was good correlation between tissue dopamine levels and the number of mazindol binding sites.

Sensitization of Dopamine-Stimulated Adenylyl Cyclase in the Striatum of 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine-Treated Rhesus Monkeys and Patients with Idiopathic Parkinson's Disease

Dopamine-stimulated adenylyl cyclase activity was measured in striatal homogenates of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated rhesus monkeys and humans with idiopathic Parkinson's disease and compared with the activity in control tissue. No differences between parkinsonian and control tissue were found in the presence of 20 mM NaCl. However, when 120 mM NaCl was included in the assay medium, a significantly higher increase in the Vmax of dopamine-stimulated adenylyl cyclase activity was observed in the caudate of MPTP-parkinsonian rhesus monkeys and the putamen of patients with idiopathic Parkinson's disease. No such sensitization was seen in the MPTP-treated rhesus putamen or human Parkinson's disease caudate tissue. A role of D2 receptors in this sensitization could be ruled out by the concomitant use of the D2 antagonist l-sulpiride and by [3H]spiperone saturation analysis of the D2 receptor density, which was found at control level in the caudate tissue of MPTP-treated rhesus monkeys. Similarly, on the basis of saturation binding with the D1 selective ligand 125I-SCH 23982, there was no difference in caudate nucleus D1 receptor densities between control and MPTP-treated monkeys. Our results point to a region-specific functional sensitization of D1 receptors as a consequence of severe dopaminergic denervation of the striatum and suggest the possibility of a therapeutic potential of a D1 agonist with full intrinsic activity in Parkinson's disease.

Differential vulnerability of primate caudate-putamen and striosome-matrix dopamine systems to the neurotoxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

The meperidine analogue derivative 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces nigrostriatal fiber damage and severe parkinsonism in humans and animals. MPTP-induced parkinsonism has been proposed as a model of Parkinson disease, but doubts have been raised about whether the patterns of nigrostriatal fiber loss in the two conditions are similar. We report here observations on [3H]mazindol monoamine (principally dopamine) uptake-site binding in the striatum of monkeys (Saimiri sciureus) exposed to low doses of MPTP. We show that this treatment can produce a pattern of nigrostriatal degeneration characteristic of that seen in Parkinson disease, in which there is greater depletion of dopaminergic markers in the putamen than in the caudate nucleus, especially posteriorly. Moreover, within the regions of diminished uptake-site binding in the MPTP-treated monkeys, there is differential preservation of binding in striosomes relative to the surrounding matrix. We suggest that both regional and striosome/matrix patterns of nigrostriatal depletion are key features of MPTP-induced neurodegeneration and that both patterns may provide clues to the mechanisms underlying neurodegeneration in Parkinson disease as well.

Mechanisms of neuronal loss in Parkinson's disease: a neuroanatomical-biochemical perspective

It is shown that the specific inter- and subregional patterns of striatal dopamine loss in idiopathic Parkinson's disease can serve as a criterion for the evaluation of neurotoxic processes suggested to play an etiological role in this disorder. Based on this premise, the possibility is examined that dopamine-based free radicals (oxidative stress), or a MPTP-like mechanism may be the primary cause of the substantia nigra cell death in idiopathic Parkinson's disease. It is concluded that the most likely determinant of the specific patterns of nigral cell loss and striatal dopamine deficit might be the peculiar topomorphological arrangement of the melanin-containing neurones in the human substantia nigra.