Enhanced glial cell line-derived neurotrophic factor mRNA expression upon (−)-deprenyl and melatonin treatments

Glial cell line-derived neurotrophic factor (GDNF) has been shown to be a preferentially selective neurotrophic factor for dopamine (DA) neurons. In the present study, we have examined the distribution of GDNF mRNA expression in several major DA-containing cell body and terminal areas and the regulation of GDNF mRNA expression upon various pharmacological treatments. Results indicated that there is a relatively higher GDNF mRNA level in neurons of the nigrostriatal and mesolimbic dopaminergic pathways. Upon chronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment (30 mg/kg, i.p., for 7 days), DA level was decreased, whereas GDNF mRNA expression was increased in the striatum, suggesting that more GDNF is synthesized and expressed to cope with the neurotoxin insult. Furthermore, among several DA neuron protective and/or therapeutic agents examined, both intrastriatal injections of (−)-deprenyl (1.25 μg and 2.5 μg) and melatonin (30 μg, 60 μg, and 120 μg) significantly enhanced GDNF mRNA expression in the striatum, whereas the same concentrations of (−)-deprenyl did not affect monoamine oxidase B (MAOB) activity, although it increased glutathione peroxidase (GPx) and/or superoxide dismutase (SOD) activities. Similarly, the same concentrations of melatonin did not alter SOD or GPx activities, except that the highest dose of melatonin (120 μg) increased lipid peroxidation in the striatum. Conversely, GM1 ganglioside injection (45 μg) lacked of an effect on GDNF mRNA expression. Together, these results suggest that both (−)-deprenyl and melatonin up-regulate GDNF gene expression at threshold doses lower than that needed for altering MAOB activity and/or the antioxidant enzyme systems, respectively. These results provide new information on the neuroprotective and therapeutic mechanisms of (−)-deprenyl and melatonin on DA neurons. J. Neurosci. Res. 53:593–604, 1998. © 1998 Wiley-Liss, Inc.     

1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) enhances tryptophan hydroxylase activity in mouse striatum, but not in the frontal cortex

We measured serotonin (5-HT) and 5-hydroxyindole-3-acetic acid (5-HIAA) contents and tryptophan hydroxylase (TPH) activity in mouse striatum and frontal cortex after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment (7 daily injections of 30 mg/kg). In the striatum, TPH activity was increased for at least 4 weeks after injection of MPTP, along with an increase in 5-HIAA. However, no significant change was observed in 5-HT, 5-HIAA or TPH activity in the frontal cortex. These results suggest that MPTP affects 5-HT through a change in TPH activity, specifically at nerve terminals in the striatum.     

3-Acetylpyridine results in degeneration of the extrapyramidal and cerebellar motor systems: loss of the dorsolateral striatal dopamine innervation

3-Acetylpyridine (3-AP) administration to rats results in degeneration of the dopamine (DA) innervation of the striatum as well as degeneration of the olivocerebellar system. We now report that administration of this pyridine neurotoxin results in a decrease in striatal DA concentration which is restricted to the dorsolateral aspects of the caudatoputamen. 3-AP treatment did not alter DA levels in the ventromedial striatum, the nucleus accumbens, or the anteromedial prefrontal cortex. Both 3-AP and another pyridine neurotoxin, 1-methyl-4-phenyl-1,2,3, 6-tetrahydropyridine (MPTP), potently inhibited in vitro MAOB activity and in contrast weakly inhibited MAOA activity. However, in vitro inhibition of MAOB by the selective inhibitor deprenyl did not prevent or attenuate 3-AP-induced striatal DA depletion. These data indicate that 3-AP administration to rats not only results in degeneration of the olivocerebellar system, but also effects degeneration of the DA innervation of the dorsolateral striatum, the striatal sector thought to subserve motoric and sensorimotor function. 3-AP-induced nigrostriatal degeneration differs from that elicited by MPTP in that the former is not prevented by deprenyl pretreatment. The 3-AP-induced degeneration of both extrapyramidal and cerebellar motor systems may offer insight into the mechanisms involved in degeneration of the two motor systems in certain strains of rodents (such as the Weaver mutant mouse), and suggests that the sequelae of administration of this pyridine may serve as a useful model for olivopontocerebellar atrophy-associated parkinsonism.     

Morphological, neurochemical, and behavioral characterizations associated with the combined treatment of diethyldithiocarbamate and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice

Changes in striatal dopamine (DA) neurochemistry, tyrosine hydroxylase immunocytochemistry of DA fibers, and behavior following the combined administration of diethyldithiocarbamate (DDC) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to mice were assessed. The combined treatment of DDC and MPTP produced a dose-dependent decrease in striatal DA levels and a dose-related increase in the striatal DOPAC:DA ratio. Cumulative doses of MPTP equal to or exceeding 53.0 (26.5 mg/kg x 2. i.p.), given in combination with DDC, were effective in reducing striatal DA levels to less than 25% of control levels 2 weeks after treatment. Tyrosine hydroxylase immunocytochemistry revealed large deafferentation of DA terminal regions in striatum, moderate reductions in nucleus accumbens and dendritic regions of substantia nigra, and slight reductions in the number of DA cell bodies in substantia nigra. Mice treated with DDC and MPTP became hyperactive during the light phase of their diurnal cycle: psychopharmacological data suggest that postsynaptic DA receptors were supersensitized following this treatment. These data provide evidence that the combined treatment of DDC and MPTP produces severe and enduring depletion of mesostriatal DA, and also concomitant behavioral changes in mice.     

MPTP and convulsive responses in rodents

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30 mg/kg s.c. for 5 days) to mice resulted in complete abolishment of strychnine seizure and of the tonic phase of the maximal electroshock response. Bicuculline and picrotoxin convulsions were not significantly affected by MPTP treatment. The severity of the pentylenetetrazole seizures was mildly, but significantly affected in the protective way. MPTP depleted neostriatal dopamine and its metabolites, together with hippocampal norepinephrine. No nigral neuronal was detected histologically. Strychnine seziures and the tonic phase of the maximal electroshock response are thought to depend mostly on hindbrain (bulbo-spinal) structures. Thus, these experiments suggest that a caudally projecting system originates from the substantia nigra, pars compacta, and/or locus coeruleu, controlling seizures that involve bulbo-spinal centers. While neostriatal dopamine depletion offers a good index of seizure resistance, its role in the protection from seizures remains to be established     

Time course of MPTP-induced degeneration of the nigrostriatal dopamine system in C57 BL/6 mice

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) is a parkinsonism-inducing dopamine (DA) neurotoxin most effective in primates. MPTP also causes a degeneration of both perikarya and axon terminals of the nigrostriatal DA neurons in C57 BL/6 mice. The time courses of the changes in tyrosine hydroxylase immunoreactive objects, endogenous DA concentrations and specifically bound 3H-mazindol as markers of the integrity of DA neurons were studied in substantia nigra and striatum of adult C57 BL/6 mice, after systemic treatment with MPTP or intranigral injections of the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA). A rapid decrease in the three parameters studied was found in the substantia nigra during the first 2 days after MPTP-treatment while the MPTP-induced effects in the striatum were more protracted and maximal reduction was observed 7 days after MPTP. A basically similar pattern was found when studying the 6-OHDA-induced anterograde degeneration of the nigrostriatal system. These results indicate that in C57 BL/6 mice, MPTP primarily destroys the DAergic perikarya with a subsequent anterograde degeneration of the striatal axon terminals, although a limited rapid destruction of some striatal terminals cannot be excluded.     

Drug-induced dyskinesia in primates rendered hemiparkinsonian by intracarotid administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

The right common carotid artery was surgically exposed under general anaesthesia in 6 cynomolgus monkeys and MPTP (0.5–2.2 mg/kg) directly infused. This produced a hemiparkinsonian syndrome in the contralateral limbs which responded to treatment with both levodopa and apomorphine. these drugs also precipitated dose-dependent contralateral rotation which reached a peak 2 weeks after MPTP infusion. A massive depletion of large, presumably dopaminergic cells was found from the ipsilateral substantia nigra pars compacta. Three animals receiving chronic therapy with apomorphine developed choreoathetoid movements of the limbs and the face contralateral to the infusion 2 weeks after the commencement of treatment. The severity of the dyskinesia gradually increased and after 4 weeks peak-dose hemiballistic movements were seen. Levodopa and the selective D-2 and D-1 dopamine agonists LY-171555 and SKF 38393 also reversed parkinsonian features and produced contralateral rotation and peak-dose dyskinesia. This unilateral model of parkinsonism in the primate will be of value in the elucidation of the mechanisms by which chronic levodopa or dopamine agonist therapy enhance involuntary movements in parkinsonism.     

Long-term effect of MPTP in the mouse brain in relation to aging: neurochemical and immunocytochemical analysis

The long-term effect of the parkinsonism-inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on central monoaminergic neurons in young (2-3 months) and aging (12 months) C57BL/6 mice has been studied using neurochemical and immunocytochemical techniques. MPTP treatment (4 x 20 mg/kg i.p. given 12 h apart) resulted in significant depletion of dopamine (DA) concentration in the striatum, substantia nigra, nucleus accumbens, and olfactory tubercle 1 week after treatment in both young and aging mice. Although a decreased DA concentration in the ventral tegmental area was not seen in young mice, aging mice did show a significant decrease. The extent of decrease of DA concentration was greater in aging mice than in young mice in all areas investigated except in dorsal striatum. The long-term effect of MPTP on DA neurons in young mice included considerable recovery of DA concentration in both nigrostriatal and mesolimbic DA systems following the initial profound depletion; such recovery was minimal in aging mice, even 3 months after MPTP treatment. In young mice treated with MPTP, no significant change of norepinephrine (NE) or serotonin (5-HT) concentration was observed in any area investigated while a significant decrease of NE and 5-HT concentration was seen in several brain areas investigated in aging mice. Immunocytochemical analysis revealed that the MPTP injection resulted in marked disappearance of tyrosine hydroxylase (TH)-immunoreactive (IR) fibers in striatum of both young and aging mice 1 week following treatment. Partial recovery of TH-IR fibers was seen 5 weeks or 3 months after MPTP treatment in young mice, while no such apparent recovery was seen in aging mice. Aging mice also showed significant decrease in the number of TH-positive cell bodies in the substantia nigra and ventral tegmental area through all periods investigated, while such a significant decrease was only seen in the substantia nigra of young mice 1 week after treatment. We conclude that aging mice are more sensitive to MPTP and show more widespread damage to the monoaminergic systems than young mice, suggesting that MPTP-treated aging mice provide a more useful model for studying anatomical and neurochemical characteristics of Parkinson's disease than young mice.     

1-Methyl-4-phenylpyridinium (MPP+) increases oxidation of Cytochrome-b in rat striatal slices

Effects of 1-methyl-4-phenylpyridinium, (the active metabolite of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), on reduction/oxidation activity of mitochondrial cytochromes were studied in rat striatal slices using scanning spectrophotometry. The objective was to test the hypothesis that the neurotoxin alters electron transport in the mitochondrial respiratory chain. Incubation of rat striatal slices with MPP+ (1 μM) produced a time-dependent oxidation of Cytochrome-b in a manner consistent with the concept of a block in electron transport in the intramitochondrial respiratory chain between nicotinamide adenine dinucleotide (NAD) and Cytochrome-b. This effect of MPP+ was decreased by co-incubation with a potent dopamine uptake inhibitor (mazindol), or when studied in a tissue with low dopaminergic innervation (hippocampus). The amplitude of Cytochrome-b oxidation was greater than that expected from a selective effect of MPP+ on dopaminergic neurons suggesting that neighboring cells are influenced secondary to the MPP+ effect on dopaminergic terminals.     

MPP-induced increases in extracellular potassium ion activity in rat striatal slices suggest that consequences of MPP neurotoxicity are spread beyond dopaminergic terminals

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) produces symptoms similar to idiopathic Parkinson's disease in primates. A metabolite of MPTP, MPP+ (1-methyl-4-phenylpyridinium), is actively accumulated by dopaminergic (DA) terminals and selectively destroys nigrostriatal DA neurons. The mechanism of this effect remains unknown but reports that MPP+ inhibits electron transport in isolated mitochondria and increases oxidation of cytochrome b in striatal slices suggest that depression of ATP production is involved. To relate metabolic effects of MPP+ with tissue electrophysiology, extracellular potassium ion activity [K+]o was measured by microelectrodes simultaneous to optical monitoring of reduction/oxidation (redox) activity of cytochrome b during superfusion of MPP+ onto rat striatal and hippocampal slices. MPP+ increased oxidation of cytochrome b and increased [K+]o in slices of striatum. These increases were greater than expected from a selective effect of MPP+ on DA terminals which likely comprise no more than 3% of the total striatal mass. These effects of MPP+ were slowed by a dopamine uptake inhibitor (mazindol) and did not occur in hippocampal slices. These findings indicate that MPP+ influences ion transport as well as metabolic activity and that these actions require the presence of functioning DA terminals. However, the large amplitudes of the MPP+-induced changes suggest that consequences of MPP+-neurotoxicity are not ultimately confined to DA terminals. Two hypothesis are proposed: that energy failure in DA terminals results in leakage of neurotoxic substances or metabolites altering membrane conductance properties of adjacent cells and thereby placing additional demand upon ion transport pumps and mitochondrial oxidative phosphorylation; or that there is secondary uptake of MPP+ leading to mitochondrial inhibition in cells neighboring DA terminals.     

Poly(ADP-ribose) polymerase inhibitors protect against MPTP-induced depletions of striatal dopamine and cortical noradrenaline in C57B1/6 mice

Treatment of C57B1/6 mice with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) reduced striatal dopamine and cortical noradrenaline levels by 77–83% and 43–46%, respectively, at 7 days post-treatment. Co-treatments with five different inhibitors of poly(ADP-ribose) polymerase (PARP), including benzamide, significantly prevented the MPTP-induced catecholamine depletions. Benzamide was present in the striatum, 30 min after single i.p. injection, at low millimolar concentrations known to selectively inhibit PARP in vitro. The protective activities of benzamide and its derivatives paralleled their in vitro efficacies and potencies both as neuroprotective agents and as inhibitors of PARP, while the activity of 1,5-dihydroxyisoquinoline, a structurally-unrelated compound, did not. In naive animals, the PARP inhibitors by themselves did not alter striatal dopamine levels at 7 days post-treatment. However, in acute studies, 1,5-dihydroxyisoquinoline and nicotinamide caused marked alterations in striatal dopamine metabolite levels; on the contrary, benzamide and its amino-derivatives showed little or no effect on dopamine metabolism. These results indicate that, although these compounds might act at other sites in addition to PARP, PARP inhibitors possess neuroprotective potential in vivo and suggest a role for PARP in MPTP neurotoxicity.     

Dissociation of serotoninergic and dopaminergic components in acute effects of 1-methy 1-4-pheny 1-1,2,3,6-tetrahydropyridine in mice

Behavioural and neurochemical effects of acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment in mice have been studied in order to determine the change in the neurotransmitter profile of the following areas of the brain: substantia nigra (SN), nucleus caudatus putamen (NCP), limbic system (LS; tuberculum olfactorium and nucleus accumbens), medulla oblongata (MO) and cerebellum (CER). Subcutaneous administration of MPTP (40 mg/kg) caused behavioural syndromes including restlessness, straub tail, hindlimb abduction, tremor, jumping, bradykinesia and akinesia in Balb/c mice. There existed a well-defined biphasic profile of motor activity comprising of an initial excitatory phase followed by an inhibitory phase lasting about two and a half and five hours, respectively. A significant rise in 5-hydroxytryptamine (5-HT) content together with a decreased 5-HT utilization as evidenced by lower 5-hydroxyindole acetic acid (5-HIAA) to 5-HT ratio in the above brain areas demarcated the excitatory phase, whereas the inhibitory phase was distinguished by a significant decrease in dopamine (DA) content along with an increased turnover of the amine as shown by a higher homovanillic acid (HVA) to DA ratio in the functionally important nuclei of the extrapyramidal system like SN, NCP and LS. Methysergide, a nonspecific 5-HT receptor blocker, but not ketanserin, a specific 5-HT2 antagonist, prevented the occurrence of the initial excitatory phase without affecting the depressive phase. Administration of apomorphine, a dopamine agonist, 30 minutes prior to MPTP was ineffective, whereas its application 90 minutes after MPTP prevented the occurrence of bradykinesia and akinesia. Interestingly, treatment with haloperidol, the dopamine (D1/D2) antagonist, before and after MPTP administration caused an early onset and prolongation of the inhibitory phase without affecting the initial hyperexcitement. The results provide direct evidence for the involvement of serotoninergic and dopaminergic mechanisms in the genesis of the early and late syndromes of acute MPTP poisoning respectively.     

Protection and potentiation of MPTP-induced toxicity by cytochrome P-450 inhibitors and inducer: in vitro studies with brain slices

Exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) causes loss of dopaminergic neurons in humans, primates and mice. Exposure of sagittal slices of mouse brain to MPTP (100 pM) caused inhibition of mitochondrial NADH-dehydrogenase activity. Leakage of lactate dehydrogenase from the slice into the medium was observed following incubation of slices with 1 nM MPTP. Neurotoxicity induced by MPTP was prevented by prior exposure of the slices to the dopamine uptake inhibitor GBR 12935. Deprenyl and pargyline (inhibitors of monoamine oxidase), also protected the slices from MPTP-induced toxicity. However, both pargyline and deprenyl also inhibited cytochrome P-450 mediated aminopyrine N-demethylase activity in brain slices. Pargyline, when administered in vivo to mice, decreased brain cytochrome -450 levels significantly. Other cytochrome P-450 inhibitors, namely, piperonyl butoxide and SKF 525A were found to offer protection against MPTP induced neurotoxicity in slices without affecting monoamine oxidase activity. MPTP toxicity was potentiated significantly in brain slices prepared from mice pretreated with phenobarbital, an inducer of cytochrome P-450. The present study suggests the possible involvement of cytochrome P-450 in MPTP-induced neurotoxicity, in vitro, in brain slices.     

Differences in the disposition and toxicity of 1-methyl-4-phenylpyridinium in cultured rat and mouse astrocytes

Species difference in the susceptibility to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was investigated in cultured rat and mouse astrocytes, where 1-methyl-4-phenylpyridinium (MPP⁺), the toxic mediator of MPTP, is formed. Type A monoamine oxidase (MAO) predominated in both rat and mouse astrocytes, while its activity was slightly higher in mouse cells compared to rat cells; MAO-B activity, on the other hand, was significantly lower in mouse astrocytes than in rat astrocytes. Because both types of MAO have been reported to make similar contributions to MPP⁺ production in astrocytes, their total activity was examined and results indicated that there was no significant difference between these two species. In additon, MPP^± caused a dose dependent loss of cell viability as judged by the amount of lactate dehydrogenase released into the incubation medium. The toxicity of MPP^± on astrocytes started to be seen after a 2 day incubation period. Mouse astrocytes were more vulnerable to MPP^± than rat astrocytes. The threshhold values for MPP^± toxicity in mouse and rat cultures were 10 ±M and 70 ±M, respectively. After addition of [³H] MPP^± to the medium, intracellular [³H] MPP^± was found to increase in both cultures. Mouse astrocytes accumulated more MPP^± than rat astrocytes (150 pmol/mg protein vs. 65 pmol/mg protein). When astrocytes were allowed to accumulate [³H] MPP^± and then incubated in fresh medium medium not containing [³H] MPP^±, intracellular levels of [³H] MPP^± in both cells rapidly declined (110 pmol/protein in mouse vs. 40 pmol/mg protein in rat of MPP^± been released). These results indicated that (1) MPP^± could cross the plasma membrane of astrocytes despite of its charged chemical structure, (2) mouse astrocytes had a higher capacity for MPP^± accumulation (approximately 2-fold), as well as release (approximately 2.7-fold), than rat astrocytes, and (3) mouse astrocytes were more vulnerable to MPP^± than rat astrocytes.     

Levodopa or D2 agonist induced dyskinesia in MPTP monkeys: correlation with changes in dopamine and GABAA, receptors in the striatopallidal complex

Dopamine D1 and D2 receptors as well as the GABA/benzodiazepine receptor complex in the striatum and the globus pallidus (internal: GPi and external: GPe) were studied by autoradiography using [³H]SCH 23390, [³H]spiperone, and [³H]flunitrazepam ([³H]FNZ) respectively, in five groups of cynomolgus monkeys. These included (i) untreated 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-monkeys; (ii) MPTP monkeys treated chronically with levodopa injections; (iii) MPTP monkeys treated chronically with injections of the novel D2 agonist U91356A; (iv) MPTP monkeys treated chronically with U91356A delivered through an osmotic mini-pump; and (5) naive controls. Animals treated in a pulsatile mode with U91356A or levodopa injections showed progressive sensitization to their respective drug and developed choreic dyskinesia. In contrast, animals treated in a continuous mode with U91356A showed behavioral tolerance but did not develop dyskinesia. A trend for a down-regulation of putaminal D2 receptors was observed following D2 agonist stimulation with U913356A. Striatal [³H]FNZ binding was significantly decreased only in animals treated in a continuous mode with U91356A. The dopamine receptor decrease in the striatum could be implicated with the development of tolerance but cannot explain the appearnce of dyskinesia. Denervation by MPTP was associated with a decrease of the GPe/GPi [³H]FNZ binding ratio which reflects an imbalance of striatal output pathways; this ratio was not reversed by any of the treatments although changes were observed in the GPe and GPi. Indeed, pulsatile U91356A treatment restored the decreased [³H]FNZ binding in the GPe near control values and levodopa showed a similar tendency. A significant increase of [³H]FNZ binding in the GPi only of dyskinetic monkeys, namely those treated with pulsatile U91356A or levodopa was seen compared to untreated MPTP or naive controls. This GABA_A receptor up-regulation might lead to a supersensitive state of the GPi to gabaergic input which may be involved in the mechanism underlying the development of dopaminomimetic-induced dyskinesia.     

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurotoxicity in non-human primates is antagonized by pretreatment with nimodipine at the nigral, but not at the striatal level

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) has been shown to induce parkinsonism in man and non-human primates. Hypotheses concerning the mechanism of action of MPTP have been related to the pathogenesis of nigral cell death in Parkinson's disease. For instance, alterations of calcium influxes have been reported to be implicated in both MPTP-induced parkinsonism and Parkinson's disease. Recently, we reported that nimodipine, a blocker of L-type calcium channels, prevents dopaminergic MPTP-induced neurotoxicity in C57B1/6 black mice. The present study extended these rodent findings to the non-human primate model of Parkinson's disease and assessed the effects of nimodipine, continuously applied by pellet for 18 days, on behavioural, biochemical and histological parameters, following systemic application of MPTP in common marmosets (Callithrix jacchus). The experimental design involved five groups of common marmosets and a total of 24 animals. Monkeys assigned to group I (n = 4) received subcutaneously implanted vehicle pellets 7 days prior to subcutaneous saline injections (control). Monkeys of group II (n = 4) were treated with nimodipine pellets (80 mg) and saline injections. Marmosets in group III (n = 8) were treated with vehicle pellets and received 4 times MPTP (MPTP-HCI, 2 mg/kg body weight subcutaneously, separated by an interval of 24 h for a total of 4 days). Monkeys in group IV (n = 4) and V (n = 4) were treated as group-III animals except for the implantation of nimodipine pellets (80 mg and 120 mg, respectively) 7 days prior to toxin exposure. In common marmosets MPTP induced severe parkinsonian symptoms, a pronounced dopamine depletion in the caudate-putamen (more than 99% of control) and a loss of tyrosine hydroxylase immunoreactive cells in the substantia nigra (50% percent of control) 7 days after MPTP-administration. Pretreatment with nimodipine (120 mg pellets) did neither attenuate the behavioural impairments in MPTP-treated animals nor antagonize the striatal neurotoxin-induced dopamine depletion, but almost completely prevented (in a dose-dependent manner) the MPTP-induced decrease of nigral tyrosine hydroxylase immunoreactive cells. These data suggest that application of nimodipine, during the observation period of 7 days, protects against MPTP-induced neurotoxicity in common marmosets at the cellular nigral level, but not at the synaptic striatal level, implicating differential mechanisms of actions of MPTP-induced neurotoxicity at the nigral versus the striatal level.     

Cholinergic deficits in aged rat spinal cord: restoration by GM1 ganglioside

Cholinergic neurons of spinal cord are central for the processing of motor, autonomic, and sensory modalities. Aging is associated with a variety of motor and autonomic symptoms that might be attributed, in part, to impaired spinal cord function. We found that cholinergic neurochemistry is diminished in the spinal cord of 22–24-month-old rats compared with 3-month-old rats. Choline acetyltransferase, high-affinity choline transport and hemicholinium-3 binding to the choline carrier were reduced in the aged spinal cord. The activity of the choline transporter and the hemicholinium-3 binding were decreased in all spinal segments, cervical, thoracic, lumbar and sacral. Hemicholinium-3 binding was reduced in ventral and dorsal horns along all spinal segments. The activity of choline acetyltransferase was decreased only in cervical and lumbar cord. Treatment of aged animals with GM1 induced the recovery of the presynaptic cholinergic markers in the aged spinal cord.     

Disappearance of circadian rhythms in Parkinson''s disease model induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in dogs

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to dogs produces clinical, pathological and neurological features in dog resembling human Parkinson's disease. Using this animal model, we studied the changes in diurnal rhythms of urine volume, creatinine in urine, and vasopressin, aldosterone and renin activity in plasma. Before MPTP treatment, urine volume showed a peak between 17.00 and 1.00 and plasma vasopressin concentration also showed a clear circadian rhythm with a peak at 13.00 and a minimum level at 5.00. Two weeks after MPTP treatment (2.5 mg/kg i.v.), the rhythm of urine volume disappeared and that of vasopressin became less clear. Plasma renin activity increased 2 and 4 weeks after MPTP treatment. The increase was, however, not enough to change the concentration of plasma aldosterone. We examined the effect of L-3,4-dihydroxyphenylalanine (levodopa), on the circadian pattern of urine volume and vasopressin attenuated by MPTP. Levodopa (4 mg/kg/day) was administered orally every day from the first week after MPTP treatment. The circadian rhythms of urine volume and vasopressin reappeared within one week after the start of levodopa administration.     

Responses of pallidal neurons to striatal stimulation in monkeys with MPTP-induced parkinsonism

Extracellular single unit activity was recorded from neurons of the internal (GPi) and external (GPe) pallidal segments, and from 'border cells' (Bor) which are part of the nucleus basalis, in 2 cynomolgus monkeys rendered parkinsonian by MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine). Cell counts showed that at least 90% of the nigral neurons of the compacta-type were degenerated. Electrical stimulation was applied to 3 sites bilaterally in the striatum: one in the caudate nucleus and 2 in the putamen. The results were compared to those obtained in intact monkeys. In the parkinsonians, more neurons of the 3 types responded to ipsilateral stimulation. The difference was even greater for contralateral responses, except in the case of Bor neurons. Greater proportions of the 3 types of neurons also responded to 2 and 3 sites and showed convergent responses to both the caudate nucleus and the putamen. The magnitude of the responses was larger. These results are in accordance with the excessive and unselective responses of the same neurons to passive limb movement, obtained in the same animals and described previously. The electrical stimulation allowed more detailed analyses of the responses. The major change in the responses of GPi and Bor neurons was the more frequent and larger late inhibitions, whereas the excitations were larger in GPe neurons. Long lasting oscillatory responses occurred frequently in the parkinsonians, mainly in GPi, and at frequencies close to the tremor displayed by the animals. Responses beginning with early inhibition were displayed by neurons located in the center of the pallidal zone of influence of each striatal stimulation site, as in intact animals, but in the GPi of the parkinsonians they were less frequently curtailed by excitation. Moreover, in the parkinsonians, the zones of influence were larger in both GPi and GPe, mainly because of the expansion of their periphery, where responses began with excitation and had lower thresholds than in intact animals. The dopamine agonist apomorphine normalized the responses in the parkinsonians. Thus, both the temporal and spatial magnitudes of inhibitions and excitations are abnormal at the output of the basal ganglia in parkinsonism.     

SKF-38393, a dopamine receptor agonist, attenuates 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced neurotoxicity

Parkinson's disease (PD) is characterized by progressive degeneration of nigrostriatal dopaminergic neurons. Several factors such as inhibition of the mitochondrial respiration, generation of hydroxyl radicals and reduced free radical defense mechanisms causing oxidative stress, have been postulated to contribute to the degeneration of dopaminergic neurons. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treated animals is a useful experimental model of PD, exhibiting most of the clinical features, as well as the main biochemical and pathologic symptoms of the disease. In the present study, we have examined a dopaminergic (D1) receptor agonist, SKF-38393 HCl (SKF) for its possible neuroprotective action against MPTP-induced insults on dopaminergic neurons. MPTP is converted by monoamine oxidase-B (MAO-B) to its neurotoxic metabolite 1-methyl-4-phenyl-pyridinium (MPP+), which is then taken up into the dopaminergic neurons. SKF-38393 had no effects either on total or monoamine oxidase B in the striatum. SKF-38393 blocked the MPTP-induced depletion of glutathione and attenuated MPTP-induced depletion of dopamine. Furthermore, it enhanced the activity of superoxide dismutase and hence mimicked the action of selegiline. The results of these studies are interpreted to suggest that SKF-38393 may prove a valuable drug in the treatment of Parkinson's disease.