Comparison of cytotoxicity of a quaternary pyridinium metabolite of haloperidol (HP+) with neurotoxin N-methyl-4-phenylpyridinium (MPP+) towards cultured dopaminergic neuroblastoma cells

Haloperidol has recently been found to be metabolized to its pyridinium ion (HP+). This conversion of haloperidol to HP+ appears to be similar to the activation of the dopaminergic neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to N-methyl-4-phenyl pyridinium ion (MPP+). MPP+ is responsible for the damage of striatal dopaminergic neurons induced by MPTP in humans and animals. It seemed sensible to investigate whether or not HP+ might be toxic towards dopaminergic neurons and perhaps associated with some of the residual moto-function side effects of haloperidol. We therefore investigated the neurotoxicity of HP+ toward cultured human dopamine neuroblastoma cells (SH-SY5Y) and compared it with that of MPP+. HP+ reduced the viability as measured by MTT and [3H]thymidine incorporation methods in SH-SY5Y cells. Cell membrane integrity is reduced by the treatment of HP+ as measured by intracellular LDH levels. The toxicity was concentration and time dependent. Interestingly, HP+ appeared to be more toxic than MPP+ towards the SH-SY5Y cells in early phase in cultures. The toxicity of MPP+ appear to be progressive and subsequently become more than HP+ with prolonged cultivation. In contrary to MPP+, the toxic effect of HP+ towards a dopamine transporter transfected SK-N-MC cell line is not different from its wild type. This indicates that dopamine uptake system is probably not involved in the cytotoxicity caused by HP+.

Effects of unilateral 6-hydroxydopamine lesions on neuropeptide immunoreactivity in the basal ganglia of the common marmoset, Callithrix jacchus, a quantitative immunohistochemical analysis

Previous immunocytochemical studies in rats have indicated that striatal dopamine depletion leads to an increase in enkephalin-immunoreactivity and a decrease in substance P-immunoreactivity in the striatum. Similar studies in primates have lead to contradictory results. In the present study changes in tyrosine hydroxylase-, met-enkephalin- and substance P-immunoreactivity were determined in the basal ganglia of 6 common marmosets Callithrix jacchus following dopamine depletion by unilateral intracerebral 6-hydroxydopamine (6-OHDA) injections using three different survival times. The non-lesioned side served as an intra-individual control. Tyrosine hydroxylase immunoreactivity was strongly reduced in the entire ipsilateral striatum. Enkephalin-immunoreactivity was increased throughout the striatum. Substance P-immunoreactivity was significantly increased in only one case in the caudate nucleus and in two cases in the putamen, while in other cases either a non-significant increase or decrease was found. Therefore, the results of the present study indicate that in marmosets dopamine has a inhibiting effect on the levels of striatal enkephalin, while its effect on substance P (SP) appears to be absent.

Riluzole prevents MPTP-induced parkinsonism in the rhesus monkey: a pilot study

Previous studies have shown that riluzole (2-amino-6-trifluoromethoxy-benzothiazole), a drug which interferes with glutamate neurotransmission, has a neuroprotective action in rodent models of global and focal cerebral ischemia. In this pilot study, the protective and palliative effects of riluzole have been examined using an animal model of Parkinson's disease. Two monkeys were rendered hemiparkinsonian by one intracarotid injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and motor signs were evaluated using clinical examination and electromyographic recordings. When riluzole (4 mg/kg) was administered before the injection of MPTP, parkinsonian motor symptoms, in particular bradykinesia and rigidity, were absent. When injected daily in one monkey which presented stable motor symptoms, bradykinesia and rigidity were significantly reduce d. Riluzole pretreatment induced a persistent increase in dopamine turnover when compared to MPTP alone. Thus, a possible neuroprotection and a facilitation of dopamine release may explain the behavioural effects reported with riluzole treatment. These preliminary results suggest that riluzole could possess neuroprotective and palliative effects in a primate model of Parkinson's disease.

Poly(ADP-ribose) synthetase activation: an early indicator of neurotoxic DNA damage

DNA damage activates a nuclear enzyme poly(ADP-ribose) synthetase (PARS) that facilitates DNA repair by adding multiple ADP-ribose groups to nuclear proteins such as histones and PARS itself. N-Methyl-D-aspartate neurotoxicity may involve DNA damage excessively activating PARS to deplete its substrate NAD, as PARS inhibitors prevent this toxicity. We now show that PARS is rapidly and markedly activated in PC12 cells following treatment with neurotoxic agents, including the amyloid beta-protein, hydrogen peroxide, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and its active metabolite N-methyl-4-phenylpyridine (MPP+). With MPP+, PARS activity is increased fivefold in 1 h and 20-fold by 3 h. By contrast, direct measurement of DNA damage by the terminal-deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling assay shows no significant increase by 3 h and less than fourfold by 24 h. These findings indicate that PARS activity can provide a simple, sensitive, and early index of DNA damage following neurotoxic insults.

Time course and morphology of dopaminergic neuronal death caused by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

Mechanisms responsible for 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopamine (DA) neuronal death remain unknown and in mice it is even unclear whether neuronal death does occur. In vitro studies suggest that 1-methyl-4-phenylpyridinium ion (MPP+), the active metabolite of MPTP, kills neurons by apoptosis. Herein, we investigated whether MPTP induces DA neuronal death in vivo in mice and whether the mechanism is that of apoptosis. C57/bl Mice received different doses of MPTP administered in four intraperitoneal injections every 2 hours and were sacrificed at different time points for analyses of tyrosine hydroxylase (TH) immunohistochemistry, silver staining, and Nissl staining within the mesencephalon. We found that MPTP induces neuronal destruction in the substantia nigra pars compacta (SNpc) and the ventral tegmental area (VTA). The active phase of degeneration began at 12 h postinjection and continued up to 4 days. During this period, there was a greater decrease in TH-defined neurons than in Nissl-stained neurons suggesting that MPTP can cause a loss in TH without necessarily destroying the neuron. Thereafter, neuronal counts by both techniques equalized and there was no further loss of DA neurons. Dying neurons showed shrunken eosinophilic cytoplasm and shrunken darkly stained nuclei. Double staining revealed degenerating neurons solely among TH positive neurons of SNpc and VTA. At no time point and at no dose of MPTP was apoptosis observed. In addition, in situ labelling revealed no evidence of DNA fragmentation. This study demonstrates that the MPTP mouse model replicates several key features of neurodegeneration of DA neurons in PD and provides no in vivo evidence that, using this specific paradigm of injection, MPTP kills DA neurons by apoptosis.

MPTP- and MPP(+)-induced effects on body temperature exhibit age- and strain-dependence in mice

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is toxic toward the dopaminergic nigrostriatal system of a plethora of species including rodents, nonhuman primates and humans. The present study was designed to evaluate if systemic administration of MPTP or its metabolite, 1-methyl-4-phenylpyridinium ion (MPP+), has significant effects on body temperature (BT) and whether such effects might play a role in the neurotoxicity. A single intraperitoneal (i.p.) dose of either MPTP (50 mg/kg) or MPP+ (12.5 mg/kg) leads to a decrease in BT in both C57BL/6N (C57) and CD-1 mice. The hypothermia induced by MPTP can be blocked by pretreatment with deprenyl (30 mg/kg, i.p.), an MAO-B inhibitor. However, the hypothermia elicited by MPP+ is refractive to MAO-B inhibition. These findings suggest that MPP+ is responsible for the BT reduction and that the primary site of action lies outside the blood-brain barrier. An initial hyperthermic phase in the CD-1 mice, which leads to the induction of heat shock protein-72 (HSP-72) throughout the brain, differentiates their response to MPTP from that of C57 mice. This initial hyperthermia appears to be protective since its prevention by dosing at a low ambient temperature enhances striatal dopamine (DA) depletion in CD-1 mice. The temperature effects of both MPTP and MPP+ also display an age-dependence in the C57 strain of mice, with the magnitude of the effects correlating positively with age. However, profound hypothermia could be induced by MPP+ in the absence of striatal DA depletion. The latter finding suggests that while a positive correlation was found between age and the magnitude of the hypothermia, DA depletion and hypothermia are not causally related. The apparent protective effect of the initial hyperthermia in the CD-1 strain of mice, however, suggests that BT is an important parameter in the neurotoxicity of MPTP.

Neurotoxicity, drugs and abuse, and the CuZn-superoxide dismutase transgenic mice

Administration of methamphetamine (METH) to animals causes loss of DA terminals in the brain. The manner by which METH causes these changes in neurotoxicity is not known. We have tested the effects of this drug in copper/zinc (CuZn)-superoxide dismutase transgenic (SOD Tg) mice, which express the human CuZnSOD gene. In nontransgenic (non-Tg) mice, acute METH administration causes significant decreases in DA and dihydroxyphenylacetic acid (DOPAC) in the striata of non-Tg mice. In contrast, there were on significant decreases in striatal DA in the METH administration caused decreases in striatal DA and DOPAC in the non-Tg mice, but not in the SOD-Tg mice. Similar studies were carried out with 1-methyl-1,2,3,6-tetrahydropyridine (MPTP), which also causes striatal DA and DOPAC depletion. As in the case of METH, MPTP causes marked depletion of DA and DOPAC in the non-Tg mice, but not in the SOD Tg mice. These results suggest that the mechanisms of toxicity of both METH and MPTP involved superoxide radical formation.

Neuronal antioxidant system and MPTP-induced oxidative stress in the striatum and brain stem of the rat

Levels of ascorbic acid (AA), dehydroascorbic acid (DHAA), glutathione (GSH), uric acid, dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3-methoxytyramine (3-MT), noradrenaline (NA), 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), and 1-methyl-4-phenylpyridinium ion (MPP+) were determined in the striatum, striatal synaptosomes, and/or brain stem of 3- and 6-month-old male Wistar rats given MPTP 35-52 mg/kg IP. In older rats, MPTP 35 mg/kg caused a 38% death rate within 15 min-12 h. Levels of MPTP and MPP+ in the striatum, synaptosomes, and brain stem were directly correlated with the absolute MPTP dose/rat. MPTP decreased striatal DA metabolites and NA levels in the striatum and brain stem, and increased uric acid levels in all regions in all rats. All these changes were significantly correlated with MPP+ levels. GSH levels were increased in younger rats and decreased in older rats. AA oxidation was increased mainly in older rats. We conclude that acute lethality and regional brain MPTP and MPP+ levels depend upon the absolute dose of MPTP/rat rather than the relative dose/kg. In younger rats, the neuronal antioxidant GSH system is more efficient than in older rats, in which the response to MPP(+)-induced oxidative stress also involves AA oxidation. The increase in uric acid levels provides further evidence for a mechanism of MPTP neurotoxicity involving oxidative stress mediated by xanthine oxidase.

Effect of MPTP on dopaminergic neurons in the goldfish brain: a light and electron microscope study

The neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) causes a Parkinsonian syndrome in the goldfish (Carassius auratus), characterized by transient bradykinesia, the accumulation of MPP+ in the brain, and a decrease in the forebrain and midbrain content of catecholamines (Pollard et al., FASEB J., 6 (1992) 3108-3116). Using light and electron microscopy, we studied the effect of MPTP on the distribution and ultrastructure of tyrosine hydroxylase (TH)-immunoreactive, dopaminergic neurons, and on the ultrastructure of other selected areas of the goldfish brain. Goldfish were treated with MPTP (50 mg/kg) in the absence or presence of L-deprenyl (10 mg/kg) or clorgyline (10 mg/kg). In the medial part of the central telencephalon, the nucleus telencephali, pars medialis, MPTP caused a decrease in the number of TH-immunoreactive neurons and distortions in their labelling pattern. Electron microscopic observations showed that MPTP caused swelling of cell processes, changes in neuronal nuclear profiles, dilation of endoplasmic reticulum, intracellular vacuolization and membrane distortions, and degeneration of neuronal fibers in this brain area. MPTP also caused a small reduction and some diffuseness in the labelling of dopaminergic neurons in several diencephalic periventricular nuclei. Moreover, MPTP induced cell swelling and degeneration in the subependymal cell layers along the forebrain ventricles. In all areas, L-deprenyl appeared to partially prevent the MPTP-induced degenerative changes. We conclude that in the goldfish MPTP causes marked histochemical changes in selected dopaminergic brain systems coincident with the Parkinson-like locomotor and neurochemical deficits.

Effect of adding the D-1 agonist CY 208-243 to chronic bromocriptine treatment of MPTP-monkeys: regional changes of brain dopamine receptors

1. Eleven monkeys were administered N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP): eight were treated with bromocriptine for one week and then CY 208-243 (four monkeys) or saline (four monkeys) was added to the bromocriptine treatment. 2. Addition of CY 208-243 increased the therapeutic response observed with the ergot alone without inducing dyskinesia. 3. Following MPTP, [3H]-SCH 23390 specific binding to D-1 receptors as well as [3H]-spiperone and [3H]-N-n-propylnorapomorphine specific binding to D-2 receptors increased in posterior striatum compared to control animals, whereas [3H]-SKF 38393 binding to D-1 receptors tended to decrease. 4. Dopamine receptor density was unchanged in anterior striatum of untreated MPTP-monkeys. 5. In the posterior striatum, both dopaminergic treatments decreased towards control values [3H]-SCH 23390, [3H]-spiperone and [3H]-N-n-propylnorapomorphine binding whereas they did not significantly change [3H]-SKF 38393 specific binding. [3H]-SKF 38393 specific binding increased in anterior striatum of bromocriptine-treated MPTP-monkeys, compared to untreated MPTP-animals, and this increase was abolished in animals treated with bromocriptine+CY 208-243. 6. The present study shows that in MPTP-monkeys, treated or not with DA agonists, the D1 and D2 receptor changes are concentrated in the posterior striatum and that denervation appears to cause a shift from the high to the low affinity agonist state of D1 receptors but not for the D2 subtype.

Relative resistance of rabbits to MPTP neurotoxicity

The neurotoxic actions of MPTP and its 4-(O-tolyl) analog (2'-Me-MPTP) on two breeds of rabbits were investigated. MPTP, but not 2'-Me-MPTP, causes a reduction (about 40%) in striatal dopamine content in rabbits of the "little silver-black" breed. The dopamine content of striata of "chinchilla" rabbits was not affected by either agent.

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.

Depletion of copper and manganese in brain after MPTP treatment of mice

The mechanism of action of MPTP, a parkinsonism-inducing drug has been related to trace metals as a result of the observed potentiation of the neurotoxic action of the drug when diethyldithiocarbamate is concurrently administered. Diethyldithiocarbamate is a well-known chelator of trace metals, particularly copper. In the present study we analyzed the concentrations of copper and manganese in four brain regions of mice treated with neurotoxic doses of MPTP, in order to further substantiate the relationship between trace metals of MPTP-induced neurotoxicity. Male Swiss albino mice were administered with MPTP (30 mg/kg) for either three or five days. Seven days after the last MPTP administration, they were sacrificed and the content of manganese and copper in the following regions was determined by graphite furnace atomic absorption spectrophotometry: cortex, cerebellum, midbrain and corpus striatum. Results indicate a significant depletion of manganese in corpus striatum (19.5% versus control) in the mice treated with MPTP for 5 days. Copper was also found to be decreased in corpus striatum (17.3% in mice treated for 3 days and 51.3% in mice treated for 5 days). Midbrain copper was depleted by 42.9% in the group of mice treated for 5 days with MPTP. Results indicate that MPTP induced a diminution of both copper and manganese in corpus striatum, suggesting that this alteration could be related to MPTP mechanism of action.

Combination treatment of the partial D2 agonist terguride with the D1 agonist SKF 82958 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned parkinsonian cynomolgus monkeys

The optimal combination of a dopamine D2 agonist and a D1 agonist was evaluated for symptomatic treatment of Parkinson's disease. Behavioral effects of combination treatment of the full D2 agonist quinpirole or the partial D2 agonist terguride with the full D1 agonist SKF 82958 [(I) 6-Chloro-7, 8-dihydroxy-3-allyl-1-phenyl-2, 3, 4, 5-tetra-hydro-1H-3-benzazepine] were investigated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned parkinsonian cynomolgus monkeys with attention to the induction of hyperactivity such as irritability, excitability and aggressiveness and of dyskinesias such as licking of paws, chewing and biting. Both quinpirole and SKF 82958 alone improved the parkinsonism with a slight induction of the hyperactivity and dyskinesias. Terguride also improved the parkinsonism but did not induce the hyperactivity and dyskinesias. Combination treatment of quinpirole with SKF 82958 not only showed a tendency to augment the antiparkinsonian effects but also induced the marked hyperactivity and dyskinesias. On the other hand, combination treatment of terguride with SKF 82958 also augmented the antiparkinsonian effects but did not induce any hyperactivity and dyskinesias. These findings suggest that combination therapy with a partial D2 agonist and a full D1 agonist or monotherapy with a dopamine agonist that has both partial D2 and full D1 agonist properties might be beneficial for treating motor dysfunction in Parkinson's disease without inducing dopaminergic side effects.

Coenzyme Q10 and nicotinamide and a free radical spin trap protect against MPTP neurotoxicity

1-Methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP) produces Parkinsonism in both experimental animals and in man. MPTP is metabolized to 1-methyl-4-phenylpridinium, an inhibitor of mitochondrial complex I. MPTP administration produces ATP depletions in vivo, which may lead to secondary excitotoxicity and free radical generation. If this is the case then agents which improve mitochondrial function or free radical scavengers should attenuate MPTP neurotoxicity. In the present experiments three regimens of MPTP administration produced varying degrees of striatal dopamine depletion. A combination of coenzyme Q10 and nicotinamide protected against both mild and moderate depletion of dopamine. In the MPTP regimen which produced mild dopamine depletion nicotinamide or the free radical spin trap N-tert-butyl-alpha-(2-sulfophenyl)-nitrone were also effective. There was no protection with a MPTP regimen which produced severe dopamine depletion. These results show that agents which improve mitochondrial energy production (coenzyme Q10 and nicotinamide) and free radical scavengers can attenuate mild to moderate MPTP neurotoxicity.

Heavy metals and the etiology of Parkinson's disease and other movement disorders

Heavy metals, such as iron and manganese, are involved in neurologic disease. Most often these diseases are associated with abnormal environmental exposures or abnormal accumulations of heavy metals in the body. There is increasing recognition that heavy metals normally present in the body also may play a role in disease pathogenesis through free radical formation. When a part of the brain known as the basal ganglia is affected, movements become disordered. Parkinson's disease is one of the most common movement disorders and is related to destruction of neurons in the substantia nigra pars compacta (SNpc) of the basal ganglia. The combination of high concentration of iron and the neurotransmitter, dopamine, may contribute to the selective vulnerability of the SNpc. Dopamine can auto-oxidize to produce free radicals particularly in the presence of iron and other heavy metals.

Enhanced restoration of striatal dopamine concentrations by combined GM1 ganglioside and neurotrophic factor treatments

Intraperitoneal injection of GM1 ganglioside or intracerebroventricular infusion of basic fibroblast growth factor (FGF-2) or epidermal growth factor (EGF) partially restored dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) levels in the striatum of young MPTP-treated mice. Combined treatments of GM1 ganglioside with FGF-2 or EGF produced a greater restoration of striatal dopamine levels than treatments with GM1 or either of the neurotrophic factors alone. GM1 treatment, but not trophic factor treatments caused significant sparing of substantia nigra pars compacta (SNc) tyrosine hydroxylase (TH)-positive neurons. These results confirm previous findings that GM1 provides trophic support for damaged dopamine neurons and suggests that GM1, FGF-2, and EGF may also enhance dopaminergic function in residual neurons. The results also suggest that a potentially fruitful approach to treating degenerative disorders of the dopamine system may be the use of combined trophic factor therapies.

Continuous administration decreases and pulsatile administration increases behavioral sensitivity to a novel dopamine D2 agonist (U-91356A) in MPTP-exposed monkeys

We compared the behavioral effects of a novel and highly selective dopamine D2 receptor agonist, U-91356A, administered to 6 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-exposed parkinsonian monkeys for 27 days following an intermittent (n = 3) or continuous (n = 3) schedule, using subcutaneous osmotic minipumps for the latter group. Each group received equivalent amount of drug daily. Dopamine D1 and D2 receptor binding assays were performed on striatal tissue homogenates with tritiated selective antagonists and were compared with those of 3 healthy control animals and 3 MPTP-exposed monkeys treated in parallel with daily doses of levodopa and 2 additional MPTP-exposed monkeys otherwise untreated. U-91356A quickly relieved all parkinsonian features and greatly stimulated locomotion in all animals. The pulsatile administration group showed progressive sensitization to the drug, and all 3 animals developed chorea during the first week of treatment that subsequently increased in intensity. The same pattern was seen in the levodopa-treated animals. In contrast, an apparent, incomplete tachyphylaxis were observed in 2 of 3 animals in the continuous infusion group during the first 10 days of treatment. Only 1 of these animals developed minimal and transient choreic dyskinesia. An apparent decrease of D2 receptor binding was observed. No upregulation of dopamine receptors occurred in the dyskinetic monkeys of the pulsatile group, but a tendency toward upregulation of putaminal D1 receptors was observed in the levodopa-treated, dyskinetic animals. These results confirm that the mode of administration of dopaminergic agents may result in a markedly different clinical outcome.(ABSTRACT TRUNCATED AT 250 WORDS)

Electron microscopic evidence for neurotoxicity in the basal ganglia

The dopaminergic projection from the substantia nigra to the neostriatum is vulnerable to several neurotoxins including 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), amphetamine, and 5-hydroxydopamine. We have treated rats or mice with these agents and examined various regions of their brains with a combination of Fink-Heimer, immunohistochemical, serial-section electron microscopic, and three-dimensional reconstruction methods. In addition to degenerating or swollen axons, we found darkened glial processes and some damage to postsynaptic cells and dendrites. The particular effects observed critically depend on experimental variables such as dose, time, species and strain and raise questions about the correlation of light and electron microscopic results. These studies provide the basis for a discussion of the advantages and disadvantages of an ultrastructural examination of the effects of neurotoxins.

Neuroglial responses to the dopaminergic neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mouse striatum

We have studied the reactive responses of both astrocytes and microglia to dopaminergic denervation of the striatum by MPTP. Following MPTP treatment, increased GFAP immunoreactivity reached a peak at 2 days and persisted for at least 6 weeks. Immunoreactivity to vimentin was also markedly increased in astrocytes 48 h after MPTP treatment. Striatal laminin immunoreactivity, however, appeared to be unaffected by drug treatment. GFAP protein levels increased to 196% and 321% of control 24 and 48 hours after MPTP treatment, respectively. Concomitantly, GFAP mRNA levels increased to 560% and 1620% of control, respectively. These reactive changes in striatal astrocytes in response to MPTP treatment were also accompanied by a reactive microglial response as evidenced by increased immunohistochemical visualization of striatal microglia using antibodies to Mac-1. Our results and those reported previously by O'Callaghan et al., strongly suggest that MPTP-induced reactive gliosis in mouse striatum is associated with reactive microglia, albeit without increased interleukin-1 beta.

Neurotoxicity induced by prenatal exposure to MPTP on the monoaminergic and peptidergic systems of the marmoset brain

The neurotoxicity induced by incidental prenatal exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was studied in three marmosets. The baby marmosets exposed in utero to MPTP looked normal in the first few weeks of life but around 8 to 10 weeks of life they started to behave abnormally and were sacrificed when they were 20 weeks old. A marked reduction in DA levels was found in the baby marmosets prenatally exposed to MPTP as compared to the corresponding age-matched controls and this was highly significant in the caudate nucleus, putamen, and nucleus accumbens. Serotonin content was normal in the caudate and putamen and was only significantly reduced in the nucleus accumbens, hypothalamus, and cingulate cortex. Met-enkephalin levels were reduced in the caudate nucleus, putamen, and globus pallidus. Substance P content tended to be lower in all regions examined; however, the decrease was only statistically significant in the substantia nigra. These results indicate that prenatal exposure to MPTP induces a marked and long-lasting alteration in monoaminergic and peptidergic systems of the primate brain. This observation may provide a new insight into the role of toxins in the etiology of Parkinson's disease.