Localization of MPP+ binding sites in the brain of various mammalian species

Summary The distribution and density of³H-MPP⁺ binding sites were studied by in vitro quantitative autoradiography in the brain of the mouse, rat and monkey. The highest levels of³H-MPP⁺ specific binding were observed in rat brain. The substantia nigra in rat and monkey, and the anterior caudate-putamen formation in mouse and monkey showed the lowest density of autoradiographic grains. The presence of a relatively high density of MPP⁺ sites in the hippocampus of all species studied could be of interest to explain some effects of MPTP administration on convulsions caused by chemoconvulsants.The finding of a 60–70% reduction of³H-MPP⁺ binding sites in the rat caudate-putamen, on the side of quinolinic acid infusion and no changes after 6-hydroxydopamine lesion of dopaminergic nigrostriatal neurons suggests the presence of these sites mainly on striatal cells.The results suggest that the distribution of MPP⁺ binding sites in brain would not seem to be related to MPTP toxicity.     

Attenuation of 1-methyl-4-phenylpyridinium (MPP+) neurotoxicity by deprenyl in organotypic canine substantia nigra cultures

Summary Systemic administration of MPTP to experimental animals induces neurodegeneration of dopaminergic neurons in the central nervous system. MPTP crosses the blood-brain barrier where it is taken up by astrocytes and converted to MPP⁺ by monamine oxidase-B (MAO-B). Subsequently, MPP⁺ is selectively taken up by dopaminergic neurons upon which it exerts intracellular neurotoxic effects. Systemic administration of the selective MAO-B inhibitor deprenyl prevents the conversion of MPTP to MPP⁺ and by this mechanism is able to protect against MPTP neurotoxicity. Deprenyl has also been reported to exert neuroprotective effects that are independent of its MAO-B inhibitory properties, but since MPP⁺ itself does not cross the blood-brain barrier it is difficult to directly study the MAO-B independentin vivo effects of MPP⁺ itself. One approach is to use organotypic tissue cultures of the canine substantia nigra (CSN) which permit administration of precise concentrations of pharmacological agents directly to mature, well-developed and metabolically active dopaminergic neurons. These neurons as well as other components of the cultures exhibit morphological and biochemical characteristics identical to theirin vivo counterparts. This study was undertaken to evaluate the neuroprotective effects of deprenyl in MPP⁺-treated cultures by measuring changes in the levels of HVA as an indicator of dopamine release and metabolism by dopaminergic neurons and to correlate this indication of dopaminergic function with morphological evidence of survival or loss of dopaminergic neurons in mature CSN cultures. Mature CSN cultures, at 44 days in vitro (DIV), were exposed to either MPP⁺ alone, deprenyl alone or simultaneously to both deprenyl and MPP⁺ or to MPP⁺ following 4 day pretreatment with deprenyl. Exposure to MPP⁺ alone caused significant reduction in HVA levels, evidence of widespread injury and ultimate disappearance of large neurons in the cultures. These effects were attenuated by simultaneous exposure to MPP⁺ and deprenyl and the destructive effects of MPP⁺ appeared to be prevented by pretreatment with deprenyl. Thus the neuroprotective effects of deprenyl on MPP⁺-induced reduction of HVA levels in living cultures appears similar to the effects of deprenyl on dopamine levels and tyrosine hydroxylase activity reported by others in cultures previously exposed to deprenyl and MPP⁺. These studies also confirm that the neuroprotective effects of deprenyl against MPP⁺ in dopaminergic neurons are, at least in part, independent of deprenyl's inhibition of MAO-B.     

Cerebral metabolic mapping at the cellular level with dry-mount autoradiography of [H]2-deoxyglucose

The uptake and retention of radioactivity from [³H]2-deoxyglucose ([³H]2-DG) was assessed in certain regions of the rat brain under basal conditions using dry-mount autoradiography, a procedure which affords the best available conditions to accurately localize diffusable radiolabeled compounds at cellular and subcellular levels. The overall amount of radioactivity accumulated in neuropil and in neuronal cell bodies was similar in most brain regions examined. Of the regions assessed, the CA₃ pyramidal cell field of the hippocampus was the only region in which the radioactivity in cell bodies was notably greater than that of neuropil. In the somatosensory cortex and in the lateral hypothalamus, a wide range of radioactivity was found among individual neurons and among different areas of neuropil. In all brain regions examined, a subpopulation of small cells, with morphological characteristics of glial cells, accumulated [³H]2-DG to a much greater extent than other glial cells or neurons. That finding suggests that certain glial cells are in a markedly higher metabolic state than other brain cells.     

Intracerebroventricular administration of 1-methyl-4-phenylpyridinium ion in mice: Effects of simultaneously administered nomifensine,deprenyl, and 1-t-butyl-4,4-diphenylpiperidine

Summary 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) destroys nigrostriatal dopaminergic pathways and thereby produces a syndrome similar to Parkinson's disease. MPTP is oxidized by monoamine oxidase B (MAO B) to the 1-methyl-4-phenylpyridinium ion (MPP⁺), which is taken up in dopaminergic neurons through the dopamine (DA) uptake system, where it develops its toxic effect. Our observations show a new aspect of the MPP⁺ mode of action, in which deprenyl in mice has a partially protective effect against MPP⁺. Furthermore budipine, a therapeutic agent for Parkinsonism, is also able to partially prevent MPP⁺ toxicity. A MAO B-inhibitory component of budipine, as shown in receptor binding studies previously, could contribute to this effect. Comparable experiments with nomifensine do not exclude the possibility of budipine as an effect as a DA uptake inhibitor. An unexplained after effect of budipine leads to a large increase in 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) levels five weeks after the last administration.     

Metabolic rate in different rat brain areas during seizures induced by a specific delta opiate receptor agonist

The glucose utilization during specific δ opiate agonist-induced epileptiform phenomena, determined by the [¹⁴C]2-deoxyglucose technique (2-DG), was examined in various rat brain areas at different time intervals. The peak in EEG spiking response and the most intensive 2-DG uptake occured 5 min after intraventricular (i.v.t.) administration of the δ opiate receptor agonist. The most pronounced 2-DG uptake at this time interval can be observed in the subiculum, including the CA1 hippocampal area, frontal cortex and central amygdala. A general decrease of glucose consumption, compared to control values, is observed after 10 min, in all regions, with exception of the subiculum.Since functional activity and 2-DG uptake are correlated, we suggest that the subiculum and/or CA1 area, are probably the brain regions most involved in the enkephalin-induced epileptic phenomena.     

Stimulus-dependent labeling of cultured ganglionic cell with [C]2-deoxyglucose

We prepared cultures of dissociated cells from the ciliary (CG) and dorsal root ganglion (DRG) of 10–12-day-old chick embryos, and applied [¹⁴C]2-deoxyglucose ([¹⁴C]2-DG) to the cultured cells to examine the effects of stimulation on the labeling with [¹⁴C]2-DG at the single cell level. Electrical current stimulation increased [¹⁴C]2-DG uptake in CG and DRG neurons. The increase depended on frequency of the stimulation. These effects were potentiated by the application of tetraethylammonium, but suppressed by tetrodotoxin. Externally applied potassium ions increased the [¹⁴C]2-DG uptake in the CG cell, depending logarithmically on the concentration of applied KC1. The concentration-dependent increase agreed with potassium effect on the equilibrium potential. For CG cells, acetylcholine (ACh), glutamate, γ-aminobutyric acid (GABA) and glycine induced remarkable increases of the [¹⁴C]2-DG uptake, while dopamine did not induce any change. For DRG cells, GABA and glycine facilitated the [¹⁴C]2-DG uptake, while ACh, glutamate and dopamine did not have any significant effects on it. These facilitatory actions of neurotransmitters on the [¹⁴C]2-DG uptake are mostly consistent with the excitatory effects of the substrates on both CG and DRG cells in culture. The results suggest that the [¹⁴C]2-DG uptake in single cells is intimately correlated with action potential generation and change in the resting potential.     

甲基—苯基—四氢吡啶增加脑糖代谢与Deprenyl对其拮抗作用的实验研究

应用[~3H]2-脱氧葡萄糖(2-DG)放射自显影法观察单胺氧化酶B型(MAO-B)抑制剂Deprenyl和神经毒素甲基-苯基-四氢吡啶(MPTP)对小鼠脑2-DG摄取的影响。腹腔注射MPTP后,模型组鼠的黑质和蓝斑区的2-DG摄取量较对照组鼠明显增加,并表现出明显的行为异常反应。预先口服Deprenyl的拮抗组鼠,2-DG摄取量与对照组相同,且行为反应轻微。结果表明MPTP对小鼠黑质和蓝斑区的局部糖利用有明显影响;Deprenly能有效防止MPTP的这一有害作用。     

Effects of substantia nigra lesions on forebrain 2-deoxyglucose retention in the rat

A method was developed for the measurement of regional 2-deoxyglucose (2-DG) retention in rat brain by injecting tracer quantities of tritiated 2-DG intravenously, dissecting out individual brain regions, making extracts of the tissue, and counting aliquots of the extracts. This technique permits the separation of unreacted 2-DG from 2-deoxyglucose-6-phosphate (2-DGP) by ion exchange chromatography as well as the performance of other biochemical measurements on the extracts.Using this method, the effect of unilateral 6-hydroxydopamine (6-OHDA) lesions of the substantia nigra on 2-DG retention and 2-DGP formation by the striattum and the cerebral cortex was investigated. Animals were studied both 3 days and 2–4 weeks after lesioning. The location and efficacy of the lesions were verified histologically, behaviorally (by observing rotational behavior), and biochemically (by assay of striatal dopamine concentration or tyrosine hydroxylase activity). The lesions induced a mean asymmetry of less than 10% in 2-DG retention and in 2-DGP formation in striatum and cerebral cortex. This result was verified by [¹⁴C]2-DG autoradiography. Systemic administration of amphetamine (5 mg/kg) or apomorphine HBr (1.5 mg/kg) elicited rotational behavior, but did not induce a marked asymmetry of 2-DG retention in the regions studied. It is concluded that unilateral lesions of the nigrostriatal dopaminergic pathway have, at most, a modest effect on 2-DG retention by forebrain structures. We also conclude that vehicle injections may produce morphological and chemical evidence of brain injury, including small but reproducible changes in deoxyglucose retention.     

The role of the cAMP-PKA system in the short-term regulation of striatal [C]-2-deoxyglucose uptake in freely moving rats

The cyclic adenosine monophosphate (cAMP)-protein kinase (PK) A system has been shown to have stimulatory effects on glucose utilization in various tissues in vitro. However, little is known about the influence of cAMP on glucose utilization in vivo. In the present study, we examined how cAMP-related compounds affected [¹⁴C]-2-deoxyglucose (DG) uptake in the striatum of freely moving rats. An intrastriatal injection of dibutyryl-cyclic adenosine monophosphate (db-cAMP), although increasing local cerebral blood flow, was found to decrease the uptake of [¹⁴C]-2-DG in the striatum. This decrease of [¹⁴C]-2-DG uptake in the striatum was completely blocked by pretreatment with Rp-adenosine-3′,5′-cyclic monophosphorothioate triethylamine (Rp-cAMPS). Moreover, intrastriatal infusion of Rp-cAMPS alone produced a striking increase of [¹⁴C]-2-DG uptake in the striatum. These results strongly suggest that transient activation of the cAMP-PKA system can depress the glucose phosphorylation process of the rat brain in vivo.     

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

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

Neuroprotective effect of the angiotensin-converting enzyme inhibitor perindopril in MPTP-treated mice

Abstract

The angiotensin -converting enzyme (ACE) inhibitor perindopril has been shown to exert benefical effects on the dopaminergic system. Here, we investigated the effects of perindopril on the dopaminergic system in mice after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment, in comparison with a Ca²⁺ antagonist, amlodipine. Administration of perindopril showed dose-dependent neuroprotective effects against MPTP-induced striatal dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) depletion. However, administration of amlodipine showed no significant effects on striatal dopamine depletion after MPTP treatment. In our immunohistochemical studies with antibodies against tyrosine hydroxylase (TH), microtubule-associated protein 2a, b (MAP2), dopamine transporter (DAT), parvalbumin (PV), glial fibrillary acidic protein (GFAP) and Cu/Zn-superoxide dismutase (Cu/Zn-SOD), the administration of perindopril significantly attenuated MPTP-induced substantia nigra and striatal damage. This drug also blocked the increases in GFAP-positive astrocytes in the striatum and substantia nigra after MPTP treatment. Furthermore, the administration of perindopril showed a protective effect against the intense Cu/Zn-SOD immunoreactivity in the neurons and glial cells in both the striatum and substantia nigra after MPTP treatment. These results indicated that the ACE inhibitor perindopril can protect against MPTP-induced striatal dopamine and DOPAC depletion in mice. The protective effect may be, at least in part, caused by the reduction of free radicals caused by MPTP. The present study also demonstrated that perindopril is effective against MPTP-induced neurodegeneration of the nigro-striatal dopaminergic pathway. Furthermore, our results provided further evidence that free radical scavengers may be effective in the treatment of neurodegenerative diseases such as Parkinson's disease.     

H-2-Deoxyglucose uptake after electrical stimulation of cardioactive sites in insular cortex and mediodorsal nucleus of the thalamus in rabbits

The uptake of ³H-2-deoxyglucose (³H-2-DG) in selected brain structures was determined subsequent to electrical stimulation of insular cortex (Ins) and the mediodorsal (MD) nucleus of the thalamus in rabbits. Stimulation of Ins elicited parasympathetic-like responding (i.e., bradycardia and depressor responses); whereas MD stimulation produced sympathetic-like responses (bradycardia and pressor responses). Stimulation of Ins also resulted in increased ³H-2-DG activity in ipsilateral MD and the ventromedial/ventroposterior complex as well as the contralateral Ins compared to nonstimulated control subjects. The central nucleus of the amygdala also showed increased activity after Ins stimulation. In 2 animals stimulation of Ins resulted in increased ³H-2-DG activity in the caudate/putamen complex. Stimulation of MD resulted in ipsilateral increases in ³H-2-DG activity in the midline, agranular prefrontal cortex, as well as the ipsilateral Ins, and the caudate nucleus and putamen/globus pallidus complex. Two animals also showed increases in ³H-2-DG activity in ipsilateral substantia nigra. However, no increased activity was observed in the lateral hypothalamus, the parabrachial nuclei, the nucleus tractus solitarius, or the dorsal motor nucleus of the vagus, although it has been shown that efferents from Ins reach these areas. A more significant finding however, was that the reciprocal connections of MD and Ins appear to be activated by stimulation of either structure, even though their relationship to autonomic function appears to be quite different.     

FGF-2-mediated protection of cultured mesencephalic dopaminergic neurons against MPTP and MPP+: Specificity and impact of culture conditions,non-dopaminergic neurons,and astroglial cells

The protective role of basic fibroblast growth factor (FGF-2) for 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)- and methylpyridiniumion (MPP⁺)-lesioned dopaminergic (DAergic) nigrostriatal neurons was studied, using dissociated cell cultures of embryonic day (E) 14 rat mesencephalon. Cells were grown in different culture media and received FGF-2 (5 ng/ml) and/or the toxins (5 μM) at various schedules, but were consistently allowed to differentiate for 3 days prior to becoming exposed to the toxin. Survival of tyrosine hydroxylase (TH)-immunoreactive cells at 7 days was only markedly impaired by MPTP, if horse serum (HS) or bovine serum albumine (BSA) were omitted from the culture medium. FGF-2 increased the number of TH-immunoreactive cells, and this increase not diminished by MPTP under any culture condition. Uptake of ³H-DA was significantly reduced by MPTP in HS- and BSA-containing, but not in protein-less cultures. A protective effect by FGF-2 was only seen in the presence of BSA. MPP⁺ caused a more pronounced reduction in ³H-DA uptake than MPTP, and this effect was partially reversed by the addition of FGF-2, unless cultures contained HS. Neurofilament protein (NF), an indirect measure for the total number of neurons present in the cultures, was not significantly reduced by MPTP or MPP⁺ corroborating the specificity of the toxin for DAergic neurons, which constitute only a minor fraction in these cultures. In line with the wide spectrum of target neurons of FGF-2, this factor significantly increased NF contents under any culture condition. Quantification of the amounts of glial fibrillary acidic protein (GFAP) revealed stimulatory effects of FGF-2 (2.5- to 4-fold) and at least 10-fold higher levels in the presence as compared to the absence of HS. These data show that FGF-2 can protect DAergic neurons against MPTP- and MPP⁺-mediated damage. However, the effects of the toxins as well as of FGF-2 are partially dependent on culture conditions. Variations in the effectiveness of toxins and FGF-2 are not overtly related to the total numbers of neurons or astroglial cells, but may reflect culture type-dependent alterations of neuronal and glial metabolism. © 1993 Wiley-Liss, Inc.     

Neither adrenergic nor cholinergic antagonists in the central nervous system affect 2-deoxy-d-glucose(2-DG)-induced hyperglycemia

To investigate whether the brain adrenergic and cholinergic neurotransmitter systems are involved in the regulation of 2-deoxy-d-glucose (2-DG)-induced hyperglycemia, we studied the effects of adrenergic and cholinergic antagonists on 2-DG-induced secretion of epinephrine and glucagon, and hyperglycemia, in anesthetized fed rats. When 2-DG (10 mg/10 μl) was injected into the third cerebral ventricle, hepatic venous plasma glucose, glucagon, and epinephrine concentrations were significantly increased. Co-administration of phentolamine, propranolol, atropine and hexamethonium (1 × 10⁻⁷ mol) with 2-DG did not modify the hyperglycemia responses normally observed after the administration of 2-DG alone. From this evidence we concluded that neither brain adrenoceptive nor cholinoceptive neurons are involved in the regulation of 2-DG-induced hyperglycemia.     

6-[F]Fluoro-

Mutations in the parkin gene cause autosomal recessive familial Parkinson's disease (PD). Parkin-deficient mouse models fail to recapitulate nigrostriatal dopaminergic neurodegeneration as seen in PD, but produce deficits in dopaminergic neurotransmission and noradrenergic-dependent behavior. Since sporadic PD is thought to be caused by a combination of genetic susceptibilities and environmental factors, we hypothesized that neurotoxic insults from catecholaminergic toxins would render parkin knockout mice more vulnerable to neurodegeneration. Accordingly, we investigated the susceptibility of catecholaminergic neurons in parkin knockout mice to the potent dopaminergic and noradrenergic neurotoxins 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) respectively. We report that nigrostriatal dopaminergic neurons in parkin knockout mice do not show increased susceptibility to the parkinsonian neurotoxin, MPTP, in acute, subacute and chronic dose regimens of the neurotoxin. Additionally, parkin knockout mice do not show increased vulnerability to the noradrenergic neurotoxin, DSP-4, regarding levels of norepinephrine in cortex, brain stem and spinal cord. These findings suggest that absence of parkin in mice does not increase susceptibility to the loss of catecholaminergic neurons upon exposure to both dopaminergic and noradrenergic neurotoxins.     

MPTP and DSP-4 susceptibility of substantia nigra and locus coeruleus catecholaminergic neurons in mice is independent of parkin activity

Mutations in the parkin gene cause autosomal recessive familial Parkinson's disease (PD). Parkin-deficient mouse models fail to recapitulate nigrostriatal dopaminergic neurodegeneration as seen in PD, but produce deficits in dopaminergic neurotransmission and noradrenergic-dependent behavior. Since sporadic PD is thought to be caused by a combination of genetic susceptibilities and environmental factors, we hypothesized that neurotoxic insults from catecholaminergic toxins would render parkin knockout mice more vulnerable to neurodegeneration. Accordingly, we investigated the susceptibility of catecholaminergic neurons in parkin knockout mice to the potent dopaminergic and noradrenergic neurotoxins 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) respectively. We report that nigrostriatal dopaminergic neurons in parkin knockout mice do not show increased susceptibility to the parkinsonian neurotoxin, MPTP, in acute, subacute and chronic dose regimens of the neurotoxin. Additionally, parkin knockout mice do not show increased vulnerability to the noradrenergic neurotoxin, DSP-4, regarding levels of norepinephrine in cortex, brain stem and spinal cord. These findings suggest that absence of parkin in mice does not increase susceptibility to the loss of catecholaminergic neurons upon exposure to both dopaminergic and noradrenergic neurotoxins.     

Nigrostriatal dopaminergic neurotoxicity of L-cysteine after stereotaxic administration into the substantia nigra of rats: Potential implications for MPTP-induced neurotoxicity and parkinson’s disease

Stereotaxic administration of L-cysteine (CySH) into the rat substantia nigra pars compacta (SN_C) evokes a dose-dependent fall of striatal levels of dopamine. This, together with decreased tyrosine hydroxylase immunoreactivity in the striatum and SN_cand decreased nigral staining for Niss1 substance indicate that CySH is a dopaminergic neurotoxin. The neurotoxic effects of CySH infusion into the rat SN_C were blocked by prior administration of the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801. Previous studies have demonstrated that administration of the neurotoxin l-methyl-4-phenyl-l,2,3,6-tetrahydropyridine (MPTP) not only evokes the degeneration of nigrostriatal dopamine neurons but also causes a significant fall of glutathione (GSH) without corresponding increases of glutathione disulfide (GSSG). Furthermore, microdialysis studies have demonstrated that when perfusions of l-methyl-4-phenylpyridinium (MPP⁺), the active metabolite of MPTP, into the rat SN_C are discontinued extracellular levels of GSH massively but transiently increase followed by a prolonged elevation of extracellular CySH, the latter effect being blocked by inhibition of γ-glutamyl transpeptidase (γ-GT). These observations, together with the present results, suggest that the delayed but prolonged elevation of extracellular CySH that occurs as a MPP⁺-induced dopaminergic SN_ccell energy impairment begins to subside might evoke NMDA receptor mediated excitotoxicity. The potential roles of elevated extracellular CySH in MPTP/MPP⁺-induced dopaminergic neurotoxicity and in the pathogenesis of Parkinson’s disease are discussed.     

Acute Restraint Stress Augments 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine Neurotoxicity <Emphasis Type="Italic">via</Emphasis> Increased Toxin Uptake into the Brain in C57BL/6 Mice

As an environmental risk factor, psychological stress may trigger the onset or accelerate the progression of Parkinson’s disease (PD). Here, we evaluated the effects of acute restraint stress on striatal dopaminergic terminals and the brain metabolism of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which has been widely used for creating a mouse model of PD. Exposure to 2 h of restraint stress immediately after injection of a low dose of MPTP caused a severe loss of striatal dopaminergic terminals as indicated by decreases in the dopamine transporter protein and dopamine levels compared with MPTP administration alone. Both striatal 1-methyl-4-phenylpyridinium ion (MPP⁺) and MPTP concentrations were significantly increased by the application of restraint stress. Striatal monoamine oxidase-B, which catalyzes the oxidation of MPTP to MPP⁺, was not changed by the restraint stress. Our results indicate that the enhanced striatal dopaminergic terminal loss in the stressed mice is associated with an increase in the transport of neurotoxin into the brain.     

Progressive loss of striatal dopamine terminals in MPTP-induced acute parkinsonism in cynomolgus monkeys using vesicular monoamine transporter type 2 PET imaging([18F]AV-133)

The 1-methyl-4-phenyl-1,2,3,4-tetrahydropyridine (MPTP)-induced parkinsonism model, particularly in non-human primates, remains the gold-standard for studying the pathogenesis and assessing novel therapies for Parkinson’s disease. However, whether the loss of dopaminergic neurons in this model is progressive remains controversial, mostly due to the lack of objective in vivo assessment of changes in the integrity of these neurons. In the present study, parkinsonism was induced in cynomolgus monkeys by intravenous administration of MPTP (0.2 mg/kg) for 15 days; stable parkinsonism developed over 90 days, when the symptoms were stable. Noninvasive positron emission tomographic neuroimaging of vesicular monoamine transporter 2 with 9-[¹⁸F] fluoropropyl-(+)-dihydrotetrabenazine ([¹⁸F]AV-133) was used before, and 15 and 90 days after the beginning of acute MPTP treatment. The imaging showed evident progressive loss of striatal uptake of [¹⁸F]AV-133. The dopaminergic denervation severity had a significant linear correlation with the clinical rating scores and the bradykinesia subscores. These findings demonstrated that [¹⁸F]AV-133 PET imaging is a useful tool to noninvasively evaluate the evolution of monoaminergic terminal loss in a monkey model of MPTP-induced parkinsonism.