Early signs of neuronal apoptosis in the substantia nigra pars compacta of the progressive neurodegenerative mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid model of Parkinson's disease

Parkinson's disease is associated with a progressive loss of substantia nigra pars compacta dopaminergic neurons. The cellular and molecular mechanisms underlying Parkinson's disease neurodegeneration have not been fully determined. Clinical investigations and subacute in vivo studies using the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine have generated some observations suggesting that apoptosis is involved in neurodegeneration; however, this view remains equivocal. In this study, the substantia nigra pars compacta neurodegenerative process was examined in the chronic mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid model of Parkinson's disease treated with 10 doses of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (25 mg/kg) and probenecid (250 mg/kg) over five weeks. One day after chronic treatment, numerous terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells were detected specifically in the substantia nigra pars compacta displaying shrunken volume, chromatin condensation, and DNA fragmentation. The number of apoptotic cells declined over time. No terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells were found in untreated or probenecid-treated control animals. Cytomorphometric analysis of substantia nigra pars compacta nuclear loci revealed eccentric nucleoli dislocation and vesicular degranulation in all of the apoptotic neurons for the mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid model for Parkinson's disease. The terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells phenotypically showed neuronal origin (NeuN-positive) with a loss of tyrosine hydroxylase immunoreactivity. While the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling-positive cells were not co-localized with astroglial (GFAP-positive) cells, some apoptotic cells were clearly associated with the activated microglial (macrophage antigen complex-1 and isolectin B(4)-positive) cells suggesting an active process of dead cell removal. In the one-day and seven-day post-treated mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid model for Parkinson's disease, marked depression of tyrosine hydroxylase immunoreactivity in the substantia nigra pars compacta and striatum was observed, which was correlated with significant reductions of striatal dopamine content and uptake. These results suggest that initial neuronal apoptosis and morphological changes are involved, at least in part, in the chronic neurodegeneration of mouse 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine/probenecid model for Parkinson's disease.     

An immunohistochemical study of the acute and long-term effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the marmoset

Administration of the drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine induces a parkinsonian syndrome in primates. Intraperitoneal injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the common marmoset (Callithrix jacchus) produced symptoms of rigidity, akinesia and tremor which persisted for at least one month. However, after this time, considerable behavioural recovery occurred, although animals were still severely bradykinetic compared with controls. Marmosets were allowed to survive for 1, 3 1/2 or 7 months prior to histological and immunocytochemical analysis. Detection of catecholaminergic neurons using antibodies directed against the enzyme tyrosine hydroxylase revealed a profound (80%) loss of dopaminergic cells from the substantia nigra one month after initiation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment. This was accompanied by a severe gliosis. Fewer cells were lost from the adjacent ventral tegmental area (45%), but dopamine-containing cells in other brain areas were not obviously affected. At longer survival times the substantia nigra was less damaged, with a proliferation of glia in the pars compacta and a loss of approximately 20% of the dopaminergic perikarya. Using immunohistochemical techniques, the distribution of neuropeptides substance P, [Met]enkephalin and dynorphin 1-17-like immunoreactivity were examined and found to exhibit distinctive patterns in the marmoset substantia nigra. The integrity of these systems appeared intact at all times after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment. These results support the hypothesis that the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine produces a clinical syndrome, indistinguishable from Parkinson's disease, via a selective destruction only of neurons with perikarya in the substantia nigra pars compacta and the ventral tegmental area. The findings that the peptidergic input to these cells together with most non-nigral dopaminergic cell groups are not damaged, indicate that the selectivity of the lesion produced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine appears greater than that seen in idiopathic Parkinson's disease. The neurotoxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the marmoset may not be permanent since both behavioural and biochemical recovery were observed after several months.     

Protection against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism by the catecholamine uptake inhibitor nomifensine: behavioral analysis in monkeys with partial striatal dopamine depletions

The neurotoxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine on dopamine neurons in monkeys were found to be reduced when the catecholamine uptake inhibitor nomifensine was administered during several weeks after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The obtained protection was partial, leading to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced changes in dopamine levels to 8, 16, 52 and 59% of control values in the caudate nucleus and to 10, 16, 101 and 99% in the putamen of four animals, respectively. At the same doses, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine alone is known to deplete striatal dopamine levels to 0.5-7% of control values. Extra-nigrostriatal monoamine neurons were generally well protected by nomifensine. Neurological examinations revealed modest hypokinesia for a maximum of 10 days after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the two more severely affected animals. Reaction times of arm and eye movements were measured in a formal task in two of the monkeys having a moderate and a more important depletion of striatal dopamine, respectively. Only moderate impairments were seen during the initial 2 weeks after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in both animals. All parameters recovered to control levels thereafter. At 3.5 and 5.5 months after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, task performance was significantly better than control. The speed of arm movement remained largely unaffected during all periods of experimentation. Spontaneous eye movements were reduced in frequency and amplitude during the initial 1-2 weeks after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and recovered completely thereafter. These data suggest a substantial reduction of neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine by inhibition of catecholamine uptake. Particularly striking was the absence of major and permanent impairments in behavioral tests in which monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine alone were severely impaired. These results may warrant the development of new catecholamine uptake inhibitors for protecting nigrostriatal dopamine neurons against potential environmental toxins.     

Fluoro-Jade C染色方法显示神经毒物MPTP和红藻氨酸致小鼠中脑黑质神经元的变性死亡

为探讨Fluoro-JadeC荧光染色检测神经毒物MPTP和红藻氨酸(KA)损伤致中脑黑质神经元变性死亡的方法,本研究采用小鼠腹腔注射MPTP或黑质定位注射KA制备黑质损伤模型,然后进行Fluoro-JadeC染色标记和计数分析黑质内变性死亡神经元。结果显示:Fluoro-JadeC(FJC)染色可清晰地显示MPTP或KA致小鼠黑质损伤后出现的变性神经元,包括变性神经元的细胞胞体和突起。在中脑组织切片上,MPTP模型与KA模型黑质致密部内有许多FJC染色阳性的变性神经元,而对照组动物黑质内未见FJC染色阳性的变性神经元分布。本研究结果表明:FJC方法能够很好地显示MPTP和KA动物模型黑质内神经元的变性死亡,具备很高的对比度和分辨率,是一种特异性标记黑质变性神经元树突、轴突和胞体的优良染色方法。     

Induction of hippocampal LTD requires nitric-oxide-stimulated PKG activity and Ca2+ release from cyclic ADP-ribose-sensitive stores.

Long-term depression (LTD) of synaptic transmission can be induced by several mechanisms, one thought to involve Ca2+-dependent activation of postsynaptic nitric oxide (NO) synthase and subsequent diffusion of NO to the presynaptic terminal. We used the stable NO donor S-nitroso-N-acetylpenicillamine (SNAP) to study the NO-dependent form of LTD at Schaffer collateral-CA1 synapses in vitro. SNAP (100 microM) enhanced the induction of LTD via a cascade that was blocked by the N-methyl-D-aspartate receptor antagonist D-2-amino-5-phosphonopentanoic acid (50 microM), NO guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (10 microM), and the PKG inhibitor KT5823 (1 microM). We further show that LTD induced by low-frequency stimulation in the absence of SNAP also is blocked by KT5823 or Rp-8-(4-chlorophenylthio)-guanosine 3',5'-cyclic monophosphorothioate (10 microM), cyclic guanosine 3',5' monophosphate-dependent protein kinase (PKG) inhibitors with different mechanisms of action. Furthermore SNAP-facilitated LTD was blocked when release from intracellular calcium stores was inhibited by ryanodine (10 microM). Finally, two cell-permeant antagonists of the cyclic ADP-ribose binding site on ryanodine receptors also were able to block the induction of LTD. These results support a cascade for induction of homosynaptic, NO-dependent LTD involving activation of guanylyl cyclase, production of guanosine 3',5' cyclic monophosphate and subsequent PKG activation. This process has an additional requirement for release of Ca2+ from ryanodine-sensitive stores, perhaps dependent on the second-messenger cyclic ADP ribose.     

Neural mechanisms underlying parkinsonian symptoms based upon regional uptake of 2-deoxyglucose in monkeys exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

The 2-deoxyglucose metabolic mapping technique has been used to investigate the neural mechanisms which underlie the symptoms of Parkinsonism in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine primate model of Parkinson's disease. In six cynomolgus monkeys, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine was either (a) administered intravenously to induce generalized Parkinsonism, or (b) infused into one carotid artery to induce unilateral Parkinsonism. Post-mortem examination revealed profound cell loss from the substantia nigra, pars compacta either bilaterally or unilaterally in the two groups, respectively. In addition, there was pathological involvement of the ventral tegmental area and locus coeruleus in animals receiving intravenous 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. 2-Deoxyglucose autoradiography revealed widespread changes in 2-deoxyglucose uptake in the brains of parkinsonian animals when compared to controls. Most of these changes were in basal ganglia and related structures and were qualitatively similar in the two groups of experimental animals. Prominent increases in 2-deoxyglucose uptake were observed in the lateral segment of the globus pallidus (24-27%), the ventral anterior and ventral lateral nuclei of the thalamus (14-22%) and the nucleus tegmenti pedunculopontinus of the caudal midbrain (17-69%). A profound decrease (17-26%) in 2-deoxyglucose uptake was observed in the subthalamic nucleus. We propose these data to indicate that in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism there is the following pattern of abnormal neuronal activity in basal ganglia circuitry: (i) increased activity in the projection from the putamen to the lateral segment of the globus pallidus; (ii) decreased activity in the projection from the putamen to the medial segment of the globus pallidus; (iii) decreased activity in the projection from the lateral segment of the globus pallidus to the subthalamic nucleus; (iv) increased activity in the projection from the subthalamic nucleus to the globus pallidus; and (v) increased activity in neurons of the medial segment of the globus pallidus projecting to the ventral anterior/ventral lateral thalamus and the pedunculopontine nucleus. These results are compared to the 2-deoxyglucose uptake findings in previous studies from this laboratory in hemiballism and hemichorea in the monkey. The central importance of the subthalamic nucleus in all three conditions is proposed, and supportive evidence for the excitatory nature of subthalamic efferent fibres is adduced.     

Histochemical mapping of nitric oxide synthase in the rat brain.

The NADPH-diaphorase histochemical technique provides a simple and robust method to stain select populations of neurons throughout the brain. We have recently identified the enzyme responsible for this histochemical reaction to be nitric oxide synthase. This enzyme is responsible for the calcium-dependent synthesis of nitric oxide from arginine. Nitric oxide acts as a novel neural messenger by stimulating soluble guanylyl cyclase thereby increasing the levels of cyclic guanosine 3',5'-monophosphate in target cells. Thus the NADPH-diaphorase histochemical method allows the direct visualization of the neurons which use this novel signal transduction pathway. We now describe the detailed distribution of this enzyme in the rat brain. Our results suggest a widespread role for the nitric oxide-cyclic guanosine monophosphate system in the nervous system.     

Histochemical localization of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine oxidation in the mouse brain

The sites in the mouse brain where 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine can be oxidized to the toxic metabolite 1-methyl-4-phenylpyridine were determined using a histochemical technique. The method involved the demonstration of monoamine oxidase activity using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine as the substrate by means of a sensitive coupled peroxidase technique. The distribution of neurons displaying the ability to oxidize 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine via a monoamine oxidase catalysed reaction was compared to that of various amine systems identified with immunohistochemistry. Dopamine neurons, and in particular the nigrostriatal dopamine cells, did not display the capacity to oxidize 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Noradrenergic neurons showed intense monoamine oxidase activity when 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine was used as substrate, and this activity was blocked by the monoamine oxidase-A inhibitor clorgyline. Serotonin neurons and histamine neurons were also able to oxidize 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The reaction in these neurons was blocked by deprenyl, an inhibitor of monoamine oxidase-B. Pretreatment with inhibitors of monoamine oxidase-B has been previously shown to prevent the neurotoxic action of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine on dopaminergic neurons. Therefore, since serotonin and histamine neurons are able to oxidize 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine by means of monoamine oxidase-B, these neurons may be involved in the production of the toxic metabolites of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in vivo.     

The nitric oxide-guanosine 3',5'-cyclic monophosphate pathway regulates dopamine efflux in the medial preoptic area and copulation in male rats

Dopamine in the medial preoptic area (MPOA) plays a significant role in regulation of male copulation. One mediator of the MPOA dopamine level is nitric oxide. In the current study, we investigated the role of the nitric oxide-guanosine 3',5'-cyclic monophosphate (cGMP) pathway in the regulation of MPOA dopamine and copulation in male rats. The reverse-dialysis of a membrane-permeable analog, 8-Br-cGMP, increased, while a soluble guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ), significantly reduced basal dopamine and its metabolite levels. ODQ successfully blocked a nitric oxide donor-induced increase in dopamine levels, while a neuronal nitric oxide synthase (nNOS) inhibitor was ineffective in blocking an 8-Br-cGMP-induced increase in dopamine, indicating that cGMP is "downstream" of nitric oxide. Furthermore, 8-Br-cGMP facilitated, while ODQ inhibited copulation. Given the steroid-sensitive nature of nNOS functions and the multiple roles nitric oxide plays in the MPOA, we propose that nitric oxide provides important integration of various neurochemical and neuroendocrine signals. The involvement of the central nitric oxide-cGMP pathway in the regulation of copulation also raises an interesting therapeutic possibility, as the manipulation of the same pathway in peripheral tissue is already utilized in treatment of male sexual dysfunction.     

Does ORP150/HSP12A protect dopaminergic neurons against MPTP/MPP(+)-induced neurotoxicity?

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and its metabolite 1-methyl-4-phenylpyridinium (MPP(+)) are drugs that are widely used in experimental Parkinson disease (PD) models. What is the significance of ORP150/HSP12A, a molecular chaperone in the endoplasmic reticulum (ER), in the nigrostriatal system? Dopaminergic neuroblastoma SH-SY5Y cells and dopaminergic neurons of the substantia nigra pars compacta (SNpc) were examined. Our observations led to the hypothesis that ORP150 protects against MPTP/MPP(+)-induced neurotoxicity, and indicate the importance of the ER environment in maintaining the nigrostriatal pathways.     

Deficits in behavioral initiation and execution processes in monkeys with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism

Administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to two monkeys led to hypokinesia, tremor, rigidity, adipsia and aphagia. Quantitative assessment of hypokinesia revealed increased reaction time, delayed onset of muscle activity and prolonged movement time in a forelimb reaching task after selective degeneration of the nigrostriatal dopamine (DA) system sparing mesocortical dopamine neurons. The losses of pars compacta cells of substantia nigra, of striatal [3H]mazindol binding and of striatal DA content (more than 90%) quantitatively paralleled the severity of behavioral deficits. Additional monoamine systems were affected with stronger MPTP effects.     

Possible sources and sites of action of the nitric oxide involved in synaptic plasticity at spinal lamina I projection neurons

The synaptic long-term potentiation between primary afferent C-fibers and spinal lamina I projection neurons is a cellular model for hyperalgesia [Ikeda H, Heinke B, Ruscheweyh R, Sandkühler J (2003) Synaptic plasticity in spinal lamina I projection neurons that mediate hyperalgesia. Science 299:1237-1240]. In lamina I neurons with a projection to the periaqueductal gray, this long-term potentiation is dependent on nitric oxide. In the present study, we used immunohistochemistry to detect possible sources and sites of action of the nitric oxide necessary for the long-term potentiation at lamina I spino-periaqueductal gray neurons in rats. None of the three isoforms of the nitric oxide synthase was expressed in a significant number of lamina I spino-periaqueductal gray neurons or primary afferent C-fibers (as evaluated by staining of their cell bodies in the dorsal root ganglia). However, endothelial and inducible nitric oxide synthase were found throughout the spinal cord vasculature and neuronal nitric oxide synthase was present in a number of neurons in laminae II and III. The nitric oxide target soluble guanylyl cyclase was detected in most lamina I spino-periaqueductal gray neurons and in approximately 12% of the dorsal root ganglion neurons, all of them nociceptive as evaluated by coexpression of substance P. Synthesis of cyclic 3',5'-guanosine monophosphate upon stimulation by a nitric oxide donor confirmed the presence of active guanylyl cyclase in at least a portion of the spino-periaqueductal gray neuronal cell bodies. We therefore propose that nitric oxide generated in neighboring neurons or blood vessels acts on the spino-periaqueductal gray neuron and/or the primary afferent C-fiber to enable long-term potentiation. Lamina I spino-parabrachial neurons were stained for comparison and yielded similar results.     

The nNOS/cGMP signal transducing system is involved in the cardiovascular responses induced by activation of NMDA receptors in the rostral ventrolateral medulla of cats

Nitric oxide (NO) is synthesized from -arginine by NO synthase (NOS). NO stimulates the soluble form of guanylyl cyclase (sGC) and induces accumulation of cyclic guanosine monophosphate (cGMP). The purpose of this study was to examine whether the cardiovascular responses induced by N-methyl- -aspartate (NMDA) in the rostral ventrolateral medulla (RVLM) depend on the actions of NOS and sGC. In anesthetized cats, the extracellular NO level was measured by in vivo voltammetry using a nafion/porphyrine/o-phenylenediamine-coated carbon-fiber electrode. Microinjection of NMDA into the RVLM produced hypertension and bradycardia associated with NO formation. These NMDA-induced responses were attenuated by prior injections of 7-nitroindazole, a neuronal NO synthase (nNOS) inhibitor, and 1H-[1, 2 and 4]oxadiazolo[4,3-a]quinoxalin-1-one, a sGC inhibitor. These findings suggest that NO is involved in the NMDA-induced cardiovascular responses in the RVLM.     

Regional localization of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) uptake: mismatch between its uptake and neurotoxic sites.

Three to 24 h following intraventricular injections of radioactive 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) into the rat, accumulations of radiolabel were widely detected, in varying degree, over neuronal perikarya in motor-related structures below the midbrain. Pretreatment with the monoamine oxidase B inhibitor pargyline largely eliminated the perikaryal radiolabeling in the substantia nigra, dorsal raphe and cerebellum, leaving that in the other regions intact. These results indicate that there exists a certain mismatch between MPTP uptake and neurotoxic sites, and that invulnerable cells can accumulate MPTP without being converted to its major active metabolite 1-methyl-4-phenylpyridine (MPP+).     

Estrogen, neuroinflammation and neuroprotection in Parkinson's disease: glia dictates resistance versus vulnerability to neurodegeneration

Post-menopausal estrogen deficiency is recognized to play a pivotal role in the pathogenesis of a number of age-related diseases in women, such as osteoporosis, coronary heart disease and Alzheimer's disease. There are also sexual differences in the progression of diseases associated with the nigrostriatal dopaminergic system, such as Parkinson's disease, a chronic progressive degenerative disorder characterized by the selective degeneration of mesencephalic dopaminergic neurons in the substancia nigra pars compacta. The mechanism(s) responsible for dopaminergic neuron degeneration in Parkinson's disease are still unknown, but oxidative stress and neuroinflammation are believed to play a key role in nigrostriatal dopaminergic neuron demise. Estrogen neuroprotective effects have been widely reported in a number of neuronal cell systems including the nigrostriatal dopaminergic neurons, via both genomic and non-genomic effects, however, little is known on estrogen modulation of astrocyte and microglia function in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine model of Parkinson's disease. We here highlight estrogen modulation of glial neuroinflammatory reaction in the protection of mesencephalic dopaminergic neurons and emphasize the cardinal role of glia-neuron crosstalk in directing neuroprotection vs neurodegeneration. In particular, the specific role of astroglia and its pro-/anti-inflammatory mechanisms in estrogen neuroprotection are presented. This study shows that astrocyte and microglia response to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine injury vary according to the estrogenic status with direct consequences for dopaminergic neuron survival, recovery and repair. These findings provide a new insight into the protective action of estrogen that may possibly contribute to the development of novel therapeutic treatment strategies for Parkinson's disease.     

Engrailed protects mouse midbrain dopaminergic neurons against mitochondrial complex I insults

Mice heterozygous for the homeobox gene Engrailed-1 (En1) display progressive loss of mesencephalic dopaminergic (mDA) neurons. We report that exogenous Engrailed-1 and Engrailed-2 (collectively Engrailed) protect mDA neurons from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a mitochondrial complex I toxin used to model Parkinson's disease in animals. Engrailed enhances the translation of nuclearly encoded mRNAs for two key complex I subunits, Ndufs1 and Ndufs3, and increases complex I activity. Accordingly, in vivo protection against MPTP by Engrailed is antagonized by Ndufs1 small interfering RNA. An association between Engrailed and complex I is further confirmed by the reduced expression of Ndufs1 and Ndufs3 in the substantia nigra pars compacta of En1 heterozygous mice. Engrailed also confers in vivo protection against 6-hydroxydopamine and α-synuclein-A30P. Finally, the unilateral infusion of Engrailed into the midbrain increases striatal dopamine content, resulting in contralateral amphetamine-induced turning. Therefore, Engrailed is both a survival factor for adult mDA neurons and a regulator of their physiological activity.     

Symptomatic and asymptomatic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated primates: biochemical changes in striatal regions

Administration of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, to primates produces an excellent behavioral model of idiopathic Parkinson's disease. In the vervet monkey, regional biochemical differences in the striatum of two 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated groups were examined one to two months after treatment and compared with controls; one group displayed no observable gross motor abnormalities after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment (asymptomatic), whereas the other group became markedly parkinsonian (symptomatic). In both 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated groups massive depletions of dopamine and homovanillic acid concentrations were observed in the striatum; generally, dopamine losses in the symptomatic group (greater than 95%) were greater than in the asymptomatic group (greater than 75%). However, in striatum, a marked heterogeneity in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine susceptibility was found; certain striatal regions having 99% depletion of dopamine even in asymptomatic monkeys. Overall, in ventromedial regions of striatum the losses of dopamine and homovanillic acid concentrations were less than in dorsolateral regions at the same coronal level. There was a significant negative correlation between control homovanillic acid/dopamine ratios and susceptibility of examined regions to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine toxicity. Unlike idiopathic, but similar to postencephalitic, Parkinson's disease, dopamine and homovanillic acid levels in caudate nucleus were not spared relative to putamen; in fact, in the asymptomatic group caudate nucleus dopamine and homovanillic acid concentrations were depleted to a greater extent than in putamen.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of locus coeruleus lesions on parkinsonian signs, striatal dopamine and substantia nigra cell loss after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in monkeys: a possible role for the locus coeruleus in the progression of Parkinson's disease

Six pairs of female squirrel monkeys were given a daily intraperitoneal injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) for 9-14 days, beginning the same day on which they received either a bilateral 6-hydroxydopamine lesion or a sham lesion of the locus coeruleus. Sham animals developed typical parkinsonian signs (i.e. tremor, bradykinesia, hypokinesia and reduced blink rate) which largely recovered by six to nine weeks after the start of MPTP treatment. At nine weeks, post mortem levels of striatal dopamine in these same animals were partially reduced (by 45%), and this only in the putamen, compared to values obtained from three non-operated, normal control animals. Additionally, histological examination revealed a moderate loss of neuronal cell bodies in the substantia nigra, pars compacta. In marked contrast, the locus coeruleus-lesioned monkeys exhibited little or no recovery from the parkinsonian signs induced by MPTP. Post mortem examination of these animals revealed profound decreases in caudate (by 84%) and putamen (by 91%) dopamine content, and severe neuronal cell loss in the substantia nigra pars compacta of all animals. These neurological, biochemical and histological assessments indicate that lesioning of the locus coeruleus impairs the recovery which usually occurs from the parkinsonian manifestations induced by MPTP in squirrel monkeys. The results support the hypothesis that deficient locus coeruleus noradrenergic mechanisms underlie the progression of Parkinson's disease.     

l-dopa-induced reversal in striatal glutamate following partial depletion of nigrostriatal dopamine with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

We have reported that 1 month following acute (20mg/kg x 4) or subchronic (30 mg/kg/day x 7d) administration of the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, there is an increase or decrease, respectively, in the extracellular level of striatal glutamate as determined by in vivo microdialysis [Robinson S, Freeman P, Moore C, Touchon JC, Krentz L, Meshul CK (2003) Acute and subchronic MPTP administration differentially affects striatal glutamate synaptic function. Exp Neurol 180:73-86]. The goal of this study was to determine the effects of treatment with l-dopa (15 mg/kg) for 21 days on striatal glutamate starting on day 8 after the first dose of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine was administered to mice. Following acute administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, the increase in extracellular striatal glutamate due to lesion of the nigrostriatal pathway was completely reversed to a level below that found in the vehicle-treated group after l-dopa treatment. Subchronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment resulted in a decrease in striatal extracellular glutamate that was reversed to the level close to that observed in the vehicle-treated group. There was no change in the density of nerve terminal glutamate immunolabeling associated with the synaptic vesicle pool, suggesting that the alterations in extracellular glutamate most likely originated from the calcium-independent pool. There was a similar decrease in the relative density of tyrosine hydroxylase immunolabeling, a marker for dopamine terminals, within the dorsolateral striatum in both the acute and subchronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated groups that had been administered l-dopa. There was a decrease in the relative density of immunolabeling within the dorsolateral striatum for the glutamate transporter, GLT-1, following acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine treatment in the groups administered either vehicle or l-dopa. There was no change in GLT-1 immunolabeling following subchronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. The results demonstrate that the reversal in the extracellular level of striatal glutamate following l-dopa treatment in both the acute and subchronic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated groups is not due to changes in either striatal dopamine nerve terminals or in the density of the glutamate transporter, GLT-1.     

Reduction of [125I]Bolton Hunter CCK8 and [3H]MK-329 (devazepide) binding to CCK receptors in the substantia nigra/VTA complex and its forebrain projection areas following MPTP-induced hemi-parkinsonism in the monkey.

Cholecystokinin (CCK) receptors were visualized autoradiographically using [125I]Bolton Hunter CCK8 ([125I]BHCCK8) in the fore- and midbrain of 3 monkeys rendered hemi-parkinsonian by unilateral intra-carotid infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). More specifically, CCK-A receptors were detected using [3H]MK-329 (devazepide), a peripheral-type (CCK-A) receptor antagonist. In the substantia nigra pars compacta, ipsilateral to the toxin infusion, where dopamine D2 receptors (labelled with [3H]sulpiride) were lost, there was a decrease in the binding of both [125I]BHCCK8 and [3H]MK-329. Binding of the two CCK ligands was also reduced in the ipsilateral nucleus accumbens and most medial part of the caudate nucleus, whereas 3H-sulpiride binding was increased in the lateral caudate nucleus and putamen. These results indicate that CCK-A receptors may be located on dopaminergic cells within the substantia nigra, which are lost in the parkinsonian brain, and may also be present on dopaminergic terminals within restricted regions of nigral/ventral tegmental area projection sites.