Patterns of age related changes for phosphodiesterase type-10A in comparison with dopamine D2/3 receptors and sub-cortical volumes in the human basal ganglia: A PET study with 18F-MNI-659 and 11C-raclopride with correction for partial volume effect.

Phosphodiesterase 10A enzyme (PDE10A) is an important striatal target that has been shown to be affected in patients with neurodegenerative disorders, particularly Huntington´s disease (HD). PDE10A is expressed on striatal neurones in basal ganglia where other known molecular targets are enriched such as dopamine D2/3 receptors (D2/3 R). The aim of this study was to examine the availability of PDE10A enzyme in relation with age and gender and to compare those changes with those related to D2/3 R and volumes in different regions of the basal ganglia. As a secondary objective we examined the relative distribution of D2/3 R and PDE10A enzyme in the striatum and globus pallidus. Forty control subjects (20F/20M; age: 44±11y, age range 27-69) from an ongoing positron emission tomography (PET) study in HD gene expansion carriers were included. Subjects were examined with PET using the high-resolution research tomograph (HRRT) and with 3T magnetic resonance imaging (MRI). The PDE10A radioligand 18F-MNI-659 and D2/3 R radioligand 11C-raclopride were used. The outcome measure was the binding potential (BPND) estimated with the two-tissue compartment model (18F-MNI-659) and the simplified reference tissue model (11C-raclopride) using the cerebellum as reference region. The PET data were corrected for partial volume effects. In the striatum, PDE10A availability showed a significant age-related decline that was larger compared to the age-related decline of D2/3 R availability and to the age-related decline of volumes measured with MRI. In the globus pallidus, a less pronounced decline of PDE10A availability was observed, whereas D2/3 R availability and volumes seemed to be rather stable with aging. The distribution of the PDE10A enzyme was different from the distribution of D2/3 R, with higher availability in the globus pallidus. These results indicate that aging is associated with a considerable physiological reduction of the availability of PDE10A enzyme in the striatum. Moreover as result of the analysis, in the striatum for both the molecular targets, we observed a gender effect with higher BPND the female group.

MEKK1 Associated with Neuronal Apoptosis Following Intracerebral Hemorrhage.

The JNKs have been implicated in a variety of biological functions in mammalian cells, including apoptosis and the responses to stress. However, the physiological role of these pathways in the intracerebral hemorrhage (ICH) has not been fully elucidated. In this study, we identified a MAPK kinase kinase (MAPKKK), MEKK1, may be involved in neuronal apoptosis in the processes of ICH through the activation of JNKs. From the results of western blot, immunohistochemistry and immunofluorescence, we obtained a significant up-regulation of MEKK1 in neurons adjacent to the hematoma following ICH. Increasing MEKK1 level was found to be accompanied with the up-regulation of p-JNK 3, p53, and c-jun. Besides, MEKK1 co-localized well with p-JNK in neurons, indicating its potential role in neuronal apoptosis. What's more, our in vitro study, using MEKK1 siRNA interference in PC12 cells, further confirmed that MEKK1 might exert its pro-apoptotic function on neuronal apoptosis through extrinsic pathway. Thus, MEKK1 may play a role in promoting the brain damage following ICH.

G protein-coupled receptor kinases as regulators of dopamine receptor functions.

Actions of the neurotransmitter dopamine in the brain are mediated by dopamine receptors that belong to the superfamily of G protein-coupled receptors (GPCRs). Mammals have five dopamine receptor subtypes, D1 through D5. D1 and D5 couple to Gs/olf and activate adenylyl cyclase, whereas D2, D3, and D4 couple to Gi/o and inhibit it. Most GPCRs upon activation by an agonist are phosphorylated by GPCR kinases (GRKs). The GRK phosphorylation makes receptors high-affinity binding partners for arrestin proteins. Arrestin binding to active phosphorylated receptors stops further G protein activation and promotes receptor internalization, recycling or degradation, thereby regulating their signaling and trafficking. Four non- visual GRKs are expressed in striatal neurons. Here we describe known effects of individual GRKs on dopamine receptors in cell culture and in the two in vivo models of dopamine-mediated signaling: behavioral response to psychostimulants and L-DOPA- induced dyskinesia. Dyskinesia, associated with dopamine super-sensitivity of striatal neurons, is a debilitating side effect of L-DOPA therapy in Parkinson's disease. In vivo, GRK subtypes show greater receptor specificity than in vitro or in cultured cells. Overexpression, knockdown, and knockout of individual GRKs, particularly GRK2 and GRK6, have differential effects on signaling of dopamine receptor subtypes in the brain. Furthermore, deletion of GRK isoforms in select striatal neuronal types differentially affects psychostimulant-induced behaviors. In addition, anti-dyskinetic effect of GRK3 does not require its kinase activity: it is mediated by the binding of its RGS-like domain to Gαq/11, which suppresses Gq/11 signaling. The data demonstrate that the dopamine signaling in defined neuronal types in vivo is regulated by specific and finely orchestrated actions of GRK isoforms.

Targeting the cannabinoid CB2 receptor to attenuate the progression of motor deficits in LRRK2-transgenic mice.

Most of cases of Parkinson's disease (PD) have a sporadic origin, with their causes mostly unknown, although overexposure to some environmental factors has been found to occur in some cases. Other forms of parkinsonism are the consequence of dominant or recessive mutations in specific genes, e.g. α-synuclein, parkin and, more recently, leucine-rich repeat kinase 2 (LRRK2), whose G2019S mutation represents the most prevalent form of late-onset, autosomal dominant familial PD. A transgenic mouse model expressing the G2019S mutation of LRRK2 is already available and apparently may represent a valuable experimental model for investigating PD pathogenesis and novel treatments. We designed a long-term study with these animals aimed at: (i) elucidating the changes experienced by the endocannabinoid signaling system in the basal ganglia during the progression of the disease in these mice, paying emphasis in the CB2 receptor, which has emerged as a promising target in PD, and (ii) evaluating the potential of compounds selectively activating this CB2 receptor, as disease-modifying agents in these mice. Our results unequivocally demonstrate that LRRK2 transgenic mice develop motor impairment consisting of small anomalies in rotarod performance (presumably reflecting a deficit in motor coordination and dystonia) and a strong deficiency in the hanging-wire test (reflecting muscle weakness), rather than hypokinesia which was difficult to be demonstrated in the actimeter. These behavioral responses occurred in absence of any evidence of reactive gliosis and neuronal losses, as well as synaptic deterioration in the basal ganglia, except an apparent impairment in autophagy reflected by elevated LAMP-1 immunolabelling in the striatum and substantia nigra. Furthermore, there were no changes in the status of the CB2 receptor, as well as in other elements of the endocannabinoid signaling, in the basal ganglia, but, paradoxically, the selective activation of this receptor partially reversed the deficits in the hanging-wire test of LRRK2 transgenic mice. This was accompanied by normalization in LAMP-1 immunolabelling in the basal ganglia, although it is possible that other CNS structures, remaining to be identified, are involved in the behavioral improvement. In summary, our data support the interest of the CB2 receptor as a potential pharmacological target in LRRK2 transgenic mice, although the neuronal substrates underlying these benefits might be not completely related to the basal ganglia and to the presumed parkinsonian features of these mice.

Matrix metalloproteinase levels in early HIV infection and relation to in vivo brain status.

Matrix metalloproteinases (MMPs) have been implicated in human immunodeficiency virus (HIV)-associated neurological injury; however, this relationship has not been studied early in infection. Plasma levels of MMP-1, MMP-2, MMP-7, MMP-9, and MMP-10 measured using Luminex technology (Austin, TX, USA) were compared in 52 HIV and 21 seronegative participants of the Chicago Early HIV Infection study. MMP levels were also examined in HIV subgroups defined by antibody reactivity, viremia, and antiretroviral status, as well as in available cerebrospinal fluid (CSF) samples (n = 9). MMPs were evaluated for patterns of relationship to cognitive function and to quantitative magnetic resonance measurements of the brain derived in vivo. Plasma MMP-2 levels were significantly reduced in early HIV infection and correlated with altered white matter integrity and atrophic brain changes. MMP-9 levels were higher in the treated subgroup than in the naïve HIV subgroup. Only MMP-2 and MMP-9 were detected in the CSF; CSF MMP-2 correlated with white matter integrity and with volumetric changes in basal ganglia. Relationships with cognitive function were also identified. MMP-2 levels in plasma and in CSF correspond to early changes in brain structure and function. These findings establish a link between MMPs and neurological status previously unidentified in early HIV infection.

Edaravone ameliorates oxidative stress associated cholinergic dysfunction and limits apoptotic response following focal cerebral ischemia in rat.

Stroke is a life-threatening disease with major cause of mortality and morbidity worldwide. The neuronal damage following cerebral ischemia is a serious risk to stroke patients. Oxidative stress and apoptotic damage play an important role in cerebral ischemic pathogenesis and may represent a target for treatment. The objective of this study was to test the hypothesis that administration of edaravone (Edv) maintains antioxidant status in brain, improves the cholinergic dysfunction and suppresses the progression of apoptosis response in rat. To test this hypothesis, male Wistar rats were subjected to middle cerebral artery occlusion (MCAO) of 2 h followed by reperfusion for 22 h. Edv was administered (10 mg/kg bwt) intraperitoneally 30 min before the onset of ischemia and 1 h after reperfusion. After reperfusion, rats were tested for neurobehavioral activities and were sacrificed for the infarct volume, estimation of oxidative damage markers. Edv treatment significantly reduced ischemic lesion volume, improved neurological deficits, contended oxidative loads, and suppressed apoptotic damage. In conclusion, treatment with Edv ameliorated the neurological and histological outcomes with elevated endogenous anti-oxidants status as well as reduced induction of apoptotic responses in MCA occluded rat. We theorized that Edv is among the pharmacological agents that reduce free radicals and its associated cholinergic dysfunction and apoptotic damage and have been found to limit the extent of brain damage following stroke.

Activation of acetylcholinesterase after U-74389G administration in a porcine model of intracerebral hemorrhage.

Spontaneous intracerebral hemorrhage (ICH) accounts for 10-15% of all strokes. Despite high incidence, morbidity and mortality, the precise pathophysiology of spontaneous ICH is not fully understood, while there is little data concerning the mechanisms that follow the primary insult of the hematoma formation. The cholinergic system, apart from its colossal importance as a neurotransmission system, seems to also play an important role in brain injury recovery. It has been recently suggested that the brain possesses a cholinergic anti-inflammatory pathway that counteracts the inflammatory responses after ICH, thereby limiting damage to the brain itself. We, herein, report the findings of our study concerning the role of acetylcholinesterase (AChE; a crucial membrane-bound enzyme involved in cholinergic neurotransmission) in a porcine model of spontaneous ICH, with a focus on the first 4 and 24 h following the lesion's induction, in combination with a study of the effectiveness of the lazaroid antioxidant U-74389G administration. Our study demonstrates the activation of AChE activity following U-74389G administration. The lazaroid U-74389G seems to be an established neuroprotectant and this is the first report of its supporting role in the enhancement of cholinergic response to the induction of ICH.

Cholinergic imaging in corticobasal syndrome, progressive supranuclear palsy and frontotemporal dementia.

Corticobasal syndrome, progressive supranuclear palsy and frontotemporal dementia are all part of a disease spectrum that includes common cognitive impairment and movement disorders. The aim of this study was to characterize brain cholinergic deficits in these disorders. We measured brain acetylcholinesterase activity by [11C] N-methylpiperidin-4-yl acetate and positron emission tomography in seven patients with corticobasal syndrome (67.6+/-5.9 years), 12 with progressive supranuclear palsy (68.5+/-4.1 years), eight with frontotemporal dementia (59.8+/-6.9 years) and 16 healthy controls (61.2+/-8.5 years). Two-tissue compartment three-parameter model and non-linear least squares analysis with arterial input function were performed. k3 value, an index of acetylcholinesterase activity, was calculated voxel-by-voxel in the brain of each subject. The k3 images in each disease group were compared with the control group by using Statistical Parametric Mapping 2. Volume of interest analysis was performed on spatially normalized k3 images. The corticobasal syndrome group showed decreased acetylcholinesterase activity (k3 values) in the paracentral region, frontal, parietal and occipital cortices (P<0.05, cluster corrected). The group with progressive supranuclear palsy had reduced acetylcholinesterase activity in the paracentral region and thalamus (P<0.05, cluster corrected). The frontotemporal dementia group showed no significant differences in acetylcholinesterase activity. Volume of interest analysis showed mean cortical acetylcholinesterase activity to be reduced by 17.5% in corticobasal syndrome (P<0.001), 9.4% in progressive supranuclear palsy (P<0.05) and 4.4% in frontotemporal dementia (non-significant), when compared with the control group. Thalamic acetylcholinesterase activity was reduced by 6.4% in corticobasal syndrome (non-significant), 24.0% in progressive supranuclear palsy (P<0.03) and increased by 3.3% in frontotemporal dementia (non-significant). Both corticobasal syndrome and progressive supranuclear palsy showed brain cholinergic deficits, but their distribution differed somewhat. Significant brain cholinergic deficits were not seen in frontotemporal dementia, which may explain the unresponsiveness of this condition to cholinergic modulation therapy.

Monoamine oxidase A inhibition as monotherapy reverses parkinsonism in the MPTP-lesioned marmoset.

Monoamine oxidase (MAO) type B (MAO-B) inhibition was shown to confer anti-parkinsonian benefit as monotherapy and adjunct to L-3,4-dihydroxyphenylalanine (L-DOPA) in clinical trials. Here, we explore the anti-parkinsonian effect of MAO type A (MAO-A) inhibition as monotherapy, as the enzyme MAO-A is also encountered within the primate and human basal ganglia, where it metabolises dopamine, albeit to a lesser extent than MAO-B. In six 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets, we assessed the anti-parkinsonian effect of the reversible MAO-A inhibitor moclobemide (0.1 and 1 mg/kg) as monotherapy and compared it to that of L-DOPA and vehicle treatments. Moclobemide significantly reversed parkinsonism (by 39%, P < 0.01), while eliciting only mild dyskinesia and psychosis-like behaviours (PLBs). In contrast, L-DOPA anti-parkinsonian effect was accompanied by marked dyskinesia and PLBs. MAO-A inhibition with moclobemide may provide anti-parkinsonian benefit when administered without L-DOPA and might perhaps be considered as monotherapy for the treatment of Parkinson's disease in the early stages of the condition.

Monoamine oxidase A inhibition with moclobemide enhances the anti-parkinsonian effect of L-DOPA in the MPTP-lesioned marmoset.

Whereas monoamine oxidase (MAO) type B inhibitors are used as adjunct to L-3,4-dihydroxyphenylalanine (L-DOPA) in the treatment of Parkinson's disease (PD), the enzyme MAO type A (MAO-A) also participates in the metabolism of dopamine in the human and primate striatum. Here, we sought to assess the effect of the selective reversible MAO-A inhibitor moclobemide on L-DOPA anti-parkinsonian in the gold standard animal model of PD, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned primate. We also assessed the effect of moclobemide on L-DOPA-induced dyskinesia and psychosis-like behaviours (PLBs). Experiments were performed in six MPTP-lesioned marmosets chronically treated with L-DOPA and exhibiting stable dyskinesia and PLBs upon each administration. In a randomised within-subject design, animals were administered a therapeutic dose of L-DOPA in combination with moclobemide (0.1, 1 and 10 mg/kg) or its vehicle, after which the severity of parkinsonism, dyskinesia, and PLBs was rated by an experienced blinded rater. Moclobemide significantly reduced the global parkinsonian disability (- 36% with 0.1 mg/kg, P < 0.05; - 38% with 1 mg/kg, P < 0.01; - 47% with 10 mg/kg, P < 0.01), when compared with its vehicle. This reduction of parkinsonism was not accompanied by an exacerbation of dyskinesia or PLBs. Reversible MAO-A inhibition with moclobemide appears as an effective way to increase the anti-parkinsonian action of L-DOPA, without negatively affecting dyskinesia or dopaminergic psychosis.

Parkinson's disease: activity of L-dopa decarboxylase in discrete brain regions.

The activity of L-dopa decarboxylase was greatly reduced in the striatum, less so in the hypothalamus, and unchanged in the cortex of brains of patients with Parkinson's disease. However, it appears that even in the striatum enough activity remained to allow for the formation of dopamine from L-dopa in patients treated with large doses of L-dopa.

Mental symptoms in Huntington's disease and a possible primary aminergic neuron lesion.

Monoamine oxidase activity was higher in the cerebral cortex and basal ganglia of patients dying from Huntington's disease than in controls. Enzyme kinetics and multiple substrate studies indicated that the increased activity was due to elevated concentrations of monoamine oxidase type B. Concentrations of homovanillic acid were increased in the cerebral cortex but not in the basal ganglia of brains of patients with Huntington's disease. These changes may represent a primary aminergic lesion that could underlie some of the mental symptoms of this disease.

Lesch-Nyhan syndrome: preventive control by prenatal diagnosis.

The Lesch-Nyhan syndrome was detected in a fetus at a time sufficiently early to allow termination of the pregnancy. The feasibility of a preventive program for control of a severe sex-linked neurological disease through prenatal diagnosis is thus demonstrated.

MPTP intoxication in mice: a useful model of Leigh syndrome to study mitochondrial diseases in childhood.

The basal ganglia, which are interconnected in the striato-nigral dopaminergic network, are affected in several childhood diseases including Leigh syndrome (LS). LS is the most common mitochondrial disorder affecting children and usually arise from inhibition of the respiratory chain. This vulnerability is attributed to a particular susceptibility to energetic stress, with mitochondrial inhibition as a common pathogenic pathway. In this study we developed a LS model for neuroprotection trials in mice by using the complex I inhibitor MPTP. We first verified that MPTP significantly inhibits the mitochondrial complex I in the brain (p = 0.018). This model also reproduced the biochemical and pathological features of LS: MPTP increased plasmatic lactate levels (p = 0.023) and triggered basal ganglia degeneration, as evaluated through dopamine transporter (DAT) autoradiography, tyrosine hydroxylase (TH) immunohistochemistry, and dopamine dosage. Striatal DAT levels were markedly decreased after MPTP treatment (p = 0.003). TH immunoreactivity was reduced in the striatum and substantia nigra (p = 0.005), and striatal dopamine was significantly reduced (p < 0.01). Taken together, these results confirm that acute MPTP intoxication in young mice provides a reproducible pharmacological paradigm of LS, thus opening new avenues for neuroprotection research.

In vitro phosphodiesterase 10A (PDE10A) binding in whole hemisphere human brain using the PET radioligand [18F]MNI-659.

Highly specific and sensitive biomarkers for pathologies related to dysfunctions in the basal ganglia circuit are of great value to assess therapeutic efficacy not only clinically to establish an early diagnosis, but also in terms of monitoring the efficacy of therapeutic interventions and decelerated neurodegeneration. The phosphodiesterase 10A (PDE10A) enzyme plays a central role in striatal signaling and is implicated in several neuropsychiatric disorders involving striatal pathology, such as Huntingtons disease (HD) and schizophrenia. Inhibition of PDE10A activates the neurons in the striatum and consequently leads to alteration of behavioral aspects modulated by the striatal circuit. [18F]MNI-659, (2-(2-(3-(4-(2-[18F]fluoroethoxy)phenyl)-7-methyl-4-oxo-3,4-dihydroquinazolin-2-yl)ethyl)-4-isopropoxyisoindoline-1,3-dione), is a newly developed PET radioligand that shows a high binding to PDE10A in the human brain in vivo. In the present study, we examined the in vitro binding of [18F]MNI-659 in human postmortem brain to gain a better understanding of the presence, density, disease-related alterations and therapy related to changes in PDE10A expression. The results show high specific binding of [18F]MNI-659 in the caudate nucleus, putamen and the hippocampal formation. Low specific [18F]MNI-659 binding was detected in nucleus accumbens in comparison to the caudate nucleus and putamen. In vitro binding studies with [18F]MNI-659 will facilitate in elucidating better understanding of the role of PDE10A activity in health and disease that may lead to new diagnostic opportunities in HD.

Neuronal nitric oxide synthase immunopositive neurons in cat claustrum--a light and electron microscopic study.

Nitric oxide is a unique neurotransmitter, which participates in many physiological and pathological processes in the organism. Nevertheless there are little data about the neuronal Nitric Oxide Synthase immunoreactive (nNOS-ir) neurons and fibers in the dorsal claustrum (DC) of a cat. In this respect the aims of this study were: (1) to demonstrate nNOS-ir in the neurons and fibers of the DC; (2) to describe their light microscopic morphology and distribution; (3) to investigate and analyze the ultrastructure of the nNOS-ir neurons, fibers and synaptic terminals; (4) to verify whether the nNOS-ir neurons consist a specific subpopulation of claustral neurons; (5) to verify whether the nNOS-ir neurons have a specific pattern of organization throughout the DC. For demonstration of the nNOS-ir the Avidin-Biotin-Peroxidase Complex method was applied. Immunopositive for nNOS neurons and fibers were present in all parts of DC. On the light microscope level nNOS-ir neurons were different in shape and size. According to the latter they were divided into three groups-small (with diameter under 15 microm), medium-sized (with diameter from 16 to 20 microm) and large (with diameter over 21 microm). Some of nNOS-ir neurons were lightly-stained while others were darkly-stained. On the electron microscope level the immunoproduct was observed in neurons, dendrites and terminal boutons. Different types of nNOS-ir neurons differ according to their ultrastructural features. Three types of nNOS-ir synaptic boutons were found. As a conclusion we hope that the present study will contribute to a better understanding of the functioning of the DC in cat and that some of the data presented could be extrapolated to other mammals, including human.

Polychlorinated biphenyl-induced oxidative stress in organotypic co-cultures: experimental dopamine depletion prevents reductions in GABA.

Polychlorinated biphenyls (PCBs) are ubiquitous environmental contaminants that have been demonstrated to be toxic to the dopamine (DA) systems of the central nervous system. One proposed mechanism for PCB-induced DA neurotoxicity is inhibition of the vesicular monoamine transporter (VMAT); such inhibition results in increased levels of unsequestered DA and DA metabolism leading to oxidative stress. We have used an organotypic co-culture system of developing rat striatum and ventral mesencephalon (VM) to determine whether alterations in the vesicular storage of DA, resulting from PCB exposure and consequent induction of oxidative stress, leads to GABA and DA neuronal dysfunction. Twenty-four-hour exposure to an environmentally relevant mixture of PCBs reduced tissue DA and GABA concentrations, increased medium levels of DA and measures of oxidative stress in both the striatum and VM. Alterations in neurochemistry and increases in measures of oxidative stress were blocked in the presence of n-acetylcysteine (NAC). Although NAC treatment did not alter PCB-induced changes in DA neurochemistry, it did protect against reductions in GABA concentration. To determine whether alterations in the vesicular storage of DA were responsible for PCB-induced oxidative stress and consequent reductions in GABA levels, we depleted DA from the co-cultures using alpha-methyl-p-tyrosine (AMPT). AMPT reduced striatal and VM DA levels by 90% and 70%, respectively. PCB exposure, following DA depletion, neither increased levels of oxidative stress nor resulted in GABA depletion. These results suggest that PCB-induced alterations in the vesicular storage of DA, resulting in increased levels of unsequestered DA, leads to increased oxidative stress, depletion of tissue glutathione, and consequent reductions in tissue GABA concentrations.

Hyperbaric oxygen preconditioning activates ribosomal protein S6 kinases and reduces brain swelling after intracerebral hemorrhage.

BACKGROUND: New protein synthesis is key to ischemic tolerance induced by preconditioning and ribosomal protein S6 kinases (p70 S6 K) are important enzymes in protein synthesis. Hyperbaric oxygen preconditioning (HBOP) reduces ischemic brain damage. This study investigated if HBOP can activate p70 S6 K and increase new protein synthesis and if HBOP induces brain tolerance against brain swelling after intracerebral hemorrhage (ICH). METHODS: There were two parts of the studies. 1) Rats received five consecutive sessions of HBOP. Twenty-four hours after HBOP, the rats had an ICH and were sacrificed one or three days later for brain edema measurement. 2) Rats received five sessions of HBOP or control pretreatment and were sacrificed for Western blot analysis and immunohistochemistry of activated p70 S6 K and heme oxygenase-1 (HO-1). FINDINGS: Five sessions of HBOP significantly reduced brain edema in the ipsilateral basal ganglia after ICH. Western blot analysis showed that HBOP activated p70 S6 K and increased HO-1 levels in the basal ganglia. Strong activated p70 S6 K immunoreactivity was also found in the basal ganglia. CONCLUSIONS: Our results suggest activation of p70 S6 K may have a role in heat shock protein synthesis after HBOP and may contribute to HBOP-induced brain protection.

Effects of chronic aspartame consumption on MPTP-induced Parkinsonism in male and female mice.

BACKGROUND: Parkinson's disease is a progressive neurodegenerative disorder. Aspartame (l-aspartyl-l-phenylalanine methyl ester), a low calorie sweetener used in foods and beverages. OBJECTIVES: This study investigated the effect of chronic aspartame intake on Parkinsonism induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). METHOD: Forty-eight mice (24 males and 24 females): control, aspartame, MPTP, and aspartame + MPTP groups tested by Y-maze, stepping, forced swimming and olfactory preference tests. Brain tissues examined for dopamine content, tyrosine hydroxylase, inducible nitric oxide synthase (iNOS), glutathione peroxidase, phosphorylated tau and α-synuclein protein. Histopathological evaluation of brain sections at the level of basal ganglia was done. RESULTS: Decreased dopamine content, tyrosine hydroxylase expression, glutathione peroxidase expression and increased iNOS, tau and α-synuclein expression in groups received aspartame, MPTP or both agents simultaneously in both males and females group. CONCLUSIONS: Increased dopaminergic degeneration and complications with chronic aspartame consumption and more injury in male groups.

Dopamine D2 receptor-dependent modulation of striatal NO synthase activity.

RATIONALE: Striatal nitric oxide (NO)-producing interneurons receive synaptic contacts from midbrain dopamine (DA) neurons and are regulated by phasic DA transmission. Classic antipsychotic drugs elevate neuronal NO synthase (NOS) expression in the rat striatum. Given that NO signaling potently modulates the membrane excitability of striatal projection neurons, it is plausible that up-regulation of NOS activity after DA D2 receptor blockade contributes to the therapeutic efficacy and/or motor side effects associated with antipsychotic drugs. OBJECTIVES: This study assessed the impact of DA D(2) receptor activation on striatal NOS activity in vivo. Characterization of the dopaminergic regulation of striatal NO signaling will be relevant for understanding the mechanism(s) of action of antipsychotic drugs. MATERIALS AND METHODS: Striatal NO efflux, evoked via electrical stimulation of the substantia nigra (SN) or systemic administration of the DA D(1) receptor agonist SKF 81297, was assessed in anesthetized rats using an NO-selective amperometric microsensor. RESULTS: The facilitatory effect of SN stimulation on striatal NO efflux was attenuated by systemic administration of the DA D(2) receptor agonist quinpirole. Conversely, administration of the DA D(2) receptor antagonist eticlopride augmented evoked NO efflux. NO efflux induced by systemic administration of SKF 81297 was attenuated by quinpirole and restored by co-administration of quinpirole and eticlopride. The facilitatory effect of SKF 81297 on NO efflux was also significantly attenuated after pretreatment with the non-specific NOS inhibitor methylene blue. CONCLUSIONS: Activation of NO synthesis by phasic DA transmission is down-regulated via a DA D2 receptor-dependent mechanism. DA D(2) receptor activation opposes DA D(1) receptor activation of NO synthesis at a site postsynaptic to the DA terminal. Further studies examining NO-DA dynamics may have potential to reveal novel therapeutic strategies to treat various brain disorders.