Herein we describe the discovery and optimization of a new series of 2,3-disubstituted and 2,3,6-trisubstituted muscarinic acetylcholine receptor 4 (M4 ) positive allosteric modulators (PAMs). Iterative libraries enabled rapid exploration of one-dimensional structure-activity relationships (SAR) and identification of potency-enhancing heterocycle and N-alkyl pyrazole substituents. Further optimization led to identification of the potent, receptor-subtype-selective, brain-penetrant tool compound 24 (7-[3-[1-[(1-fluorocyclopentyl)methyl]pyrazol-4-yl]-6-methyl-2-pyridyl]-3-methoxycinnoline). It is efficacious in preclinical assays that are predictive of antipsychotic effects, producing dose-dependent reversal of amphetamine-induced hyperlocomotion in rats and mice, but not in M4 knockout mice. Cholinergic-related adverse effects observed in rats treated with 24 at unbound plasma concentrations more than 3-fold higher than an efficacious dose in the hyperlocomotion assay were fewer and less severe than those observed in rats treated with the nonselective M4 agonist xanomeline, suggesting a receptor-subtype-selective PAM has the potential for an improved safety profile.

Adenosine A2A receptors are predominantly localized on striatopallidal gamma-aminobutyric acid (GABA) neurons, where they are colocalized with dopamine D2 receptors and are involved in the regulation of movement. Adenosine A2A receptor antagonists have been evaluated as a novel treatment for Parkinson׳s disease and have demonstrated efficacy in a broad spectrum of pharmacological and toxicological rodent and primate models. Fewer studies have been performed to evaluate the efficacy of adenosine A2A receptor antagonists in genetic models of hypodopaminergic states. SCH 412348 is a potent and selective adenosine A2A receptor antagonist that shows efficacy in rodent and primate models of movement disorders. Here we evaluated the effects of SCH 412348 in the MitoPark mouse, a genetic model that displays a progressive loss of dopamine neurons. The dopamine cell loss is associated with a profound akinetic phenotype that is sensitive to levodopa (l-dopa). SCH 412348 (0.3–10 mg/kg administered orally) dose dependently increased locomotor activity in the mice. Moreover, SCH 412348 retained its efficacy in the mice as motor impairment progressed (12–22 weeks of age), demonstrating that the compound was efficacious in mild to severe Parkinson׳s disease–like impairment in the mice. Additionally, SCH 412348 fully restored lost functionality in a measure of hind limb bradykinesia and partially restored functionality in a rotarod test. These findings provide further evidence of the anti-Parkinsonian effects of selective adenosine A2A receptor antagonists and predict that they will retain their efficacy in both mild and severe forms of motor impairment.

There is growing evidence that activation of metabotropic glutamate receptor 4 (mGlu4) leads to anxiolytic- and antipsychotic-like efficacy in rodent models, yet its relevance to depression-like reactivity remains unclear. Here, we present the pharmacological evaluation of ADX88178 [5-methyl-N-(4-methylpyrimidin-2-yl)-4-(1H-pyrazol-4-yl)thiazol-2-amine], a novel potent, selective, and brain-penetrant positive allosteric modulator of the mGlu4 receptor in rodent models of anxiety, obsessive compulsive disorder (OCD), fear, depression, and psychosis. ADX88178 dose-dependently reduced the number of buried marbles in the marble burying test and increased open-arm exploration in the elevated plus maze (EPM) test, indicative of anxiolytic-like efficacy. Target specificity of the effect in the EPM test was confirmed using male and female mGlu4 receptor knockout mice. In mice, ADX88178 reduced the likelihood of conditioned freezing in the acquisition phase of the fear conditioning test, yet had no carryover effect in the expression phase. Also, ADX88178 dose-dependently reduced duration of immobility in the forced swim test, indicative of antidepressant-like efficacy. ADX88178 reduced DOI (2,5-dimethoxy-4-iodoamphetamine)-mediated head twitches (albeit with no dose-dependency), and MK-801 [(5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine]–induced locomotor hyperactivity in mice, but was inactive in the conditioned avoidance response test in rats. The compound showed good specificity as it had no effect on locomotor activity in mice and rats at efficacious doses. Thus, allosteric activation of mGlu4 receptors can be a promising new therapeutic approach for treatment of anxiety, OCD, fear-related disorders, and psychosis.

Dual orexin receptor antagonists (DORAs) are a potential treatment for insomnia that function by blocking both the orexin 1 and orexin 2 receptors. The objective of the current study was to further confirm the impact of therapeutic mechanisms targeting insomnia on locomotor coordination and ethanol interaction using DORAs and gamma-aminobutyric acid (GABA)-A receptor modulators of distinct chemical structure and pharmacological properties in the context of sleep-promoting potential. The current study compared rat motor co-ordination after administration of DORAs, DORA-12 and almorexant, and GABA-A receptor modulators, zolpidem, eszopiclone, and diazepam, alone or each in combination with ethanol. Motor performance was assessed by measuring time spent walking on a rotarod apparatus. Zolpidem, eszopiclone and diazepam [0.3-30 mg/kg administered orally (PO)] impaired rotarod performance in a dose-dependent manner. Furthermore, all three GABA-A receptor modulators potentiated ethanol- (0.25-1.5 g/kg) induced impairment on the rotarod. By contrast, neither DORA-12 (10-100 mg/kg, PO) nor almorexant (30-300 mg/kg, PO) impaired motor performance alone or in combination with ethanol. In addition, distinct differences in sleep architecture were observed between ethanol, GABA-A receptor modulators (zolpidem, eszopiclone, and diazepam) and DORA-12 in electroencephalogram studies in rats. These findings provide further evidence that orexin receptor antagonists have an improved motor side-effect profile compared with currently available sleep-promoting agents based on preclinical data and strengthen the rationale for further evaluation of these agents in clinical development.

Read the full article P2X7 ATP receptor-induced death of motor neurons by a peroxynitrite/FAS-dependent pathway' on doi:

Positive allosteric modulators (PAMs) of metabotropic glutamate receptor 4 (mGluR4) have been proposed as a novel therapeutic approach for the treatment of Parkinson's disease. However, evaluation of this proposal has been limited by the availability of appropriate pharmacological tools to interrogate the target. In this study, we describe the properties of a novel mGluR4 PAM. 5-Methyl-N-(4-methylpyrimidin-2-yl)-4-(1H-pyrazol-4-yl)thiazol-2-amine (ADX88178) enhances glutamate-mediated activation of human and rat mGluR4 with EC(50) values of 4 and 9 nM, respectively. The compound is highly selective for mGluR4 with minimal activities at other mGluRs. Oral administration of ADX88178 in rats is associated with high bioavailability and results in cerebrospinal fluid exposure of >50-fold the in vitro EC(50) value. ADX88178 reverses haloperidol-induced catalepsy in rats at 3 and 10 mg/kg. It is noteworthy that this compound alone has no impact on forelimb akinesia resulting from a bilateral 6-hydroxydopamine lesion in rats. However, coadministration of a low dose of L-DOPA (6 mg/kg) enabled a robust, dose-dependent reversal of the forelimb akinesia deficit. ADX88178 also increased the effects of quinpirole in lesioned rats and enhanced the effects of L-DOPA in MitoPark mice. It is noteworthy that the enhancement of the actions of L-DOPA was not associated with an exacerbation of L-DOPA-induced dyskinesias in rats. ADX88178 is a novel, potent, and selective mGluR4 PAM that is a valuable tool for exploring the therapeutic potential of mGluR4 modulation. The use of this novel tool molecule supports the proposal that activation of mGluR4 may be therapeutically useful in Parkinson's disease.

Introduction: Poly ADP-ribose polymerase (PARP) maintains genomic integrity by repairing DNA strand breaks, however over-activation of PARP following neural tissue injury is hypothesized to cause neuronal death. Therefore, PARP inhibitors have potential for limiting neural injury under certain conditions. A reliable method for assessing PARP activity in brain is critical for development of novel inhibitors with CNS activity. We developed the PARP In Situ Activity (PISA) assay to provide a direct, quantitative assessment of CNS PARP activity in vitro or in vivo. Methods: The assay utilized brain sections from rats with striatal kainic acid (KA) lesions and H-3- or biotinylated NAD(+) as the substrate to assess PARP activity. Following optimization of the assay, it was used to assess in vitro and in vivo efficacy of known and novel PARP inhibitors. The assay also was used to assess PARP activity in male and female gonad-intact and ovariectomized rats. Results: Using H-3-NAD(+) as the substrate, PARP activity was greater (p<0.01) in tissue from KA-lesioned vs. non-lesioned rats. Using biotinylated NAD(+) it was revealed that PARP activity was present ipsilateral to the KA injection site, and labeling was blocked by incubation with excess unlabeled NAD(+) or PARP inhibitors. The PARP inhibitor, 3-aminobenzamide and several novel inhibitors reduced (p<0.01) polymerase activity in vitro. Furthermore, the inhibitor MRLSD303 reduced (p<0.001) PARP activity in vivo in both male and female rats. Finally, administration of the novel PARP inhibitor MRLIT115 dose-dependently reduced (p<0.001) polymerase activity in vivo. Discussion: The PISA assay provides a direct, quantitative method for assessing PARP activity in vitro and provides critical information on factors underlying in vivo efficacy of chemical inhibitors including brain penetration and target engagement. These findings support use of the PISA assay as a screening tool for testing efficacy of PARP inhibitors in brain. (C) 2010 Elsevier Inc. All rights reserved.

Coenzyme Q10 (CoQ10), a potential neuroprotective compound, was previously investigated at a dosage of 600 mg/day in Huntington's disease (HD) patients and demonstrated a trend toward slowing disease progression. Higher CoQ10 dosages may prove beneficial. We investigated the tolerability and blood levels associated with 1,200, 2,400, and 3,600 mg/day of CoQ10 in HD and healthy subjects. Twenty‐eight subjects (20 HD, 8 healthy) enrolled in a 20‐week open‐label trial. Subjects started on 1,200 mg/day of CoQ10, increasing every 4 weeks by 1,200 mg to a maximum dosage of 3,600 mg/day. Monthly evaluations included review of adverse events and CoQ10 blood levels. Twenty‐three subjects (82%) achieved the target dosage of 3,600 mg/day. Six subjects (2 healthy, 4 HD) withdrew prematurely (gastrointestinal (GI) symptoms in 3, worsening HD in 2, and 1 because of a fall). All three serious adverse events occurred in a single subject, and were deemed unrelated to CoQ10. The most common adverse events seen were GI symptoms. Mean (± SD) CoQ10 blood levels achieved over the course of the trial were as follows: 1.26 ± 1.27 μg/mL (baseline, n = 28), 5.59 ± 2.24 μg/mL (1,200 mg/day, week 4, n = 26), 6.38 ± 3.25 μg/mL (2,400 mg/day, week 8, n = 25), 7.49 ± 4.09 μg/mL (3,600 mg/day, week 12, n = 23), and 6.78 ± 3.36μg/mL (3,600 mg/day, week 20, n = 20). CoQ10 was well tolerated with over 80% of subjects achieving the target dosage. Dosages of 2,400 mg/day may provide the best balance between tolerability and blood level achieved. Further studies examining the efficacy of 2,400 mg/day are planned. © 2010 Movement Disorder Society.

A mechanistic link between cellular energetic defects and the pathogenesis of Huntington's disease (HD) has long been hypothesized based on the cardinal observations of progressive weight loss in patients and metabolic defects in brain and muscle. Identification of respiratory chain deficits in HD postmortem brain led to the use of mitochondrial complex II inhibitors to generate acute toxicity models that replicate aspects of HD striatal pathology in vivo . Subsequently, the generation of progressive genetic animal models has enabled characterization of numerous cellular and systematic changes over disease etiology, including mitochondrial modifications that impact cerebral metabolism, calcium handling, oxidative damage, and apoptotic cascades. This review focuses on how HD animal models have influenced our understanding of mechanisms underlying HD pathogenesis, concentrating on insight gained into the roles of mitochondria in disease etiology. One outstanding question concerns the hierarchy of mitochondrial alterations in the cascade of events following mutant huntingtin (mhtt)‐induced toxicity. One hypothesis is that a direct interaction of mhtt with mitochondria may trigger the neuronal damage and degeneration that occurs in HD. While there is evidence that mhtt associates with mitochondria, deleterious consequences of this interaction have not yet been established. Contrary evidence suggests that a primary nuclear action of mhtt may detrimentally influence mitochondrial function via effects on gene transcription. Irrespective of whether the principal toxic action of mhtt directly or secondarily impacts mitochondria, the repercussions of sufficient mitochondrial dysfunction are catastrophic to cells and may arguably underlie many of the other disruptions in cellular processes that evolve during HD pathogenesis.

Recent studies have demonstrated that activated microglia play an important role in dopamine (DA) neuronal degeneration in Parkinson disease (PD) by generating NADPH-oxidase (NADPHO)-derived superoxide. However, the molecular mechanisms that underlie microglial activation in DA cell death are still disputed. We report here that matrix metalloproteinase-3 (MMP-3) was newly induced and activated in stressed DA cells, and the active form of MMP-3 (actMMP-3) was released into the medium. The released actMMP-3, as well as catalytically active recombinant MMP-3 ( cMMP-3) led to microglial activation and superoxide generation in microglia and enhanced DA cell death. cMMP-3 caused DA cell death in mesencephalic neuron-glia mixed culture of wild-type (WT) mice, but this was attenuated in the culture of NADPHO subunit null mice (gp9(1phox-/-)), suggesting that NADPHO mediated the cMMP-3-induced microglial production of superoxide and DA cell death. Furthermore, in the N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)- injected animal model of PD, nigrostriatal DA neuronal degeneration, microglial activation, and superoxide generation were largely attenuated in MMP-3-/- mice. These results indicate that actMMP-3 released from stressed DA neurons is responsible for microglial activation and generation of NADPHO-derived superoxide and eventually enhances nigrostriatal DA neuronal degeneration. Our results could lead to a novel therapeutic approach to PD.

The Journal of Clinical PharmacologyVolume 47, Issue 12 p. 1580-1586 A Randomized Study of the Bioavailability of Different Formulations of Coenzyme Q10 (Ubiquinone) Dr Radu Constantinescu MD, Dr Radu Constantinescu MD Department of Neurology, Clinical Trials Coordination Center, University of Rochester Medical Center, Rochester, New YorkSearch for more papers by this authorDr Michae P. McDermott PhD, Dr Michae P. McDermott PhD Department of Biostatistics and Computational Biology, University of Rochester Medical Center, Rochester, New YorkSearch for more papers by this authorDr Robert DiCenzo PharmD, Dr Robert DiCenzo PharmD Department of Pharmacy Practice, University at Buffalo, SUNY Buffalo, New YorkSearch for more papers by this authorElisabet A. de Blieck MPA, CCRC, Elisabet A. de Blieck MPA, CCRC Department of Neurology, Clinical Trials Coordination Center, University of Rochester Medical Center, Rochester, New YorkSearch for more papers by this authorDr H. Christopher Hyson MD, FRCPC, Dr H. Christopher Hyson MD, FRCPC London Health Sciences Centre, London, Ontario, CanadaSearch for more papers by this authorDr M. Flint Beal MD, Dr M. Flint Beal MD Weill Medical College/Cornell University, New YorkSearch for more papers by this authorDr Edwar M. Bednarczyk PharmD, Dr Edwar M. Bednarczyk PharmD Department of Pharmacy Practice, University at Buffalo, SUNY Buffalo, New YorkSearch for more papers by this authorDr Mikhail Bogdanov MD, PhD, Dr Mikhail Bogdanov MD, PhD Weill Medical College/Cornell University, New YorkSearch for more papers by this authorMs Lind J. Metakis BA, Ms Lind J. Metakis BA Weill Medical College/Cornell University, New YorkSearch for more papers by this authorDr Susa E. Browne PhD, Dr Susa E. Browne PhD Weill Medical College/Cornell University, New YorkSearch for more papers by this authorMs Beverl J. Lorenzo BS, Ms Beverl J. Lorenzo BS Weill Medical College/Cornell University, New YorkSearch for more papers by this authorDr Bernard Ravina MD, MSCE, Dr Bernard Ravina MD, MSCE Department of Neurology, Clinical Trials Coordination Center, University of Rochester Medical Center, Rochester, New YorkSearch for more papers by this authorDr Karl Kieburtz MD, MPH, Corresponding Author Dr Karl Kieburtz MD, MPH Department of Neurology, Clinical Trials Coordination Center, University of Rochester Medical Center, Rochester, New YorkAddress for correspondence: Karl Kieburtz, MD, MPH, 1351 Mt Hope Avenue, Suite 223, Rochester, NY 14620; e-mail: [email protected].Search for more papers by this author Dr Radu Constantinescu MD, Dr Radu Constantinescu MD Department of Neurology, Clinical Trials Coordination Center, University of Rochester Medical Center, Rochester, New YorkSearch for more papers by this authorDr Michae P. McDermott PhD, Dr Michae P. McDermott PhD Department of Biostatistics and Computational Biology, University of Rochester Medical Center, Rochester, New YorkSearch for more papers by this authorDr Robert DiCenzo PharmD, Dr Robert DiCenzo PharmD Department of Pharmacy Practice, University at Buffalo, SUNY Buffalo, New YorkSearch for more papers by this authorElisabet A. de Blieck MPA, CCRC, Elisabet A. de Blieck MPA, CCRC Department of Neurology, Clinical Trials Coordination Center, University of Rochester Medical Center, Rochester, New YorkSearch for more papers by this authorDr H. Christopher Hyson MD, FRCPC, Dr H. Christopher Hyson MD, FRCPC London Health Sciences Centre, London, Ontario, CanadaSearch for more papers by this authorDr M. Flint Beal MD, Dr M. Flint Beal MD Weill Medical College/Cornell University, New YorkSearch for more papers by this authorDr Edwar M. Bednarczyk PharmD, Dr Edwar M. Bednarczyk PharmD Department of Pharmacy Practice, University at Buffalo, SUNY Buffalo, New YorkSearch for more papers by this authorDr Mikhail Bogdanov MD, PhD, Dr Mikhail Bogdanov MD, PhD Weill Medical College/Cornell University, New YorkSearch for more papers by this authorMs Lind J. Metakis BA, Ms Lind J. Metakis BA Weill Medical College/Cornell University, New YorkSearch for more papers by this authorDr Susa E. Browne PhD, Dr Susa E. Browne PhD Weill Medical College/Cornell University, New YorkSearch for more papers by this authorMs Beverl J. Lorenzo BS, Ms Beverl J. Lorenzo BS Weill Medical College/Cornell University, New YorkSearch for more papers by this authorDr Bernard Ravina MD, MSCE, Dr Bernard Ravina MD, MSCE Department of Neurology, Clinical Trials Coordination Center, University of Rochester Medical Center, Rochester, New YorkSearch for more papers by this authorDr Karl Kieburtz MD, MPH, Corresponding Author Dr Karl Kieburtz MD, MPH Department of Neurology, Clinical Trials Coordination Center, University of Rochester Medical Center, Rochester, New YorkAddress for correspondence: Karl Kieburtz, MD, MPH, 1351 Mt Hope Avenue, Suite 223, Rochester, NY 14620; e-mail: [email protected].Search for more papers by this author First published: 07 March 2013 https://doi.org/10.1177/0091270007307571Citations: 15Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. 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Previously, uridine pro-drug 2′,3′,5′-tri-O-acetyluridine (PN401) was shown to be protective in the mitochondrial complex II inhibitor 3-nitropropionic acid model of Huntington's disease (HD). In this study, PN401 increased survival and improved motor function on the rotarod in both R6/2 and N171-82Q polyglutamine repeat mouse models of HD. PN401 significantly decreased neurodegeneration in both the piriform cortex and striatum although PN401 decreased huntingtin protein aggregates only in the striatum. Cortical and striatal brain-derived neurotrophic factor (BDNF) protein levels were reduced in the +/− compared to the −/− N171-82Q mice and PN401 treatment significantly increased cortical BDNF in both +/− and −/− mice, but PN401 did not affect striatal BDNF. These results suggest that PN401 may have beneficial effects in the treatment of neurodegenerative diseases such as HD.

Multiple cell death pathways are implicated in the etiology of amyotrophic lateral sclerosis (ALS), but the cause of the characteristic motor neuron degeneration remains unknown. To determine whether CNS metabolic defects are critical for ALS pathogenesis, we examined the temporal evolution of energetic defects in the G93A SOD1 mouse model of familial ALS. [14C]-2-deoxyglucose in vivo autoradiography in G93A mice showed that glucose utilization is impaired in components of the corticospinal and bulbospinal motor tracts prior to either pathologic or bioenergetic changes in the spinal cord. This was accompanied by significant depletions in cortical ATP content in presymptomatic mice, which was partially ameliorated by creatine administration. Findings suggest that bioenergetic defects are involved in the initial stages of mSOD1-induced toxicity in G93A mice and imply that the selective dysfunction and degeneration of spinal cord motor neurons in this model may be secondary to dysfunction within cerebral motor pathways.

It has been five years since the elucidation of the genetic mutation underlying the pathogenesis of Huntington's disease (HD) (97), however the precise mechanism of the selective neuronal death it propagates still remains an enigma, Several different etiological processes may play roles, and strong evidence from studies in both humans and animal models suggests the involvement of energy metabolism dysfunction, excitotoxic processes, and oxidative stress. Importantly, the recent development of transgenic mouse models of HD led to the identification of neuronal intranuclear inclusion bodies in affected brain regions in both mouse models and in HD brain, consisting of protein aggregates containing fragments of mutant huntingtin protein. These observations opened new avenues of investigation into possible huntingtin protein interactions and their putative pathogenetic sequelae, Amongst these studies, findings of elevated levels of oxdative damage products such as malondialdehyde, 8-hydroxy-deoxyguanosine, 3-nitrotyrosine and heme oxygenase in areas of degeneration in HD brain, and of increased free radical production in animal models, indicate the involvement of oxidative stress either as a causative event, or as a secondary constituent of the cell death cascade in the disease, Here we review the evidence for oxidative damage and potential mechanisms of neuronal death in HD.

Huntington's disease (HD) is a devastating neurodegenerative disorder characterized by the progressive development of involuntary choreiform movements, cognitive impairment, neuropsychiatric symptoms, and premature death. These phenotypes reflect neuronal dysfunction and ultimately death in selected brain regions, the striatum and cerebral cortex being principal targets. The genetic mutation responsible for the HD phenotype is known, and its protein product, mutant huntingtin (mhtt), identified. HD is one of several "triplet repeat" diseases, in which abnormal expansions in trinucleotide repeat domains lead to elongated polyglutamine stretches in the affected gene's protein product. Mutant htt-mediated toxicity in the brain disrupts a number of vital cellular processes in the course of disease progression, including energy metabolism, gene transcription, clathrin-dependent endocytosis, intraneuronal trafficking, and postsynaptic signaling, but the crucial initiation mechanism induced by mhtt is still unclear. A large body of evidence, however, supports an early and critical involvement of defects in mitochondrial function and CNS energy metabolism in the disease trigger. Thus, downstream death-effector mechanisms, including excitotoxicity, apoptosis, and oxidative damage, have been implicated in the mechanism of selective neuronal damage in HD. Here we review the current evidence supporting a role for oxidative damage in the etiology of neuronal damage and degeneration in HD.

Transglutaminase activity was found to be present in highly purified non-synaptosomal rat brain mitochondria. A 78-kDa protein in these organelles was shown to be a transglutaminase 2 substrate, and incubation of a non-synaptosomal mitochondrial lysate with transglutaminase 2 yielded high-Mr proteins. The 78-kDa protein was identified as mitochondrial aconitase by MALDI-TOF analysis. Aconitase activity was decreased in a dose-dependent manner when non-synaptosomal rat brain mitochondria were incubated with transglutaminase 2. Transglutaminase activity is increased about 2-fold in the mitochondrial fraction of HD caudate. Moreover, Western blotting of the mitochondrial fraction revealed that most of the mitochondrial aconitase in HD caudate is present as high-Mr aggregates. Aconitase activity was previously shown to be decreased in Huntington disease (HD) caudate (a region severely damaged by the disease). The present findings suggest that an increase of transglutaminase activity in HD caudate may contribute to mitochondrial dysfunction by incorporating aconitase into inactive polymers.

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by selective loss of CNS motor neurons, leading to rapidly progressing muscle weakness, wasting, paralysis, and ultimately death. Multiple cell death pathways have been implicated in ALS pathogenesis, but the causal event remains unknown. One hypothesis is that metabolic dysfunction underlies pathogenesis, since alterations in energy metabolism and mitochondrial function occur in patients. In addition, expression of mutant Cu,Zn-superoxide dismutase (mSOD1), associated with approximately 25% of patients with familial ALS (fALS), can induce mitochondrial abnormalities. To determine whether metabolic defects contribute to disease onset in vivo, we examined the association between energetic defects and the onset of symptoms and pathologic events in fALS transgenic mice over-expressing the G93A SOD1 mutation. We measured glucose use rates in 49 brain regions and 9 spinal cord regions in conscious 60 and 120 day-old G93A mice (n=6/group) and wild-type littermates (n=9/group) by quantitative [14C]-2-deoxyglucose autoradiography. Glucose utilization rates were impaired in multiple brain components of the motor system in G93A mice as early as 60 days of age. This precedes the first detectable pathologic changes in G93A mice (in spinal motor neuron mitochondria at 70–80 days), and symptom onset (hind-limb weakness at 90–100 days; mice die at 130-150 days). At 60 days, glucose use was reduced in components of the corticospinal projection, notably primary motor cortex (Fr1) layers I-III (innervation sites) and V (projection zones) (-19%, p<0.005, Student's unpaired t-test). A pattern of hypometabolism also emerged in several areas synaptically associated with Fr1, including the pontine nuclei (-25%, p<0.05) and the pontine reticular formation (-17%, p<0.05) of the bulbospinal pathway, and in several thalamic relay nuclei. In contrast, within the rubrospinal pathway glucose use was significantly reduced in the red nucleus only at 120 days (-28%, p<0.005), and sensorimotor cortical regions showed no alterations. In the spinal cord, generally regarded as the crucial site of neurodegeneration in ALS, glucose metabolism remained normal at 60 days, but was markedly impaired in cervical and thoracic grey matter by 120 days. In an additional experiment, 21 month-old mice overexpressing human wildtype SOD1 showed no alterations in cerebral or spinal cord glucose use with age, implying that the changes detected in G93A mice are due to the SOD1 mutation rather than SOD1 overexpression. We also examined metabolite levels in G93A brain and spinal cord. HPLC revealed depletions in ATP levels in the cerebral cortex of G93A mice concomitant with glucose use changes, which was partially rescued by administration of creatine. Further, cortical ATP levels were reduced by >40% as early as 30 days of age, implying that reduced neuronal energy generation is an extremely early consequence of mSOD1 expression. In conclusion, these studies demonstrate that energetic defects occur earlier than any other pathogenic processes reported to date in G93A mice, and suggest that dysfunction within the corticospinal projection may precede alterations in spinal neurons in this ALS model. Overall, results support a critical role for metabolic dysfunction in the pathogenesis of ALS.

Huntington’s disease (HD) is an autosomal dominantly inherited, fatal neurodegenerative disorder, named for George Huntington, the author of the first definitive report of the condition in 1872. It is characterized by the progressive development of involuntary choreiform movements, although neuropsychiatric symptoms are sometimes the earliest and often the most devastating features of HD. These include detrimental emotional disturbances, behavioral and personality changes, and cognitive impairment. Gross pathological changes are restricted to the brain. Degeneration of specific basal ganglia neurons is a hallmark of HD, but dysfunction in multiple central nervous system pathways contributes to the motor and neuropsychiatric phenotype. HD is caused by an abnormal expansion of a trinucleotide repeat in the huntingtin gene. It is a relatively rare disease with highest prevalence rates of 5 to 10 per 100,000 found in Europe and the United States, whereas incidence is extremely low in Japan and Africa. The typical duration of disease before premature death is 15 to 20 years. Age of onset is associated with the size of the trinucleotide expansion and is generally in adulthood, although approx 10% of cases have juvenile onset. There are currently no effective treatments for the disease.