ascorbic-acid and Huntington-Disease

This review summarizes evidence for dysfunctional connectivity between cortical and striatal neurons in Huntington's disease (HD), a fatal neurodegenerative condition caused by a single gene mutation. The focus is on data derived from recording of electrophysiological signals in behaving transgenic mouse models.. Firing patterns of individual neurons and the frequency oscillations of local field potentials indicate a disruption in corticostriatal processing driven, in large part, by interactions between cells that contain the mutant gene rather than the mutant gene alone. Dysregulation of glutamate, an excitatory amino acid released by cortical afferents, plays a key role in the breakdown of corticostriatal communication, a process modulated by ascorbate, an antioxidant vitamin found in high concentration in striatum. Up-regulation of glutamate transport by drug administration or viral-vector delivery improves ascorbate homeostasis and neurobehavioral processing in HD mice. Further analysis of electrophysiological data, including the use of sophisticated computational strategies, is required to discern how behavioral demands modulate the flow of corticostriatal information and its disruption by HD.. Long before massive cell loss occurs, HD impairs the mechanisms by which cortical and striatal neurons communicate. A key problem identified in transgenic animal models is dysregulation of the dynamic changes in extracellular glutamate and ascorbate. Improved understanding of how these neurochemical systems impact corticostriatal communication is necessary before an effective therapeutic strategy can emerge.

Topics: Animals; Ascorbic Acid; Glutamic Acid; Humans; Huntington Disease; Neural Pathways; Neurons

Failure in energy metabolism and oxidative damage are associated with Huntington's disease (HD). Ascorbic acid released during synaptic activity inhibits use of neuronal glucose, favouring lactate uptake to sustain brain activity. Here, we observe a decreased expression of GLUT3 in STHdhQ111 cells (HD cells) and R6/2 mice (HD mice). Localisation of GLUT3 is decreased at the plasma membrane in HD cells affecting the modulation of glucose uptake by ascorbic acid. An ascorbic acid analogue without antioxidant activity is able to inhibit glucose uptake in HD cells. The impaired modulation of glucose uptake by ascorbic acid is directly related to ROS levels indicating that oxidative stress sequesters the ability of ascorbic acid to modulate glucose utilisation. Therefore, in HD, a decrease in GLUT3 localisation at the plasma membrane would contribute to an altered neuronal glucose uptake during resting periods while redox imbalance should contribute to metabolic failure during synaptic activity.

Topics: Animals; Antioxidants; Ascorbic Acid; Blotting, Western; Cell Membrane; Cells, Cultured; Disease Models, Animal; Energy Metabolism; Female; Fluorescent Antibody Technique; Glucose; Glucose Transporter Type 3; Huntington Disease; Male; Mice; Neurons; Oxidation-Reduction; Oxidative Stress; Rats; Rats, Wistar; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger

Dysregulation of cortical and striatal neuronal processing plays a critical role in Huntington's disease (HD), a dominantly inherited condition that includes a progressive deterioration of cognitive and motor control. Growing evidence indicates that ascorbate (AA), an antioxidant vitamin, is released into striatal extracellular fluid when glutamate is cleared after its release from cortical afferents. Both AA release and glutamate uptake are impaired in the striatum of transgenic mouse models of HD owing to a downregulation of glutamate transporter 1 (GLT1), the protein primarily found on astrocytes and responsible for removing most extracellular glutamate. Improved understanding of an AA-glutamate interaction could lead to new therapeutic strategies for HD.. Increased expression of GLT1 following treatment with ceftriaxone, a beta-lactam antibiotic, increases striatal glutamate uptake and AA release and also improves the HD behavioral phenotype. In fact, treatment with AA alone restores striatal extracellular AA to wild-type levels in HD mice and not only improves behavior but also improves the firing pattern of neurons in HD striatum.. Although evidence is growing for an AA-glutamate interaction, several key issues require clarification: the site of action of AA on striatal neurons; the precise role of GLT1 in striatal AA release; and the mechanism by which HD interferes with this role.. Further assessment of how the HD mutation alters corticostriatal signaling is an important next step. A critical focus is the role of astrocytes, which express GLT1 and may be the primary source of extracellular AA.

Topics: Animals; Ascorbic Acid; Biological Transport; Cerebral Cortex; Corpus Striatum; Disease Models, Animal; Glutamic Acid; Humans; Huntington Disease; Mice; Mice, Transgenic

Huntington's disease has been associated with a failure in energy metabolism and oxidative damage. Ascorbic acid is a powerful antioxidant highly concentrated in the brain where it acts as a messenger, modulating neuronal metabolism. Using an electrophysiological approach in R6/2 HD slices, we observe an abnormal ascorbic acid flux from astrocytes to neurons, which is responsible for alterations in neuronal metabolic substrate preferences. Here using striatal neurons derived from knock-in mice expressing mutant huntingtin (STHdhQ cells), we study ascorbic acid transport. When extracellular ascorbic acid concentration increases, as occurs during synaptic activity, ascorbic acid transporter 2 (SVCT2) translocates to the plasma membrane, ensuring optimal ascorbic acid uptake for neurons. In contrast, SVCT2 from cells that mimic HD symptoms (dubbed HD cells) fails to reach the plasma membrane under the same conditions. We reason that an early impairment of ascorbic acid uptake in HD neurons could lead to early metabolic failure promoting neuronal death.

Topics: Animals; Ascorbic Acid; Astrocytes; Cell Line; Cell Membrane; Disease Models, Animal; Energy Metabolism; Female; Huntingtin Protein; Huntington Disease; Male; Mice; Mice, Transgenic; Nerve Tissue Proteins; Neuroglia; Neurons; Protein Transport; Rats, Wistar; Sodium-Coupled Vitamin C Transporters

A corticostriatal-dependent deficit in the release of ascorbate (AA), an antioxidant vitamin and neuromodulator, occurs concurrently in striatum with dysfunctional GLT1-dependent uptake of glutamate in the R6/2 mouse model of Huntington's disease (HD), an autosomal dominant condition characterized by overt corticostriatal dysfunction. To determine if deficient striatal AA release into extracellular fluid is related to altered GLT1 activity in HD, symptomatic R6/2 mice between 6 and 9 weeks of age and age-matched wild-type (WT) mice received single daily injections of 200 mg/kg ceftriaxone, a β-lactam antibiotic that elevates the functional expression of GLT1, or saline vehicle for five consecutive days. On the following day, in vivo voltammetry was coupled with corticostriatal afferent stimulation to monitor evoked release of AA into striatum. In saline-treated mice, we found a marked decrease in evoked extracellular AA in striatum of R6/2 relative to WT. Ceftriaxone, in contrast, restored striatal AA in R6/2 mice to WT levels. In addition, intra-striatal infusion of either the GLT1 inhibitor dihydrokainic acid or dl-threo-beta-benzyloxyaspartate blocked evoked striatal AA release. Collectively, our results provide compelling evidence for a link between GLT1 activation and release of AA into the striatal extracellular fluid, and suggest that dysfunction of this system is a key component of HD pathophysiology.

Topics: Animals; Ascorbic Acid; Ascorbic Acid Deficiency; Aspartic Acid; Ceftriaxone; Cerebral Cortex; Corpus Striatum; Electric Stimulation; Excitatory Amino Acid Transporter 2; Extracellular Fluid; Genotype; Huntington Disease; Kainic Acid; Male; Mice; Mice, Transgenic; Microinjections; Transcription, Genetic; Up-Regulation

A behavior-related deficit in the release of ascorbate (AA), an antioxidant vitamin, occurs in the striatum of R6/2 mice expressing the human mutation for Huntington's disease (HD), a dominantly inherited condition characterized by striatal dysfunction. To determine the role of corticostriatal fibers in AA release, we combined slow-scan voltammetry with electrical stimulation of cortical afferents to measure evoked fluctuations in extracellular AA in wild-type (WT) and R6/2 striatum. Although cortical stimulation evoked a rapid increase in AA release in both groups, the R6/2 response had a significantly shorter duration and smaller magnitude than WT. To determine if corticostriatal dysfunction also underlies the behavior-related AA deficit in R6/2s, we measured striatal AA release in separate groups of mice treated with d-amphetamine (5 mg/kg), a psychomotor stimulant known to release AA from corticostriatal terminals independently of dopamine. Relative to WT, both AA release and behavioral activation were diminished in R6/2 mice. Collectively, our results show that the corticostriatal pathway is directly involved in AA release and that this system is dysfunctional in HD. Moreover, because AA release requires glutamate uptake, a failure of striatal AA release in HD is consistent with an overactive glutamate system and diminished glutamate transport, both of which are thought to be central to HD pathogenesis.

Topics: Amphetamine; Analysis of Variance; Animals; Ascorbic Acid; Cerebral Cortex; Corpus Striatum; Disease Models, Animal; Electrochemistry; Huntington Disease; Male; Mice; Mice, Transgenic; Motor Activity; Mutation; Neural Pathways; Reverse Transcriptase Polymerase Chain Reaction; Trinucleotide Repeat Expansion

Ethological assessment of murine models of Huntington's disease (HD), an inherited neurodegenerative disorder, enables correlation between phenotype and pathophysiology. Currently, the most characterized model is the R6/2 line that develops a progressive behavioral and neurological phenotype by 6 weeks of age. A recently developed knock-in model with 140 CAG repeats (KI) exhibits a subtle phenotype with a longer progressive course, more typical of adult-onset HD in humans. We evaluated rotarod performance, open-field behavior, and motor activity across the diurnal cycle in KI mice during early to mid-adulthood. Although we did not observe any effects of age, relative to wild-type (WT) mice, KI mice showed significant deficits in both open-field climbing behavior and home-cage running wheel activity during the light phase of the diurnal cycle. An interesting sex difference also emerged. KI females spent more time in the open-field grooming and more time running during the diurnal dark phase than KI males and WT mice of both sexes. In striatum, the primary site of HD pathology, we measured behavior-related changes in extracellular ascorbate (AA), which is abnormally low in the R6/2 line, consistent with a loss of antioxidant protection in HD. KI males exhibited a 20-40% decrease in striatal AA from anesthesia baseline to behavioral activation that was not observed in other groups. Collectively, our results indicate behavioral deficits in KI mice that may be specific to the diurnal cycle. Furthermore, sex differences observed in behavior and striatal AA release suggest sex-dependent variation in the phenotype and neuropathology of HD.

Topics: Analysis of Variance; Animals; Ascorbic Acid; Behavior, Animal; Body Weight; Circadian Rhythm; Disease Models, Animal; Exploratory Behavior; Female; Huntingtin Protein; Huntington Disease; Male; Mice; Mice, Transgenic; Motor Activity; Neostriatum; Nerve Tissue Proteins; Nuclear Proteins; Rotarod Performance Test; Sex Factors; Trinucleotide Repeat Expansion

Membrane and morphological abnormalities occur in the striatum of R6/2 transgenics, a widely used mouse model of Huntington's disease. To assess changes in behavior-related neuronal activity, we implanted micro-wire bundles in the striatum of symptomatic R6/2 mice and wild-type controls. Unit activity was recorded in an open-field arena once weekly for the next several weeks. For each recording session, firing rate was monitored before, during, and after a period of light anesthesia to assess the influence of behavioral arousal. Because low ascorbate in striatal extracellular fluid may contribute to Huntington's disease symptoms, all animals received an injection of either 300 mg/kg sodium ascorbate or vehicle for three consecutive days prior to each recording session. In R6/2 mice, regardless of treatment, striatal unit activity was significantly faster than in wild-type controls. The difference in mean (+/-S.E.M.) firing was most apparent during wakefulness (6.4+/-0.8 vs. 3.5+/-0.3 spikes/s) but also persisted during anesthesia (2.0+/-0.3 vs. 0.7+/-0.1 spikes/s). Assessment of treatment duration indicated that R6/2 mean waking discharge rate was significantly slower after three weeks than after one week of ascorbate treatment (3.1+/-0.6 vs. 10.2+/-2.7 spikes/s). Vehicle-treated R6/2s showed no such decline in striatal activity ruling out an age- or injection-related effect. Slow-scan voltammetry in separate animals confirmed that ascorbate-injections returned the level of striatal extracellular ascorbate in R6/2 mice to that of wild-type controls. Our results indicate that although striatal neurons modulate firing in relation to behavioral state, impulse activity is consistently elevated in transgenic relative to wild-type mice. Restoring extracellular ascorbate to the wild-type level reverses this effect suggesting a role for ascorbate in normalizing neuronal function in Huntington's disease striatum.

Topics: Anesthesia; Animals; Antioxidants; Ascorbic Acid; Consciousness; Corpus Striatum; Disease Models, Animal; Electrodes, Implanted; Electrophysiology; Huntington Disease; Male; Mice; Mice, Transgenic; Neurons

The R6/2 mouse line expresses exon 1 of the human gene for Huntington disease (HD) and shows behavioral symptoms as early as 6 weeks of age. In the striatum, a forebrain target of HD, these animals show a behavior-related deficit in extracellular ascorbate, the deprotonated form of vitamin C. We report here that this deficit may contribute to the HD behavioral phenotype. Regular injections of ascorbate (300 mg/kg/day, 4 days/week) beginning at symptom onset restored the behavior-related release of ascorbate in striatum and also improved behavioral responding. Compared to vehicle, ascorbate treatment significantly attenuated the neurological motor signs of HD without altering overall motor activity. Ascorbate regulation of striatal function appears key for understanding HD.

Topics: Animals; Ascorbic Acid; Humans; Huntingtin Protein; Huntington Disease; Male; Mice; Motor Activity; Nerve Tissue Proteins; Nuclear Proteins; Phenotype

The extracellular fluid of the striatum contains a high level of ascorbate, an antioxidant vitamin known to play a key role in behavioral activation. We assessed the extracellular dynamics of ascorbate in R6/2 mice engineered to express the gene for Huntington's disease (HD), an autosomal dominant condition characterized by the loss of striatal neurons. Slow-scan voltammetry was used to measure striatal ascorbate during anesthesia and subsequent behavioral recovery. Although both the HD mice and their littermate controls had comparable ascorbate levels during anesthesia, the gradual return of behavioral activation over the next 120 min led to dramatically different ascorbate responses: a progressive increase in controls and a 25-50% decline in HD mice. In contrast, 3,4-dihydroxyphenylacetic acid, a major dopamine metabolite, showed no group differences. Behaviorally, HD mice were less active overall than controls and showed a relatively restricted range of spontaneous movements. Both the ascorbate and behavioral deficits were evident in 6-week-old HD mice and persisted in all subsequent test sessions through 10 weeks of age. Collectively, although these results are consistent with inadequate antioxidant protection in the HD striatum, they indicate that the ascorbate deficit is confined to periods of behavioral activation.

Topics: 3,4-Dihydroxyphenylacetic Acid; Animals; Ascorbic Acid; Behavior, Animal; Body Weight; Corpus Striatum; Disease Models, Animal; Disease Progression; Electrochemistry; Extracellular Space; Huntington Disease; Male; Mice; Mice, Transgenic; Microelectrodes; Motor Activity; Phenotype; Spatial Behavior

Huntington's disease is an autosomal dominant hereditary neurodegenerative disorder characterized by severe striatal cell loss. Dopamine (DA) has been suggested to play a role in the pathogenesis of the disease. We have previously reported that transgenic mice expressing exon 1 of the human Huntington gene (R6 lines) are resistant to quinolinic acid-induced striatal toxicity. In this study we show that with increasing age, R6/1 and R6/2 mice develop partial resistance to DA- and 6-hydroxydopamine-mediated toxicity in the striatum. Using electron microscopy, we found that the resistance is localized to the cell bodies and not to the neuropil. The reduction of dopamine and cAMP regulated phosphoprotein of a molecular weight of 32 kDa (DARPP-32) in R6/2 mice does not provide the resistance, as DA-induced striatal lesions are not reduced in size in DARPP-32 knockout mice. Neither DA receptor antagonists nor a N-methyl-d-aspartate (NMDA) receptor blocker reduce the size of DA-induced striatal lesions, suggesting that DA toxicity is not dependent upon DA- or NMDA receptor-mediated pathways. Moreover, superoxide dismutase-1 overexpression, monoamine oxidase inhibition and the treatment with the free radical scavenging spin-trap agent phenyl-butyl-tert-nitrone (PBN) also did not block DA toxicity. Levels of the antioxidant molecules, glutathione and ascorbate were not increased in R6/1 mice. Because damage to striatal neurons following intrastriatal injection of 6-hydroxydopamine was also reduced in R6 mice, a yet-to-be identified antioxidant mechanism may provide neuroprotection in these animals. We conclude that striatal neurons of R6 mice develop resistance to DA-induced toxicity with age.

Topics: Aging; Animals; Ascorbic Acid; Dopamine; Dopamine and cAMP-Regulated Phosphoprotein 32; Dose-Response Relationship, Drug; Drug Resistance; Exons; Glutathione; Huntington Disease; Mice; Mice, Knockout; Mice, Transgenic; Microscopy, Electron; Neostriatum; Nerve Tissue Proteins; Neurons; Neurotoxins; Oxidative Stress; Oxidopamine; Phosphoproteins; Quinolinic Acid; Retrograde Degeneration; Substantia Nigra; Superoxide Dismutase; Superoxide Dismutase-1; Uric Acid

Intrastriatal injection of the glutamate agonist kainic acid (KA) in rats has been used to produce an animal model to investigate the mechanism of acetylcholine and GABA cell death associated with Huntington's disease. In the present study, the time course of low (10(-5) M) and high (5 x 10(-3) M) concentrations of KA on striatal dopamine and serotonin release was studied in freely moving rats by using in vivo voltammetry. The response to low concentrations of KA varied between animals, either increasing dopamine release during the injection or increasing dopamine and serotonin after the injection for an extended time, suggesting that 10(-5) KA is near the threshold for KA toxicity in the striatum in rats. High concentrations of KA suppressed dopamine release during injection, with both dopamine and serotonin release increasing and remaining elevated for 1-4 and 7-21 days, respectively. KA-induced changes were inhibited by 6-cyano-7-nitroquinoxaline-2,3-dione and bicuculline increased the release of dopamine but not serotonin. These findings suggest that KA-induced changes in dopamine release resulted from a disinhibition of dopamine neurons due to KA-mediated toxicity of striatal GABA neurons. An alternate possibility is that the change in dopamine and serotonin release may have arisen from a functional modification or degeneration of presynaptic terminals.

Topics: 3,4-Dihydroxyphenylacetic Acid; Animals; Ascorbic Acid; Circadian Rhythm; Corpus Striatum; Dopamine; Electrochemistry; Huntington Disease; Kainic Acid; Kinetics; Male; Microinjections; Rats; Rats, Wistar; Serotonin; Time Factors