51
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Cummings DM, Alaghband Y, Hickey MA, Joshi PR, Hong SC, Zhu C, Ando TK, André VM, Cepeda C, Watson JB, Levine MS. A critical window of CAG repeat-length correlates with phenotype severity in the R6/2 mouse model of Huntington's disease. J Neurophysiol 2011; 107:677-91. [PMID: 22072510 DOI: 10.1152/jn.00762.2011] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The R6/2 mouse is the most frequently used model for experimental and preclinical drug trials in Huntington's disease (HD). When the R6/2 mouse was first developed, it carried exon 1 of the huntingtin gene with ~150 cytosine-adenine-guanine (CAG) repeats. The model presented with a rapid and aggressive phenotype that shared many features with the human condition and was particularly similar to juvenile HD. However, instability in the CAG repeat length due to different breeding practices has led to both decreases and increases in average CAG repeat lengths among colonies. Given the inverse relationship in human HD between CAG repeat length and age at onset and to a degree, the direct relationship with severity of disease, we have investigated the effect of altered CAG repeat length. Four lines, carrying ~110, ~160, ~210, and ~310 CAG repeats, were examined using a battery of tests designed to assess the basic R6/2 phenotype. These included electrophysiological properties of striatal medium-sized spiny neurons, motor activity, inclusion formation, and protein expression. The results showed an unpredicted, inverted "U-shaped" relationship between CAG repeat length and phenotype; increasing the CAG repeat length from 110 to 160 exacerbated the R6/2 phenotype, whereas further increases to 210 and 310 CAG repeats greatly ameliorated the phenotype. These findings demonstrate that the expected relationship between CAG repeat length and disease severity observed in humans is lost in the R6/2 mouse model and highlight the importance of CAG repeat-length determination in preclinical drug trials that use this model.
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Affiliation(s)
- Damian M Cummings
- Intellectual and Developmental Disabilities Research Center, Semel Institute for Neuroscience and Human Behavior, University of California at Los Angeles, California 90095, USA
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52
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Walker AG, Ummel JR, Rebec GV. Reduced expression of conditioned fear in the R6/2 mouse model of Huntington's disease is related to abnormal activity in prelimbic cortex. Neurobiol Dis 2011; 43:379-87. [PMID: 21515374 PMCID: PMC3114205 DOI: 10.1016/j.nbd.2011.04.009] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Revised: 03/18/2011] [Accepted: 04/10/2011] [Indexed: 01/29/2023] Open
Abstract
Prefrontal cortex (PFC) dysfunction is common in patients with Huntington's disease (HD), a dominantly inherited neurological disorder, and has been linked to cognitive disruption. We previously reported alterations in neuronal firing patterns recorded from PFC of the R6/2 mouse model of HD. To determine if PFC dysfunction results in behavioral impairments, we evaluated performance of wild-type (WT) and R6/2 mice in a fear conditioning and extinction behavioral task. Fear conditioning and extinction retrieval were similar in both genotypes, but R6/2s exhibited less fear during extinction by freezing less than WTs. A fear reinstatement test after extinction retrieval indicated that faster extinction was not due to poor memory for conditioning. During initial extinction and extinction retrieval training, neuronal activity was recorded from prelimbic (PL) cortex, a subregion of PFC known to be important for fear expression. In WTs, a large number of neurons were activated by the conditioned stimulus during initial extinction and this activation was significantly impaired in R6/2s. Notably, there was no genotype difference in PFC activity during extinction retrieval. Thus, altered extinction is likely a result of reduced fear expression due to impairments in PL activation. Collectively, our results suggest that PFC dysfunction may play a key role in R6/2 cognitive impairments.
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Affiliation(s)
- Adam G. Walker
- Department of Psychological & Brain Science and Program in Neuroscience, Indiana University, Bloomington, IN
| | - Jason R. Ummel
- Department of Psychological & Brain Science and Program in Neuroscience, Indiana University, Bloomington, IN
| | - George V. Rebec
- Department of Psychological & Brain Science and Program in Neuroscience, Indiana University, Bloomington, IN
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53
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Höhn S, Dallérac G, Faure A, Urbach YK, Nguyen HP, Riess O, von Hörsten S, Le Blanc P, Desvignes N, El Massioui N, Brown BL, Doyère V. Behavioral and in vivo electrophysiological evidence for presymptomatic alteration of prefrontostriatal processing in the transgenic rat model for huntington disease. J Neurosci 2011; 31:8986-97. [PMID: 21677182 PMCID: PMC6622938 DOI: 10.1523/jneurosci.1238-11.2011] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2011] [Accepted: 04/22/2011] [Indexed: 11/21/2022] Open
Abstract
Cognitive decline precedes motor symptoms in Huntington disease (HD). A transgenic rat model for HD carrying only 51 CAG repeats recapitulates the late-onset HD phenotype. Here, we assessed prefrontostriatal function in this model through both behavioral and electrophysiological assays. Behavioral examination consisted in a temporal bisection task within a supra-second range (2 vs.8 s), which is thought to involve prefrontostriatal networks. In two independent experiments, the behavioral analysis revealed poorer temporal sensitivity as early as 4 months of age, well before detection of overt motor deficits. At a later symptomatic age, animals were impaired in their temporal discriminative behavior. In vivo recording of field potentials in the dorsomedial striatum evoked by stimulation of the prelimbic cortex were studied in 4- to 5-month-old rats. Input/output curves, paired-pulse function, and plasticity induced by theta-burst stimulation (TBS) were assessed. Results showed an altered plasticity, with higher paired-pulse facilitation, enhanced short-term depression, as well as stronger long-term potentiation after TBS in homozygous transgenic rats. Results from the heterozygous animals mostly fell between wild-type and homozygous transgenic rats. Our results suggest that normal plasticity in prefrontostriatal circuits may be necessary for reliable and precise timing behavior. Furthermore, the present study provides the first behavioral and electrophysiological evidence of a presymptomatic alteration of prefrontostriatal processing in an animal model for Huntington disease and suggests that supra-second timing may be the earliest cognitive dysfunction in HD.
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Affiliation(s)
- Sophie Höhn
- Université Paris-Sud, Centre de Neurosciences Paris-Sud, Unité Mixte de Recherche 8195, F-91405 Orsay, France
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54
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Changes in striatal procedural memory coding correlate with learning deficits in a mouse model of Huntington disease. Proc Natl Acad Sci U S A 2011; 108:9280-5. [PMID: 21576479 DOI: 10.1073/pnas.1016190108] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
In hereditary neurodegenerative Huntington disease (HD), early cognitive impairments before motor deficits have been hypothesized to result from dysfunction in the striatum and cortex before degeneration. To test this hypothesis, we examined the firing properties of single cells and local field activity in the striatum and cortex of pre-motor-symptomatic R6/1 transgenic mice while they were engaged in a procedural learning task, the performance on which typically depends on the integrity of striatum and basal ganglia. Here, we report that a dramatically diminished recruitment of the vulnerable striatal projection cells, but not local interneurons, of R6/1 mice in coding for the task, compared with WT littermates, is associated with severe deficits in procedural learning. In addition, both the striatum and cortex in these mice showed a unique oscillation at high γ-frequency. These data provide crucial information on the in vivo cellular processes in the corticostriatal pathway through which the HD mutation exerts its effects on cognitive abilities in early HD.
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55
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Miller BR, Walker AG, Barton SJ, Rebec GV. Dysregulated Neuronal Activity Patterns Implicate Corticostriatal Circuit Dysfunction in Multiple Rodent Models of Huntington's Disease. Front Syst Neurosci 2011; 5:26. [PMID: 21629717 PMCID: PMC3100808 DOI: 10.3389/fnsys.2011.00026] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2011] [Accepted: 04/27/2011] [Indexed: 12/12/2022] Open
Abstract
Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder that targets the corticostriatal system and results in progressive deterioration of cognitive, emotional, and motor skills. Although cortical and striatal neurons are widely studied in animal models of HD, there is little information on neuronal function during expression of the HD behavioral phenotype. To address this knowledge gap, we used chronically implanted micro-wire bundles to record extracellular spikes and local field potentials (LFPs) in truncated (R6/1 and R6/2) and full-length (knock-in, KI) mouse models as well as in transgenic HD rats (tgHD rats) behaving in an open-field arena. Spike activity was recorded in the striatum of all models and in prefrontal cortex (PFC) of R6/2 and KI mice, and in primary motor cortex (M1) of R6/2 mice. We also recorded LFP activity in R6/2 striatum. All HD models exhibited altered neuronal activity relative to wild-type (WT) controls. Although there was no consistent effect on firing rate across models and brain areas, burst firing was reduced in striatum, PFC, and M1 of R6/2 mice, and in striatum of KI mice. Consistent with a decline in bursting, the inter-spike-interval coefficient of variation was reduced in all regions of all models, except PFC of KI mice and striatum of tgHD rats. Among simultaneously recorded neuron pairs, correlated firing was reduced in all brain regions of all models, while coincident bursting, which measures the temporal overlap between bursting pairs, was reduced in striatum of all models as well as in M1 of R6/2s. Preliminary analysis of striatal LFPs revealed aberrant behavior-related oscillations in the delta to theta range and in gamma activity. Collectively, our results indicate that disrupted corticostriatal processing occurs across multiple HD models despite differences in the severity of the behavioral phenotype. Efforts aimed at normalizing corticostriatal activity may hold the key to developing new HD therapeutics.
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Affiliation(s)
- Benjamin R Miller
- Program in Neuroscience and Department of Psychological and Brain Sciences, Indiana University Bloomington, IN, USA
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56
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Abstract
Mouse models for Huntington's Disease (HD) and HD patients demonstrate motor and behavioral dysfunctions, such as progressive loss of coordination and memory, and share similar transcriptional profiles and striatal neuron atrophy. Clear differences between the mouse and human diseases include almost complete striatal degeneration and rarity of intranuclear inclusions in HD, and the fact that mice expressing full-length mutant huntingtin do not demonstrate a shortened life span characteristic of HD. While no clinical interventions tested in mouse models to date have delayed disease progression, the mouse models provide an invaluable tool for both investigating the underlying pathogenic processes and developing new effective therapies. Inherent differences between humans and mice must be considered in the search for efficacious treatments for HD, but the striking similarities between human HD and mouse models support the view that these models are a biologically relevant system to support the identification and testing of potential clinical therapies.
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Affiliation(s)
- Zachary R Crook
- The David H. Koch Institute for Integrative Cancer Research at MIT, 500 Main Street, Building 76-553, Cambridge, MA 02139, USA
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57
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Dallérac GM, Vatsavayai SC, Cummings DM, Milnerwood AJ, Peddie CJ, Evans KA, Walters SW, Rezaie P, Hirst MC, Murphy KPSJ. Impaired long-term potentiation in the prefrontal cortex of Huntington's disease mouse models: rescue by D1 dopamine receptor activation. NEURODEGENER DIS 2011; 8:230-9. [PMID: 21282937 DOI: 10.1159/000322540] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2010] [Accepted: 11/04/2010] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The introduction of gene testing for Huntington's disease (HD) has enabled the neuropsychiatric and cognitive profiling of human gene carriers prior to the onset of overt motor and cognitive symptoms. Such studies reveal an early decline in working memory and executive function, altered EEG and a loss of striatal dopamine receptors. Working memory is processed in the prefrontal cortex and modulated by extrinsic dopaminergic inputs. OBJECTIVE We sought to study excitatory synaptic function and plasticity in the medial prefrontal cortex of mouse models of HD. METHODS We have used 2 mouse models of HD, carrying 89 and 116 CAG repeats (corresponding to a preclinical and symptomatic state, respectively) and performed electrophysiological field recording in coronal slices of the medial prefrontal cortex. RESULTS We report that short-term synaptic plasticity and long-term potentiation (LTP) are impaired and that the severity of impairment is correlated with the size of the CAG repeat. Remarkably, the deficits in LTP and short-term plasticity are reversed in the presence of a D(1) dopamine receptor agonist (SKF38393). CONCLUSION In a previous study, we demonstrated that a deficit in long-term depression (LTD) in the perirhinal cortex could also be reversed by a dopamine agonist. These and our current data indicate that inadequate dopaminergic modulation of cortical synaptic function is an early event in HD and may provide a route for the alleviation of cognitive dysfunction.
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Affiliation(s)
- G M Dallérac
- Huntington's Disease Research Forum, Department of Life Sciences, The Open University, Milton Keynes, UK
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58
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Milnerwood AJ, Raymond LA. Early synaptic pathophysiology in neurodegeneration: insights from Huntington's disease. Trends Neurosci 2010; 33:513-23. [PMID: 20850189 DOI: 10.1016/j.tins.2010.08.002] [Citation(s) in RCA: 209] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2010] [Revised: 07/26/2010] [Accepted: 08/11/2010] [Indexed: 01/22/2023]
Abstract
Investigations of synaptic transmission and plasticity in mouse models of Huntington's disease (HD) demonstrate neuronal dysfunction long before the onset of classical disease indicators. Similarly, recent human studies reveal synaptic dysfunction decades before predicted clinical diagnosis in HD gene carriers. These studies guide premanifest tracking of disease and the development of treatment assessment tools. New discoveries of mechanisms underlying early neuronal dysfunction, including elevated pathogenic extrasynaptic NMDA receptor signaling, reduced synaptic connectivity and loss of brain-derived neurotrophic factor (BDNF) support have led to pharmacological interventions that can reverse or delay phenotype onset and disease progression in HD mice. Further understanding the primary effects of gene mutations associated with late-onset neurodegeneration should translate to novel treatments for HD families and guide therapeutic strategies for other neurodegenerative diseases.
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Affiliation(s)
- Austen J Milnerwood
- Department of Psychiatry and Brain Research Centre, University of British Columbia, Vancouver, Canada
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59
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Electrophysiological measures as potential biomarkers in Huntington's disease: Review and future directions. ACTA ACUST UNITED AC 2010; 64:177-94. [DOI: 10.1016/j.brainresrev.2010.03.004] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2009] [Revised: 03/24/2010] [Accepted: 03/29/2010] [Indexed: 01/18/2023]
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60
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Miller BR, Bezprozvanny I. Corticostriatal circuit dysfunction in Huntington's disease: intersection of glutamate, dopamine and calcium. FUTURE NEUROLOGY 2010; 5:735-756. [PMID: 21977007 DOI: 10.2217/fnl.10.41] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Huntington's disease (HD) is a noncurable and progressive autosomal-dominant neurodegenerative disorder that results from a polyglutamine expansion in the amino-terminal region of the huntingtin protein. The generation of rodent HD models has revealed that cellular dysfunction, rather than cell death alone, occurs early in the disease progression, appearing even before overt symptom onset. Much evidence has now established that dysfunction of the corticostriatal circuit is key to HD symptomology. In this article, we summarize the most current findings that implicate glutamate, dopamine and calcium signaling in this system and discuss how they work in concert to disrupt corticostriatal function. In addition, we highlight therapeutic strategies related to altered corticostriatal signaling in HD.
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Affiliation(s)
- Benjamin Ray Miller
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75390, USA
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61
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Sari Y, Prieto AL, Barton SJ, Miller BR, Rebec GV. Ceftriaxone-induced up-regulation of cortical and striatal GLT1 in the R6/2 model of Huntington's disease. J Biomed Sci 2010; 17:62. [PMID: 20663216 PMCID: PMC2918547 DOI: 10.1186/1423-0127-17-62] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2010] [Accepted: 07/27/2010] [Indexed: 12/31/2022] Open
Abstract
Background Huntington's disease (HD) is an inherited neurodegenerative disorder characterized by cortico-striatal dysfunction and loss of glutamate uptake. At 7 weeks of age, R6/2 mice, which model an aggressive form of juvenile HD, show a glutamate-uptake deficit in striatum that can be reversed by treatment with ceftriaxone, a β-lactam antibiotic that increases GLT1 expression. Only at advanced ages (> 11 weeks), however, do R6/2 mice show an actual loss of striatal GLT1. Here, we tested whether ceftriaxone can reverse the decline in GLT1 expression that occurs in older R6/2s. Results Western blots were used to assess GLT1 expression in both striatum and cerebral cortex in R6/2 and corresponding wild-type (WT) mice at 9 and 13 weeks of age. Mice were euthanized for immunoblotting 24 hr after five consecutive days of once daily injections (ip) of ceftriaxone (200 mg/kg) or saline vehicle. Despite a significant GLT1 reduction in saline-treated R6/2 mice relative to WT at 13, but not 9, weeks of age, ceftriaxone treatment increased cortical and striatal GLT1 expression relative to saline in all tested mice. Conclusions The ability of ceftriaxone to up-regulate GLT1 in R6/2 mice at an age when GLT1 expression is significantly reduced suggests that the mechanism for increasing GLT1 expression is still functional. Thus, ceftriaxone could be effective in modulating glutamate transmission even in late-stage HD.
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Affiliation(s)
- Youssef Sari
- Program in Neuroscience, Indiana University, 1101 East 10th Street, Bloomington, IN, USA
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62
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Gambazzi L, Gokce O, Seredenina T, Katsyuba E, Runne H, Markram H, Giugliano M, Luthi-Carter R. Diminished activity-dependent brain-derived neurotrophic factor expression underlies cortical neuron microcircuit hypoconnectivity resulting from exposure to mutant huntingtin fragments. J Pharmacol Exp Ther 2010; 335:13-22. [PMID: 20624994 DOI: 10.1124/jpet.110.167551] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Although previous studies of Huntington's disease (HD) have addressed many potential mechanisms of striatal neuron dysfunction and death, it is also known, based on clinical findings, that cortical function is dramatically disrupted in HD. With respect to disease etiology, however, the specific molecular and neuronal circuit bases for the cortical effects of mutant huntingtin (htt) have remained largely unknown. In the present work, we studied the relationship between the molecular effects of mutant htt fragments in cortical cells and the corresponding behavior of cortical neuron microcircuits by using a novel cellular model of HD. We observed that a transcript-selective diminution in activity-dependent brain-derived neurotrophic factor (BDNF) expression preceded the onset of a synaptic connectivity deficit in ex vivo cortical networks, which manifested as decreased spontaneous collective burst-firing behavior measured by multielectrode array substrates. Decreased BDNF expression was determined to be a significant contributor to network-level dysfunction, as shown by the ability of exogenous BDNF to ameliorate cortical microcircuit burst firing. The molecular determinants of the dysregulation of activity-dependent BDNF expression by mutant htt seem to be distinct from previously elucidated mechanisms, because they do not involve known neuron-restrictive silencer factor/RE1-silencing transcription factor-regulated promoter sequences but instead result from dysregulation of BDNF exon IV and VI transcription. These data elucidate a novel HD-related deficit in BDNF gene regulation as a plausible mechanism of cortical neuron hypoconnectivity and cortical function deficits in HD. Moreover, the novel model paradigm established here is well suited to further mechanistic and drug screening research applications.
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Affiliation(s)
- Luca Gambazzi
- Laboratory of Neural Microcircuitry, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
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63
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Zuccato C, Valenza M, Cattaneo E. Molecular Mechanisms and Potential Therapeutical Targets in Huntington's Disease. Physiol Rev 2010; 90:905-81. [DOI: 10.1152/physrev.00041.2009] [Citation(s) in RCA: 626] [Impact Index Per Article: 44.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Huntington's disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the gene encoding for huntingtin protein. A lot has been learned about this disease since its first description in 1872 and the identification of its causative gene and mutation in 1993. We now know that the disease is characterized by several molecular and cellular abnormalities whose precise timing and relative roles in pathogenesis have yet to be understood. HD is triggered by the mutant protein, and both gain-of-function (of the mutant protein) and loss-of-function (of the normal protein) mechanisms are involved. Here we review the data that describe the emergence of the ancient huntingtin gene and of the polyglutamine trait during the last 800 million years of evolution. We focus on the known functions of wild-type huntingtin that are fundamental for the survival and functioning of the brain neurons that predominantly degenerate in HD. We summarize data indicating how the loss of these beneficial activities reduces the ability of these neurons to survive. We also review the different mechanisms by which the mutation in huntingtin causes toxicity. This may arise both from cell-autonomous processes and dysfunction of neuronal circuitries. We then focus on novel therapeutical targets and pathways and on the attractive option to counteract HD at its primary source, i.e., by blocking the production of the mutant protein. Strategies and technologies used to screen for candidate HD biomarkers and their potential application are presented. Furthermore, we discuss the opportunities offered by intracerebral cell transplantation and the likely need for these multiple routes into therapies to converge at some point as, ideally, one would wish to stop the disease process and, at the same time, possibly replace the damaged neurons.
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Affiliation(s)
- Chiara Zuccato
- Department of Pharmacological Sciences and Centre for Stem Cell Research, Università degli Studi di Milano, Milan, Italy
| | - Marta Valenza
- Department of Pharmacological Sciences and Centre for Stem Cell Research, Università degli Studi di Milano, Milan, Italy
| | - Elena Cattaneo
- Department of Pharmacological Sciences and Centre for Stem Cell Research, Università degli Studi di Milano, Milan, Italy
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64
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Alterations in striatal synaptic transmission are consistent across genetic mouse models of Huntington's disease. ASN Neuro 2010; 2:e00036. [PMID: 20585470 PMCID: PMC2888168 DOI: 10.1042/an20100007] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2010] [Revised: 04/23/2010] [Accepted: 05/05/2010] [Indexed: 11/28/2022] Open
Abstract
Since the identification of the gene responsible for HD (Huntington's
disease), many genetic mouse models have been generated. Each employs a unique
approach for delivery of the mutated gene and has a different CAG repeat length
and background strain. The resultant diversity in the genetic context and
phenotypes of these models has led to extensive debate regarding the relevance
of each model to the human disorder. Here, we compare and contrast the striatal
synaptic phenotypes of two models of HD, namely the YAC128 mouse, which carries
the full-length huntingtin gene on a yeast artificial chromosome, and the CAG140
KI (knock-in) mouse, which carries a human/mouse chimaeric gene that is
expressed in the context of the mouse genome, with our previously published data
obtained from the R6/2 mouse, which is transgenic for exon 1 mutant huntingtin.
We show that striatal MSNs (medium-sized spiny neurons) in YAC128 and CAG140 KI
mice have similar electrophysiological phenotypes to that of the R6/2 mouse.
These include a progressive increase in membrane input resistance, a reduction
in membrane capacitance, a lower frequency of spontaneous excitatory
postsynaptic currents and a greater frequency of spontaneous inhibitory
postsynaptic currents in a subpopulation of striatal neurons. Thus, despite
differences in the context of the inserted gene between these three models of
HD, the primary electrophysiological changes observed in striatal MSNs are
consistent. The outcomes suggest that the changes are due to the expression of
mutant huntingtin and such alterations can be extended to the human
condition.
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Key Words
- ACSF, artificial cerebrospinal fluid
- AP5, dl-2-amino-5-phosphonovaleric acid
- BIC, bicuculline methobromide
- CAG 140 knock-in mouse model
- CNQX, 6-cyano-7-nitroquinoxaline-2,3-dione
- EPSC, excitatory postsynaptic current
- GABAA, γ-aminobutyric acid type A
- HD, Huntington's disease
- HF, high frequency
- Huntington's disease
- IPSC, inhibitory postsynaptic current
- KI, knock-in
- LF, low frequency
- MSN, medium-sized spiny neuron
- WT, wild-type
- YAC128 mouse model
- electrophysiology
- striatum
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65
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Genetic mouse models of Huntington's disease: focus on electrophysiological mechanisms. ASN Neuro 2010; 2:e00033. [PMID: 20396376 PMCID: PMC2850512 DOI: 10.1042/an20090058] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Revised: 03/11/2010] [Accepted: 03/16/2010] [Indexed: 11/21/2022] Open
Abstract
The discovery of the HD (Huntington’s disease) gene in 1993 led to the creation of genetic mouse models of the disease and opened the doors for mechanistic studies. In particular, the early changes and progression of the disease could be followed and examined systematically. The present review focuses on the contribution of these genetic mouse models to the understanding of functional changes in neurons as the HD phenotype progresses, and concentrates on two brain areas: the striatum, the site of most conspicuous pathology in HD, and the cortex, a site that is becoming increasingly important in understanding the widespread behavioural abnormalities. Mounting evidence points to synaptic abnormalities in communication between the cortex and striatum and cell–cell interactions as major determinants of HD symptoms, even in the absence of severe neuronal degeneration and death.
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Key Words
- AMPA, α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate
- BAC, bacterial artificial chromosome
- BDNF, brain-derived neurotrophic factor
- DA, dopamine
- EPSC, excitatory postsynaptic current
- GABA, γ-aminobutyric acid
- HD, Huntington’s disease
- Huntington’s disease
- IPSC, inhibitory postsynaptic current
- IR-DIC, infrared differential interference contrast
- MSSN, medium-sized spiny projection neuron
- NII, neuronal intranuclear inclusion
- NMDA, N-methyl-d-aspartate
- WT, wild-type
- YAC, yeast artificial chromosome
- enk, enkephalin
- excitatory amino acid
- htt, huntingtin
- mouse model
- neurodegeneration
- striatum
- synaptic activity
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66
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Miller BR, Walker AG, Fowler SC, von Hörsten S, Riess O, Johnson MA, Rebec GV. Dysregulation of coordinated neuronal firing patterns in striatum of freely behaving transgenic rats that model Huntington's disease. Neurobiol Dis 2010; 37:106-13. [PMID: 19818852 PMCID: PMC2787873 DOI: 10.1016/j.nbd.2009.09.013] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2009] [Revised: 09/04/2009] [Accepted: 09/27/2009] [Indexed: 10/20/2022] Open
Abstract
Altered neuronal activity in the striatum appears to be a key component of Huntington's disease (HD), a fatal, neurodegenerative condition. To assess this hypothesis in freely behaving transgenic rats that model HD (tgHDs), we used chronically implanted micro-wires to record the spontaneous activity of striatal neurons. We found that relative to wild-type controls, HD rats suffer from population-level deficits in striatal activity characterized by a loss of correlated firing and fewer episodes of coincident spike bursting between simultaneously recorded neuronal pairs. These results are in line with our previous report of marked alterations in the pattern of striatal firing in mouse models of HD that vary in background strain, genetic construct, and symptom severity. Thus, loss of coordinated spike activity in striatum appears to be a common feature of HD pathophysiology, regardless of HD model variability.
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Affiliation(s)
- Benjamin R Miller
- Program in Neuroscience and Department of Psychological and Brain Sciences, Indiana University, Bloomington, IN 47405, USA
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