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The Journal of Neuroscience, August 19, 2009, 29(33):10371-10386; doi:10.1523/JNEUROSCI.1592-09.2009

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Neurobiology of Disease
Alterations in Cortical Excitation and Inhibition in Genetic Mouse Models of Huntington's Disease

Damian M. Cummings, Véronique M. André, Besim O. Uzgil, Steven M. Gee, Yvette E. Fisher, Carlos Cepeda, and Michael S. Levine

Mental Retardation Research Center, David Geffen School of Medicine, Semel Institute for Neuroscience and Human Behavior, University of California at Los Angeles, Los Angeles, California 90095

Correspondence should be addressed to Michael S. Levine, Mental Retardation Research Center Room 58-258, 760 Westwood Plaza, University of California at Los Angeles, Los Angeles, CA 90095. Email: mlevine{at}mednet.ucla.edu

Previously, we identified progressive alterations in spontaneous EPSCs and IPSCs in the striatum of the R6/2 mouse model of Huntington's disease (HD). Medium-sized spiny neurons from these mice displayed a lower frequency of EPSCs, and a population of cells exhibited an increased frequency of IPSCs beginning at 40 d, a time point when the overt behavioral phenotype begins. The cortex provides the major excitatory drive to the striatum and is affected during disease progression. We examined spontaneous EPSCs and IPSCs of somatosensory cortical pyramidal neurons in layers II/III in slices from three different mouse models of HD: the R6/2, the YAC128, and the CAG140 knock-in. Results revealed that spontaneous EPSCs occurred at a higher frequency, and evoked EPSCs were larger in behaviorally phenotypic mice whereas spontaneous IPSCs were initially increased in frequency in all models and subsequently decreased in R6/2 mice after they displayed the typical R6/2 overt behavioral phenotype. Changes in miniature IPSCs and evoked IPSC paired-pulse ratios suggested altered probability of GABA release. Also, in R6/2 mice, blockade of GABA_A receptors induced complex discharges in slices and seizures in vivo at all ages. In conclusion, altered excitatory and inhibitory inputs to pyramidal neurons in the cortex in HD appear to be a prevailing deficit throughout the development of the disease. Furthermore, the differences between synaptic phenotypes in cortex and striatum are important for the development of future therapeutic approaches, which may need to be targeted early in the development of the phenotype.

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Received April 2, 2009; revised June 17, 2009; accepted July 7, 2009.

Correspondence should be addressed to Michael S. Levine, Mental Retardation Research Center Room 58-258, 760 Westwood Plaza, University of California at Los Angeles, Los Angeles, CA 90095. Email: mlevine{at}mednet.ucla.edu

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