Mice representing precise genetic replicas of Huntington's disease (HD) were made using gene targeting to replace the short CAG repeat of the mouse Huntington's disease gene homolog (HDH:) with CAG repeats within the length range found to cause HD in humans. Mice with alleles of approximately 150 units in length exhibit late-onset behavioral and neuroanatomic abnormalities consistent with HD. These symptoms include a motor task deficit, gait abnormalities, reactive gliosis and the formation of neuronal intranuclear inclusions predominating in the striatum. This model differs from previously described HDH: knock-ins by its method of construction, longer repeat length and more severe phenotype. To our knowledge, this is the first knock-in mouse model of HD to show increased glial fibrillary acidic protein immunoreactivity in the striatum, suggesting that these mice have neuronal injury similar to that found early in the course of HD. These mice will serve as useful reagents in experiments designed to reveal the molecular nature of neuronal dysfunction underlying HD.

The mutations responsible for several human neurodegenerative disorders are expansions of translated CAG repeats beyond a normal size range. To address the role of repeat context, we have introduced a 146-unit CAG repeat into the mouse hypoxanthine phosphoribosyltransferase gene (Hprt). Mutant mice express a form of the HPRT protein that contains a long polyglutamine repeat. These mice develop a phenotype similar to the human translated CAG repeat disorders. Repeat containing mice show a late onset neurological phenotype that progresses to premature death. Neuronal intranuclear inclusions are present in affected mice. Our results show that CAG repeats do not need to be located within one of the classic repeat disorder genes to have a neurotoxic effect.

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The aggregation of mutant polyglutamine (polyQ) proteins has sparked interest in the role of protein quality-control pathways in Huntington's disease (HD) and related polyQ disorders. Employing a novel knock-in HD mouse model, we provide in vivo evidence of early, sustained alterations of autophagy in response to mutant huntingtin (mhtt). The HdhQ200 knock-in model, derived from the selective breeding of HdhQ150 knock-in mice, manifests an accelerated and more robust phenotype than the parent line. Heterozygous HdhQ200 mice accumulate htt aggregates as cytoplasmic aggregation foci (AF) as early as 9 weeks of age and striatal neuronal intranuclear inclusions (NIIs) by 20 weeks. By 40 weeks, striatal AF are perinuclear and immunoreactive for ubiquitin and the autophagosome marker LC3. Striatal NIIs accumulate earlier in HdhQ200 mice than in HdhQ150 mice. The earlier appearance of aggregate pathology in HdhQ200 mice is paralleled by earlier and more rapidly progressive motor deficits: progressive imbalance and decreased motor coordination by 50 weeks, gait deficits by 60 weeks and gross motor impairment by 80 weeks of age. At 80 weeks, heterozygous HdhQ200 mice exhibit striatal and cortical astrogliosis and a approximately 50% reduction in striatal dopamine receptor binding. Increased LC3-II protein expression, which is noted early and sustained throughout the disease course, is paralleled by increased expression of the autophagy-related protein, p62. Early and sustained expression of autophagy-related proteins in this genetically precise mouse model of HD suggests that the alteration of autophagic flux is an important and early component of the neuronal response to mhtt.

The mouse mutant medJ contains a splice site mutation in the neuronal sodium channel Scn8a that results in a very low level of expression. On a C57BL/6J genetic background, medJ homozygotes exhibit progressive paralysis and juvenile lethality. The C3H genetic background has an ameliorating effect, producing viable adults with a novel dystonic phenotype. The dystonic mice exhibit movement-induced, sustained abnormal postures of the trunk and limbs. A dominant modifier locus responsible for the difference between strains was mapped to a 4.5 +/- 1.3 cM interval on mouse chromosome 3. Our findings establish a role for ion channels in dystonia and demonstrate the impact of genetic background on its severity and progression. This new model suggests that SCN8A on chromosome 12q13 and SCNM1 on chromosome 1p21-1q21 may contribute to human inherited dystonia.

Two-color immunofluorescence histochemistry and immunohistochemistry in combination with retrograde tract-tracing techniques were used to examine the relationship of alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA)-selective glutamate receptor subunits (GluR1, GluR2/3/4c and GluR4) to identified populations of striatal projection neurons and interneurons. The majority of striatonigral and striatopallidal neurons were double-labeled for GluR2/3/4c. These findings were confirmed using calbindin to label matrix projection neurons. In contrast, immunostaining of the GluR1 subunit was not observed to co-localize with any striatal projection neurons. Striatal interneurons immunostained for parvalbumin were also labeled by antibodies directed against the GluR1 subunit. Approximately 50% of parvalbumin neurons also contained GluR2/3/4c. Somatostatin immunoreactivity did not co-localize with either the GluR1 or GluR2/3/4c subunits. GluR4-immunoreactive neurons were not observed in striatum. This study demonstrates that AMPA-selective glutamate receptors are differentially localized on subpopulations of striatal neurons and interneurons. These findings suggest that discrete striatal neuron populations may express different AMPA receptor subunit combinations which may account for their functional specificity.

Quantitative autoradiography was used to examine the density and distribution of excitatory amino acid (EAA) binding site subtypes in the principal sensory and spinal trigeminal nuclei of the rat trigeminal complex. The highest densities of N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), kainate and metabotropic receptors were found in the superficial laminae (I and II) of subnucleus caudalis, a region known to be densely innervated by primary afferent nociceptive terminals. Lower densities of EAA binding sites were observed in spinal subnuclei interpolaris and oralis and within the principal sensory nucleus. These results are consistent with the hypothesis that EAAs are involved in primary afferent nociceptive neurotransmission.