Neuropeptide Y modifies the disease course in the R6/2 transgenic model of Huntington's disease

Huntington's disease (HD) is an inherited neurodegenerative disorder characterized by progressive neuronal dysfunction and cell loss, especially striatal GABAergic neurons, generating motor, cognitive and affective problems. Although the disease-causing gene is known, the exact mechanism by which it induces its pathological effect remains unknown, and no cure is currently available for this disease. Interestingly, striatal neurons that express neuropeptide Y (NPY) are preferentially spared in HD and the number of such cells is increased in the striatum of HD patients. Furthermore, neurogenesis in the subventricular zone (SVZ) also appears to be up-regulated in HD patients, and previously we also demonstrated in wild-type mice that intracerebroventricular (ICV) NPY promotes SVZ neurogenesis with migration of the newborn cells towards the striatum where they differentiate into GABAergic neurons.Therefore, we sought to determine whether NPY could be of therapeutic benefit in a transgenic mouse model of HD (R6/2) through an action on SVZ neurogenesis. We found that a single ICV injection of NPY in R6/2 mice increased survival time through reduced weight loss as well as having a beneficial effect on motor function as evidenced by improving rotarod performance and reducing paw-clasping. We also demonstrated that the degree of cerebral and striatal atrophy was reduced following such a single NPY injection and that whilst the peptide also increased the number of BrdU-positive cells in the SVZ (but not in the dentate gyrus) of R6/2 mice, this was not sufficient to account for the changes in anatomy and function that we found.. These results suggest that NPY may be of some therapeutic interest in patients with HD, although further work is needed to ascertain exactly how it mediates its beneficial effects.     

Chronology of behavioral symptoms and neuropathological sequela in R6/2 Huntington's disease transgenic mice

Genetic murine models play an important role in the study of human neurological disorders by providing accurate and experimentally accessible systems to study pathogenesis and to test potential therapeutic treatments. One of the most widely employed models of Huntington's disease (HD) is the R6/2 transgenic mouse. To characterize this model further, we have performed behavioral and neuropathological analyses that provide a foundation for the use of R6/2 mice in preclinical therapeutic trials. Behavioral analyses of the R6/2 mouse reveal age-related impairments in dystonic movements, motor performance, grip strength, and body weight that progressively worsen until death. Significant neuropathological sequela, identified as increasing marked reductions in brain weight, are present from 30 days, whereas decreased brain volume is present from 60 days and decreased neostriatal volume and striatal neuron area, with a concomitant reduction in striatal neuron number, are present at 90 days of age. Huntingtin-positive aggregates are present at postnatal day 1 and increase in number and size with age. Our findings suggest that the R6/2 HD model exhibits a progressive HD-like behavioral and neuropathological phenotype that more closely corresponds to human HD than previously believed, providing further assurance that the R6/2 mouse is an appropriate model for testing potential therapies for HD.     

Progressive abnormalities in skeletal muscle and neuromuscular junctions of transgenic mice expressing the Huntington's disease mutation

Huntington's disease (HD) is a neurodegenerative disorder with complex symptoms dominated by progressive motor dysfunction. Skeletal muscle atrophy is common in HD patients. Because the HD mutation is expressed in skeletal muscle as well as brain, we wondered whether the muscle changes arise from primary pathology. We used R6/2 transgenic mice for our studies. Unlike denervation atrophy, skeletal muscle atrophy in R6/2 mice occurs uniformly. Paradoxically however, skeletal muscles show age-dependent denervation-like abnormalities, including supersensitivity to acetylcholine, decreased sensitivity to mu-conotoxin, and anode-break action potentials. Morphological abnormalities of neuromuscular junctions are also present, particularly in older R6/2 mice. Severely affected R6/2 mice show a progressive increase in the number of motor endplates that fail to respond to nerve stimulation. Surprisingly, there was no constitutive sprouting of motor neurons in R6/2 muscles, even in severely atrophic muscles that showed other denervation-like characteristics. In fact, there was an age-dependent loss of regenerative capacity of motor neurons in R6/2 mice. Because muscle fibers appear to be released from the activity-dependent cues that regulate membrane properties and muscle size, and motor axons and nerve terminals become impaired in their capacity to release neurotransmitter and to respond to stimuli that normally evoke sprouting and adaptive reinnervation, we speculate that in these mice there is a progressive dissociation of trophic signalling between motor neurons and skeletal muscle. However, irrespective of the cause, the abnormalities at neuromuscular junctions we report here are likely to contribute to the pathological phenotype in R6/2 mice, particularly in late stages of the disease.     

Impaired glucose tolerance in the R6/1 transgenic mouse model of Huntington's disease

Previous reports have highlighted a possible link between Huntington's disease (HD) and diabetes mellitus (DM), but the association has not been characterised in detail. A transgenic mouse model for HD, the R6/2 mouse, also develops diabetes. In the present study, we examined the R6/1 mouse, which carries a shorter CAG repeat than the R6/2 mouse, and found that, although not diabetic, the mice showed several signs of impaired glucose tolerance. First, following i.p. glucose injection, the blood glucose concentration was approximately 30% higher in young R6/1 mice (10 weeks) compared to wild-type mice (P = 0.004). In older mice (38 weeks), glucose tolerance was further impaired in both R6/1 and wild-type animals. Second, during glucose challenge, the R6/1 mice reached higher plasma insulin levels than wild-type mice, but the peripheral insulin sensitivity was normal as measured by injection of human or mouse insulin or when evaluated by the quantitative insulin sensitivity check index (QUICKI). Third, the beta cell volume was 17% and 39% smaller at 10 and 38 weeks of age, respectively, compared to age-matched wild-type littermates and the reduction was not caused by apoptosis at either age. Finally, we demonstrated the presence of the HD gene product, huntingtin (htt), in both alpha- and beta-cells in R6/1 islets of Langerhans. Since pancreatic beta cells and neurons share several common traits, clarification of the mechanism associating neurodegenerative diseases with diabetes might improve our understanding of the pathogenic events leading to both groups of diseases.     

CAG repeat lengths ≥ 335 attenuate the phenotype in the R6/2 Huntington's disease transgenic mouse

With spontaneous elongation of the CAG repeat in the R6/2 transgene to ≥ 335, resulting in a transgene protein too large for passive entry into nuclei via the nuclear pore, we observed an abrupt increase in lifespan to > 20 weeks, compared to the 12 weeks common in R6/2 mice with 150 repeats. In the ≥ 335 CAG mice, large ubiquitinated aggregates of mutant protein were common in neuronal dendrites and perikaryal cytoplasm, but intranuclear aggregates were small and infrequent. Message and protein for the ≥ 335 CAG transgene were reduced to one-third that in 150 CAG R6/2 mice. Neurological and neurochemical abnormalities were delayed in onset and less severe than in 150 CAG R6/2 mice. These findings suggest that polyQ length and pathogenicity in Huntington's disease may not be linearly related, and pathogenicity may be less severe with extreme repeats. Both diminished mutant protein and reduced nuclear entry may contribute to phenotype attenuation.     

The antidepressant sertraline improves the phenotype, promotes neurogenesis and increases BDNF levels in the R6/2 Huntington's disease mouse model

Huntington's disease (HD) is an inherited progressive neurodegenerative disorder characterized by progressive movement, psychiatric and cognitive disturbances. Previous studies have indicated that HD pathogenesis may be mediated in part by loss of brain derived neurotrophic factor (BDNF). Antidepressants selectively blocking serotonin reuptake can increase BDNF levels, and also may increase neurogenesis. Here we report that an SSRI antidepressant, sertraline, prolongs survival, improves motor performance, and ameliorates brain atrophy in the R6/2 HD mouse model. Six-week-old R6/2 mice and nontransgenic control mice were administered either sertraline or vehicle daily. Motor function was assessed in an accelerating rotarod test and evaluated at 10 weeks. R6/2 mice exhibited reduced time on the rod. Sertraline treatment improved the motor performance in R6/2 mice, but did not affect nontransgenic mice. R6/2 mice showed significant striatal atrophy which was reduced by sertraline treatment. These beneficial effects of sertraline are associated with enhanced neurogenesis and increased BDNF levels in brain treated with sertraline. The effective serum and brain levels of sertraline are comparable to the levels achieved in human antidepressant treatment. Our findings provide evidence that sertraline is neuroprotective in this HD model. Successful treatment with sertraline in depressed HD patients has been reported; moreover, sertraline is safe and well-tolerated for long-term administration, including in HD patients. Our findings suggest that a clinical trial of SSRI treatment in order to retard disease progression in human HD may be warranted.     

Differential changes in striatal projection neurons in R6/2 transgenic mice for Huntington's disease

In early adult-onset Huntington's disease (HD), enkephalinergic striatopallidal projection neurons show preferential loss, reduced preproenkephalin (PPE) expression in surviving striatopallidal neurons, and loss of fibers in their projection target area. We examined PPE and PPT (preprotachykinin) gene expression in striatal projection neurons and in striatal projection fibers immunoreactive for the PPE product enkephalin (ENK) and the PPT product substance P (SP) in a transgenic HD model, the R6/2 mouse, to see if changes occur in these neuron types similar to those seen in early adult-onset HD. The results show that PPE mRNA level, the number of striatal neurons expressing PPE, and the staining intensity of fibers immunoreactive for ENK in the pallidum were all decreased. By contrast, the SP-containing striatal projection systems to the pallidum and substantia nigra were relatively normal in R6/2 mice. The selective reduction in striatal PPE in R6/2 mice is reminiscent of adult-onset HD, but the preservation of the striatonigral projection system is not. Thus, R6/2 mice do not strictly mimic adult-onset HD in their striatal pathology.     

Increased calbindin-D28k immunoreactivity in striatal projection neurons of R6/2 Huntington's disease transgenic mice

Striatal degeneration in Huntington's disease (HD) is associated with increases in perikaryal calbindin immunolabeling in yet-surviving striatal projection neurons. Since similar increases have also been observed in surviving striatal projection neurons after intrastriatal injection of the excitotoxin quinolinic acid, the increased calbindin in HD striatum has been interpreted to suggest an excitotoxic process in HD. We used immunolabeling to assess if calbindin is elevated in striatal projection neurons of R6/2 HD transgenic mice. These mice bear exon 1 of the human huntingtin gene with 144 CAG repeats and show some of the neuropathological signs (e.g., neuronal intranuclear inclusions) and clinical traits (e.g., wasting prior to early death) of HD. We found an increased frequency of calbindin-immunoreactive neuronal perikarya in the striatum of 6- and 12-week-old R6/2 mice compared to wild-type controls. This increase was most notable in the normally calbindin-poor dorsolateral striatum. We found no significant changes in the total area of striatum occupied by the calbindin-negative striosomes and no consistent changes in striatal calbindin mRNA. The increase in calbindin in R6/2 striatal neurons was thus limited to the matrix compartment, and it may be triggered by increased Ca2+ entry due to the demonstrated heightened NMDA sensitivity of these neurons. The data further support the similarity of R6/2 mice to HD, and are consistent with the occurrence of an excitotoxic process in striatum in both.     

"Brain training" improves cognitive performance and survival in a transgenic mouse model of Huntington's disease

Environmental enrichment (EE) has been shown to improve neurological function and cognitive performance in animal models of Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD). We have shown recently that even when they are already living in an enriched environment, additional EE had beneficial effects in R6/2 mice. Here we examined the effects of three different enrichment paradigms on cognitive dysfunction in R6/2 mice in a longitudinal study. The EE consisted of either enforced physical exercise on the Rotarod (predominantly motor stimulation), training in a novel type of maze, the 'noughts and crosses' (OX) maze (mainly cognitive stimulation), or access to a playground, that gave the mice the opportunity for increased, self-motivated activity using running wheels and other toys in a social context (mixed EE). We designed the OX maze to test spatial memory in the R6/2 mouse while minimizing motor demands. Control mice remained in their home cages during the training period. Mice were given enrichment between 6 and 8 weeks of age, followed by cognitive (Lashley maze) and motor testing (Rotarod) between 8 and 10 weeks. Mice were then given a further period of enrichment between 10 and 12 weeks, and their behavior was re-tested between 12 and 14 weeks of age. We also collected body weights and age at death from all mice. The OX maze was as sensitive for detecting learning deficits in the R6/2 mice as other types of mazes (such as the Morris water maze). Interestingly, providing cognitive stimulation via training in the OX maze produced significant improvements in subsequent cognitive performance by male, but not female, R6/2 mice in the Lashley maze task. OX maze training also significantly improved loss of body weight and survival in male R6/2 mice. These effects became apparent after as little as 2 weeks of training in the OX maze. These data suggest that there is a cognitive reserve that may be exploited in neurodegenerative disease. While brain training was not beneficial for all mice, it produced no deleterious effects, and so warrants further study in rodent models of HD.     

Single alcohol exposure in early life damages hippocampal stem/progenitor cells and reduces adult neurogenesis

Alcohol exposure during pregnancy may cause fetal alcohol syndrome (FAS), characterized by impaired cognitive functions. Neurogenesis occurs in the adult hippocampus and is functionally associated with learning, memory, and mood disorders. However, whether early postnatal exposure to alcohol impairs neurogenesis and through which mechanisms it occurs is poorly understood. Here, we report that a single episode of alcohol exposure in postnatal day 7 (P7) decreases neurogenesis in the adult hippocampus. Furthermore, we demonstrate a co-localization of glial fibrillar acidic protein, nestin, and vimentin with activated caspase-3 12 h after ethanol treatment. Finally, we show that the number of primary neurospheres derived from the hippocampi of alcohol-exposed mice is reduced compared to controls. These findings suggest that alcohol exposure in postnatal mice reduces the pool of neural stem/progenitor cells in the DG, and subsequently results in a decrease of adult neurogenesis. This may explain certain aspects of impaired hippocampal functions in FAS.     

Chronic lithium chloride treatment has variable effects on motor behaviour and survival of mice transgenic for the Huntington's disease mutation

Expression of the Huntington's disease (HD) mutation in mice (R6/2 line) causes a progressive neurological phenotype that includes deterioration of motor function resembling that seen in HD. The current study sought to determine whether or not chronic treatment of R6/2 mice with lithium chloride would have an effect on the progression of the phenotype, in light of lithium's reported neuroprotective and anti-depressive properties. Treatment began either before or after the onset of symptoms. Chronic treatment with lithium caused a significant improvement in rotarod performance when treatment was started post- but not pre-symptomatically. There was no overall effect on survival in either group, but further analysis revealed that in the post-symptomatic group, mice could be assigned to one of two distinct groups, depending on the effects of lithium. One subgroup of mice lost weight faster, died earlier and showed rotarod performance similar to the vehicle-treated controls. The other subgroup lost weight at a normal rate, died at a similar age, but showed greatly improved motor performance compared to controls. The improvement in rotarod performance suggests that lithium may improve motor symptoms as well as depression in some HD patients.     

The metabolic profile of early Huntington's disease--a combined human and transgenic mouse study

Huntington's disease (HD) is a debilitating autosomal dominant, neurodegenerative disease with a fatal prognosis. Classical symptoms include motor disturbances, subcortical dementia and psychiatric symptoms but are not restricted to this triad. Patients often experience other problems such as weight loss, although why and when this occurs in the disease course is not known. We studied metabolism using whole body indirect calorimetry in both early stage HD patients and in the R6/2 transgenic mouse model of HD, at times before and after they displayed signs of disease. Using this combined approach we found that patients with early HD tended to be in negative energy balance for reasons not related to their movement disorder, which was paralleled in the transgenic R6/2 mice. These mice had significantly elevated total energy expenditure as they developed overt disease with weight loss due primarily to a loss of muscle bulk. This study has shown for the first time that in HD there is the development of early negative energy balance, which in turn may cause weight loss with loss of muscle bulk in particular. The reason for this is not known but may reflect a catabolic state secondary to hypothalamic pathology, as abnormalities have been reported in the hypothalamus early in the disease course.     

Impaired learning-dependent cortical plasticity in Huntington's disease transgenic mice

Huntington's disease (HD) is a genetically transmitted neurodegenerative disorder. The neuropathology in HD is a selective neuronal cell death in several brain regions including cortex. Although changes in synaptic plasticity were shown within the hippocampus and striatum of HD transgenic mice, there are no studies considering neocortical synaptic plasticity abnormalities in HD. We examined the impact of the HD transgene upon learning-dependent plasticity of cortical representational maps. The effect of associative learning, in which stimulation of a row of vibrissae was paired with appetitive stimulus, upon functional representations of vibrissae in the barrel cortex, was investigated with 2-deoxyglucose brain mapping in presymptomatic R6/1 HD mice. In wild-type mice, cortical representation of the row of vibrissae involved in the training was expanded, while in HD mice the representation of this row was not expanded. The results suggest that presymptomatic R6/1 HD transgenic mice show deficits in plasticity of primary somatosensory cortex.     

Ghrelin‐mediated improvements in the metabolic phenotype in the R6/2 mouse model of Huntington's disease

Huntington's disease (HD) is a heritable neurodegenerative disorder, characterised by metabolic disturbances, along with cognitive and psychiatric impairments. Targeting metabolic HD dysfunction via the maintenance of body weight and fat mass and restoration of peripheral energy metabolism can improve the progression of neurological symptoms. In this respect, we focused on the therapeutic potential of the orexigenic peptide hormone ghrelin, which plays an important role in promoting a positive energy balance. In the present study, we found a significant disruption of circadian metabolic regulation in a R6/2 mouse HD model in the late stage of disease. Daily circadian rhythms of activity, energy expenditure, respiratory exchange ratio and feeding were strongly attenuated in R6/2 mice. During the rest phase, R6/2 mice had a higher total activity, elevated energy expenditure and excessive water consumption compared to control mice. We also found that, in the late stage of disease, R6/2 mice had ghrelin axis deficiency as a result of low circulating ghrelin levels, in addition to down‐regulation of the ghrelin receptor and several key signalling molecules in the hypothalamus, as well as a reduced responsiveness to exogenous peripheral ghrelin. We demonstrated that, in pre‐symptomatic mice, responsiveness to ghrelin is preserved. Chronic ghrelin treatment efficiently increased lean body mass and decreased the energy expenditure and fat utilisation of R6/2 mice in the early stage of disease. In addition, ghrelin treatment was also effective in the normalisation of drinking behaviour and the rest activity of these mice. Ghrelin treatment could provide a novel therapeutic possibility for delaying disease progression; however, deficiency in ghrelin receptor expression could limit its therapeutic potential in the late stage of disease.     

Adenosine A2A receptor antagonism increases nNOS-immunoreactive neurons in the striatum of Huntington transgenic mice

Medium spiny GABAergic projection neurons are progressively lost in Huntington's disease (HD), whereas there is preferential sparing of the few interneurons co-expressing NPY, somatostatin and neuronal nitric oxide synthase.We investigated the effect of the selective adenosine A_2A receptor antagonist SCH58261 (0.01 mg/kg, acutely and chronically administered i.p.) on nNOS striatal expression and motor impairment in R6/2 transgenic mice in clearly symptomatic phase (10–11-week old). SCH58261 chronically administered increased the number of nNOS-immunoreactive neurons (nNOS-IR) in the striatum of R6/2 mice. No glial activation was detected in the striatum or cortex. SCH58261 also improved walking in the inclined plane test but not motor capability evaluated by the rotarod test. These findings demonstrate for the first time a role of adenosine A_2A receptors in regulating nNOS expression in the striatum. We suggest that the protective effect of A_2A antagonism in HD is related to the increase in striatal nNOS-IR neurons.     

Calcineurin inhibitors cause an acceleration of the neurological phenotype in a mouse transgenic for the human Huntington's disease mutation

Calcineurin (CaN) is a Ca(2+)- and calmodulin-dependent protein serine-threonine phosphatase that is thought to play an important role in the neuronal response to changes in the intracellular Ca(2+) concentration. CaN has been implicated in numerous physiological processes including learning and memory. Decreases in CaN expression are thought to be responsible for some of the pathological features seen in brain ischemia, Down's syndrome and Alzheimer's disease. In this study, we examined the possibility of CaN playing a role in the progressive neurological phenotype of the R6/2 mouse of Huntington's disease. We studied the effects of the CaN inhibitors cyclosporin A and FK506 on the progressive neurological phenotype in the R6/2 mouse. We found that an immunosuppressive dose of both drugs dramatically accelerated the main features of the neurological phenotype in R6/2 mice. This was unlikely to be due solely to the immunosuppressive action of these drugs, since treatment with cyclophosphamide, an immunosuppressant drug with a mechanism of action that is not mediated via CaN, did not have deleterious effects on the R6/2 mouse. If anything, cyclophosphamide improved the neurological symptoms in the R6/2 mice. Together, our data suggest a central role for CaN in the deleterious phenotype of the R6/2 mouse. Treatments aimed at preventing the loss of CaN or stimulating its function may be beneficial in the treatment of HD.     

Depletion of rabphilin 3A in a transgenic mouse model (R6/1) of Huntington's disease, a possible culprit in synaptic dysfunction

Huntington's disease (HD) is a hereditary neurodegenerative disorder characterized by progressive psychiatric, cognitive, and motor disturbances. We studied the expression of synaptic vesicle proteins in the R6/1 transgenic mouse model of HD. We observed that the levels of rabphilin 3A, a protein involved in exocytosis, is substantially decreased in synapses of most brain regions in R6/1 mice. The appearance of the reduction coincides with the onset of motor deficits and behavioral disturbances. Double immunohistochemistry did not show colocalization between rabphilin 3A and huntingtin aggregates in the HD mice. Using in situ hybridization, we demonstrated that rabphilin 3A mRNA expression was substantially reduced in the R6/1 mouse cortex compared to wild-type mice. Our results indicate that a decrease in mRNA levels underlie the depletion of protein levels of rabphilin 3A, and we suggest that this reduction may be involved in causing impaired synaptic transmission in R6/1 mice.     

Beneficial effects of rolipram in the R6/2 mouse model of Huntington's disease

We have previously showed that rolipram, a phosphodiesterase type IV inhibitor, displays a neuroprotective effect in a rat quinolinic acid model of HD [DeMarch Z., Giampa C., Patassini S., Martorana A., Bernardi G. and Fusco F.R., (2007) Beneficial effects of rolipram in a quinolinic acid model of striatal excitotoxicity. Neurobiol. Dis. 25:266–273.]. In this study, we sought to determine if rolipram exerts a neuroprotective effect in R6/2 mutant mice, which recapitulates, in many aspects, human HD [Mangiarini L., Sathasivam K., Seller M., Cozens B., Harper A., Hetherington C., Lawton M., Trottier Y., Lehrach H., Davies S.W. and Bates G.P. (1996) Exon 1 of the HD gene with an expanded CAG repeat is sufficient to cause a progressive neurological phenotype in transgenic mice. Cell. 87:493–506]. Transgenic mice were treated with rolipram 1.5 mg/kg daily starting from 4 weeks of age. After transcardial perfusion, histological and immunohistochemical studies were performed. We found that rolipram-treated R6/2 mice survived longer and displayed less severe signs of neurological dysfunction than the vehicle treated ones. Primary outcome measures such as brain volume, striatal atrophy, size and morphology of striatal neurons, neuronal intranuclear inclusions and microglial reaction confirmed a neuroprotective effect of the compound. Rolipram was effective in increasing significantly the levels of activated CREB and of BDNF the striatal spiny neurons, which might account for the beneficial effects observed in this model. Our findings show that rolipram could be considered as a valid therapeutic approach for HD.     

The methamphetamine-sensitive circadian oscillator is dysfunctional in a transgenic mouse model of Huntington's disease

A progressive disintegration of the rest-activity rhythm has been observed in the R6/2 mouse model of Huntington's disease (HD). Rest-activity rhythm is controlled by a circadian clock located in the suprachiasmatic nuclei (SCN) of the hypothalamus, although SCN-independent oscillators such as the methamphetamine (MAP)-sensitive circadian oscillator (MASCO) can also control rhythmicity, even in SCN-lesioned animals. We aimed to test whether or not the administration of MAP could restore a normal rest-activity rhythm in R6/2 mice, via the activation of the MASCO. We administered chronic low doses of MAP to wild-type (WT) and presymptomatic (7-8 weeks) R6/2 mice, in constant darkness. As expected, ~ 40% of the WT mice expressed a rest-activity rhythm controlled by the MASCO, with a period of around 32 h. By contrast, the MASCO was missing from almost 95% of the R6/2 mice, even at early stages of disease. Interestingly, although the MASCO was deficient, initially MAP was able to stabilize the day/night activity ratio in R6/2 mice and delay the onset of disintegration of the rest-activity rhythm driven by the SCN. Furthermore, in presymptomatic R6/2 mice treated with L-DOPA, a MASCO-like component began to emerge, although this never became established. Our data show a major dysfunction of the MASCO in presymptomatic R6/2 mice that is likely to be due to an early abnormality of the catecholaminergic systems. We suggest that the dysfunction of the MASCO in humans could be partially responsible for circadian disturbances observed in HD patients, as well as patients with other neurological diseases in which both catecholaminergic and circadian abnormalities are present, such as Parkinson's disease and schizophrenia.     

Long-term lentiviral-mediated expression of ciliary neurotrophic factor in the striatum of Huntington's disease transgenic mice

Ciliary neurotrophic factor (CNTF) has been shown to prevent behavioral deficits and striatal degeneration in neurotoxic models of Huntington's disease (HD), but its effect in a genetic model has not been evaluated. Lentiviral vectors expressing the human CNTF or LacZ reporter gene were therefore injected in the striatum of wild-type (WT) and transgenic mice expressing full-length huntingtin with 72 CAG repeats (YAC72). Behavioral analysis showed increased locomotor activity in 5- to 6-month-old YAC72-LacZ mice compared to WT-LacZ animals. Interestingly, CNTF expression reduced the activity levels of YAC72 mice compared to control animals. In both WT and YAC72 mice, CNTF expression was demonstrated in striatal punches, up to a year after lentiviral injection. Stereological analysis revealed that the number of LacZ and DARPP-32-positive neurons were decreased in YAC72-LacZ mice compared to WT-LacZ animals. Assessment of the benefit of CNTF expression in the YAC72 mice was, however, complicated by a down-regulation of DARPP-32 and to a lesser extent of NeuN in all mice treated with CNTF. The expression of the neuronal marker NADPH-d was unaffected by CNTF, but expression of the astrocytic marker glial fibrillary acidic protein (GFAP) was increased. Finally, a reduction of the number of striatal dark cells was observed in YAC mice treated with CNTF compared to LacZ. These data indicate that sustained striatal expression of CNTF can be achieved with lentiviruses. Further studies are, however, needed to investigate the intracellular signaling pathways mediating the long-term effects of CNTF expression on dopamine signaling, glial cell activation and how these changes may affect HD pathology.