SMAD transcription factors are altered in cell models of HD and regulate HTT expression.

Transcriptional dysregulation is observable in multiple animal and cell models of Huntington's disease, as well as in human blood and post-mortem caudate. This contributes to HD pathogenesis, although the exact mechanism by which this occurs is unknown. We therefore utilised a dynamic model in order to determine the differential effect of growth factor stimulation on gene expression, to highlight potential alterations in kinase signalling pathways that may be in part responsible for the transcriptional dysregulation observed in HD, and which may reveal new therapeutic targets. We demonstrate that cells expressing mutant huntingtin have a dysregulated transcriptional response to epidermal growth factor stimulation, and identify the transforming growth factor-beta pathway as a novel signalling pathway of interest that may regulate the expression of the Huntingtin (HTT) gene itself. The dysregulation of HTT expression may contribute to the altered transcriptional phenotype observed in HD.

Amelioration of non-motor dysfunctions after transplantation of human dopamine neurons in a model of Parkinson's disease.

BACKGROUND: Patients suffering from Parkinson's disease (PD) display cognitive and neuropsychiatric dysfunctions, especially with disease progression. Although these impairments have been reported to impact more heavily upon a patient's quality of life than any motor dysfunctions, there are currently no interventions capable of adequately targeting these non-motor deficits. OBJECTIVES: Utilizing a rodent model of PD, we investigated whether cell replacement therapy, using intrastriatal transplants of human-derived ventral mesencephalic (hVM) grafts, could alleviate cognitive and neuropsychiatric, as well as motor, dysfunctions. METHODS: Rats with unilateral 6-hydroxydopamine lesions to the medial forebrain bundle were tested on a complex operant task that dissociates motivational, visuospatial and motor impairments sensitive to the loss of dopamine. A subset of lesioned rats received intrastriatal hVM grafts of ~9 weeks gestation. Post-graft, rats underwent repeated drug-induced rotation tests and were tested on two versions of the complex operant task, before post-mortem analysis of the hVM tissue grafts. RESULTS: Post-graft behavioural testing revealed that hVM grafts improved non-motor aspects of task performance, specifically visuospatial function and motivational processing, as well as alleviating motor dysfunctions. CONCLUSIONS: We report the first evidence of human VM cell grafts alleviating both non-motor and motor dysfunctions in an animal model of PD. This intervention, therefore, is the first to improve cognitive and neuropsychiatric symptoms long-term in a model of PD.

The 6-OHDA mouse model of Parkinson's disease - Terminal striatal lesions provide a superior measure of neuronal loss and replacement than median forebrain bundle lesions.

Unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway produce side-biased motor impairments that reflect the motor deficits seen in Parkinson's disease (PD). This toxin-induced model in the rat has been used widely, to evaluate possible therapeutic strategies, but has not been well established in mice. With the advancements in mouse stem cell research we believe the requirement for a mouse model is essential for the therapeutic potential of these and other mouse-derived cells to be efficiently assessed. This aim of this study focused on developing a mouse model of PD using the 129 P2/OLA Hsd mouse strain as this is widely used in the generation of mouse embryonic stem cells. Both unilateral 6-OHDA medial forebrain bundle (MFB) and striatal lesion protocols were compared, with mice analysed for appropriate drug-induced rotational bias. Results demonstrated that lesioned mice responded to d-amphetamine with peak rotation dose at 5mg/kg and 10mg/kg for MFB and striatal lesions respectively. Apomorphine stimulation produced no significant rotational responses, at any dose, in either the MFB or striatal 6-OHDA lesioned mice. Analysis of dopamine neuron loss revealed that the MFB lesion was unreliable with little correlation between dopamine neuron loss and rotational asymmetry. Striatal lesions however were more reliable, with a strong correlation between dopamine neuron loss and rotational asymmetry. Functional recovery of d-amphetamine-induced rotational bias was shown following transplantation of E13 mouse VM tissue into the lesioned striatum; confirming the validity of this mouse model.

The lateral neostriatum is necessary for compensatory ingestive behaviour after intravascular dehydration in female rats.

Aberrant striatal function results in an array of physiological symptoms, including impaired consummatory and regulatory behaviours, which can lead to weight loss and dehydration. It was hypothesised, therefore, that cell loss in the neostriatum may contribute to altered fluid intake by regulating physiological signals related to dehydration status. To test this theory, rats with lesions of the lateral neostriatum and sham controls underwent a series of physiological challenges, including the experimental induction of intracellular and intravascular dehydration. No baseline differences in prandial or non-prandial drinking were observed, nor were differences in locomotor activity evident between groups. Furthermore, intracellular dehydration increased water intake in lesion rats in a manner comparable to sham rats. Interestingly, a specific impairment was evident in lesion rats after subcutaneous injection of poly-ethylene glycol was used to induce intravascular dehydration, such that lesion rats failed to adapt their water intake to this physiological change. The results suggest that the striatal lesions resulted in regulatory dysfunction by impairing motivational control over compensatory ingestive behaviour after intravascular hydration, while the physiological signals related to dehydration remain intact. Loss of these cells in neurodegenerative disorders, such Huntington's disease, may contribute to regulatory changes evident in the course of the disease.

Repair of the CNS using endogenous and transplanted neural stem cells.

Restoration of the damaged central nervous system is a vast challenge. However, there is a great need for research into this topic, due to the prevalence of central nervous system disorders and the devastating impact they have on people's lives. A number of strategies are being examined to achieve this goal, including cell replacement therapy, enhancement of endogenous plasticity and the recruitment of endogenous neurogenesis. The current chapter reviews this topic within the context of Parkinson's disease, Huntington's disease and stroke. For each disease exogenous cell therapies are discussed including primary (foetal) cell transplants, neural stem cells, induced pluripotent stem cells and marrow stromal cells. This chapter highlights the different mechanistic approaches of cell replacement therapy versus cells that deliver neurotropic factors, or enhance the endogenous production of these factors. Evidence of exogenously transplanted cells functionally integrating into the host brain, replacing cells, and having a behavioural benefit are discussed, along with the ability of some cell sources to stimulate endogenous neuroprotective and restorative events. Alongside exogenous cell therapy, the role of endogenous neurogenesis in each of the three diseases is outlined and methods to enhance this phenomenon are discussed.

Intrastriatal excitotoxic lesion or dopamine depletion of the neostriatum differentially impairs response execution in extrapersonal space.

Dysfunction of the neostriatum, a primary feature of several neurodegenerative disorders, including Parkinson's disease and Huntington's disease, has been found to result in impaired localisation of, and reaction to, contralateral stimuli. On the basis of previous findings, it is hypothesised that, with increasing eccentricity of the response option, striatal cell loss may impair response localisation at the furthest levels of eccentricity, whereas dopamine (DA) depletion may not impact adversely upon responses executed in this extrapersonal space. In order to elucidate more fully the function of the striatum, the present study examined the differential impact of unilateral DA depletion or excitoxic lesion on response execution in ipsilateral and contralateral space at up to four levels of eccentricity. The results confirmed that, after both types of striatal dysfunction, the sensory ability to detect stimuli remains intact, whereas the ability to direct responses in absolute contralateral space is impaired. Distinct differences in the profiles of impairment were, however, evident, with a marked increase in response omissions observed after DA depletion, which may reflect decreased motivational processing, and recovery of function observed in rats with excitotoxic lesions, which suggests the ability to re-learn. Furthermore, the data demonstrate that, after cell loss, responding in near contralateral space is controlled by competing striata, whereas responding in extrapersonal space relies on the contralateral hemisphere. These results have implications for understanding the role of the striatum in egocentrically defined response localisation, as well as for unravelling the behavioural impact of striatal cell loss or aberrant DA transmission observed in neurodegenerative diseases.

Early onset deficits on the delayed alternation task in the Hdh(Q92) knock-in mouse model of Huntington's disease.

A number of genetic mouse models of Huntington's disease have been created, in order to examine the pathogenesis of Huntington's disease and to test potential therapeutics. In the present study we demonstrate that the full-length knock-in homozygote Hdh(Q92) mice exhibit impairments at 5 months of age on the delayed alternation task, conducted in 9-hole operant chambers. This test is sensitive to cortico-striatal dysfunction and demonstrates again that although Hdh(Q92) mice do not display an overt motor phenotype, they do exhibit clear impairments that can be related to deficits seen in HD patients. This indicates that if appropriately sensitive tasks are used, the more subtle and specific Hdh(Q92) knock-in model could be of use for the examination of pathogenic mechanisms in Huntington's disease and to test potential therapeutics.

Operant-based instrumental learning for analysis of genetically modified models of Huntington's disease.

Huntington's disease is the result of an expanded CAG repeat in the gene that codes for the protein huntingtin and results in a progressive sequelae of motor, cognitive and psychiatric symptoms. The development of genetically modified rodent models of Huntington's disease has led to the need for sensitive behavioural phenotyping. Operant tests for rodents have been developed that can determine the functional deficits in these genetically modified models, from motor, cognitive and emotional domains. The current review discusses tests that employ operant equipment, an automated and highly flexible method for testing rodents. Different operant paradigms are examined in relation to their relevance to Huntington's disease symptomology, as well as summarising research to date on genetic models with these tests.

Gene expression and behaviour in mouse models of HD.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease, resulting in expansion of the CAG repeat in exon 1 of the HTT gene. The resulting mutant huntingtin protein has been implicated in the disruption of a variety of cellular functions, including transcription. Mouse models of HD have been central to the development of our understanding of gene expression changes in this disease, and are now beginning to elucidate the relationship between gene expression and behaviour. Here, we review current mouse models of HD and their characterisation in terms of gene expression. In addition, we look at how this can inform behaviours observed in mouse models of disease. The relationship between gene expression and behaviour in mouse models of HD is important, as this will further our knowledge of disease progression and its underlying molecular events, highlight new treatment targets, and potentially provide new biomarkers for therapeutic trials.

Five choice serial reaction time performance in the HdhQ92 mouse model of Huntington's disease.

Huntington's disease is an autosomal dominant genetic disorder, with motor, cognitive and psychiatric symptoms. To date there is no cure. In order to understand better this disease and to develop novel treatments, many genetically modified animal models of Huntington's disease have been created. However, to utilize these models fully, appropriate functional assays need to be developed for behavioural assessments of the mice. Various facets of attention have been reported to be affected in Huntington's disease patients, and the Hdh(Q92/Q92) mice have been shown to have deficits on operant tasks which have attentional components. In the present study, the Hdh(Q92/Q92) mouse model is assessed on a well established test of attentional function, the operant 5-choice serial reaction time task (5-CSRT), in which the mice must respond with a nose poke to light stimuli presented randomly across a 5 hole light array to receive a reward. In the present paper, the Hdh(Q92/Q92) mice exhibited deficits on the 5-CSRT when pseudorandomly presented with stimuli of different durations. However, alterations in the pacing of the task, therefore requiring an increase in sustained attention, did not affect the Hdh(Q92/Q92) mice more than their wildtype littermates. This study indicates that the Hdh(Q92/Q92) mice may have deficits in aspects of attentional function, in particular disruption in the ability to maintain attention in the visuospatial domain, suggesting that this knock-in mouse model of Huntington's disease may be a relevant model of the disease for the testing of novel therapeutic interventions.

Increased efficacy of the 6-hydroxydopamine lesion of the median forebrain bundle in small rats, by modification of the stereotaxic coordinates.

The 6-hydroxydopamine (6-OHDA) lesion is the most widely used rat model of Parkinson's disease. A single unilateral injection of 6-OHDA into the median forebrain bundle (MFB) selectively destroys dopamine neurons in the ipsilateral substantia nigra pars compacta (SNc) and ventral tegmental area (VTA), removing more than 95% of the dopamine innervation from target areas. The stereotaxic coordinates used to deliver 6-OHDA to the MFB have been used in our laboratory successfully for more than 25 years. However, in recent years we have observed a decline in the success rate of this lesion. Previously regular success rates of >80% of rats lesioned, have become progressively more variable, with rates as low as 20% recorded in some experiments. Having excluded variability of the neurotoxin and operator errors, we hypothesized that the change seen might be due to the use of smaller rats at the time of first surgery. An attempt to proportionally adjust the lesion coordinates base on head size did not increase lesion efficacy. However, in support of the small rat hypothesis it was observed that, using the standard coordinates, rat's heads had a "nose-up" position in the stereotaxic fame. Adjustment of the nose bar to obtain a flat head position during surgery improved lesion success, and subsequent adjustments of the lesion coordinates to account for smaller head size led to a greatly increased lesion efficacy (>90%) as assessed by amphetamine induced rotation.

Medical terminations of pregnancy: a viable source of tissue for cell replacement therapy for neurodegenerative disorders.

"Proof-of-principle" that cell replacement therapy works for neurodegeneration has been reported, but only using donor cells collected from fetal brain tissue obtained from surgical terminations of pregnancy. Surgical terminations of pregnancy represent an increasingly limited supply of donor cells due to the tendency towards performing medical termination in much of Europe. This imposes a severe constraint on further experimental and clinical cell transplantation research. Therefore, we explore here the feasibility of using medical termination tissue as a donor source. Products of conception were retrieved from surgical terminations over the last 7 years and from medical terminations over the last 2.5 years. The number of collections that yielded fetal tissue, viable brain tissue, and identifiable brain regions (ganglionic eminence, ventral mesencephalon, and neocortex) were recorded. We studied cell viability, cell physiological properties, and differentiation potential both in vitro and following transplantation into the central nervous system of rodent models of neurodegenerative disease. Within equivalent periods, we were able to collect substantially greater numbers of fetal remains from medical than from surgical terminations of pregnancy, and the medical terminations yielded a much higher proportion of identifiable and dissectible brain tissue. Furthermore, we demonstrate that harvested cells retain the capacity to differentiate into neurons with characteristics appropriate to the region from which they are dissected. We show that, contrary to widespread assumption, medical termination of pregnancy-derived fetal brain cells represent a feasible and more readily available source of human fetal tissue for experimental cell transplantation with the potential for use in future clinical trials in human neurodegenerative disease.

Context-driven changes in L-DOPA-induced behaviours in the 6-OHDA lesioned rat.

Both contralateral rotational behaviour and dyskinetic abnormal involuntary movements (AIMs) are induced by the administration of l-DOPA in the unilateral 6-OHDA lesioned rat model of Parkinson's disease. Since rotational responses can be conditioned to environmental cues we have investigated the extent to which drug-induced AIMS may also be conditioned by exteroceptive cues and experience. In Experiment I, 6-OHDA lesioned rats received repeated daily injections of l-DOPA either in their home cage (control) or in association with a brief (20 mins) exposure to the rotometers (paired). To assess conditioning, all animals then received two tests in the rotometer bowls. Following injection of saline the paired group both rotated more contralaterally and displayed manifest AIMs, neither of which were exhibited by the control rats. Moreover, following injection of l-DOPA, the paired group showed a trend for increased AIMs compared to controls. Two further studies provided longer exposure to the conditioning environments in counterbalanced designs. Although, using these parameters, re-exposure in the presence of saline did not induce context-dependent AIMs, a strong context-specific component of the sensitised response to l-DOPA was seen; chronic administration of drug produced a significantly stronger behavioural response in animals paired with a particular environment for drug administration than controls. This data suggests that part of the sensitisation of behavioural responding to l-DOPA administration is not solely a pharmacological phenomenon, but is also conditioned to the environmental context in which the drug is administered. This has clear implications for the clinical observation and experimental measurement of drug-induced dyskinesia in Parkinson's disease patients and animal models.

Aberrant dopamine transmission and cognitive dysfunction in animal models of Parkinson's disease.

Due to the relative success of therapeutic interventions aimed at treating the overt motor symptoms evident in Parkinson's disease (PD), a greater appreciation of the non-motor aspects of the disease has emerged in recent time. Indeed, evidence suggests that impairments in emotional processing, behavioural control and cognitive function may emerge early in the onset of the disease. Decades of experimental research have seen the development of diverse animal models, all of which have aimed to mimic the characteristic features of the disease process including the dopaminergic neural cell loss, the molecular neuropathology and the concomitant behavioural impairments. The following review provides an overview of the use of animal, particularly rodent, models in the quest to obtain a greater understanding of the role of corticostriatal dopamine in cognitive and neuropsychiatric functions. Given the limitations of using the available rodent models of PD, including altered motor and motivational function, it has become necessary to employ a range of techniques to eke out the precise function of this neurotransmitter in corticostriatal function. Combinations of lesion and pharmacological studies have allowed the assessment of dopamine depletion and precise receptor populations in the learning or expression of a range of executive functions, which has gained us considerable insight into the relationship between the neuropathology that occurs in PD and the resulting impairments in cognitive and neuropsychiatric function.

Challenges facing quantification of rat locomotion along beams of varying widths.

Optoelectronic motion capture systems have been widely used to investigate temporal gait parameters in humans and animals in order to understand function and behavioural attributes of different pathologies, e.g. Parkinson's disease (PD). The aim of the present paper was to investigate the practicality of utilising this system to investigate the effects of a unilateral 6-hydroxydopamine (6-OHDA) lesion on rat locomotion while walking on beams of varying widths (graduated, narrow, and wide). Temporal gait parameters of ten male Lister Hooded rats (five controls and five hemiparkinsonian) were observed using passive markers placed in locations that were representative of their four limbs and their body axis. The results demonstrate that marker-based motion capture can provide an effective and simple approach to quantifying temporal gait parameters for rat models of PD. They also reveal how the width of the path affects the locomotion in both experimental cohorts. Such measurements can be compared with human motion analysis to explore correlations between the animal model and human behaviour, which is an important step for translational medicine.

A simple breeding protocol for the procurement of accurately staged rat donor embryos for neural transplantation.

Obtaining accurately staged rat embryos can be difficult because of the variety of breeding protocols employed and because precise staging cannot be confirmed until excision of the embryos from the dam. The detection of estrus, pairing of animals, and confirmation of pregnancies is generally left to commercial suppliers, as in-house breeding can be laborious and unpredictable. Here we describe a simple, reliable in-house breeding protocol for the generation of accurately staged embryos as assessed by measurements of average crown to rump length (CRL).