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Stephen B Dunnett

Publications and source records attributed to Stephen B Dunnett.

At least 19 recordsLinked to original sources
PubMed2006

Assessment of the relationship between pre-chip and post-chip quality measures for Affymetrix GeneChip expression data.

BACKGROUND: Gene expression microarray experiments are expensive to conduct and guidelines for acceptable quality control at intermediate steps before and after the samples are hybridised to chips are vague. We conducted an experiment hybridising RNA from human brain to 117 U133A Affymetrix GeneChips and used these data to explore the relationship between 4 pre-chip variables and 22 post-chip outcomes and quality control measures. RESULTS: We found that the pre-chip variables were significantly correlated with each other but that this correlation was strongest between measures of RNA quality and cRNA yield. Post-mortem interval was negatively correlated with these variables. Four principal components, reflecting array outliers, array adjustment, hybridisation noise and RNA integrity, explain about 75% of the total post-chip measure variability. Two significant canonical correlations existed between the pre-chip and post-chip variables, derived from MAS 5.0, dChip and the Bioconductor packages affy and affyPLM. The strongest (CANCOR 0.838, p < 0.0001) correlated RNA integrity and yield with post chip quality control (QC) measures indexing 3'/5' RNA ratios, bias or scaling of the chip and scaling of the variability of the signal across the chip. Post-mortem interval was relatively unimportant. We also found that the RNA integrity number (RIN) could be moderately well predicted by post-chip measures B_ACTIN35, GAPDH35 and SF. CONCLUSION: We have found that the post-chip variables having the strongest association with quantities measurable before hybridisation are those reflecting RNA integrity. Other aspects of quality, such as noise measures (reflecting the execution of the assay) or measures reflecting data quality (outlier status and array adjustment variables) are not well predicted by the variables we were able to determine ahead of time. There could be other variables measurable pre-hybridisation which may be better associated with expression data quality measures. Uncovering such connections could create savings on costly microarray experiments by eliminating poor samples before hybridisation.

Artifacts↗
PubMed2006

Fronto-striatal disconnection disrupts operant delayed alternation performance in the rat.

The hypothesis that an intact corticostriatal system is necessary to mediate accurate performance of an operant version of a classic prefrontal cortical task, delayed alternation, is tested using a crossover lesion paradigm in rats. Following an initial midline transection of the genu of the corpus callosum to separate the hemispheres, crossed lesions of the striatum in one hemisphere and the prefrontal cortex in the other produced a significant and stable impairment in delayed alternation performance whereas similar lesions made on the same side had little detectable effect. Accuracy and signal detection analysis of performance across different intertrial intervals indicated that the crossed lesions induced delay-dependent deficits in working memory aspects of corticostriatal function, without changes in low levels of response bias.

Animals↗
PubMed2006

Impaired bidirectional synaptic plasticity and procedural memory formation in striatum-specific cAMP response element-binding protein-deficient mice.

The striatum has a well documented role in procedural learning and memory. However, the synaptic and molecular mechanisms of acquisition and storage of this form of memory remain poorly understood. We examined procedural memory and plasticity in transgenic mice reversibly expressing a dominant-negative cAMP response element-binding protein (CREB) mutant in the dorsal striatum. In these transgenic mice, corticostriatal long-term potentiation and depression are abolished, indicating that CREB function is essential for bidirectional long-term synaptic plasticity in this structure. Importantly, CREB-deficient animals show reversible alterations in several forms of striatum-dependent memory, including footshock avoidance learning and "response" learning in the cross maze. These findings implicate transcriptional regulation by CREB family transcription factors in striatum-dependent information processing and provide the first clear correlation between procedural learning and memory and synaptic plasticity at the corticostriatal synapse.

Animals↗
PubMed2006

Striatal grafts alleviate bilateral striatal lesion deficits in operant delayed alternation in the rat.

In order to assess the capacity of striatal grafts to alleviate cognitive deficits of the frontal type that arise following bilateral striatal lesions, control, lesion and grafted rats were tested in an operant test of delayed alternation. Bilateral striatal lesions induced a marked impairment in choice accuracy, and signal detection analysis indicated that the lesion animals were reliably impaired on both parametric and non-parametric indices of discriminative sensitivity but not of response bias. The impairment was apparent at all intertrial interval delays, including the very shortest, suggesting the deficit is one of frontal-type executive function rather than of short-term memory. The grafted animals exhibited a significant alleviation of the deficit, again apparent at all delays. Histological analyses indicated good graft survival, and injections of a dextran amine anterograde tracer bilaterally into the host prefrontal cortex indicated reformation of extensive projections into the grafted tissues. Since performance of the operant delayed alternation task is dependent upon the integrity of corticostriatal connections, which is disrupted bilaterally by the lesions and restored to the grafts in the transplanted animals, the results corroborate the hypothesis that striatal grafts can alleviate complex cognitive functions of the frontal type by a mechanism that involves functional integration of the grafted neurons into the neural circuits of the host brain.

Animals↗
PubMed2006

The effects of lateralized training on spontaneous forelimb preference, lesion deficits, and graft-mediated functional recovery after unilateral striatal lesions in rats.

The ability of striatal embryonic grafts to promote functional recovery on complex behavioral tasks depends on various factors, including the amount of striatal-like tissue within the grafts and the duration of post-graft training. However, how the innate paw bias of animals is affected by experience, or influences recovery following injury, is less known. Here, we have examined the effects of intrinsic side bias and lateralized limb use training on spontaneous forelimb preference and graft-mediated functional recovery in a skilled reaching task in a rodent model of Huntington's disease. Naïve rats were assessed on their baseline paw preferences when reaching between the bars of their cage to retrieve sugar pellets from a tray attached outside. Next, rats were lesioned unilaterally in the lateral dorsal striatum with quinolinic acid, and 7-10 days later, half of the animals were given suspension grafts prepared from E15 whole ganglionic eminence implanted into the lesioned striatum. The animals then received extensive unilateral training, either ipsi- or contralateral to the side of the lesion and graft in separate subgroups, on the 'staircase' task until asymptotic performance was obtained. As reported previously, the grafts alleviated lesion-induced deficits in retrieving pellets from the contralateral staircase. Spontaneous biases were then reassessed in the cage-reaching task. Irrespective of whether the animal received ipsilateral or contralateral staircase training, the unilateral lesions induced a significant shift in spontaneous bias towards the ipsilateral paw. Grafted animals showed a similar shift in bias if staircase training was given to the ipsilateral paw but showed no change in spontaneous bias (similar to controls) if they had received contralateral training during the post-transplantation period. The results suggest that striatal grafts can alleviate lesion-induced changes in their spontaneous side preferences, but only if they receive extensive training in the use of the contralateral limb, compatible with the notion that recovery is use-dependent.

Animals↗
PubMed2006

Pharmaceutical, cellular and genetic therapies for Huntington's disease.

HD (Huntington's disease) is a devastating neurodegenerative disorder caused by a polyglutamine expansion in the gene encoding the huntingtin protein. Presently, there is no known cure for HD and existing symptomatic treatments are limited. However, recent advances have identified multiple pathological mechanisms involved in HD, some of which have now become the focus of therapeutic intervention. In this review, we consider progress made towards developing safe and effective pharmaceutical-, cell- and genetic-based therapies, and discuss the extent to which some of these therapies have been successfully translated into clinical trials. These new prospects offer hope for delaying and possibly halting this debilitating disease.

Animals↗
PubMed2006

Re-examining the ontogeny of substantia nigra dopamine neurons.

Recently, the need to detail the precise ontogeny of nigrostriatal dopamine neurons has grown significantly. It is now thought that the gestational day on which the majority of these neurons are born is important not only for maximizing the yield of primary cells for transplantation but also for extracting suitable dopamine neural precursors (as stem cells) for expansion in vitro. Historically, peak ontogeny of substantia nigra pars compacta (SNc) dopamine neurons in the rat has been considered to occur around embryonic day (E)14. However, such a concept is at odds with recent studies that reveal not only that substantial numbers of tyrosine hydroxylase-immunopositive cells reside in the ventral mesencephalic region of rats at E14 but that many of these cells have matured extensive axonal projections to the ventral forebrain. Here, then, the ontogeny of SNc neurons in rats commonly used as a source of donor tissue for experimental cell transplantation in animal models of Parkinson's disease has been re-examined. Using a combination of bromodeoxyuridine (BrdU) administration at E11, E12, E13 or E14 with immunocytochemical stainings for both BrdU and tyrosine hydroxylase after 4 weeks of postnatal development, this characterization reveals that the vast majority (perhaps 80%) of SNc dopamine neurons are probably born on E12 in Sprague-Dawley rats. Such findings are important in refining the use of embryonic tissues for primary cell transplantation and may provide more precise timing for identifying the cellular and molecular events that drive neural stem cells toward a dopaminergic phenotype during development.

Animals↗
PubMed2005

EGF and FGF-2 responsiveness of rat and mouse neural precursors derived from the embryonic CNS.

EGF and FGF-2 induce the proliferation of embryonic neural precursors (ENPs) in vitro from a number of different species. In this study, we demonstrate that embryonic age is a crucial determinant of the number and differentiation potential of rat embryonic neural precursor cells responding to either EGF and/or FGF-2, in that (i) there is a differential response to the two growth factors (both alone and in combination) according to the gestational age of isolation and (ii) when allowed to differentiate, there are temporal changes in the ability of these cells to produce neurons. Furthermore, for cultures of all gestational ages, there is a defined pattern of senescence, with cultures expanding longest when cells are isolated earlier in gestation. The suggestion is that rat ENPs in this study consist predominantly of neural progenitor cells with limited division potential rather than self-renewing multipotential neural stem cells. In contrast, mouse ENPs appeared to expand indefinitely and thus allow for longer studies to be carried out looking at the effects of growth factor concentrations. The effect of varying the concentration of EGF was assessed using mouse ENPs.

Animals↗
PubMed2005

The Corridor Task: a simple test of lateralised response selection sensitive to unilateral dopamine deafferentation and graft-derived dopamine replacement in the striatum.

In this experiment, we report a novel drug-free behavioural test of lateralised neglect which is sensitive to unilateral dopamine-denervating lesions and subsequent graft-derived striatal dopamine replacement. For the task, white plastic lids containing sugar pellets were placed along the left and right sides of the floor of a long narrow corridor at regular intervals. Hungry female Sprague-Dawley rats were placed individually into the corridor where they were allowed to make up to 20 pellet retrievals. The number of retrievals each rat made from its left and right sides was counted. Complete mesencephalic or partial nigrostriatal lesions were induced by injection of 6-hydroxydopamine into the medial forebrain bundle or striatum, respectively. Both lesions induced a pronounced ipsilateral retrieval bias in the task. Five weeks after lesion surgery, half of the rats from each lesion group were given E14 ventral mesencephalic cell suspension transplants into the denervated striatum, and were then re-tested in the Corridor Task 5 and 10 weeks later. There was no amelioration of the side bias in rats with medial forebrain bundle lesions. In contrast, in nigrostriatal-lesioned rats, the graft significantly reduced the lesion-induced ipsilateral bias. We conclude that the Corridor Task is a sensitive test of lateralised sensorimotor response selection, and is suitable for assessing deficits and recovery associated with lesions and grafts within the nigrostriatal system.

Animals↗
PubMed2005

Comparison of 6-hydroxydopamine-induced medial forebrain bundle and nigrostriatal terminal lesions in rats using a lateralised nose-poking task with low stimulus-response compatibility.

Experimental therapies for Parkinson's disease are commonly validated in unilateral rat lesion models using simple tests of motor asymmetry such as rotation. However, the human disorder is considerably more complex than this, and alternative tests that yield a more relevant evaluation of the lesion-induced deficit could provide a powerful behavioural tool for analysis of novel therapies. This study evaluated the potential of a lateralised nose-poking task for detailed assessment of the deficit in rats with complete unilateral and partial nigrostriatal terminal lesions induced by unilateral injection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle (MFB) or striatum, respectively. To maximise the task's potential for revealing chronic deficits, a version of the task that requires rats to nose-poke away from visual stimuli associated with food rewards was used. Because of its low stimulus-response compatibility, performance of this version is not mediated by the rats innate tendencies, and thus, is less likely to spontaneously recover after partial lesions. Two weeks and 4 months after lesion surgery, both groups of lesioned rats developed an ipsilateral responding bias with a corresponding drop in contralateral accuracy. Rats with complete (but not partial) lesions also developed a deficit in attempting trials, reacting to stimuli requiring a contralateral nose-poke and executing movements bilaterally. This experiment suggests that the version of the lateralised nose-poking task requiring an arbitrary stimulus-response association may be a powerful behavioural tool for assessment of complete or partial dopamine lesions, and any subsequent dopamine replacement strategy.

Animals↗
PubMed2005

A combination drug therapy improves cognition and reverses gene expression changes in a mouse model of Huntington's disease.

Huntington's disease is a genetic disease caused by a single mutation. It is characterized by progressive movement, emotional and cognitive deficits. R6/2 mice transgenic for exon 1 of the HD gene with 150+ CAG repeats have a progressive neurological phenotype, including deterioration in cognitive function. The mechanism underlying the cognitive deficits in R6/2 mice is unknown, but dysregulated gene expression, reduced neurotransmitter levels and abnormal synaptic function are present before the cognitive decline becomes pronounced. Our goal here was to ameliorate the cognitive phenotype in R6/2 mice using a combination drug therapy (tacrine, moclobemide and creatine) aimed at boosting neurotransmitter levels in the brain. Treatment from 5 weeks of age prevented deterioration in two different cognitive tasks until at least 12 weeks. However, motor deterioration continued unabated. Microarray analysis of global gene expression revealed that many genes significantly up- or down-regulated in untreated R6/2 mice had returned towards normal levels after treatment, though a minority were further dysregulated. Thus dysregulated gene expression was reversed by the combination treatment in the R6/2 mice and probably underlies the observed improvements in cognitive function. Our study shows that cognitive decline caused by a genetic mutation can be slowed by a combination drug treatment, and gives hope that cognitive symptoms in HD can be treated.

Age Factors↗
PubMed2005

Lentivector-mediated delivery of GDNF protects complex motor functions relevant to human Parkinsonism in a rat lesion model.

Although viral vector-mediated delivery of glial cell-line derived neurotrophic factor (GDNF) to the brain has considerable potential as a neuroprotective strategy in Parkinson's disease (PD), its ability to protect complex motor functions relevant to the human condition has yet to be established. In this study, we used an operant task that assesses the selection, initiation and execution of lateralized nose-pokes in Lister Hooded rats to assess the efficacy with which complex behaviours are protected against neurotoxic lesions by prior injection of a lentiviral vector expressing GDNF. Unilateral injection of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle (MFB) caused rats to attempt fewer trials and to make more procedural errors. Lesioned rats also developed a pronounced ipsilateral bias, with a corresponding drop in contralateral accuracy. They were also slower to react to contralateral stimuli and to execute movements bilaterally. Rats that were pre-treated 4 weeks prior to lesion surgery with an equine infectious anaemia virus (EIAV) vector carrying GDNF [EIAV-GDNF, injected into the striatum and above the substantia nigra (SN)] performed significantly better on all of these parameters than control rats. In addition to the operant task, EIAV-GDNF successfully rescued contralateral impairments in the corridor, staircase, stepping and cylinder tasks, and prevented drug-induced rotational asymmetry. This study confirms that GDNF can protect against 6-OHDA-induced impairments in complex as well as simple behaviours, and reinforces the use of EIAV-based vectors for the treatment of PD.

Amphetamine↗
PubMed2005

The survival of neural precursor cell grafts is influenced by in vitro expansion.

Embryonic neural precursor cells (ENPs) provide a potential alternative for transplantation in neurodegenerative diseases, as they can be expanded in culture, avoiding many of the practical obstacles that limit the application of transplanting primary neurones. However, grafts of ENPs into animal models show variable survival and limited differentiation into neurones. The effect of expansion time on their ability to survive and differentiate may be an important factor in this and has not been examined directly. In these experiments, murine and human ENPs were expanded for short (4 weeks) and long (20 weeks) periods before transplantation into the adult rat striatum. Whereas grafts of both short- and long-term expanded human ENPs survived for 4 weeks following transplantation, by 20 weeks all long-term expanded grafts had disappeared. Murine ENPs behaved similarly: only grafts of short-term expanded ENPs survived at 12 weeks following transplantation. RT-PCR analysis of ENP cultures after 4 and 20 weeks of expansion demonstrated changes in expression of a number of different groups of genes. We conclude that long-term expansion of ENPs profoundly impairs their ability to survive long-term after transplantation into the adult brain. This has implications for the potential use of these cells for neural transplantation strategies.

Animals↗
PubMed2005

Optimising plasticity: environmental and training associated factors in transplant-mediated brain repair.

With progressively ageing populations, degeneration of nerve cells of the brain, due to accident or disease, represents one of the major problems for health and welfare in the developed world. The molecular environment in the adult brain promotes stability limiting its ability to regenerate or to repair itself following injury. Cell transplantation aims to repair the nervous system by introducing new cells that can replace the function of the compromised or lost cells. Alternatives to primary embryonic tissue are actively being sought but this is at present the only source that has been shown reliably to survive grafting into the adult brain and spinal cord, connect with the host nervous system, and influence behaviour. Based on animal studies, several clinical trials have now shown that embryonic tissue grafts can partially alleviate symptoms in Parkinson's disease, and related strategies are under evaluation for Huntington's disease, spinal cord injury, stroke and other CNS disorders. The adult brain is at its most plastic in the period following injury, offering a window of opportunity for therapeutic intervention. Enriched environment, behavioural experience and grafting can each separately influence neuronal plasticity and recovery of function after brain damage, but the extent to which these factors interact is at present unknown. To improve the outcome following brain damage, transplantation must make use of the endogenous potential for plasticity of both the host and the graft and optimise the external circumstances associated with graft-mediated recovery. Our understanding of mechanisms of brain plasticity subsequent to brain damage needs to be associated with what we know about enhancing intrinsic recovery processes in order to improve neurobiological and surgical strategies for repair at the clinical level. With the proof of principle beginning to emerge from clinical trials, a rich area for innovative research with profound therapeutic application, even broader than the specific context of transplantation, is now opening for investigation.

Animals↗
PubMed2004

Implicit learning in a serial choice visual discrimination task in the operant 9-hole box by intact and striatal lesioned mice.

Within a broader programme developing murine models of Huntington's disease (HD), we have sought to develop a test of implicit learning for the mouse. Mice were trained in a novel serial visual discrimination task in the '9-hole box' operant test apparatus, followed by retesting after either bilateral quinolinic acid striatal lesions or sham lesions. In the task, each trial involves two sequential responses: an initial light stimulus is presented randomly in one of five holes, to which a nose-poke response results in the first light being extinguished and a second light is illuminated in a different hole. Response to the second light results in food reward, followed by a brief interval before the next trial. When the first light was in one of three of the five holes, the location of the second light was unpredictable in any of the remaining four holes; by contrast, if the first light occurred in one of the other two of the five holes, then the location of the second light was entirely predictable, being the hole two steps to the left or to the right, respectively. Reaction times and accuracy of responding were recorded to both stimuli. The mice learned the task with a degree of accuracy, and they demonstrated clear implicit learning, as measured by increased accuracy and reduced latency to respond to the presentation of the predictable stimulus. Striatal lesions disrupted performance, reducing accuracy for both the first and second stimuli and increasing response latencies for the second stimuli. The decrease in accuracy by the lesioned animals was accompanied by increases in perseverative nose-poking and inappropriate magazine entries throughout the trials, but the lesioned mice still showed a similar benefit (albeit, against a lower baseline of performance) from the implicit knowledge provided on predictable trials. The data validates the task as a sensitive probe for determining implicit learning deficits in the mouse, and suggests that the consequences of striatal lesions, while disrupting performance of skilled stimulus-response habits, are not selective to the process underlying implicit learning.

Animals↗
PubMed2004

Validation of the l-dopa-induced dyskinesia in the 6-OHDA model and evaluation of the effects of selective dopamine receptor agonists and antagonists.

Current treatments for Parkinson's disease (PD) rely on a dopamine replacement strategy and are reasonably effective, particularly in the early stages of the disease. However, chronic dopaminergic therapy is limited by the development of a range of side effects, including dyskinesia. This has led to a search for alternative treatments. Transplantation of foetal nigral dopamine neurons is a rational approach and many studies have shown that it can improve motor functions in parkinsonian rodents, primates and man. Recently, however, two clinical trials have reported an exacerbation of dyskinesias in some transplanted patients, raising concerns about the safety of the transplantation strategy. To study this issue, we have reproduced the l-dopa-induced dyskinesia model developed by Cenci et al. [M.A. Cenci, C.S. Lee, A. Bjorklund, l-DOPA-induced dyskinesia in the rat is associated with striatal overexpression of prodynorphin- and glutamic acid decarboxylase mRNA, Eur. J. Neurosci. 10 (1998) 2694-2706] in the rat. We find that their abnormal involuntary movements rating scale is easy to apply and consistent to use. Moreover, the Schallert forelimb placing test has been used to assess l-dopa-induced recovery of function and we find that the rats continue to show good recovery on this test, even while they are exhibiting abnormal dyskinetic side effects. To further evaluate this model, we have studied the effects of selective dopamine receptor antagonists and agonists for D1, D2 and D3 receptors. Antagonists of all three receptors are able to block the l-dopa-induced dyskinesia without interfering with the beneficial effects of l-dopa on the placing test. This indicates that the effects of chronic l-dopa on recovery of parkinsonian symptoms and on induction of dyskinetic side effects can be dissociated, which may provide the basis for developing novel combination treatments, e.g. using grafts while blocking the unwanted adverse effects of the drugs.

Animals↗