Improved survival of young donor age dopamine grafts in a rat model of Parkinson's disease

In an attempt to improve the survival of implanted dopamine cells, we have readdressed the optimal embryonic donor age for dopamine grafts. In a rat model of Parkinson's disease, animals with unilateral 6-hydroxydopamine lesions of the median forebrain bundle received dopamine-rich ventral mesencephalic grafts derived from embryos of crown to rump length 4, 6, 9, or 10.5 mm (estimated embryonic age (E) 11, E12, E13 and E14 days post-coitus, respectively). Grafts derived from 4 mm embryos survived poorly, with less than 1% of the implanted dopamine cells surviving. Grafts derived from 9 mm and 10.5 mm embryos were similar to those seen in previous experiments with survival rates of 8% and 7% respectively. The best survival was seen in the group that received 6 mm grafts, which were significantly larger than all other graft groups. Mean dopamine cell survival in the 6 mm group (E12) was 36%, an extremely high survival rate for primary, untreated ventral mesencephalic grafts applied as a single placement, and more than fivefold larger than the survival rate observed in the 10.5 mm (E14) group. As E12 ventral mesencephalic tissues contain few, if any, differentiated dopamine cells we conclude that the large numbers of dopamine cells seen in the 6 mm grafts must have differentiated post-implantation. We consider the in vivo conditions which allow this differentiation to occur, and the implications for the future of clinical trials based on dopamine cell replacement therapy.

Amphetamine induced rotation in the assessment of lesions and grafts in the unilateral rat model of Parkinson's disease

In the unilateral rat model of Parkinson's disease (PD), amphetamine induced rotation is widely used as an index of both lesion deficits and of graft-derived recovery. We have analysed the time course of the rotational response in lesioned rats, and in rats with lesions and dopamine grafts. In lesioned rats, the rotation exhibited a typical dose-dependent response, with low rates of rotation in the first 10 min after injection, rising gradually to a maximum after 20-30 min. Grafted rats exhibited a peak of rotation in the first 10 min after injection, which then fell to a minimum after 30 min. We demonstrate that the response seen in grafted rats is both drug and dose-dependent and show that the rotational profile results from interaction of the grafted and intact striata which exhibit differential temporal responses to the amphetamine.

An investigation of the problem of two-layered immunohistochemical staining in paraformaldehyde fixed sections

In sections of paraformaldehyde fixed brain tissue, stained using immunohistochemical methods, the distribution of staining within the sections is not uniform. Whilst stained cells are seen at the top and bottom surfaces, the central thicknesses of the sections contain little or no immunoreactivity. This presents a major problem for quantification, as each section contains a population of cells that is not visualized by the staining method. Following extensive investigation of this phenomenon, we report that the failure of full thickness, immunohistochemical staining is not a failure of the immunohistochemical methodology per se, nor is it related directly to the thickness of the sections used. Rather, the problem lies in the chemistry of the tissue itself, and originates during fixation of the tissues using paraformaldehyde-based perfusion methods, which render the cell membranes impermeable to one or more components of the staining protocol. We show that this impermeability is affected by addition of membrane-disrupting agents to the fixative, and by a reduction of exposure to paraformaldehyde during fixation. The present investigation contributes to the development of new fixation protocols, optimised for use in both immunohistochemical methods and morphometric analyses.

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.

Comparison of incremental and accelerating protocols of the rotarod test for the assessment of motor deficits in the 6-OHDA model

The rotarod test, in which animals must balance on a rotating drum, is widely used to assess motor deficit in neurodegenerative disease models in rodents. Performance is measured by the duration that an animal stays on the rod as a function of drum speed. Two different protocols are widely used, incremental fixed speeds or an accelerating protocol, but there is little information on their equivalence or the relative power, reliability and sensitivity of the two protocols. The present study was undertaken to compare the incremental fixed-speed and accelerating rotarod protocols on two different lesions of the ascending forebrain dopamine pathways. Three groups of rats were used, controls, rats with 6-OHDA lesions of nigrostriatal bundle, and rats with terminal 6-OHDA lesions within the striatum. Rats were tested at different time points after the lesion. We report that whereas the incremental protocol is more sensitive to detect the presence of a lesion, the accelerating protocol provides a more discriminative test to correlate motor deficits against lesion size.

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.

Delivery of sonic hedgehog or glial derived neurotrophic factor to dopamine-rich grafts in a rat model of Parkinson's disease using adenoviral vectors Increased yield of dopamine cells is dependent on embryonic donor age

The poor survival of dopamine grafts in Parkinson's disease is one of the main obstacles to the widespread application of this therapy. One hypothesis is that implanted neurons, once removed from the embryonic environment, lack the differentiation factors needed to develop the dopaminergic phenotype. In an effort to improve the numbers of dopamine neurons surviving in the grafts, we have investigated the potential of adenoviral vectors to deliver the differentiation factor sonic hedgehog or the glial cell line-derived neurotrophic factor GDNF to dopamine-rich grafts in a rat model of Parkinson's disease. Adenoviral vectors containing sonic hedgehog, GDNF, or the marker gene LacZ were injected into the dopamine depleted striatum of hemiparkinsonian rats. Two weeks later, ventral mesencephalic cell suspensions were prepared from embryos of donor ages E12, E13, E14 or E15 and implanted into the vector-transduced striatum. Pre-treatment with the sonic hedgehog vector produced a three-fold increase in the numbers of tyrosine hydroxylase-positive (presumed dopaminergic) cells in grafts derived from E12 donors, but had no effect on E13-E15 grafts. By contrast, pre-treatment with the GDNF vector increased yields of dopamine cells in grafts derived from E14 and E15 donors but had no effect on grafts from younger donors. The results indicate that provision of both trophic and differentiation factors can enhance the yields of dopamine neurons in ventral mesencephalic grafts, but that the two factors differ in the age and stage of embryonic development at which they have maximal effects.

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.

In vivo transgene expression from an adenoviral vector is altered following a 6-OHDA lesion of the dopamine system

We have investigated the in vivo dynamics of an adenovirus-based, LacZ expressing vector, RAd36, at different doses, when injected unilaterally into the corpus striatum of normal rats. We have further investigated the characteristics of this vector in the presence of a 6-OHDA lesion of the nigrostriatal pathway. The dopamine-depleting lesion had an effect on both the number and the distribution of cells transduced by the adenoviral vector. The lesioned side of the brain contained significantly greater numbers of beta-galactosidase positive cells than the unlesioned side at 3 days, 1 week and 4 weeks post-injection and the distribution of transduced cells was altered by the presence of a dopamine lesion. We conclude that the increased levels of transgene expression seen in the lesioned hemisphere are due to a change in the diffusion characteristics of the injected vector in the lesioned hemisphere. These results indicate that, when investigating the use of virus-based vectors, ultimately for use in gene therapies in the CNS, the in vivo dynamics of the vector need to be assessed not only in the normal brain, but also in the pathological brain state such as animal models of target diseases.

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.

Spatially and temporally restricted chemoattractive and chemorepulsive cues direct the formation of the nigro-striatal circuit

Identifying cellular and molecular mechanisms that direct the formation of circuits during development is thought to be the key to reconstructing circuitry lost in adulthood to neurodegenerative disorders or common traumatic injuries. Here we have tested whether brain regions situated in and around the developing nigro-striatal pathway have particular chemoattractive or chemorepulsive effects on mesencephalic dopamine axons, and whether these effects are temporally restricted. Mesencephalic explants from embryonic day (E)12 rats were either cultured alone or with coexplants from the embryonic, postnatal or adult medial forebrain bundle region (MFB), striatum, cortex, brain stem or thalamus. Statistical analysis of axon growth responses revealed a potent chemoattraction to the early embryonic MFB (i.e. E12-15) that diminished (temporally) in concert with the emergence of chemoattraction to the striatum in the late embryonic period (i.e. E19+). Repulsive responses by dopaminergic axons were obvious in cocultures with embryonic brain stem and cortex, however, there was no effect by the thalamus. Such results suggest that the nigro-striatal circuit is formed via spatially and temporally distributed chemoattractive and chemorepulsive elements that: (i) orientate the circuit in a rostral direction (via brain stem repulsion); (ii) initiate outgrowth (via MFB attraction); (iii) prevent growth beyond the target region (via cortical repulsion); and (iv) facilitate target innervation (via striatal chemoattraction). Subsequent studies will focus on identifying genes responsible for these events so that their products may be exploited to increase the integration of neuronal transplants to the mature brain, or provide a means to (re)establish the nigro-striatal circuit in vivo.

Latency associated promoter transgene expression in the central nervous system after stereotaxic delivery of replication-defective HSV-1-based vectors

The herpes simplex virus type 1 (HSV-1) latency associated promoter (LAP) has been shown to sustain long-term reporter gene expression within sensory neurones. Its activity within the CNS is, however, less well understood. In this study we characterise the activity of the LAP after stereotaxic delivery of recombinant HSV-1-based vectors to the brain. Two classes of vectors were utilised in these studies: (1) a replication-defective vector lacking the glycoprotein H and thymidine kinase genes, designated CS1, and (2) a virus mutant severely impaired for immediate-early (IE) gene expression which lacks functional VP16, ICP4 and ICP0 genes, designated in1388. Both vectors contain the LacZ gene under the control of the LAP. Following delivery of either vector to the striatum, beta-gal expression was detected within anatomically related CNS regions distal to the site of injection. At these sites the number of beta-gal-positive cells increased with time and remained stable up to 4 weeks p.i. beta-Gal expression could not be detected at the site of injection after delivery of CS1 but beta-gal expression within neurones located at this site was observed after delivery of in1388, indicating reduced toxicity of this severely disabled virus. Transgene expression decreased dramatically with both vectors at later time-points (>4 weeks after delivery), but PCR analysis demonstrated that viral genomes were stably maintained for up to 180 days following delivery, indicating that the loss of beta-gal-positive neurones was not likely to be due to a loss of vector-transduced cells. Moreover, after delivery of an equivalent virus to the rat striatum in situ hybridisation analysis showed a similar decrease in the number of neurones expressing the endogenous LATs with time. These data indicate that although the HSV-1 LAP can drive the expression of foreign genes in a variety of CNS neurones, in these cells there is a slow down-regulation of the viral promoter which eventually results in the loss of detectable transgene expression.

The T cell oncogene Tal2 is necessary for normal development of the mouse brain

Transcription factors are commonly involved in leukemia by activation through chromosomal translocations and normally function in cell type(s) that differ from that of the tumor. TAL2 is a member of a basic helix-loop-helix gene family specifically involved in T cell leukemogenesis. Null mutations of Tal2 have been made in mice to determine its function during development. Tal2 null mutant mice show no obvious defects of hematopoiesis. During embryogenesis, Tal2 expression is restricted to the developing midbrain, dorsal diencephalon, and rostroventral diencephalic/telencephalic boundary, partly along presumptive developing fiber tracts. The null mutant mice are viable at birth but growth become progressively retarded and they do not survive to reproductive age. Tal2-deficient mice show a distinct dysgenesis of the midbrain tectum. Due to loss of superficial gray and optical layers, the superior colliculus is reduced in size and the inferior colliculus is abnormally rounded and protruding. Death is most likely due to progressive hydrocephalus which appears to be caused by obstruction of the foramen of Monro (the connection between the ventricles of the forebrain). Thus, in addition to its oncogenicity when ectopically expressed, Tal2 normally plays a pivotal role in brain development and without this gene, mice cannot survive to maturity.

Antioxidant strategy to counteract the side effects of antipsychotic therapy: an in vivo study in rats

The effects of long-term administration of the dopamine D(2) receptor antagonist haloperidol on Parkinsonian symptoms have been shown to persist after cessation of the drug treatment. In order to determine whether the level of tyrosine hydroxylase could be affected by subchronic administration of haloperidol, we examined tyrosine hydroxylase-positive immunoreactive cells in the substantia nigra after blockade of dopaminergic receptors with this antipsychotic. Three weeks of injections with haloperidol (1.5 mg/kg, i.p.) caused a significant decrease in tyrosine hydroxylase-positive cell counts at 24 h (27%), 5 days (21%) and 2 weeks (10%) after the last administration, an effect that was blocked by concurrent administration of the antioxidant, vitamin C. The level of tyrosine hydroxylase returned to baseline after 4 weeks withdrawal, no change being observed at later time-points. Nissl staining demonstrated that no damage to the cell bodies was observed, suggesting that the decrease in tyrosine hydroxylase-positive cells was not due to dopaminergic cell loss. These results demonstrate a depleting action of a short course of haloperidol on nigral tyrosine hydroxylase that outlasts the period of application by 2-4 weeks. Moreover, the current study has shown the effect of the antioxidant vitamin C in protecting haloperidol effects on tyrosine hydroxylase-immunostaining.

The influence of excitotoxic basal ganglia lesions on motor performance in the common marmoset

Huntington's disease is a genetically inherited neurodegenerative disorder for which currently there is no effective treatment or cure. In order to gauge the potential therapeutic benefits of neuroprotective or restorative treatments, it is necessary to create an animal model that is associated with readily measurable and long-lasting functional impairments. The undifferentiated neostriatum and limited behavioural repertoire of rodents have led to the extension of our investigations into the common marmoset. We have used quinolinic acid to create unilateral excitotoxic lesions of the caudate nucleus or the putamen in this small non-human primate. Following rigorous investigation of each monkey on a battery of behavioural tests, we found that the unilateral putamen lesion was associated with a contralateral motor impairment that persisted for at least 9 months and withstood repeated testing. However, the unilateral caudate nucleus lesion did not appear to be associated with any detectable motor deficit. The stability and the reproducibility of the unilateral putamen lesion in the marmoset provide a suitable tool for the investigation of potential treatments for neurodegenerative disorders that attack this region of the brain.

Behavioral recovery after transplantation into a rat model of Huntington's disease: dependence on anatomical connectivity and extensive postoperative training

Rats were trained to perform a conditioned stimulus-response task known to be sensitive to striatal damage, after which they received unilateral excitotoxic striatal lesions. The subsequent implantation of graft tissue into the lesioned striatum was either immediate (9 days) or substantially delayed (70 days). When retested 14 weeks later, all graft and lesion rats were equally impaired initially and biased their responding toward the ipsilateral side. Graft-associated recovery was evident with repeated postoperative testing, but only in rats that had received transplants 9 days postlesion. It is suggested that this training-dependent, graft-associated recovery is mediated specifically by the restored host-graft connections.

Behavioural recovery following striatal transplantation: effects of postoperative training and P-zone volume

Rats were trained on an operant task and then received striatal lesions and grafts. Grafts were derived either from whole-ganglionic eminences or restricted to the lateral eminence. When retested 4 months later; graft-associated behavioural recovery was only apparent with extensive retesting. There was no difference in performance between rats that received whole-dissection or lateral-dissection grafts, and no correlation between performance and the amount of striatal-like (P-zone) tissue within the graft. It is suggested that P-zone reconstruction may be necessary, but not sufficient for behavioural recovery, which may additionally depend upon rehabilitative training.

Myelination and behaviour of tenascin-C null transgenic mice

The extracellular matrix glycoprotein tenascin-C is widely expressed during development and repair, making it surprising that few abnormalities have been found in transgenic mice lacking this molecule. We have therefore re-examined the transgenic mice described by Saga et al. [Saga, Y., Yagi, T., Ikawa, Y., Sakakura, T. & Aizawa, S. (1992) Genes Dev., 6 1821-1831] in which tenascin-C was knocked-out by homologous recombination, focusing on two aspects of the nervous system likely to reveal any abnormalities that might follow the loss of tenascin-C. First, we have determined the pattern of myelin and distribution of oligodendrocyte precursor cells in those areas, such as the optic nerve and retina where local concentrations of tenascin-C have been proposed to act as barriers to oligodendrocyte precursor migration and so prevent inappropriate myelination. Secondly, we have examined the behaviour of the mice in a number of well-characterized tests, e.g. beam-walking, passive avoidance and the Morris water maze. We find no abnormalities of myelination or oligodendrocyte precursor distribution in adult mice, showing that local concentrations of tenascin-C are not the sole mechanism responsible for the pattern of myelination in these regions of CNS. However, we do find a number of behavioural abnormalities in these mice and show that hyperlocomotion and deficits in coordination during beam walking can be ascribed to tenascin-C deficiency. The effects on coordination are, however, not seen on a 129 genetic background. Taken together, these results significantly extend the phenotype associated with tenascin-C deficiency but argue against a role in myelination.

Subthalamic nucleus lesions induce deficits as well as benefits in the hemiparkinsonian rat

Lesions of the subthalamic nucleus can restore some imbalances in motor output of the basal ganglia induced by nigrostriatal dopamine depletion, and have been proposed as a potential therapy for Parkinson's disease. Although there is substantial supporting evidence from experimental studies in both rats and primates, there is less information on the effects of subthalamic lesions alone. In order to characterize potential side effects, the present study evaluates the behavioural effects of unilateral excitotoxic lesions of the subthalamic nucleus in rats that have previously received either unilateral saline or 6-hydroxydopamine injections into the nigrostriatal bundle on the same side. The 6-hydroxydopamine lesions induced ipsilateral orientation asymmetries in head position and body axis bias, rotational asymmetries following injections of direct or indirect dopamine agonists, neglect of contralateral stimuli, and a reduction in the numbers of pellets retrieved with the contralateral paw in a skilled reaching task. Subsequent excitotoxic lesions of the subthalamic nucleus reduced (but did not abolish) rotational asymmetries, had no effects on the measures of neglect and skilled paw-reaching, and produced contralateral orientation biases in head turning and body axis curling. Rats that received subthalamic lesions alone exhibited de novo impairments comprising contralateral biases in the orientation tests. These results support a neuromodulatory role of the subthalamic nucleus in regulating motor outputs of the basal ganglia, and caution that there may be distinct side effects of the lesion by itself. Whereas some impairments attributable to dopamine depletion may be alleviated by subthalamic manipulations, other symptoms are not, or may even be aggravated.

Striatal transplantation in a transgenic mouse model of Huntington's disease

Striatal grafts have been proposed as a potential strategy for striatal repair in Huntington's disease, but it is unknown whether the diseased brain will compromise graft survival. A transgenic mouse line has recently been described in which hemizygotes with an expanded CAG repeat in exon 1 of the HD gene exhibit a progressive neurological phenotype similar to the motor symptoms of Huntington's disease. We have therefore evaluated the effects of the transgenic brain environment on the survival, differentiation, and function of intrastriatal striatal grafts and undertaken a preliminary analysis of the effects of the grafts on the development of neurological deficits in the host mice. Hemizygote transgenic and wild-type littermate female mice received striatal grafts at 10 weeks of age and were allowed to survive 6 weeks. Normal healthy grafts were seen to survive and differentiate within the striatum of transgenic mice in a manner comparable to that seen in control mice. The transgenic mice exhibited a progressive decline in body weight from 9 weeks of age and a progressive hypoactivity in an open field test of general locomotor behavior. Although striatal grafts exerted a statistically significant influence on several indices of this impairment, all behavioral effects were small and did not exert any clinically relevant effect on the profound neurological deficiency of the transgenic mice.

Effects of surgical anaesthesia on the viability of nigral grafts in the rat striatum

Only a small proportion of dopamine neurons in nigral grafts typically survive transplantation into the adult striatum. Since many anaesthetics reduce blood flow and disturb a variety of brain metabolites, surgical anaesthesia may be one of the factors that compromise graft survival. Conversely, the lowered core body temperature induced by some anaesthetics might promote the survival of grafted cells by slowing their metabolism. In an initial screen, the widely-used surgical anaesthetic, equithesin, was found to reduce core temperature, mean arterial blood pressure, and to increase the partial pressure of oxygen in arterial blood without producing any significant alteration in arterial pH or the partial pressure of carbon dioxide. In the main experiment, rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal bundle received dopamine-rich embryonic nigral grafts injected into the deafferented neostriatum via previously implanted guide cannulae, which allowed comparison to be made of graft survival after transplantation into awake and in re-anaesthetised animals. There were no significant differences between groups in either the functional effects of the grafts to compensate amphetamine-induced rotation, or in the survival and growth of the grafts as measured in post mortem histology. We therefore conclude that anaesthesia per se is not a major contributory factor in the relatively poor survival of dopamine neurons following transplantation into the rat striatum.

Effects of metformin on fibrinogen levels in obese patients with type 2 diabetes

OBJECTIVE

To determine fibrinogen levels in obese patients with type 2 diabetes and assess its changes with the use of metformin.

METHODS

60 obese patients (BMI > 27) with type 2 diabetes were studied in an open, two phase, prospective, randomized and comparative study. The pre-treatment phase was a period of four weeks of a controlled diet. In the treatment phase they were divided in two subgroups of 30. One received metformin as a daily single tablet of 850 mg and increasing the dosage to two or three tablets depending on their metabolic control. The second subgroup received 24 units of DNA-recombinant insulin subcutaneously (two thirds of dose before breakfast, and the remaining third before dinner). The insulin dosage was adjusted according to the metabolic response. A control group was formed by 60 non diabetic obese patients with only the controlled diet.

RESULTS

The mean values of plasma glucose, fibrinogen levels and body mass index did not change in the pretreatment phase in controls and diabetics. These parameters decreased significantly in the metformin subgroup in the treatment phase (p < 0.001). Only glucose decreased in the insulin subgroup. There were no changes in the controls.

CONCLUSIONS

In addition to improving metabolic control, metformin showed to be a good therapeutic alternative in modifying fibrinogen levels in type 2 diabetic patients.

Functional integration of striatal allografts in a primate model of Huntington's disease

Huntington's disease is an autosomal dominant, inherited disorder that results in progressive degeneration of the basal ganglia (especially the neostriatal caudate nucleus and putamen) and other forebrain structures and is associated with a clinical profile of movement, cognitive and psychiatric impairments for which there is at present no effective therapy. Neuropathological, neurochemical and behavioral features of the disease can all be reproduced in experimental animals by local injection of excitotoxic or metabolic toxins into the neostriatum. All these features of the disease can be alleviated, at least in rats, by transplantation of embryonic striatal tissue into the degenerated striatum, which was the basis for commencing the first clinical trials of striatal transplantation in Huntington's patients. However, although rat striatal xenografts may temporarily reduce apomorphine-induced dyskinesias in monkeys, there has been no demonstration that allograft techniques that work well in rats translate effectively to the much larger differentiated striatum of primates. Here we demonstrate good survival, differentiation and integration of striatal allografts in the primate neostriatum, and recovery in a test of skilled motor performance. Long-term graft survival in primates indicates probable success for clinical transplants in Huntington's disease; in addition, our data suggest that graft placement has a direct influence on the pattern and extent of functional recovery.

A lateralised grip strength test to evaluate unilateral nigrostriatal lesions in rats

A modified grip strength meter was designed to enable the separate measurement of lateralised grip strength in the two forelimbs of rats, in order to allow assessment of deficits in animals with unilateral lesions and grafts within the basal ganglia. Unilateral 6-hydroxydopamine lesions of the dopaminergic nigrostriatal bundle induced a significant asymmetry, marked by an increased grip strength on the side contralateral to the lesion. Lesioned animals with additional implants of embryonic nigral cell suspensions into the dopamine-denervated neostriatum showed a reduced (but not significant) deficit and did not differ from control performance. The lateralised nature of the deficit excludes explanation based on global activational changes; rather the unilateral deficit may provide a simple test of unilateral 'rigidity' in a widely used rodent model of Parkinson's disease.