Skilled Forelimb Use Research Articles

Colour-coded pellets increase the sensitivity of the staircase test to differentiate skilled forelimb performances of control and 6-hydroxydopamine lesioned rats

The Montoya staircase test has previously been used to study the skilled forelimb performance of mice and rats following lesions and cell implants in different parts of the central nervous system. Here we describe a modification of the original test design which introduces differently coloured food pellets for each step, and present the results of the new and modified method. In this study unilaterally 6-hydroxydopamine (6-OHDA) lesioned rats and healthy control rats were used. The new evaluation of reaching and grasping movements takes into consideration the various levels of reaching difficulty. The coloured food pellets code for different steps of the staircase. The comparison between the original versus the modified test methods revealed significant differences most prominently on the lower steps. It is important to notice that the pattern of grasping movements in the hemiparkinsonian rats changes from precise reaching (prior to lesion) to shuffling and unsuccessfully trying to reach pellets. The observation of this change in behaviour would not have been obtained through the evaluation of the original staircase test. In summary, the modified staircase test introduces a colour-coded pellet system which obviously increases the test sensitivity and discloses new insights into the skilled forelimb use in a rat model of Parkinson's disease. It may therefore become a valuable tool in future studies related to plasticity-induced changes in skilled forelimb reaching and grasping movements.

Amphetamine promotes task-dependent recovery following focal cortical ischaemic lesions in the rat

This study investigated the effect of amphetamine (AMP) on skilled forelimb use following focal cortical ischaemic lesions in the rat. Unilateral lesions were produced by a novel method of intracortical microinjection of endothelin-1 (ET-1), intended to principally target the forelimb representation zone in primary motor–primary somatosensory cortex. Lesions were placed in the hemisphere contralateral to the preferred limb and produced deficits in skilled forelimb use on two tasks: the paw reach (PR) test and the foot fault (FF) test. Beginning on post-lesion day (D) 2, animals received injections of 2 mg/kg AMP and were injected every third day until D26. Animals were tested both during, and 24 h after, AMP administration. AMP facilitated recovery of skilled forelimb use on the PR test when assessed during drug-free test sessions. No such effect was seen on the FF test. These results demonstrate that sub-acute administration of AMP following a unilateral focal ischaemic lesion of FL can facilitate task-dependent recovery of skilled forelimb use in the rat. They also demonstrate that different behavioural tasks measuring superficially similar behavioural outputs may show different sensitivities to such drug effects.

Impairment of skilled forelimb use after ablation of striatal interneurons expressing substance P receptors in rats: an analysis using a pasta matrix reaching task

Local injection of substance P (SP)-saporin can cause selective ablation of striatal interneurons expressing SP receptors (SPR). In this study, we evaluated quantitatively the impairment of skilled forelimb use after unilateral ablation of the striatal interneurons using a pasta matrix reaching task in rats. We found a significant decrease of the number of the pasta pieces (uncooked spaghetti) retrieved using the paw of the experimental side contralateral to the ablation, whereas the number of the pasta pieces retrieved using the paw of the intact side increased significantly. These findings, with our previous reports, suggest that the modulation of the cortico-striato-entopeduncular direct pathway by striatal interneurons is important for maintaining normal basal-ganglia control for skilled forelimb movements.

Nicotine stimulates dendritic arborization in motor cortex and improves concurrent motor skill but impairs subsequent motor learning

The effect of the premature commitment of neurons to exuberant growth by nicotine on concurrent and subsequent learning is unknown and was the focus of the present study. Animals were trained on a tray reaching for food task (where lots of pieces of chicken feed were available) for 3 weeks before they received two daily injections of nicotine (0.3 mg/kg) or 0.9% saline for 12 days. Measures of tray-reaching performance were obtained before the administration of nicotine and every other week for a total of 7 weeks. Starting on week 8, animals were given a novel motor skill problem that required them to learn to use a forepaw to reach through a slot in a cage for single food pellets located on an external shelf. Pyramidal cells in the forelimb area of both hemispheres were then examined for dendritic length and branching using a Golgi-Cox procedure. Animals treated with saline displayed excellent performance in both reaching tasks and an increase in neuronal branching in Layer V pyramidal cells in the motor cortex contralateral to the reaching paw. In contrast, animals treated with nicotine showed bilateral increases in neuronal branching. Behavioral results showed that nicotine improved forelimb use in the concurrently administered tray-reaching task, but severely degraded quantitative and qualitative scores of skilled forelimb use in the subsequently administered single-pellet reaching task. The results suggest that plasticity coincidence with skilled training is essential to skilled motor learning, but this expenditure can impair subsequent learning.

Behavioral recovery and anatomical plasticity in adult rats after cortical lesion and treatment with monoclonal antibody IN-1

We have previously reported that monoclonal antibody (mAb) IN-1 treatment after ischemic infarct in adult rats results in significant recovery of skilled forelimb use. Such recovery was correlated with axonal outgrowth from the intact, opposite motor cortex into deafferented subcortical motor areas. In the present study, we investigated the effects of mAb IN-1 treatment after adult sensorimotor cortex (SMC) aspiration lesion on behavioral recovery and neuroanatomical plasticity in the corticospinal tract. Adult rats underwent unilateral SMC aspiration lesion and treatment with either mAb IN-1 or a control Ab, or no treatment. Animals were then tested over a 6-week period in the skilled forelimb use task and the skilled ladder rung walking task. We found that animals treated with mAb IN-1 after SMC lesion fully recovered the use of forelimb reaching, but showed no improvement in digit grasping as tested in the skilled forelimb use task. The mAb IN-1 treatment group was also significantly improved as compared to control groups in the skilled ladder rung walking test. Furthermore, neuroanatomical tracing revealed a significant increase in the corticospinal projections into the deafferented motor areas of the spinal cord after mAb IN-1 treatment. These results indicate that treatment with mAb IN-1 after cortical aspiration lesion induces remodeling of motor pathways resulting in recovery in only certain behavioral tasks, suggesting that the cause of brain damage influences behavioral recovery after mAb IN-1 treatment.

Middle age increases tissue vulnerability and impairs sensorimotor and cognitive recovery following traumatic brain injury in the rat

With increasing age comes an increased risk for sustaining traumatic brain injuries (TBI). However, the effect of age is rarely studied in animal models of TBI. The present study evaluated the effect of increased age on recovery of function following bilateral medial frontal cortex injury. Groups of young (3 months) and middle-aged (14 months) rats received bilateral frontal cortex contusions or sham injuries. The rats were tested on a variety of tests to measure sensorimotor performance (bilateral tactile adhesive removal test), skilled forelimb use (staircase test), and the acquisition of reference and working memory in the Morris water maze. Results indicated that injury produced significant impairments on all behavioral tests compared to sham controls. Middle-aged rats that received cortical contusions were significantly impaired on the bilateral tactile adhesive removal test, acquisition of a reference memory task, and working memory compared to young-injured rats. Histological analysis showed that middle-aged rats developed significantly larger lesion cavities but did not show an increase in the number of glial fibrillary acidic protein (GFAP +) cells compared to young-injured rats. Age alone also significantly impaired function on the bilateral adhesive tactile removal test, skilled forelimb use, the acquisition of a reference memory task, and also increased the number of GFAP + cells compared to young rats. These results indicate that middle-aged rats respond to brain injury differently than young rats and that age is an important factor to consider in pre-clinical efficacy studies.

Cortical stimulation improves skilled forelimb use following a focal ischemic infarct in the rat

Improving functional recovery following cerebral strokes in humans will likely involve augmenting brain plasticity. This study examined skilled forelimb behavior, neocortical evoked potentials, and movement thresholds to assess cortical electrical stimulation concurrent with rehabilitative forelimb usage following a focal ischemic insult. Adult rats were trained on a task that required skilled usage of both forelimbs. They then underwent an acute focal ischemic insult to the caudal forelimb area of sensorimotor cortex contralateral to their preferred forelimb. During the same procedure, they also received a stimulation electrode over the infarct area and two depth electrodes anterior to the lesion to record evoked potentials. One week following the surgery, rats received cortical stimulation during performance of the skilled task. Evoked potentials and movement thresholds were also determined. Functional assessment revealed that cortical stimulation resulted in superior performance compared to the no stimulation group, and this was initially due to a shift in forelimb preference. Cortical stimulation also resulted in enhanced evoked potentials and a reduction in the amount of current required to elicit a movement, in a stimulation frequency dependent manner. This study suggests that cortical stimulation, concurrent with rehabilitative training, results in better forelimb usage that may be due to augmented synaptic plasticity.

Treatment with vitamin B3 improves functional recovery and reduces GFAP expression following traumatic brain injury in rats.

Previous studies have shown that administration of vitamin B(3) (B(3)) in animal models of ischemia significantly reduced the size of infarction and improved functional recovery. The present study evaluated the effect of administration of B(3) on recovery of function following traumatic brain injury (TBI), incorporating the bilateral medial frontal cortex contusion injury model. Groups of rats were assigned to B(3) (500 mg/kg) or saline (1.0 ml/kg) treatment conditions and received contusion injuries or sham surgeries. Drug treatment was administered 15 min and 24 h following injury. Rats were examined on a variety of tests to measure sensorimotor performance (bilateral tactile adhesive removal), skilled forelimb use (staircase test), and cognitive ability (reference and working memory) in the Morris Water Maze. Administration of B(3) following injury significantly reduced the behavioral impairments observed on the bilateral tactile removal test, but not on skilled forelimb use. The acquisition of reference and working memory tests were also significantly improved compared to saline-treated rats. Examination of the brains revealed that administration of B(3) significantly reduced the size of the lesion compared to treatment with saline. In addition, examination of glial fibrillary acidic protein (GFAP) expression around the lesion revealed that B(3) significantly reduced the number of GFAP(+) astrocytes. These results indicate that B(3) administration significantly improved behavioral outcome following injury, reduced the size of the lesion, and reduced the expression of GFAP. The current findings suggest that B(3) may have therapeutic potential for the treatment of TBI.

The effects of intracortical endothelin-1 injections on skilled forelimb use: implications for modelling recovery of function after stroke

Different methods of inducing experimental brain lesions can result in distinct neuropathological sequelae. This could be of consequence in attempts to establish animal models of recovery of function following stroke, as differences in the progression of experimental lesion pathology may have an impact on the magnitude and rate of recovery of function observable with any particular lesioning method. In the present study, a novel method of producing a focal ischaemic lesion by intracortical microinjection of endothelin-1 (ET-1) was compared with excitotoxic (microinjection of quinolinic acid) and mechanical (aspiration) lesioning procedures. Lesions were unilateral and were targeted at the forelimb representation zone in sensorimotor cortex. It was found that all three types of lesion had an essentially identical effect with regard to reaching accuracy in a paw-reaching task. All lesioned animals displayed a similar, significant long-term deficit in reaching accuracy and limited degree of recovery relative to sham animals. Off-line analysis of the performance of animals during post-lesion week 9 indicated that animals in each lesion group also displayed a similar deficit. The current results suggest that the spontaneous behavioural consequences of a unilateral lesion of FL in the rat appear to be independent of the nature of lesion production. However, the increased face validity of an ET-1-induced lesion, coupled with the ease of control of lesion placement and extent offered by this technique make for a potentially important animal model for research into drug effects on recovery of function following stroke.

The role of pretraining on skilled forelimb use in an animal model of Huntington's disease.

After a unilateral striatal lesion, animals have generally been seen to have a bilateral impairment in paw reaching, with the contralateral paw being more affected. However, most studies to date have not used a pretraining paradigm to assess maximal capacity for paw reaching, to compare with any lesion-induced loss. This study compared animals that were pretrained with naive animals in their ability to paw reach after a striatal lesion, to address the role of the striatum in either acquisition or execution of this motor task. All lesioned animals showed a significant decrease in reaching ability with their contralateral paw compared with the ipsilateral paw. Pretrained lesioned animals showed a clear lesion deficit with the contralateral paw immediately after lesion, and no impairment whatsoever with the ipsilateral paw. Naive lesioned animals showed delayed acquisition of the task with both paws, possibly due to postural deficits, and a lasting deficit on the contralateral side. The variability of performance between animals was higher in the naive lesioned group. These results suggest that animals should be pretrained on the staircase task prior to lesion to enable maximum sensitivity in detecting both loss and recovery of function of skilled forelimb use.

Effects of neonatal hypoxic–ischemic brain injury on skilled motor tasks and brainstem function in adult rats

In an attempt to establish more sensitive long-term neurofunctional measurements for neonatal hypoxic–ischemic brain injury, we examined skilled motor task and brainstem functions in adult rats after neonatal cerebral hypoxia–ischemia (H-I), using a staircase test and auditory brainstem response (ABR), respectively. Seven-day-old rats underwent a combination of left common carotid artery ligation and exposure to 8% O 2 for 1 h ( n=16). The control animals only received sham operation ( n=16). At 3 months of age, the staircase test and ABR were performed. In the staircase test, H-I animals showed marked impairment of skilled forelimb use in the side contralateral to the occluded artery, and the degree of brain damage correlated significantly to skilled forelimb use. In the ABR, H-I animals showed brainstem dysfunction assessed by measuring interpeak latencies for waves III–V and I–V. We also examined the brainstem with antibodies specific for activated caspase-3, a protein involved in initiation of apoptosis, and observed that caspase-3 was activated in the ipsilateral inferior colliculus at 24 h after H-I. The present study shows that both the staircase test and ABR are sensitive and objective long-term neurofunctional measurements that can be used in future studies to assess therapeutic intervention in this neonatal cerebral H-I model.

Restorative Plasticity of Dopamine Neuronal Transplants Depends on the Degree of Hemispheric Dominance

The ability of dopaminergic (DA) transplants to restore complex sensorimotor behaviors in experimental Parkinson's disease is dependent on graft survival and reinnervation and is likely to be further modified by complex functional graft-host interactions. Here, we examined the impact of hemispheric dominance and extensive testing regimes on the functional capabilities of DA transplants to restore skilled forelimb movements in rats with unilateral 6-hydroxydopamine lesions. Interestingly, a near complete recovery was observed in DA-grafted animals that did not exhibit a strong hemispheric lateralization for paw use before lesion and implantation surgery, whereas animals with a clear lateralization of paw use and grafted into the contralateral hemisphere exhibited only moderate recovery. Finally, animals grafted ipsilateral to the preferred paw were most resistant to functional improvements in skilled forelimb use. However, the influence of hemispheric dominance on the degree of functional DA graft-induced restoration was specific for skilled forelimb use, whereas no such differences were observed in other tests for motor and sensory functions related to the DA system. Furthermore, functional recovery of DA-grafted animals in skilled forelimb use was significantly promoted by extensive behavioral testing regimes indicative of a "learning how to use" the transplant effect. These findings indicate the importance of the underlying functional architecture of complex sensorimotor behaviors, such as skilled forelimb use, and the DA neurotransmitter system for the plasticity of DA transplants to promoting a more complete behavioral recovery in experimental, and potentially, also in clinical forms of Parkinson's disease.

Functional Recovery of Skilled Forelimb Use in Rats Obliged to Use the Impaired Limb after Grafting of the Frontal Cortex Lesion with Homotopic Fetal Cortex

The long-term effect of transplanting embryonic frontal cortex into a unilateral frontal cortex lesion has been studied in adult rats. Before surgery, activity in an open field, muscular strength of both forelimbs, and performance in a paw-reaching-for-food task were scored in 26 rats. In 21 animals a unilateral cortex lesion was then made in the forelimb motor area of the hemisphere contralateral to the preferred paw in the paw-reaching-for-food task, while the other 5 animals were sham-operated. On retesting, the lesion animals changed the preferred paw. A solid homotopic transplant of embryonic tissue (embryonic day 17) was then placed in the lesion cavity in 11 of the lesion rats. Three months later neither lesion alone nor lesion plus transplantation affected open field behavior and muscular strength, but the lesion permanently affected performance in the paw-reaching-for-food task, as shown by a change of preferred paw and a functional deficit in the paw contralateral to the lesion. Transplantation ameliorated the deficits caused by the lesion, but this was only evident when animals were forced to reach with the paw contralateral to the lesion plus transplant. The behavioral results were independent of the size of the lesion and graft. Connections between graft and host tissue were studied by means of the fluorescent tracer 1,1′-dioctadecyl-3,3,3′3′-tetramethylindocarbocyanine perchlorate (DiI). A dense array of labeled fibers was found in the host cortex adjacent to the transplant. The results suggest that functional recovery depends on grafting but is only evident when the animal is obliged to use the affected limb.

The pasta matrix reaching task: a simple test for measuring skilled reaching distance, direction, and dexterity in rats

Skilled forelimb use has been used in many studies to examine motor system status, learning, and recovery from nervous system damage in rats. The dependent measures in many current skilled reaching models rely on endpoint measures, number of successful reaches, or qualitative measures, the movements used in performing a reach. The present study describes a new reaching task, which allows measurement of distance and direction of skilled forelimb movement while also permitting end point and qualitative measurements. Animals reached from a clear Plexiglas box through an aperture to retrieve pieces of straight, uncooked pasta from an array of 260 vertically oriented pieces of pasta arranged in rows distally and laterally away from the aperture (a matrix). By extending the range of a reach, more pasta is obtained. Limb movements, pieces of pasta removed, and the pattern of pasta removal are dependent measures. The usefulness of the test is demonstrated using control, dorsal column lesion, and unilateral dopamine depleted animals. The task uses a desired food, tests learning and skill, the range of limb movement, and the ability to reach for different distances and directions. The task can also be modified to investigate other features of limb use including skill adjustments, laterality, and force.

Comparison of unilateral and bilateral intrastriatal 6-hydroxydopamine-induced axon terminal lesions: evidence for interhemispheric functional coupling of the two nigrostriatal pathways.

Partial lesions of the nigrostriatal dopamine system can be induced reliably by the intrastriatal injection of 6-hydroxydopamine (6-OHDA) and are considered to be analogous to the early stages of human Parkinson's disease. Previous studies have established a clear correlation between different doses and placements of the 6-OHDA toxin and the degree of neurodegenerative changes and behavioral impairments. In the present study, the influence of the interdependence between the two nigrostriatal systems in both hemispheres on the effects on sensorimotor behavioral performances after terminal 6-OHDA lesions was investigated. The behavioral effects were correlated to the extent of nigral dopamine neuron cell and striatal tyrosine-hydroxylase (TH)-positive fiber loss. Sprague-Dawley rats receiving unilateral intrastriatal 6-OHDA injections (4 x 5 microg) exhibited a 30-70% reduction in striatal TH-positive fiber density along an anterior-posterior gradient, an 80% loss of nigral dopamine neurons and a mild degree of behavioral impairments as revealed by amphetamine-induced rotational asymmetry, and a reduced performance in the stepping and postural balance tests. When the same amount of toxin was injected twice into both hemispheres (2 x 4 x 5 microg), additional behavioral deficits were observed, consisting of a significant, but temporary, weight loss, a stable reduction in general locomotor activity and explorational behavior, and a long-term deficit in skilled forelimb use. This is interesting in light of the morphological findings, in which uni- and bilaterally lesioned animals did not differ significantly in the extent of TH-immunoreactive fiber and dopamine neuron loss within the nigrostriatal system in each lesioned hemisphere. These results indicate that the interdependent regulation of the two nigrostriatal systems may provide some compensatory support for the function and behavioral performance of the lesioned side via the normal unlesioned side, which is lost in animals with bilateral lesions of the nigrostriatal system. Therefore, this model of uni- and bilateral partial lesions of the nigrostriatal system, as characterized in the present study, may foster further exploration of compensatory functional mechanisms active in the early stages of Parkinson's disease and promote development of novel neuroprotective and restorative strategies.

Efficacy of disodium 4-[( tert-butylimino)methyl]benzene-1,3-disulfonate N-oxide (NXY-059), a free radical trapping agent, in a rat model of hemorrhagic stroke

Because free radical mechanisms may contribute to brain injury in hemorrhagic stroke, the effect of the free radical trapping agent disodium 4-[( tert-butylimino)methyl]benzene-1,3-disulfonate N-oxide (NXY-059) was investigated on outcome following intracerebral hemorrhage (ICH) in rat. ICH was induced in 20 adult rats by infusion of collagenase into the caudate-putamen. Thirty minutes later rats were treated with NXY-059 (50 mg/kg subcutaneous plus 8.8 mg/kg/h for 3 days subcutaneous delivered via implanted osmotic pumps) or saline (equivalent volumes). Magnetic resonance imaging 24 h after ICH confirmed that the hemorrhage was uniform in the two groups, and subsequent imaging at 7 and 42 days post-ICH showed that the hematoma resolved similarly in the two groups. Behavioral testing on days 1, 3, 7, 14, and 21 after ICH showed that rats treated with NXY-059 had significantly decreased neurological impairment at all times. Deficits in skilled forelimb use 4–5 weeks post-ICH, and in striatal function 6 weeks post-ICH, were not reduced by treatment with NXY-059. Treatment with NXY-059 significantly reduced the neutrophil infiltrate observed 48 h post-hemorrhage in the vicinity of the hematoma, and the number of TUNEL-positive cells 48 h post-hemorrhage at the hematoma margin. However, by 6 weeks there were no differences in neuronal densities in treated and control rats.

Skilled reaching an action pattern: stability in rat ( Rattus norvegicus) grasping movements as a function of changing food pellet size

Many animals in different mammalian orders display skilled forelimb use for prehension, but there has been little study of the rules underlying skilled forelimb use that may provide insight into its neural organization. Inflexibility of movement would imply an underlying fixed neural control characteristic of innate action pattern, whereas flexibility of movement would imply more plastic neural control. In the present study, rat reaching was examined by analyzing movements used to obtain nine different sized food pellets, weighing between 20 and 1000 mg. The prediction was that if the rats’ reaching movements were flexible, then systematic modifications in reaching would occur as food pellet size changed; whereas if reaching was inflexible, disruptions should occur for extreme food pellet sizes. Reaching was filmed using normal (30 frames/s) and high-speed (60 frames/s) video-recording procedures. Behavior was scored in terms of successful reaches and, in addition, a new rating scale, derived from Eshkol–Wachman Movement Notation, was used to evaluate the qualitative aspects of movement. Reaching success was stable across smaller food pellet sizes but dropped sharply for larger food pellets sizes. Qualitative analysis of limb movements revealed that animals were unable to change their typical movement sequence to obtain the larger pellets. This result indicates that rat skilled reaching is relatively inflexible, supporting the position that it is produced by a complex, relatively fixed neural circuitry. This finding is discussed in relation to the evolution of skilled reaching, the modifications of skilled reaching that are observed after motor cortex and other nervous system injuries, and comparative differences in reaching in rats and primates.

Complex sensorimotor behavioral changes after terminal striatal 6-OHDA lesion and transplantation of dopaminergic embryonic micrografts.

In this study sensorimotor behavioral changes were monitored in rats following bilateral 6-hydroxydopamine (6-OHDA) axon terminal lesion and uni- or bilateral implantation of embryonic dopaminergic (DA) micrografts. A total of 28 microg of 6-OHDA was distributed over four injection tracts in the dorsolateral part of the caudate-putamen (CPU) bilaterally followed 4 months later by the implantation of DA micrografts spread over seven implantation tracts placed within the denervated area. Bilaterally 6-OHDA-lesioned animals exhibited significantly reduced behavioral performance scores in tests of explorational and stepping behavior as well as in skilled forelimb use. However, in contrast to the established medial forebrain bundle (MFB) lesion model of PD, these animals showed a spontaneous recovery in the side falling and skilled forelimb behavior and no deficits in overnight locomotor activity at 6 months after the lesion. Unilateral DA micrografts elicited a substantial amphetamine-induced rotational bias contralateral to the graft, but led to a significant impairment of contralateral skilled forelimb use and reduced scores in overnight locomotor activity. Bilateral DA micrografts caused a significant, though partial, increase in explorational and backhand stepping behavior, but resulted also in a significant decrease in performance levels in overnight locomotor activity and skilled forelimb use on both paws. In conclusion, DA grafts placed ectopically in the CPU in the partial lesion model of PD result in a double innervation of the GABAergic striatal neurons, arising from the residual nigrostriatal DA projections of the host and from the graft-derived DA efferent fibers. These two DA fiber systems may indeed function in a cooperative and competitive manner depending on their respective and different afferent and efferent connections, which, in turn, may lead to positive or negative influences on basal ganglia function and behavioral performances. The different patterns of 6-OHDA lesion and transplant-induced behavioral changes demonstrated in the present study compared to the "classical" MFB lesion model of PD may thus provide further insights in the complex functional organization of the basal ganglia and, thereby, may help to further optimize restorative strategies for neurodegenerative diseases, such as Parkinson's disease.

Chapter 11 Transplantation in the rat model of Parkinson's disease: ectopic versus homotopic graft placement

This chapter discusses the attempts to improve the functional efficacy of fetal nigral transplants, focusing on three major questions. First, to what extent is it possible to use multiple intrastriatal grafts to obtain a more complete reinnervation of the striatal complex in the 6-hydroxydopamine (6-OHDA)-lesioned rat, and will such more complete reinnervation provide functional improvements over and beyond that seen after standard more limited transplants? Second, to what extent can dopamine (DA) neurone transplants, placed homotopically in the substantia nigra, induce functional recovery in the 6-OHDA lesion model, and whether their axons can be encouraged to grow to the striatum? Third, to what extent can grafts of inhibitory GABAergic neurons be used to restore function in the rat Parkinson model? Transplantation of fetal DA neurones into the striatum in rats with complete DA-denervating lesions can restore striatal DA fibre densities to approximately 60%–70% of normal levels throughout the striatal complex. Incomplete functional recovery is reported in ectopic grafting. The results summarized in the chapter suggest that intranigral grafting of GABA-rich striatal tissue can induce some functional recovery in drug-induced rotational behavior and in skilled forelimb use. GABA released within the striatal output nuclei may provide a tonic inhibition of striatal outflow, similar to that obtained by high-frequency deep brain stimulation, and may thus offer a new route for therapeutic intervention in Parkinson's disease.

Characterization of Behavioral and Neurodegenerative Changes Following Partial Lesions of the Nigrostriatal Dopamine System Induced by Intrastriatal 6-Hydroxydopamine in the Rat

Partial lesions of the nigrostriatal dopamine system have been investigated with respect to their ability to induce consistent long-lasting deficits in movement initiation and skilled forelimb use. In eight different lesion groups 6-hydroxydopamine (6-OHDA) was injected at one, two, three, or four sites into the lateral sector of the right striatum, in a total dose of 20–30 μg. Impairments in movement initiation in a forelimb stepping test, and in skilled paw use in a paw-reaching test, was seen only in animals where the severity of the lesion exceeded a critical threshold, which was different for the different tests used: single (1×20 μg) or two-site (2×10 μg) injections into the striatum had only small affects on forelimb stepping, no effect on skilled paw use. More pronounced deficits were obtained in animals where the same total dose of 6-OHDA was distributed over three or four sites along the rostro-caudal extent of the lateral striatum or where the injections were made close to the junction of the globus pallidus. The results show that a 60–70% reduction in tyrosine hydroxylase (TH)-positive fiber density in the lateral striatum, accompanied by a 50–60% reduction in TH-positive cells in substantia nigra (SN), is sufficient for the induction of significant impairment in initiation of stepping. Impaired skilled paw-use, on the other hand, was obtained only with a four-site (4×7 μg) lesion, which induced 80–95% reduction in TH fiber density throughout the rostrocaudal extent of the lateral striatum and a 75% loss of TH-positive neurons in SN. Drug-induced rotation, by contrast, was observed also in animals with more restricted presymptomatic lesions. The results indicate that the four-site intrastriatal 6-OHDA lesion may be a relevant model of the neuropathology seen in parkinsonian patients in a manifest symptomatic stage of the disease and may be particularly useful experimentally since it leaves a significant portion of the nigrostriatal projection intact which can serve as a substrate for regeneration and functional recovery in response to growth promoting and neuroprotective agents.