Neonatal striatal grafts prevent lethal syndrome produced by bilateral intrastriatal injection of kainic acid

Longitudinal characterization of cognitive and motor deficits in an excitotoxic lesion model of striatal dysfunction in non-human primates

As research progresses in the understanding of the molecular and cellular mechanisms underlying neurodegenerative diseases like Huntington's disease (HD) and expands towards preclinical work for the development of new therapies, highly relevant animal models are increasingly needed to test new hypotheses and to validate new therapeutic approaches. In this light, we characterized an excitotoxic lesion model of striatal dysfunction in non-human primates (NHPs) using cognitive and motor behaviour assessment as well as functional imaging and post-mortem anatomical analyses. NHPs received intra-striatal stereotaxic injections of quinolinic acid bilaterally in the caudate nucleus and unilaterally in the left sensorimotor putamen. Post-operative MRI scans showed atrophy of the caudate nucleus and a large ventricular enlargement in all 6 NHPs that correlated with post-mortem measurements. Behavioral analysis showed deficits in 2 analogues of the Wisconsin card sorting test (perseverative behavior) and in an executive task, while no deficits were observed in a visual recognition or an episodic memory task at 6 months following surgery. Spontaneous locomotor activity was decreased after lesion and the incidence of apomorphine-induced dyskinesias was significantly increased at 3 and 6 months following lesion. Positron emission tomography scans obtained at end-point showed a major deficit in glucose metabolism and D2 receptor density limited to the lesioned striatum of all NHPs compared to controls. Post-mortem analyses revealed a significant loss of medium-sized spiny neurons in the striatum, a loss of neurons and fibers in the globus pallidus, a unilateral decrease in dopaminergic neurons of the substantia nigra and a loss of neurons in the motor and dorsolateral prefrontal cortex. Overall, we show that this robust NHP model presents specific behavioral (learning, execution and retention of cognitive tests) and metabolic functional deficits that, to the best of our knowledge, are currently not mimicked in any available large animal model of striatal dysfunction. Moreover, we used non-invasive, translational techniques like behavior and imaging to quantify such deficits and found that they correlate to a significant cell loss in the striatum and its main input and output structures. This model can thus significantly contribute to the pre-clinical longitudinal evaluation of the ability of new therapeutic cell, gene or pharmacotherapy approaches in restoring the functionality of the striatal circuitry.

Effects of NGF, b-FGF, and cerebrolysin on water maze performance and on motor activity of rats: short- and long-term study

The effects of 14-day treatments with nerve growth factor (NGF), basic fibroblast growth factor (b-FGF), or the peptidergic drug Cerebrolysin on postlesion acquisition of a water maze task and on motor activity were evaluated. Rats were tested in the Morris water maze 14 days (early test) and 7 to 8 months (delayed test) after a bilateral lesion of the frontoparietal (sensorimotor) cortex. Only the rats treated with Cerebrolysin performed the water maze task at the level of the nonlesioned controls in the early test. No short-term effect of NGF (6.5 ng/14 days; 38 ng/ml) or b-FGF (17 ng/14 days; 100 ng/ml) treatment was found. The delayed test revealed that water maze performance was restored in rats treated with b-FGF in comparison with intact controls. The data showed that b-FGF can support or initiate processes in the CNS that lead to a delayed functional amelioration and/or compensation for a water maze performance deficit. NGF did not influence the acquisition impairment caused by a sensorimotor cortical lesion. Two-week administration of Cerebrolysin had a time-dependent influence: it attenuated the acquisition deficit and increased the motor activity of rats, both effects declined to the level of lesioned controls within 8 months.

Neural transplantation as an experimental treatment modality for cerebral ischemia

Cerebrovascular disease exemplifies the poor regenerative capacity of the CNS. While there are methods to prevent cerebral infarction, there is no effective therapy available to ameliorate the anatomical, neurochemical and behavioral deficits which follow cerebral ischemia. Focal and transient occlusion of the middle cerebral artery (MCA) in rodents has been reported to result in neuropathology similar to that seen in clinical cerebral ischemia. Using specific techniques, this MCA occlusion can result in a well-localized infarct of the striatum. This review article will provide data accumulated from animal studies using the MCA occlusion technique in rodents to examine whether neural transplantation can ameliorate behavioral and morphological deficits associated with cerebral infarction. Recent advances in neural transplantation as a treatment modality for neurodegenerative disorders such as Parkinson's disease, have revealed that fetal tissue transplantation may produce neurobehavioral recovery. Accordingly, fetal tissue transplantation may provide a potential therapy for cerebral infarction. Preliminary findings in rodents subjected to unilateral MCA occlusion, and subsequently transplanted with fetal striatal tissue into the infarcted striatum have produced encouraging results. Transplanted fetal tissue, assessed immunohistochemically, has been demonstrated to survive and integrate with the host tissue, and, more importantly, ameliorate the ischemia-related behavioral deficits, at least in the short term. Although, this review will focus primarily on cerebral ischemia, characterized by a localized CNS lesion within the striatum, it is envisioned that this baseline data may be extrapolated and applied to cerebral infarction in other brain areas.

Time course of the neuroprotective effect of transplantation on quinolinic acid-induced lesions of the striatum

Injection of quinolinic acid in the rat striatum mimics neurochemical changes observed in Huntington's disease. We previously demonstrated that intrastriatal transplantation of fetal striatum or gelfoam protects against toxicity induced by a subsequent intrastriatal injection of quinolinic acid performed one week later. Herein, we examined whether fetal striatum or sham transplantation provides protection against quinolinic acid that lasts up to four weeks. Intrastriatal quinolinic acid injection produces neuronal loss and gliosis in Nissl staining, loss of cytochrome oxidase histochemical staining, decrease in autoradiographic binding of [3H]SCH 23390-labeled dopamine D1 and [3H]CGS 21680-labeled adenosine A2 receptors, and increase in autoradiographic binding of [3H]PK 11195-labeled peripheral benzodiazepine binding sites. None of these changes was observed in rats transplanted with fetal striatum one, two or four weeks before quinolinic acid injection. In animals transplanted with fetal striatal tissue, Nissl staining showed healthy grafts located in normal appearing striata. Although sham transplantation performed one week before quinolinic acid injection also protected against histological, histochemical and binding changes, sham transplantation performed two or four weeks before quinolinic acid injection was less effective in attenuating quinolinic acid-induced striatal toxicity. Thus, sham transplantation provides transient protection against quinolinic acid-induced striatal toxicity, whereas implantation of tissue such as fetal striatum seems to be required for long-lasting protection. Our study suggests that intracerebral transplantation may also act through other mechanisms than restoration of deficient neurotransmitters or damaged pathways, a finding which may have significant clinical implications in assessing the potential benefit of this approach for the treatment of neurodegenerative disorders such as Huntington's disease.

Unilateral grafting of fetal neocortex into a cortical cavity improves healing of a symmetric lesion in the contralateral cortex of adult rats

Fetal neocortical tissue (ED 14) was grafted unilaterally into a cortical cavity made bilaterally in the sensorimotor cortex of adult rats. Transplantation was done immediately after the lesion (group TR0, n = 8) or with 14-day delay (group TR14, n = 8). Six rats served as lesion only controls (group LES). After long-term survival (up to 15 months) the brains were photographed and surface areas of transplant and contralateral cavities were measured by means of a graphic tablet. The results show that (a) the presence of a transplant in one lesion cavity in the cortex decrease the size of a similar cavity in the contralateral cortex and that (b) the better host transplant integration there is, the greater the effect on the contralateral lesion. No correlation between the size of the transplant and the size of the symmetric traumatic lesion was found. The ameliorating effect of the transplant on the contralateral cortical lesion size is most likely related the long-term influence of growth of trophic factors released by transplanted cells which lead to the healing of the symmetric lesion.

Behavioral effects of fetal neural transplants: relevance to Huntington's disease

Animal models of Huntington's disease (HD) and other neurological disorders have proven useful for examining the anatomical, neurochemical, and behavioral alterations in these diseases. Investigators have taken advantage of new excitotoxic models that appear to successfully simulate the neurobiological and behavioral characteristics of HD with remarkable homology. Selective excitotoxic compounds allow for a more precise and controlled lesion with which to examine the relationship between striatal damage and behavioral abnormalities. In addition, these models provide new approaches for developing and testing various treatments for HD. Fetal neural tissue transplanted into the excitotoxin-lesioned animal can integrate with the host brain and promote neurochemical and functional recovery. Neural grafting paradigms may be viewed as potential therapies for treating neurodegenerative diseases and as aids in deciphering the regenerative mechanisms of the central nervous system. Further research is necessary, however, to determine the negative and positive effects of neural transplantation. In addition, existing behavioral models need to be refined to allow for better evaluation of the subtle topographic changes in behavior resulting from fetal tissue transplantation.

Striatal implants protect the host striatum against quinolinic acid toxicity

Quinolinic acid (QA) and related excitotoxins produce a pattern of neuronal loss and neurochemical changes in the rat striatum similar to that of patients suffering from Huntington's disease, suggesting neurotoxicity is important in the etiology of that disease. Thus, strategies for limiting excitotoxin-induced striatal damage, like that caused by QA, may be of great benefit to these individuals. Accordingly, we tested the ability of both neural and non-neural tissue implants to protect the rat striatum against a subsequent QA challenge. Our results demonstrated that recipients of fetal striatal grafts were significantly less affected by striatal injections of QA than non-grafted animals. In contrast to the latter, fetal striatal tissue recipients did not exhibit apomorphine-induced rotation behavior and showed a sparing of cholinergic and enkephalinergic systems normally lost following QA injections. Animals grafted with adult rat sciatic nerve, adrenal medulla or adipose tissue all showed a less dramatic behavioral protection and sparing of cholinergic and enkephalinergic systems. These results suggest that fetal striatal tissue exerts an optimal, and perhaps specific protective influence on the host brain.

Adrenal chromaffin cells as transplants in animal models of Parkinson's disease

The field of neural transplantation has moved rapidly forward in the last decade. Initially, fetal cells were used as implants to investigate their potential to ameliorate deficits in animal models of Parkinson's disease. However, because of the moral and legal problems associated with the use of fetal tissues in humans, alternative sources of donor tissue were sought which possessed the structural and functional characteristics needed to improve motor function in Parkinsonian patients. To date, one of the most promising tissues being investigated is the adrenal medulla, whose chromaffin cells possess an inherent plasticity of form and function. Transplanted chromaffin cells currently are being studied by a variety of approaches, including electron microscopy, in mouse, rat, and primate models of Parkinson's disease. An overview of the role of the chromaffin cell in this exciting and clinically important arena is briefly reviewed, with an emphasis on the fine structure of implanted chromaffin cells.

Implantation of dispersed cells into primate brain

Although several experimental therapies such as dopaminergic cell implantation in parkinsonian models and intratumoral placement of lymphokine-activated killer cells require intracerebral deposition of dispersed cell suspensions, a successful technique of needle implantation of cells into primate brain has not been demonstrated. The authors have sought to establish a stereotaxic technique to predictably deposit dispersed cells in primate brain. Human lymphocytes were cultured in recombinant interleukin-2, labeled with sodium 51 chromate (51Cr), and stereotaxically injected into the frontal white matter of six anesthetized rhesus monkeys. A 10-microliters aliquot of cell suspension (2 X 10(7) cells/ml) was deposited 16 mm deep to the dura at 5 microliters/min via Hamilton No. 22s or 26s needles. Five control aliquots were counted for each injection. Reflux out of the needle track was absorbed on gauze, and the recovered cells were counted. The animals were sacrificed 1 hour after implantation and the brain was removed and sectioned such that the cortex and white matter along the needle track were separate. The tissue sections were then counted. Recovery was expressed as the percentage of total injected radioactivity (cpm) that was present in each brain section. Two additional injected hemispheres were processed for autoradiography and histological study. Cell recovery in the brain (mean +/- standard deviation) was 87.2% +/- 13.9% (3.3% +/- 4.9% in cortex and 83.9% +/- 15.9% in white matter). The autoradiograms and histological examination showed a dense accumulation of radioactivity (cells) at the target site and minimal radioactivity (cells) in the needle track. Accurate intracerebral deposition of dispersed cells in primates was achieved with the technique described. This knowledge permits reliable stereotaxic implantation of cells into the brains of nonhuman primates and humans for investigation and therapy.

Alteration of kainic acid and quinolinic acid toxicity by neostriatal transplants in vitro

Mature (greater than 21 days in vitro) organotypic corticostriatal cultures prepared from newborn rat brain were incubated in either kainic acid (KA) 10(-3) M or quinolinic acid (QUIN) 10(-3) M for up to 48 h. Other identical cultures were similarly incubated immediately after they had received one or two additional explants of neonatal striatal tissue placed beside each corticostriatal culture. The cultures incubated with either KA or QUIN in the presence of the neonatal striatal tissue showed better preservation than cultures incubated with KA or QUIN alone. Results suggest that the neonatal striatal explants or 'transplants' afford some protective effect against the toxicity or either KA or QUIN.

Functional effects of fetal striatal transplants

Much interest has been generated in recent years by the finding that fetal brain tissue transplants into adult brain can survive and grow in the host brain. Most work has been done transplanting relatively homogeneous populations of dopaminergic nigral neurons. However, it is now clear that the more complex fetal striatal tissue, which contains multiple neuronal types, will also survive and grow when transplanted into excitotoxin-lesioned adult striatum. We review herein studies demonstrating that the fetal striatal transplants are functional in that they can elicit changes in behavior in the transplant recipients. The striatal transplants reverse the locomotor hyperactivity characteristic of bilateral excitotoxin lesions. However, there is some controversy about the reversal of the abnormal apomorphine- and amphetamine-induced locomotor responses by fetal striatal transplants into excitotoxin-lesioned striatum and the presence of absence of dopamine receptors within the transplanted tissue. We review the evidence for and against the existence of neuroanatomical connections between the host brain and the transplanted fetal striatal tissue. We also point out the possibility of neurotrophic factors mediating the recovery of spontaneous locomotor activity in light of recent evidence that neurotrophic factors may mediate the functional recovery following transplants of adrenal medulla tissue into dopaminergic deafferented striatum.

Striatal grafts provide sustained protection from kainic and quinolinic acid-induced damage

Grafts of neonatal striatal tissue were placed into the striata of adult rats. When challenged immediately with intrastriatal injections of either kainic or quinolinic acid, excitotoxic damage was prevented. Thirty days later these same graft recipients received another injection of excitotoxin. The intrastriatal grafts continued to mitigate toxin-induced damage. It is hypothesized that the grafted cells not only survive, but that they may continue to elaborate some substance or substances that prevent excitotoxin-induced injury for at least 30 days. Previous investigations indicated that grafts of neonatal striatal tissue can protect the recipient striatum from kainic acid toxicity. In the following study it is demonstrated that such grafts also protect the striatum from quinolinic acid, an endogenous excitotoxin which induces kainate-like neuronal degeneration and has been implicated in the pathogenesis of Huntington's disease. It is postulated that the salutary effect of striatal grafting may be sufficiently long lasting to mitigate a chronic toxic insult. Such grafting may therefore represent a therapy for Huntington's disease and other neurodegenerative disorders in which an endogenous or exogenous toxin has been implicated as the pathogenetic agent.

Fetal hypothalamic brain grafts reduce the obesity produced by ventromedial hypothalamic lesions

Bilateral destruction of the rat ventromedial hypothalamus (VMH) produces a syndrome characterized by hyperphagia and obesity. In the present study we examined whether grafts of fetal hypothalamus could reverse the effects of this lesion. Three groups of adult rats received bilateral electrolytic lesions of the VMH. The first group of animals was then implanted with embryonic day 14-16 hypothalamic tissue by stereotaxic injection into the lesion sites. The second series of animals received comparable-sized grafts from a variety of non-hypothalamic regions of the fetal CNS. The third group experienced similar VMH lesions but did not receive any tissue grafts. After surgery, body weight and food consumption were recorded daily for up to 8 weeks. These measures were compared with similar ones obtained from non-operated rats. Hyperphagia and obesity were consistently observed in all of the lesioned animals not bearing transplants. An initial period of weight gain was also observed in animals receiving hypothalamic grafts, but the duration of the 'dynamic' phase of this syndrome was reduced. Consequently, these graft recipients exhibited significantly less weight gain. This depressed weight gain, however, did not coincide with a statistically significant decrease in hyperphagia. Transplantation of non-hypothalamic tissue also caused an attenuation of the VMH-lesion effect but this was more modest than that induced by homotopic grafts. The results of this experiment show that homotopic transplants can alter the dynamics of weight gain induced by bilateral VMH lesions. However, lesion-induced hyperphagia was not completely reversed in these grafted animals. The fact that other regions can exert a similar effect, though of lesser magnitude, suggests that a more general property of fetal CNS tissue may be involved.

Entorhinal transplants and spatial memory abilities in rats

Transplants of embryonic entorhinal tissues, placed into the angular bundle region of adult rats, innervate appropriate areas of the host hippocampal formation and amygdala, provided that native entorhinal connections have been destroyed. In the present study, transplants were examined for their ability to restore spatial memory abilities which are lost following the bilateral destruction of native entorhinal connections. Animals were tested for their ability to perform an 8-arm radial maze task, for spontaneous alternation in a T-maze, and for their ability to learn to alternate in a T-maze for a food reward. Animals with lesions, and those with lesions + implants, remained impaired on all 3 tasks examined for as long as 6 months postimplantation. During this time, no transplant-induced behavioral recovery was observed, although behavioral stabilization was observed on the spontaneous alternation task at 6 months post-transplantation. The data suggest that these transplants may be limited in their ability to restore functions which are highly dependent upon the anatomical integrity of the damaged circuits and the precise organization of information flow through the damaged area.

Adrenal medulla grafts enhance recovery of striatal dopaminergic fibers

The drug, 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP), depletes striatal dopamine levels in primates and certain rodents, including mice, and produces parkinsonian-like symptoms in humans and nonhuman primates. To investigate the consequences of grafting adrenal medullary tissue into the brain of a rodent model of Parkinson's disease, a piece of adult mouse adrenal medulla was grafted unilaterally into mouse striatum 1 week after MPTP treatment. This MPTP treatment resulted in the virtual disappearance of tyrosine hydroxylase-immunoreactive fibers and severely depleted striatal dopamine levels. At 2, 4, and 6 weeks after grafting, dense tyrosine hydroxylase-immunoreactive fibers were observed in the grafted striatum, while only sparse fibers were seen in the contralateral striatum. In all cases, tyrosine hydroxylase-immunoreactive fibers appeared to be from the host rather than from the grafts, which survived poorly. These observations suggest that, in mice, adrenal medullary grafts exert a neurotrophic action in the host brain to enhance recovery of dopaminergic neurons. This effect may be relevant to the symptomatic recovery in Parkinson's disease patients who have received adrenal medullary grafts.