Long-term survival of fetal porcine lateral ganglionic eminence cells in the hippocampus of rats

Interneuron Origins in the Embryonic Porcine Medial Ganglionic Eminence

Interneurons contribute to the complexity of neural circuits and maintenance of normal brain function. Rodent interneurons originate in embryonic ganglionic eminences, but developmental origins in other species are less understood. Here, we show that transcription factor expression patterns in porcine embryonic subpallium are similar to rodents, delineating a distinct medial ganglionic eminence (MGE) progenitor domain. On the basis of Nkx2.1, Lhx6, and Dlx2 expression, in vitro differentiation into neurons expressing GABA, and robust migratory capacity in explant assays, we propose that cortical and hippocampal interneurons originate from a porcine MGE region. Following xenotransplantation into adult male and female rat hippocampus, we further demonstrate that porcine MGE progenitors, like those from rodents, migrate and differentiate into morphologically distinct interneurons expressing GABA. Our findings reveal that basic rules for interneuron development are conserved across species, and that porcine embryonic MGE progenitors could serve as a valuable source for interneuron-based xenotransplantation therapies.SIGNIFICANCE STATEMENT Here we demonstrate that porcine medial ganglionic eminence, like rodents, exhibit a distinct transcriptional and interneuron-specific antibody profile, in vitro migratory capacity and are amenable to xenotransplantation. This is the first comprehensive examination of embryonic interneuron origins in the pig; and because a rich neurodevelopmental literature on embryonic mouse medial ganglionic eminence exists (with some additional characterizations in other species, e.g., monkey and human), our work allows direct neurodevelopmental comparisons with this literature.

Trophic and immunoregulatory properties of neural precursor cells: benefit for intracerebral transplantation

Intracerebral xenotransplantation of porcine fetal neuroblasts (pNB) is considered as an alternative to human neuroblasts for the treatment of neurodegenerative diseases. However, pNB are systematically rejected, even in an immunoprivileged site such as the brain. Within this context, neural stem/precursor cells (NSPC), which were suggested as exhibiting low immunogenicity, appeared as a useful source of xenogeneic cells. To determine the advantage of using porcine NSPC (pNSPC) in xenotransplantation, pNB and pNSPC were grafted into the striatum of rats without immunosuppression. At day 63, all the pNB were rejected while 40% of the rats transplanted with pNSPC exhibited large and healthy grafts with numerous pNF70-positive cells. The absence of inflammation at day 63 and the occasional presence of T cells in pNSPC grafts evoked a weak host immune response which might be partly due to the immunosuppressive properties of the transplanted cells. T cell proliferation assays confirmed such a hypothesis by revealing an inhibitory effect of pNSPC on T cells through a soluble factor. In addition to their immunosuppressive effect, in contrast to pNB, very few pNSPC differentiated into tyrosine hydroxylase-positive neurons but the cells triggered an intense innervation of the striatum by rat dopaminergic fibers coming from the substantia nigra. Further experiments will be required to optimize the use of pNSPC in regenerative medicine but here we show that their immunomodulatory and trophic activities might be of great interest for restorative strategies. This article is part of a Special Issue entitled "Interaction between repair, disease, & inflammation."

Amygdalar GABAergic-rich neural grafts attenuate anxiety-like behavior in rats

Transplantation experiments have shown that neurologic deficits may be reversed by engrafting fresh tissue or engineered cells within dysfunctional neural circuitry. In experimental and clinical settings, this approach has provided insights into the pathology and treatment of neurologic diseases, primarily movement disorders. The present experiments were designed to investigate whether a similar strategy is feasible as a method to investigate, and perhaps repair, circuitry integral to emotional disorders. We focused on the amygdala, a macrostructure known to be involved in the expression of anxiety- and fear-related behaviors. GABAergic cell-rich suspensions were prepared from E17 rat lateral ganglionic eminence and engrafted bilaterally into the lateral and basolateral amygdaloid nuclei of young adult rats. After 6 weeks, increased numbers of GABAergic neurons were identified in the vicinity of the graft sites, and electron microscopy provided evidence for functional integration of transplanted cells. Rats with these grafts spent more time in the open arms of the elevated-plus maze, consistent with an anxioloytic-like phenotype. These rats were also less sensitive to the unconditioned anxiogenic effects of light on the acoustic startle response, although fear-potentiated startle was not affected, suggesting that the grafts produced an attenuation of unlearned fear but did not affect acquisition of conditioned fear. Our results raise the possibility that distinct components of emotion can be modulated by strategic neural engraftment.

Stem cells: implications in experimental ischaemic stroke therapy

Ischaemic stroke is a syndrome characterized by rapid onset of neurological injury due to interruption of blood flow to the brain. Widespread neuronal damage throughout the CNS has been shown to cause marked and multifarious functional impairments in the ischaemic brain. Recent advances as enumerated above have propelled acute ischaemic stroke management into a therapeutic era. However, once the damage from a stroke event has maximized, little can be done to recover premorbid function. Experimental animal data suggests that stem cell therapy may be an effective alternate to the conventional disease management strategies of ischaemic stroke. Therefore, the present review focuses on detailing the scope of stem cell therapy in the treatment of ischaemic stroke.

Cell Transplantation for Ischemic Stroke

Cell replacement therapy has been evaluated as a regenerative strategy for patients with fixed neurologic deficits after ischemic stroke. Animal models have identified specific cell lines which lead to regeneration and improvement in behavior and motor function after implantation into areas of ischemic injury. This has led to the development of pilot studies in humans, which have mainly investigated the safety and pilot efficacy of such approaches with promising early results. As research in this area progresses, further prospective trials are necessary not only to demonstrate clinical efficacy but also to understand the mechanisms underlying the early positive experiences, to select appropriate patients for cell replacement therapy, and to elucidate the optimal timing and mode of cell delivery.

Cell therapy for stroke

Increasing experimental evidence suggests that cell transplantation can enhance recovery from stroke in animal models of focal cerebral ischemia. Clinical trials have been investigating the effects of a human immortalized neuronal cell line and porcine fetal neurons in stroke victims with persistent and stable deficits. Preclinical studies are focusing on the effects of human stem cells from various sources including brain, bone marrow, umbilical cord, and adipose tissue. This review presents an overview of preclinical and clinical studies on cell therapy for stroke. We emphasize the current, limited knowledge about the biology of implant sources and discuss special conditions in stroke that will impact the potential success of neurotransplantation in clinical trials.

Hippocampal neurotransplantation evaluated in the rat kainic acid epilepsy model

OBJECTIVE

Neurotransplantation has focused on disorders that involve subcortical brain targets. We evaluated the concepts of epileptic focus repair and changes in animal behavior through replacement of lost hippocampal neurons. The safety of hippocampal neurotransplantation was assessed in the rat kainic acid (KA) epilepsy model.

METHODS

Sixty-three rats were studied and classified into six groups: KA plus 40,000 LBS-Neurons (Layton BioScience, Sunnyvale, CA; n = 13); KA plus 80,000 cells (n = 12); KA plus media (n = 9); no-KA plus 40,000 cells (n = 12); no-KA plus 80,000 cells (n = 12); and no-KA plus media (n = 5). Clinical observation (2 h daily) and electroencephalogram recording (3 h every other week) were performed to check for seizures until Week 11 after KA injection. On Week 12, the Morris water maze test was performed to assess spatial learning and memory.

RESULTS

Four rats were excluded because of intracranial hematoma or abscess. In the clinical observation of seizures, the no-KA plus media group had significantly fewer seizures than rats that received KA followed by injection of 40,000 cells, 80,000 cells, or media (P = 0.001, 0.0004, and 0.004, respectively). On electroencephalographic analysis, there was no significant difference between any of the groups. Transplanted rats with KA-induced epilepsy did not have an increased number of seizures. In the Morris water maze test, the hidden platform task showed that the KA plus 80,000 cell group had significantly longer swim latencies than groups with no-KA plus 40,000 cells (P = 0.035) or no-KA plus 80,000 cells (P = 0.015), demonstrating the behavioral deficits caused by KA injection. The probe trial showed no significant difference for the percentage of time in the target quadrant between any of the groups. Histological studies showed that 26 (59%) of 44 transplanted rats had evidence of graft survival.

CONCLUSION

The safety of cortical neurotransplantation was demonstrated, even in an animal model predisposed to epilepsy. We did not find evidence for cessation of seizures or improvement in behavior using this model.

Clinical prospects for neural grafting therapy for hippocampal lesions and epilepsy

OBJECTIVE

Hippocampal lesions and epilepsy may be potential clinical targets for neural grafting. We hypothesized that neural grafting could be a restorative therapy either acutely, adding unformed neural elements, or chronically, treating postlesioning epilepsy. The goal of this review was to assess the clinical reality of this hypothesis of neural grafting and to determine the problems that remain to be resolved before grafting can be applied clinically.

METHODS

We quantitatively defined graft integration within the host, on a cellular basis, by directly assessing survival of the transplanted neurons, graft cell dispersion and migration, neuronal differentiation and development, and establishment of appropriate local and long-distance synaptic connectivity.

RESULTS

Embryonic hippocampal suspension grafts demonstrate excellent survival rates (20-80%). Embryonic axons exhibit extensive, appropriate, local and long-distance connectivity, can facilitate reconstruction of excitatory and inhibitory cortical circuitry, and can prevent the formation of aberrant circuitry. Immature neural stem cells demonstrate lesser degrees of integration, likely because of a paucity of positional cues in the lesioned brain for the differentiation of stem cells into region-specific neuronal phenotypes. Labeled grafted cells may be selectively and noninvasively removed from the host with triggerable stealth toxins, for the late treatment of unanticipated graft problems.

CONCLUSION

Neural grafting with appropriate embryonic neurons may provide significant clinical benefits. However, embryonic cell availability is severely limited, and alternative sources of cells, such as stem cells, require significant additional research into the induction and maintenance of neuronal commitment and the ability of the cells to form functional synaptic connections in vivo.

Cell transplantation for stroke

Cell transplantation has emerged as an experimental approach to restore brain function after stroke. Various cell types including porcine fetal cells, stem cells, immortalized cell lines, and marrow stromal cells are under investigation in experimental and clinical stroke trials. This review discusses the unique advantages and limitations of the different graft sources and emphasizes the current, limited knowledge about their biology. The survival, integration, and efficacy of neural transplants in stroke patients will depend on the type, severity, chronicity, adequacy of circulation, and location of the stroke lesion.

Comparison of fresh and cryopreserved porcine ventral mesencephalon cells transplanted in A rat model of Parkinson's disease

To evaluate whether cryopreservation of porcine ventral mesencephalon cells influences graft survival and function in vivo, we have transplanted either freshly prepared or cryopreserved cells into the striatum of 6-hydroxydopamine-lesioned rats. A single cell suspension of porcine ventral mesencephalon cells from the same isolation either was stored at 4 degrees C and transplanted the next day or was cryopreserved for 4 weeks in liquid nitrogen vapor. The cryopreserved cells were then rapidly thawed, rinsed, and transplanted in the same manner as the fresh cells, with the same dose of viable cells. All animals received daily injections of cyclosporin A to prevent xenograft rejection. To monitor graft function, amphetamine-induced rotation was measured every 3 weeks between 6 and 15 weeks posttransplantation. After sacrifice at 15 weeks posttransplantation, histological methods were used to compare fresh cell and cryopreserved cell transplants with respect to graft survival, differentiation and integration, and host immune response. Cryopreserved cells were found to be either equivalent or in some cases superior to fresh cells with respect to rotational correction, graft survival, graft volume, numbers of graft-derived dopaminergic neurons, and host immune responses. In conclusion, the results indicate that it is feasible to cryopreserve porcine ventral mesencephalon cells for long-term storage of cells prior to transplantation in an animal model of Parkinson's disease.

Preliminary study of the behavioral effects of LBS-neuron implantation on seizure susceptibility following middle cerebral artery occlusion in the rats

Neural transplantation is a promising treatment strategy that can restore the motor, sensory and cognitive functions in the rat middle cerebral artery occlusion (MCAO) model of stroke. In particular, neuronal cells derived from a human teratocarcinoma cell line, called hNT neurons or LBS neurons (clinical grade preparation), are effective in improving behavioral recovery after stroke. In the elderly, epilepsy is a common sequela of stroke, especially if the infarction involves cerebral cortex. However, the effect of implanting neural cells on seizure susceptibility in the MCAO model has not yet been determined. The purpose of this study was to determine the susceptibility to pentylenetetrazol (PTZ)-induced seizures in normal, MCAO-lesioned and MCAO-lesioned rats in which the LBS neurons were injected. Adult, male Sprague-Dawley rats were subjected to 60 min of MCAO using the intraluminal filament technique followed 3-4 weeks later by transplantation of 80,000 LBS-neurons into the ipsilateral cortex. Susceptibility to PTZ-induced seizures was tested 4-6 weeks post-transplant at doses of 35, 50 and 70 mg/kg, administered subcutaneously. Latency to the first lethal response, latency to first generalized seizure, duration of the first generalized seizure, and the number of generalized seizures in an hour post-PTZ treatment observation period was determined. Even thought there was a tendency for groups that underwent MCAO to be more susceptible to seizures, there were no statistically significant differences between the groups and no differences between MCAO alone and MCAO animals in which cells had been implanted. While grafted cells were identified in all but one injected animal, the results suggest that the grafts may not have been healthy either from immunological rejection or PTZ-induced injury. These results suggest that while placing cells within the cortex does not reduce seizure susceptibility, it also does not increase the incidence of seizures. Further investigations are warranted.

Stem cell grafting for epilepsy: clinical promise and ethical concerns

The recent explosion of research on stem cells and neural grafting holds great promise for many neurological conditions, including epilepsy. Potential roles for cell grafting in epilepsy include remodeling of dysfunctional neuronal circuits and local delivery of neuromodulatory or neuroprotective factors. While many basic questions remain to be answered, initial human trials are underway in epilepsy as well as Parkinson's disease, Alzheimer's disease, stroke, and other conditions. It is not too early to begin ethical reflection on this dynamic field. Donor cells are often derived from human embryos, raising scarcity concerns as well as opposition from anti-abortion forces. Alternative donor sources are being actively developed. Safety concerns, adequate consent, and equitable access to care will also become important issues. Ethical issues most unique to neural grafting will revolve around redefining self-identity when personality and cognition may be altered by therapy. Views of selfhood and of being human have evolved in a historically contingent process, so that neural grafting and other consequences of the genetic revolution fall within a series of reductionist scientific developments that lead to an increasing instrumentation of our self-image. Neuroscientists and clinicians must interact with other cultural, religious, and academic groups to promote mutual understanding and richer, but scientifically accurate, views of what it means to be human. A good starting point may come by telling patients' stories, connecting scientific knowledge with the density of lived experience.

Progress report on new antiepileptic drugs: a summary of the Fifth Eilat Conference (EILAT V)

The Fifth Eilat Conference on New Antiepileptic Drugs (AEDs) took place at the Dan Hotel, Eilat, Israel, 25-29 June 2000. Basic scientists, clinical pharmacologists and neurologists from 20 countries attended the conference, whose main themes included recognition of unexpected adverse effects, new indications of AEDs, and patient-tailored AED therapy. According to tradition, the central part of the conference was devoted to a review of AEDs in development, as well to updates on AEDs that have been marketed in recent years. This article summarizes the information presented on drugs in preclinical and clinical development, including AWD 131-138, DP-valproate, harkoseride, LY300164, NPS 1776, NW 1015, pregabalin, remacemide, retigabine, rufinamide and valrocemide. The potential value of an innovative strategy, porcine embryonic GABAergic cell transplants, is also discussed. Finally, updates on felbamate, fosphenytoin, gabapentin, lamotrigine, levetiracetam, oxcarbazepine, tiagabine, topiramate, vigabatrin, zonisamide, and the antiepileptic vagal stimulator device are presented.