Transplantation Of Neural Tissue Research Articles

Principles of brain tissue engineering

AbstractIt is often presumed that effects of neural tissue transplants are due to release of neurotransmitter. In many cases, however, effects attributed to transplants may be related to phenomena such as trophic effects mediated by glial cells or even tissue reactions to injury. Any conclusion regarding causation of graft effects must be based on the control groups or other comparisons used. In human clinical studies, for example, comparing the same subject before and after transplantation allows for many interpretations of the causes of clinical changes.

Basic mechanisms and clinical applications of neural tissue transplants

Basic mechanisms and clinical applications of neural tissue transplants

Low-pressure aspiration abortion for obtaining embryonic and early gestational fetal tissue for research purposes.

Successful transplantation of cadaver embryonic neural tissue is highly dependent on the method used to obtain the tissue. It is important that the tissue not be contaminated bacteriologically by vaginal flora during the procedure, and that it not be disrupted mechanically. A low-pressure aspiration abortion technique has been developed that allows for the safe, effective obtainment of embryonic tissue and reduces the risk of transmitting infection. Tissue was cultured in vitro in 102 cases with minimal evidence of contamination by vaginal flora. Transplants of neural tissue into over 300 rodents have resulted in no intracranial abscesses, even in the setting of immunosuppression. The suction apparatus and low-pressure aspiration minimize disruption of the embryonic tissue. Use of low pressure adds no significant additional risk to the patient. In over 300 cases, there have been no medical complications specifically attributable to the technique. Because local anesthetic is used and sonography is not routinely required, the procedure can easily be performed in an outpatient setting during routine elective abortions, with minimal slowing or disruption of the clinic's surgical schedule. In conclusion, the low-pressure aspiration abortion technique can be safely and effectively used to obtain embryonic and early gestational fetal tissue that is almost always free from bacterial, fungal, and yeast contamination and that is frequently structurally intact. It requires no significant alteration in indications for abortion, risks, methodology, timing of the abortion, or patient management.

Transplantation of glial cells enhances action potential conduction of amyelinated spinal cord axons in the myelin-deficient rat.

A central issue in transplantation research is to determine how and when transplantation of neural tissue can influence the development and function of the mammalian central nervous system. Of particular interest is whether electrophysiological function in the traumatized or diseased mammalian central nervous system can be improved by the replacement of cellular elements that are missing or damaged. Although it is known that transplantation of neural tissue can lead to functional improvement in models of neurological disease characterized by neuronal loss, less is known about results of transplantation in disorders of myelin. We report here that transplantation of glial cells into the dorsal columns of neonatal myelin-deficient rat spinal cords leads to myelination and a 3-fold increase in conduction velocity. We also show that impulses can propagate into and out of the transplant region and that axons myelinated by transplanted cells do not have impaired frequency-response properties. These results demonstrate that myelination following central nervous system glial cell transplantation enhances action potential conduction in myelin-deficient axons, with conduction velocity approaching normal values.

Scientific and ethical concerns in neural fetal tissue transplantation.

This report presents a brief overview of the medical and ethical issues involved with the procurement, preparation, safety, efficacy, and subject protection of human fetal central nervous system tissue in the context of neural transplantation. The ethical perspectives from which to view the clinical use of fetal tissue include the following: 1) that fetal tissue from elective abortions is a surgical specimen; 2) that the use of such tissue involves fetal experimentation in which the fetus is a subject; and 3) that fetal tissue is considered as a cadaveric organ specimen, similar to other organs, but with special considerations compared with adult cadaveric tissue. The latter approach appears to be the most applicable and is parallel to the use of cadaveric organs and tissues after a declaration of brain death. Additional issues include the following: 1) the safety and quality of fetal tissue for implantation; 2) the hypothesis that "legitimization" and "redemption" (potentially positive effects of tissue donation in general) may lead to an increase in elective abortion rates; 3) the ethical issues of the validity and value of human experimentation involving neural grafting; and 4) the type of consent to be obtained and the appropriate timing. Elective abortions, however, probably will continue to be the primary source of fetal tissue for grafting for some time, until other tissue sources become available.

Scientific and Ethical Concerns in Neural Fetal Tissue Transplantation

Scientific and Ethical Concerns in Neural Fetal Tissue Transplantation

Hydrogels for neural tissue reconstruction and transplantation

Since the first use of hydrogels as biomaterials, interest in synthetic hydrogels in medicine has increased considerably and the range of biomedical applications has expanded. This paper discusses a novel application of the use of synthetic hydrogels that are processed to serve as artificial matrices for neural tissue reconstruction, the delivery of cells and the promotion of axonal regeneration required for successful neurotransplantation. The possibility to create hydrogels with bioactive characteristics for neural cell adhesion and growth is also presented.

Neural transplantation for neurodegenerative diseases: past, present, and future.

After almost 100 years of sporadic, and marginally successful, studies of neural transplantation in animals, we are now on the threshold of a clinical treatment of the damaged brain. The initial studies of neural transplantation have focused on Parkinson's disease, primarily as a model for a more general strategy of "repair by cellular replacement." Parkinson's is known to result from the loss of a small population of cells that produce the essential neuromodulator, dopamine, for much of the brain. Further, the disease is improved significantly, during the early part of its course, by chemical augmentation of dopamine activity through drug therapies, such as L-dopa. Finally, the disease is often fatal in spite of the best medical treatments, therefore justifying more radical therapeutic experiments. If transplantation of brain cells can be accomplished successfully in humans, as it has been in animals, then replacement of a small population of dopamine-producing cells in Parkinson's disease should have important functional effects and possibly reverse the course and symptoms of the disease. Other useful applications will surely follow for conditions affecting millions of people for whom medicine now has only palliative and ineffective treatments. Just as Parkinson's disease is a model clinical condition for testing cellular replacements, fetal neural tissue transplants are also a first step for a broader strategy of molecular and cellular therapies. Fetal cells are, in many respects, the best replacements one could imagine, since precursor cells have the capacity to develop into every cell found in the adult. So, the best replacement for a dopamine neuron would likely be a precursor dopamine neuron or "neuroblast." Animal research through 1985 had demonstrated the unique properties of such fetal cells, but survivability after transplantation had not been attained with primate or human neural tissue. Our programs developed techniques to transplant monkey fetal neural tissue, to cryopreserve it, and to reverse functional effects of the neurotoxin, MPTP, in monkeys. This technique was applied to the collection and preservation of human tissue, and preliminary successful results have been obtained in patients with idiopathic Parkinson's disease. Others have reported success with different techniques in two MPTP-Parkinsonian patients and a small number of patients with idiopathic disease. If the most dramatic improvements can be replicated consistently and the benefits last for a reasonable period without complications, a clinical treatment might develop using "random-source" fetal cadaver cells.

Behavioral effects of cholinergic grafts.

Experimental work in animals and, to a more limited extent, in humans, has demonstrated that the cholinergic system is involved in mechanisms which control learning and memory. Since there is cholinergic loss in a variety of dementing illnesses, any treatment designed to alleviate the mental symptoms of these diseases must address the issue of cholinergic dysfunction even if other treatments are also required to overcome other neurotransmitter imbalances. Work in rodents has demonstrated that cholinergic-rich fetal neural tissue transplants can, under certain circumstances, alleviate the behavioral effects of cholinergic lesions or of cholinergic decline associated with aging. More complex cognitive testing can be achieved using primates and, in this case, the common marmoset is a suitable species to use because its rapid and reliable reproductive rate aids the provision of appropriate transplant tissue. Marmosets with transection of the fornix are deprived of a cholinergic input into the dentate gyrus, posterior hippocampus and entorhinal cortex and are specifically impaired on learning tasks which require remembering a rule of responding (non-evaluative memory). Transplantation of cholinergic-rich fetal septal tissue into the hippocampus of such animals completely restores their ability to learn this type of task, whereas transplantation of cholinergic-poor fetal hippocampal tissue into the same area produces no such improvements. These results demonstrate that where a learning impairment is produced by a relatively simple procedure which has a major effect on one neurotransmitter, that function can be restored by transplantation of tissue containing that neurotransmitter even where the impairment consists of a very "high level" cognitive dysfunction.

Embryonic CNS Tissue Transplantation for Studies of Development and Regeneration

Neural tissue transplantation techniques have been used to study neuronal-target interactions during development and to study CNS repair and recovery of function after injury. We describe methods of neural tissue transplantation after spinal cord injury in newborn and adult mammals, with an emphasis on preparation of embryonic spinal cord tissue for transplantation and subsequent analysis of host-transplant interactions.

Immature neural tissue grafts in Parkinson's disease

Intracerebral transplantation of immature neural tissue is a promising therapeutical approach that has the potential of restoring damaged neuronal circuitries and reversing functional deficits. The development of the technique as a human application has progressed the furthest in Parkinson's disease (PD), with the demonstration of significant longlasting functional improvements, in combination with evidence of surviving grafted tissue, using a fluorodopa positron emission tomography (PET) scanning technique in a few patients. Although the technique is promising, and the effects observed are significant and of clinical importance for the grafted patients in the best cases so far, there are still incomplete effects and no transplantation treatment is suggested since there are still several technical aspects that might further improve the outcome. The progress of the development in the field is briefly reviewed.

Improved cryopreservative medium suitable for the freeze-storage and transplantation of fetal neural tissues

Techniques to maintain viable fetal neural tissue might be an important tool for a successful neural transplantation by giving enough time for preparation, storage, and transportation of donor tissue. In the present study, we examined the effect of freeze-storage (cryopreservation) for 7 days at liquid nitrogen temperature on the survivability of intraventricular rat fetal mesencephalic grafts (gestational day 15) when using 10% dimethyl sulfoxide (DMSO), 0.1% methylcellulose, or 10% DMSO with additional 0.1% methylcellulose (m-DMSO) as a cryoprotective agent. As a control group, the survivability of grafts transplanted immediately after dissection was examined. The volume of grafts treated with m-DMSO was 3 times as large as that of grafts treated with 10% DMSO alone. While the number of surviving neurons in 10% DMSO-treated transplants decreased down to 15% of the control value, there was no statistically significant difference in the number of surviving neurons between the m-DMSO treated group and control group. In the group treated with m-DMSO, there were a lot of well developed tyrosine hydroxylase positive neurons and fibers in the graft, and a few reactive astrocytes were observed only in the peripheral region of the grafts. In the group treated with 0.1% methylcellulose alone, no graft survival was observed in any of the animals. We conclude that the addition of methylcellulose to the commonly used cryoprotective agent (DMSO) is beneficial for the freeze-storage of fetal neural tissue.

Behavioral effects of neural transplantation.

Considerable evidence suggests that transplantation of fetal neural tissue ameliorates the behavioral deficits observed in a variety of animal models of CNS disorders. However, it is also becoming increasingly clear that neural transplants do not necessarily produce behavioral recovery, and in some cases have either no beneficial effects, magnify existing behavioral abnormalities, or even produce a unique constellation of deficits. Regardless, studies demonstrating the successful use of neural transplants in reducing or eliminating behavioral deficits in these animal models has led directly to their clinical application in human neurodegenerative disorders such as Parkinson's disease. This review examines the beneficial and deleterious behavioral consequences of neural transplants in different animal models of human diseases, and discusses the possible mechanisms by which neural transplants might produce behavior recovery.

In vivo magnetic resonance imaging of fetal cat neural tissue transplants in the adult cat spinal cord

Magnetic resonance (MR) imaging was evaluated for its possible diagnostic application in determining the survival of fetal central nervous system tissue grafts in the injured spinal cord. Hemisection cavities were made at the T11-L1 level of eight adult female cats. Immediately thereafter, several pieces of tissue, either obtained from the fetal cat brain stem on embryonic Day 37 (E-37), from the fetal neocortex on E-37, or from the fetal spinal cord on E-23, were implanted into the cavities made in seven cats. The eighth cat served as a control for the effect of the lesion only. In another group of four animals, a static-load compression injury was made at the L-2 level. Seven weeks later, the lesion was resected in three cases and fragments of either fetal brain-stem or spinal cord tissue were introduced. A small cyst was observed in a fourth cat in the compression injury group and a suspension of dissociated E-23 brain-stem cells was injected into this region of cavitation without disturbing the surrounding leptomeninges. Five months to 2 years posttransplantation, MR imaging was performed with a 2.0-tesla VIS imaging spectrometer by acquiring multislice spin-echo images (TR 1000 msec, TE 30 msec) in both the transverse and sagittal planes. Collectively, these intermediate-weighted images revealed homogeneous, slightly hyperintense signals at the graft site relative to the neighboring host tissue in seven of the 11 graft recipients. Two of the remaining four cats exhibited signals from the graft site that were approximately isointense with the adjacent host spinal cord, and the final two cats and the lesion-only control presented with very hypointense transplant/resection regions. The hyperintense and isointense images were tentatively interpreted as representing viable graft tissue, whereas the hypointense transplant/resection sites were considered to be indicative of a lack of transplant survival or the absence of tissue in the lesion-only control animal. Postmortem gross inspection of fixed specimens and light microscopy verified the MR findings in the control animal in 10 of the 11 graft recipients by showing either transplants and/or cysts corresponding to the MR images obtained. In one cat in the hemisection group, histological analysis revealed a very small piece of graft tissue that was not detected on the MR images. Therefore, it is suggested that within certain spatial- and contrast-resolution limits, MR imaging can reliably detect the presence of transplanted neural tissue in both the hemisected and compression-injured spinal cord of living animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Transplants of fetal neural tissue and autologous peripheral nerves in an attempt to repair spinal cord injuries in the adult rat

Embryonic neurons and autologous peripheral nerve segments constitute selected materials for studying central nervous system plasticity and repair in adult mammals. Transplanted to the brain or the spinal cord, the former are possible substitutes designed to replace lost or deficient host neurons while the latter have useful stimulating and guiding effects upon axonal regrowth from surviving axotomized neurons. Consequently, these techniques give rise to interesting prospects for short and medium range fundamental research as well as for possible medium and long-term clinical applications. From a basic viewpoint, utilisation of such transplants is designed to study the survival, the morphological and biochemical differentiation, the reafferentation, the expression of potentialities for plasticity, axonal growth or regeneration, synaptogenesis, of host as well as of transplanted embryonic neurons. From a clinical viewpoint these studies should attempt at finding solutions to counteract the effects of severe traumatic or neurodegenerative lesions of the brain and of the spinal cord which until now appear quite refractory to therapeutic approaches.

CNS transplants promote anatomical plasticity and recovery of function after spinal cord injury

We are using neural tissue transplantation after spinal cord injury to identify the rules which determine the response of young neurons to injury, to identify the mechanisms underlying anatomical plasticity and recovery of function following spinal cord injury, and to determine the conditions which change during development, leading to the more restricted growth capacity of mature neurons following injury. Spinal cord lesions at birth interrupt different pathways at different relative stages in their development. Neural tissue transplants modify the response of the immature central nervous system neurons to injury. In the current studies, we have used neuroanatomical and behavioral methods to compare the response of the late-developing corticospinal pathway with that of brainstem-spinal pathways which are intermediate in their development and that of the relatively mature dorsal root pathway. We find that both late-developing and regenerating neuronal populations contribute to the transplant-induced anatomical plasticity, and suggest that this anatomical plasticity underlies the transplant-mediated sparing and recovery of function.

Neural transplantation: An historical perspective

Literature on transplantation of neural and nonneural tissues into the brains of host animals is reviewed in the perspective of various issues. The two dominant issues determining this research were elucidation of embryological processes underlying the development of the nervous system and regeneration in the host brain. A comprehensive review of studies on regeneration in the central nervous system (CNS), using this technique of transplantation, indicates that regeneration of axonal fibers is small in magnitude and extent, and that it is more directly related to the trauma caused to the brain than to any other variable. This literature review attempts to provide a perspective to the contemporary research on neural transplantation and on regeneration in the CNS.

Emulation of seizure induced brain damage in neural tissue transplants to the anterior chamber of the eye

We have developed a model system in which the mechanisms of neuronal damage due to hyperexcitation can be studied in isolation and where extended observation periods can be used. Substantia nigra pars reticulata (SNPR) develops a hypermetabolic necrosis following status epilepticus (Nevander et al. 1985; Auer et al. 1986). We transplanted rat fetal nigral area alone or together with fetal frontal neocortex to the anterior chamber of the eye in adult rats. Following 3 months of transplant maturation the hosts were subjected to status epilepticus for 60 min. In single nigral transplants no sign of structural damage was found. In the double transplants of frontal cortex and the substantia nigra a tissue necrosis had developed in the nigral part. This was demonstrated by a total loss of glial fibrillary acidic protein (GFA) immunoreactivity within a circumscribed necrotic region in the nigral part of the double transplant. Such a loss of GFA immunofluorescence had also developed in the host SNPR, as we have earlier shown (Eriksdotter-Nilsson et al. 1987). Thus, intraocular brain tissue transplants provide a unique model for studies on the development of neuronal damage and functional dependence between different neuronal structures for the development of such damage.

Direct neuronal and macroglial versus indirect macrophagic labeling in transplants of fetal neural tissue incubated with gold particles

In a recent light microscopic study based on the transplantation of fetal cells previously incubated with gold-loaded Sendai viruses, S. C. Ardizzoni, A. Michaels, and G. W. Arendash (1988, Science 239: 635–637) proposed that fetal neurons could migrate out into an adult host brain. This result was puzzling in view of several previous contradictory studies, and the light microscopic identification of labeled cells as neurons could be questioned. The present study was therefore undertaken to replicate this study but using electron microscopy to definitely identify migrating gold-labeled elements. Analysis was performed in a model of thalamic transplantation in which previous labeling studies, using thymidine or horseradish peroxidase, had failed to demonstrate any neuronal migration. Gold particles combined with wheat germ agglutinin peroxidase were used to label the fetal tissue prior to transplantation. Fetal cells did incorporate the protein gold complex, and the gold particles were visualized in transplants up to at least 2.5 months after grafting. Electron microscopy analysis reveals that the gold particles are internalized and retained in the lysosomes of grafted neurons and glial cells. In no transplant could labeled grafted neurons be observed intermingled with host neurons, outside the limits of the transplant. In contrast, heavily labeled macrophages were observed surrounding the transplants and sometimes migrating away from the transplant-host interface into the host tissue. These macrophages, presumably of host origin, can be recognized at the light microscopic level by their yellowish staining, a cellular characteristic already noted by Ardizzoni et al. for gold-labeled migrating elements.

Neural Fetal Tissue Transplantation: Should We Do What We Can Do?

The following factors are relevant to ethical considerations regarding fetal tissue transplantation for treatment of neurological disorders: the empirical status of human fetuses or abortuses, different purposes and sites of tissue retrieval or implantation, the therapeutic potential of the technique, the means through which tissue becomes available, possible motives, and possible donors and recipients of transplant tissue. After examining each of these, the author concludes that (1) only dead fetuses should be used as tissue sources, (2) decisions regarding abortion and transplantation should be kept separate, (3) anonymity between donor and recipient should be observed, and (4) buying and selling of fetal tissue should not be permitted.