Co-grafts of embryonic dopamine neurons and adult sciatic nerve into the denervated striatum enhance behavioral and morphological recovery in rats

Bridges of biomaterials promote nigrostriatal pathway regeneration

Repair of central nervous system (CNS) lesions is difficulted by the lack of ability of central axons to regrow, and the blocking by the brain astrocytes to axonal entry. We hypothesized that by using bridges made of porous biomaterial and permissive olfactory ensheathing glia (OEG), we could provide a scaffold to permit restoration of white matter tracts. We implanted porous polycaprolactone (PCL) bridges between the substantia nigra and the striatum in rats, both with and without OEG. We compared the number of tyrosine-hydroxylase positive (TH+) fibers crossing the striatal-graft interface, and the astrocytic and microglial reaction around the grafts, between animals grafted with and without OEG. Although TH+ fibers were found inside the grafts made of PCL alone, there was a greater fiber density inside the graft and at the striatal-graft interface when OEG was cografted. Also, there was less astrocytic and microglial reaction in those animals. These results show that these PCL grafts are able to promote axonal growth along the nigrostriatal pathway, and that cografting of OEG markedly enhances axonal entry inside the grafts, growth within them, and re-entry of axons into the CNS. These results may have implications in the treatment of diseases such as Parkinson's and others associated with lesions of central white matter tracts. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 190-196, 2019.

A Comparative Study of Preparation Techniques for Improving the Viability of Nigral Grafts using Vital Stains, in Vitro Cultures, and in Vivo Grafts

The intracerebral transplantation of embryonic dopaminergic nigral neurons, although relatively successful, leads to a fairly low yield of surviving cells. Many factors may influence the viability of dopaminergic grafts and one of these is the preparation of the tissue prior to transplantation. We have investigated the effects of different steps during the preparation and storage of embryonic rat nigral cell suspensions on their subsequent survival at a variety of different time points using a combination of techniques and studies. For studies concerned with the first 24 h we employed vital stains, in the period covering the next 7 days we used in vitro cultures, and in the long term experiment we used in vivo grafts. The results suggest that nigral cell suspensions may remain sufficiently viable for grafting for much longer periods than previously reported. In addition a number of parameters which affect cell survival have been characterised, including the age of the embryonic donor tissue, the use of proteolytic enzymes and the trituration procedure used during the preparation of the suspension. The optimal preparation technique, therefore, uses E13-E14 embryos with the dissected ventral mesencephalon being incubated in purified 0.1% trypsin solutions for 60 min and triturated using a flame polished Pasteur pipette. This may have important implications in improving intracerebral transplantation for Parkinson's disease.

Neural Transplantation: Prospects for Clinical use

Neural transplantation has been extensively applied in Parkinson's disease, including numerous clinical studies, studies in animal models, and related basic research on cell biology. There is evidence that the clinical trials of both adrenal medulla transplantation and fetal substantia nigra transplantation have produced a detectable clinical effect, although it is not yet clear whether the clinical benefit is sufficient to justify a more widespread application of these procedures. Studies of long-term outcome and quantitative tests are important in assaying the degree of benefit produced by transplantation procedures in Parkinson's disease and for developing improved and refined procedures. Other disease-related applications of neural transplantation are beginning to be developed. These include Huntington's disease, chronic pain, epilepsy, spinal cord injury, and perhaps even demyelinating diseases and cortical ischemic injury. Although most of these applications lie in the future, it is not too soon to begin to consider the scientific justification that should be required for initiation of human clinical trials.

Cellular models to study dopaminergic injury responses

The study of immature midbrain dopamine (DA) neurons and dopaminergic cell lines in culture provides an opportunity to analyze mechanisms of cell death and avenues of potential intervention relevant to Parkinson's disease (PD) in a controlled environment. Use of cell culture models has provided evidence for different sets of intracellular changes associated with DA neuron death following exposure to the neurotoxins 6-hydroxydopamine and MPP+, supporting roles for oxidative stress and impaired energy metabolism as significant factors endangering these cells. Interference with death of cultured DA neurons has provided an initial test system that has yielded all the identified neurotrophic factors for DA neurons. More recent work suggests that combinations of molecules secreted by myelinating glial cells and their precursors provide even greater neuroprotection for DA neurons. Most recently, culture systems have been used to implicate microglial activation in DA neuron injury, providing impetus to the investigation of antiinflammatory agents as potential therapeutics for PD. Thus, cell culture models provide an important bidirectional link between mechanistic studies and clinically relevant observations.

Effects of adrenal medulla graft on recovery of GABAergic and dopaminergic neuron deficits in mice: behavioural, pharmacological and immunohistochemical study

We studied the capacity of adrenal medullary transplant to restore the deficits of GABAergic and dopaminergic neurons in mice injected with quinolinic acid (QA), using an open field test as well as pharmacological and immunohistochemical techniques. We analysed behavioural traits-total locomotor activity, peripheral and central activities, grooming, leaning and rearing in the QA-lesioned mice and mice that had undergone adrenal medulla (AM) transplantation. We found that the adrenal transplant recovered a loss of GABAergic neurons. It reduced QA-induced hyperactivity in locomotion and improved emotional indices. In addition, immunohistochemical studies of catecholaminergic markers-tyrosine hydroxylase (TH), dopamine (DA) and neuronal vesicular monoamine transporter type 2- and a single post-trial injection of tetrabenazine (TBZ; 5 mg/kg) indicated that catecholamines-synthesising chromaffin cells in the AM grafts were also involved in the beneficial effects. A likely interpretation of this behavioural pattern of results is that adrenal medullary transplants set into play an interaction between GABAergic and DAergic factors. Our results may contribute to the clarification of the beneficial effects of AM transplants in striatal function.

Involvement of adrenal medulla grafts in the open field behavior

Immunohistochemical and behavioral techniques were used to study the effects of adrenal medulla grafts, implanted in striatum after bilateral kainic acid (KA) lesions of this structure, on the open field behavior of mice. KA-induced behavioral changes in leaning, grooming and locomotor activity of the open field test were significantly improved after grafting of the adrenal medulla, and in some respects, fully restored. Immunohistochemical identification showed that grafts contained neuron-like cells with a tyrosine hydroxylase (TH), phenylethanolamine N-methyltransferase, gamma-aminobutyric acid (GABA), choline acetyltransferase (ChAT), and enkephalin-like immunostainings. A likely interpretation of this complex pattern of results is that adrenal medullary grafts may restore the deficits of GABAergic neurons which in turn reverse the abnormalities in emotionality and locomotion. Neurobiologically, these behavioral improvements probably involve GABAergic and catecholaminergic factors of adrenal medulla grafts, although other neuroactive substances, such as acetylcholine and enkephalins, cannot be excluded.

Diminished viability, growth, and behavioral efficacy of fetal dopamine neuron grafts in aging rats with long-term dopamine depletion: an argument for neurotrophic supplementation

We examined the behavioral and morphological correlates of the response to a single intrastriatal dispersed cell graft of fetal rat ventral mesencephalic tissue in male Fischer-344 rats of varying age (4, 17, and 24-26 months old) and history of mesostriatal dopamine (DA) depletion (1 or 14 months). Our goal was to determine the impact of advancing age and duration of DA depletion in the host on DA graft viability and function. The findings can be summarized as follows. (1) Fetal DA neuron grafts that were effective in completely ameliorating amphetamine-induced rotational behavior in young rats with short-term lesions were virtually without effect in aged rats with long-term lesions. Middle-aged rats with long-term lesions responded to these grafts with partial behavioral recovery. (2) Age of the host at the time of transplantation, and not duration of DA depletion, was the primary determinant of response to DA grafts. (3) Diminished efficacy of grafts in lesioned aging rats was related to decreased survival and neurite extension of transplanted DA neurons. (4) Co-grafts of DA neurons with Schwann cells as a source of neurotrophic support improved the behavioral outcome of grafts in aged lesioned rats. These findings support the view that the DA-depleted striatum of aged rats is an impoverished environment for survival, growth, and function of DA grafts. Consistent with this view, local supplementation of the neurotrophic environment of grafted DA neurons with products of co-grafted Schwann cells, a demonstrated source of neurotrophic activity for embryonic DA neurons, improved graft outcome.

Peripheral nerve-dopamine neuron co-grafts in MPTP-treated monkeys: augmentation of tyrosine hydroxylase-positive fiber staining and dopamine content in host systems

Previous studies of rats in our laboratory indicate that a molecule or molecules released by Schwann cells exert survival and growth-promoting effects on mesencephalic dopamine neurons. In the present study, we have begun to investigate the potential for Schwann cell augmentation of host dopamine fiber systems and embryonic dopamine neuron grafts in non-human primates. Ten adult male St Kitts African Green monkeys treated with the dopaminergic neurotoxin 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine one year previously, but behaviorally asymptomatic, served as hosts for implant studies. A segment of young adult monkey saphenous nerve was collected to serve as an implanted tissue source of Schwann cell-derived growth factors. Nerve was enclosed in a hollow semi-permeable polymer fiber for implantation into the lateral ventricle, with embryonic ventral mesencephalic tissue co-grafts containing developing dopamine neurons aimed at nearby locations in the caudate nucleus. Control implants consisted of an empty polymer fiber co-grafted with embryonic ventral mesencephalon. Our morphological observations indicate that while no clear augmentation of the morphology of grafted dopamine neurons attributable to co-grafted nerve was observed, this lack of influence may be related to the spatial separation of the co-grafted tissues. In contrast, some monkeys with nerve segments in the lateral ventricle exhibited increased tyrosine hydroxylase-positive fiber staining in the immediately adjacent lateral septal area and the ventricular wall of the caudate nucleus. This enhancement was not associated with empty polymer implants. Levels of dopamine and its metabolite homovanillic acid derived from tissue punches in the caudate nucleus and septal area support the view that monkeys exhibiting morphological enhancement of host dopamine systems also show biochemical increases in dopamine levels and changes in the direction of normalization of the homovanillic acid/dopamine ratio. Biochemical values from a single septal area tissue punch in one animal were an exception to this rule. This study suggests that while the utility of peripheral nerve as a source of dopamine graft augmentation in non-human primates remains to be demonstrated, grafted nerve has a stimulatory effect on host brain dopamine systems in adult, dopamine-depleted monkeys, and that this morphological effect can be dissociated from previously hypothesized injury-induced regeneration.

Enhanced synthesis of brain-derived neurotrophic factor in the lesioned peripheral nerve: different mechanisms are responsible for the regulation of BDNF and NGF mRNA

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are molecules which regulate the development and maintenance of specific functions in different populations of peripheral and central neurons, amongst them sensory neurons of neural crest and placode origin. Under physiological conditions NGF is synthesized by peripheral target tissues, whereas BDNF synthesis is highest in the CNS. This situation changes dramatically after lesion of peripheral nerves. As previously shown, there is a marked rapid increase in NGF mRNA in the nonneuronal cells of the damaged nerve. The prolonged elevation of NGF mRNA levels is related to the immigration of activated macrophages, interleukin-1 being the most essential mediator of this effect. Here we show that transsection of the rat sciatic nerve also leads to a very marked increase in BDNF mRNA, the final levels being even ten times higher than those of NGF mRNA. However, the time-course and spatial pattern of BDNF mRNA expression are distinctly different. There is a continuous slow increase of BDNF mRNA starting after day 3 post-lesion and reaching maximal levels 3-4 wk later. These distinct differences suggest different mechanisms of regulation of NGF and BDNF synthesis in non-neuronal cells of the nerve. This was substantiated by the demonstration of differential regulation of these mRNAs in organ culture of rat sciatic nerve and Schwann cell culture. Furthermore, using bioassays and specific antibodies we showed that cultured Schwann cells are a rich source of BDNF- and ciliary neurotrophic factor (CNTF)-like neurotrophic activity in addition to NGF. Antisera raised against a BDNF-peptide demonstrated BDNF-immunoreactivity in pure cultured Schwann cells, but not in fibroblasts derived from sciatic nerve.