Millimeter-scale positioning of a nerve-growth-factor source and biological activity in the brain.
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Toxicity prevents the systemic administration of many therapeutic proteins, and attempts at protein targeting via the circulatory system (i.e., "magic bullets") have failed in all but a few special cases. Direct administration at the target site is a logical alternative, particularly in the central nervous system, but the limits of direct administration have not been defined clearly. Nerve growth factor (NGF) enhances survival of cholinergic neurons and, therefore, has generated considerable interest for the treatment of Alzheimer's disease. We tested the effectiveness of local delivery by implanting small polymer pellets that slowly released NGF into the central nervous system of adult rats at controlled distances from a target site containing transplanted fetal cholinergic cells. NGF-releasing implants placed within 1-2 mm of the treatment site enhanced the biological function of cellular targets, whereas identical implants placed approximately 3 mm from the target site of treatment produced no beneficial effect. Effective NGF therapy required millimeter-scale positioning of the NGF source, and efficacy correlated with the spatial distribution of NGF concentration in the tissue; this result suggests that NGF must be delivered within several millimeters of the target to be effective in treating Alzheimer's disease. Because the human brain is divided into functional regions that are typically several centimeters in diameter and often irregular in shape, new methods for sculpting larger-scale drug fields are needed. We illustrate a concept, called pharmacotectonics, in which drug-delivery systems are arranged spatially in tissues to shape concentration fields for potent agents. (+info)
Sequential bilateral transplantation in Parkinson's disease: effects of the second graft.
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Five parkinsonian patients who had received implants of human embryonic mesencephalic tissue unilaterally in the striatum 10-56 months earlier were grafted with tissue from four to eight donors into the putamen (four patients) or the putamen plus the caudate nucleus (one patient) on the other side, and were followed for 18-24 months. After 12-18 months, PET showed a mean 85% increase in 6-L-[18F]fluorodopa uptake in the putamen with the second graft, whereas there was no significant further change in the previously transplanted putamen. Two patients exhibited marked additional improvements after their second graft: 'on-off' fluctuations virtually disappeared, movement speed increased, and L-dopa could be withdrawn in one patient and reduced by 70% in the other. The improvement in one patient was moderate. Two patients with atypical features, who responded poorly to the first graft, worsened following the second transplantation. These findings indicate that sequential transplantation in patients does not compromise the survival and function of either the first or the second graft. Moreover, putamen grafts that restore fluorodopa uptake to normal levels can give improvements of major therapeutic value. (+info)
Specification of somatosensory area identity in cortical explants.
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The H-2Z1 transgene is restricted to a subset of layer IV neurons in the postnatal mouse cortex and delineates exactly the somatosensory area. Expression of the H-2Z1 transgene was used as an areal marker to determine when the parietal cortex becomes committed to a somatosensory identity. We have shown previously that grafts dissected from embryonic day 13.5 (E13.5) H-2Z1 cortex and transplanted into the cortex of nontransgenic newborns express H-2Z1 according to their site of origin. Expression was not modified on heterotopic transplantation (). In the present study, whole cortical explants were isolated at E12.5 from noncortical tissues. The explants developed a regionalized expression of H-2Z1, indicating that regionalization takes place and is maintained in vitro. We used this property and confronted embryonic H-2Z1 cortex with presumptive embryonic sources of regionalizing signals in an in vitro grafting procedure. A great majority of E11.5-E13.5 grafts maintained their presumptive expression of H-2Z1 when grafted heterotopically on nontransgenic E13.5-E15.5 explants. However, a significantly lower proportion of E11.5 parietal grafts expressed H-2Z1 in occipital compared with parietal cortex, indicating that somatosensory identity may be partially plastic at E11.5. Earlier stages could not be tested because the E10.5 grafts failed to develop in vitro. The data suggest that commitment to the expression of a somatosensory area-specific marker coincides with the onset of neurogenesis and occurs well before the birth of the non-GABAergic neurons that express H-2Z1 in vivo. (+info)
Site-specific migration and neuronal differentiation of human neural progenitor cells after transplantation in the adult rat brain.
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Neural progenitor cells obtained from the embryonic human forebrain were expanded up to 10(7)-fold in culture in the presence of epidermal growth factor, basic fibroblast growth factor, and leukemia inhibitory growth factor. When transplanted into neurogenic regions in the adult rat brain, the subventricular zone, and hippocampus, the in vitro propagated cells migrated specifically along the routes normally taken by the endogenous neuronal precursors: along the rostral migratory stream to the olfactory bulb and within the subgranular zone in the dentate gyrus, and exhibited site-specific neuronal differentiation in the granular and periglomerular layers of the bulb and in the dentate granular cell layer. The cells exhibited substantial migration also within the non-neurogenic region, the striatum, in a seemingly nondirected manner up to approximately 1-1.5 mm from the graft core, and showed differentiation into both neuronal and glial phenotypes. Only cells with glial-like features migrated over longer distances within the mature striatum, whereas the cells expressing neuronal phenotypes remained close to the implantation site. The ability of the human neural progenitors to respond in vivo to guidance cues and signals that can direct their differentiation along multiple phenotypic pathways suggests that they can provide a powerful and virtually unlimited source of cells for experimental and clinical transplantation. (+info)
Anterior cephalic neural crest is required for forebrain viability.
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The prosencephalon, or embryonic forebrain, grows within a mesenchymal matrix of local paraxial mesoderm and of neural crest cells (NCC) derived from the posterior diencephalon and mesencephalon. Part of this NCC population forms the outer wall of capillaries within the prosencephalic leptomeninges and neuroepithelium itself. The surgical removal of NCC from the anterior head of chick embryos leads to massive cell death within the forebrain neuroepithelium during an interval that precedes its vascularization by at least 36 hours. During this critical period, a mesenchymal layer made up of intermingled mesodermal cells and NCC surround the neuroepithelium. This layer is not formed after anterior cephalic NCC ablation. The neuroepithelium then undergoes massive apoptosis. Cyclopia ensues after forebrain deterioration and absence of intervening frontonasal bud derivatives. The deleterious effect of ablation of the anterior NC cannot be interpreted as a deficit in vascularization because it takes place well before the time when blood vessels start to invade the neuroepithelium. Thus the mesenchymal layer itself exerts a trophic effect on the prosencephalic neuroepithelium. In an assay to rescue the operated phenotype, we found that the rhombencephalic but not the truncal NC can successfully replace the diencephalic and mesencephalic NC. Moreover, any region of the paraxial cephalic mesoderm can replace NCC in their dual function: in their early trophic effect and in providing pericytes to the forebrain meningeal blood vessels. The assumption of these roles by the cephalic neural crest may have been instrumental in the rostral expansion of the vertebrate forebrain over the course of evolution. (+info)
Ethical aspects of neural tissue transplantation.
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The method of neural grafting is considered to be a very promising therapeutic strategy for the treatment of certain neurodegenerative disorders such as Parkinson's disease or Huntington's disease. During the last 15 years, clinical transplantation studies have been carried out worldwide in several hundreds of patients with Parkinson's disease. In these studies, primarily fetal mesencephalic tissue derived from aborted human fetuses has been used for implantation. Neural tissue transplantation gives rise to ethical issues in two different areas that need careful examination: the first, ethical problems linked to the use of tissue from aborted human fetuses; and the second, ethical issues concerning the graft recipients in clinical trials, i.e., his or her well-being, personality, and personal identity. (+info)
Serial MR imaging of experimental autoimmune encephalomyelitis induced by human white matter or by chimeric myelin-basic and proteolipid protein in the common marmoset.
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BACKGROUND AND PURPOSE: Experimental autoimmune encephalomyelitis (EAE) in the marmoset was monitored by serial MR imaging to determine correlates to the natural-history MR studies in multiple sclerosis (MS). The relationships of MR-revealed lesions to clinical status and histopathologic findings were also explored. METHODS: We induced EAE by subcutaneous inoculation in two marmosets by human white matter (HWM) and in seven marmosets by MP4 (a chimeric recombinant fusion protein of myelin-basic and proteolipid protein) in adjuvant along with intravenous inactivated pertussis vaccine to facilitate the disease process. The HWM-inoculated animals were induced with Freund's adjuvant as the established model of marmoset EAE. The MP4-inoculated animals were induced with either Freund's incomplete adjuvant or TiterMax as part of a preclinical treatment trial. MR imaging was performed at 1.5 T at baseline, and repeated at 1- to 2-week intervals for a period of up to 16 weeks in six EAE-induced marmosets, and intermittently for up to 70 weeks in three EAE-induced and two control marmosets. Proton density- (PD-) and T2-weighted, pre- and postgadopentetate dimeglumine enhancement, T1-weighted, and magnetization transfer (MT) images were obtained. The brains were prepared for histologic evaluation of lesion distribution and counts, characterization of lesions as demyelinating or inflammatory, and histopathologic scoring. The clinical, MR, and pathologic scoring were done on grading systems, and correlated for evaluation. RESULTS: White matter (WM) changes after EAE induction were observed first at 9 days in the HWM-induced animals and at 2.5 weeks in the MP4-induced animals, with subsequent week-to-week fluctuations on PD- and T2-weighted images. Contrast-enhancing lesions were not observed in all animals. MR-revealed WM lesions correlated to histopathologic analysis of EAE lesions, measuring from 0.5 mm to 1.5 mm. The lesion count and extent of demyelination was greater in the HWM-induced animals than in the MP4-induced animals. Some MR-revealed lesions correlated directly to clinical symptoms, but the majority of lesions were clinically silent. CONCLUSION: On MR images, lesions in the EAE marmoset model were confined to the WM, and their development, resolution, distribution, and enhancing characteristics fluctuated over the duration of the study. The dynamic presentation of MR-revealed lesions confirms the parallels between EAE in the marmoset and relapsing-remitting MS. Clinical symptoms alone were not representative of ongoing pathologic brain lesions. Therefore, serial MR imaging serves as a very important adjunct to clinical and histologic surveillance of the development of new and the persistence of existing brain lesions in this animal model of MS. (+info)
Regeneration of isthmic tissue is the result of a specific and direct interaction between rhombomere 1 and midbrain.
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The midbrain-hindbrain boundary, or isthmus, is the source of signals that are responsible for regional specification of both the midbrain and anterior hindbrain. Fibroblast growth factor 8 (Fgf8) is expressed specifically at the isthmus and there is now good evidence that it forms at least part of the patterning signal. In this study, we use Fgf8 as a marker for isthmic cells to examine how interactions between midbrain and hindbrain can regenerate isthmic tissue and, thereby, gain insight into the normal formation and/or maintenance of the isthmus. We show that Fgf8-expressing tissue with properties of the isthmic organiser is generated when midbrain and rhombomere 1 tissue are juxtaposed but not when midbrain contacts any other rhombomere. The use of chick/quail chimeras shows that the isthmic tissue is largely derived from rhombomere 1. In a few cases a small proportion of the Fgf8-positive cells were of midbrain origin but this appears to be the result of a local respecification to a hindbrain phenotype, a process mimicked by ectopic FGF8. Studies in vitro show that the induction of Fgf8 is the result of a direct planar interaction between the two tissues and involves a diffusible signal. (+info)