Remodeling of lesioned kitten visual cortex after xenotransplantation of fetal mouse neopallium

A neurological comparative study of the harp seal (Pagophilus groenlandicus) and harbor porpoise (Phocoena phocoena) brain

The cetacean brain is well studied. However, few comparisons have been done with other marine mammals. In this study, we compared the harp seal (Pagophilus groenlandicus) and the harbor porpoise brain (Phocoena phocoena). Stereological methods were applied to compare three areas of interest: the entire neocortex and two subdivisions of the neocortex, the auditory and visual cortices. The total number of neurons and glial cells in the three regions was estimated. The main results showed that the harbor porpoise have an estimated 14.9 × 10(9) neocortical neurons and 34.8 × 10(9) neocortical glial cells, whereas the harp seal have 6.1 × 10(9) neocortical neurons and 17.5 × 10(9) neocortical glial cells. The harbor porpoise have significantly more neurons and glial cells in the auditory cortex than in the visual cortex, whereas the pattern was opposite for the harp seal. These results are the first to provide estimates of the number of neurons and glial cells in the neocortex of the harp seal and harbor porpoise brain and offer new data to the comparative field of mammalian brain evolution.

Plasticity of the central nervous system and formation of "auxiliary niches" after stem cell grafting: an essay

It is hoped that stem cell biology will play a major role in the treatment of a number of so far incurable diseases via transplantation therapy. Today, we know that neural stem cell grafts not only represent a valuable source of missing cells and molecules for the host nervous system, but they also bring with them biological principles and processes assuring tissue plasticity and homeostasis found in early development and in postnatal neurogenic areas. In this review, we discuss the potential of grafted neural stem/progenitor cells to induce plasticity in the adult diseased brain by mimicking the cellular and molecular processes governing the biology of endogenous stem cell niches. If confirmed, such anlagen of "auxiliary niches" could help us to optimize intercellular communication in donor cell-initiated networks of graft-host interactions and to "rejuvenate" the adult nervous system in its response to disease and injury.

Successful differentiation of mouse neural stem cells on layer-by-layer assembled single-walled carbon nanotube composite

The same properties that made carbon nanotube (CNT) composites interesting for electronics, sensing, and ultrastrong structural materials also make them an asset for biomedical engineering. The combination of electron conductivity, corrosion resistance, and strength are essential for neuroprosthetic devices. All of the studies in this area demonstrating cellular adhesion and signal transduction activity on CNT matrixes were conducted, so far, with terminally differentiated primary cells and cancerous cell lines. Neural stem cells are very plastic neural precursors capable of adapting to environmental conditions and recreating signal transduction pathways. Their intrinsic biological functionality not only makes the transition to stem cell cultures a difficult-to-avoid step but also implies several fundamentally important challenges. Here we demonstrate that mouse embryonic neural stem cells (NSCs) from the cortex can be successfully differentiated to neurons, astrocytes, and oligodendrocytes with clear formation of neurites on layer-by-layer (LBL) assembled single-walled carbon nanotube (SWNT)-polyelectrolyte multilayer thin films. Biocompatibility, neurite outgrowth, and expression of neural markers were similar to those differentiated on poly-L-ornithine (PLO), one of the most widely used growth substratums for neural stem cells.

Graft/host relationships in the developing and regenerating CNS of mammals

A new light was shed on the utility of neural grafts when it was recognized that donor tissues and cells offer more than a source of immature progenitors potentially capable of cell replacement: First, they have the inherent capacity to produce multiple trophic and tropic factors promoting cell survival and tissue plasticity often characteristic of the immature central nervous system (CNS). Second, by their interaction with the host microenvironment via cell/cell and cell/ECM interactions, these grafts are capable of re-establishing homeostasis, which can be, for example, reflected in rescue and protection of host elements from harmful influences. This second capacity of donor cells relies, in part, also on a "dormant" but still present regenerative capacity of mature or even aged CNS and on the possibility of its mobilization in the damaged nervous system by neural grafts. For this to occur efficiently after transplantation, a bi-directional dialogue between donor and host cells must gradually be established, in which both "partners" transmit signals (cell/cell contact, molecular messengers), "listen to" and "understand" each other and are able to react by modifying their own plasticity- and development-related programs. Thus, for the best possible recovery of functionality in the injured adult and aged nervous system, neurotransplantation must always try to find optimal conditions for all three of the mentioned qualities of neural grafts, especially for the protection and/or reactivation of neural circuitry embedded in non-neurogenic CNS areas. Once fully understood, this newly recognized aspect of neurotransplantation (and topic of this review) might, someday, even allow the recovery of systems that would otherwise be doomed, such as cognition- and experience-related circuitry.

Graft-induced plasticity in the mammalian host CNS

In this review we trace back the history of an idea that takes a new approach in restorative neurotransplantation by focusing on the "multifaceted dialogue" between graft and host and assigns a central role to graft-evoked host plasticity. In several experimental examples ranging from the transfer of solid fetal tissue grafts into mechanical cortical injuries to deposits of neural stem cells into hemisectioned spinal cord. MPTP-damaged substantia nigra or mutant cerebella supportive evidence is provided for the hypothesis, that in many CNS disorders regeneration of the host CNS can be achieved by taking advantage of the inherent capacity of neural grafts to induce protective and restorative mechanisms within the host. This principle might once allow us to spare even complex circuitry from neurodegeneration.

Multifaceted dialogue between graft and host in neurotransplantation

Current restorative neurotransplantation research focuses mainly on the potential of the neural graft to replace damaged or missing cell populations and to deliver needed gene products in the form of transgenes. Because of this graft-oriented bias of the procedure, possible dormant regenerative capabilities within the host have been largely underestimated and dismissed as insignificant. This review discusses existing evidence that neural grafts can have stimulating effects on host-intrinsic plasticity that can help regeneration of the mammalian central nervous system. If confirmed, the synergistic interaction between graft and host might substantially enhance our therapeutic possibilities.

Neural stem cells display an inherent mechanism for rescuing dysfunctional neurons

We investigated the hypothesis that neural stem cells (NSCs) possess an intrinsic capacity to "rescue" dysfunctional neurons in the brains of aged mice. The study focused on a neuronal cell type with stereotypical projections that is commonly compromised in the aged brain-the dopaminergic (DA) neuron. Unilateral implantation of murine NSCs into the midbrains of aged mice, in which the presence of stably impaired but nonapoptotic DA neurons was increased by treatment with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), was associated with bilateral reconstitution of the mesostriatal system. Functional assays paralleled the spatiotemporal recovery of tyrosine hydroxylase (TH) and dopamine transporter (DAT) activity, which, in turn, mirrored the spatiotemporal distribution of donor-derived cells. Although spontaneous conversion of donor NSCs to TH(+) cells contributed to nigral reconstitution in DA-depleted areas, the majority of DA neurons in the mesostriatal system were "rescued" host cells. Undifferentiated donor progenitors spontaneously expressing neuroprotective substances provided a plausible molecular basis for this finding. These observations suggest that host structures may benefit not only from NSC-derived replacement of lost neurons but also from the "chaperone" effect of some NSC-derived progeny.

Ectopic expression of the neural cell adhesion molecule L1 in astrocytes leads to changes in the development of the corticospinal tract

The cell recognition molecule L1, of the immunoglobulin superfamily, participates in the formation of the nervous system and has been shown to enhance cell migration and neurite outgrowth in vitro. To test whether ectopic expression of L1 would influence axonal outgrowth in vivo, we studied the development of the corticospinal tract in transgenic mice expressing L1 in astrocytes under the control of the GFAP-promoter. Corticospinal axons innervate their targets by extending collateral branches interstitially along the axon shaft following a precise spatio-temporal pattern. Using DiI as an anterograde tracer, we found that in the transgenic animals, corticospinal axons appear to be defasciculated, reach their targets sooner and form collateral branches innervating the basilar pons at earlier developmental stages and more diffusely than in wild type littermates. Collateral branches in the transgenic mice did not start out as distinct rostral and caudal sets, but they branched from the axon segments in a continuous rostrocaudal direction across the entire region of the corticospinal tract overlying the basilar pons. The ectopic branches are transient and no longer present at postnatal day 22. The earlier outgrowth and altered branching pattern of corticospinal axons in the transgenics is accompanied by an earlier differentiation of astrocytes. Taken together, our observations provide evidence that the ectopic expression of L1 on astrocytes causes an earlier differentiation of these cells, results in faster progression of corticospinal axons and influences the branching pattern of corticospinal axons innervating the basilar pons.

Segregation of human neural stem cells in the developing primate forebrain

Many central nervous system regions at all stages of life contain neural stem cells (NSCs). We explored how these disparate NSC pools might emerge. A traceable clone of human NSCs was implanted intraventricularly to allow its integration into cerebral germinal zones of Old World monkey fetuses. The NSCs distributed into two subpopulations: One contributed to corticogenesis by migrating along radial glia to temporally appropriate layers of the cortical plate and differentiating into lamina-appropriate neurons or glia; the other remained undifferentiated and contributed to a secondary germinal zone (the subventricular zone) with occasional members interspersed throughout brain parenchyma. An early neurogenetic program allocates the progeny of NSCs either immediately for organogenesis or to undifferentiated pools for later use in the "postdevelopmental" brain.

Neural stem cells -- a versatile tool for cell replacement and gene therapy in the central nervous system

In recent years, it has become evident that the developing and even the adult mammalian central nervous system contains a population of undifferentiated, multipotent cell precursors, neural stem cells, the plastic properties of which might be of advantage for the design of more effective therapies for many neurological diseases. This article reviews the recent progress in establishing rodent and human clonal neural stem cell lines, their biological properties, and how these cells can be utilized to a correct variety of defects, with prospects for the near future to harness their behaviour for neural stem cell-based treatment of diseases in humans.