Human fetal neocortical tissue grafted to rat brain cavities survives, leads to reciprocal nerve fiber growth, and accumulates host IgG

The Role of Tissue Geometry in Spinal Cord Regeneration

Unlike peripheral nerves, axonal regeneration is limited following injury to the spinal cord. While there may be reduced regenerative potential of injured neurons, the central nervous system (CNS) white matter environment appears to be more significant in limiting regrowth. Several factors may inhibit regeneration, and their neutralization can modestly enhance regrowth. However, most investigations have not considered the cytoarchitecture of spinal cord white matter. Several lines of investigation demonstrate that axonal regeneration is enhanced by maintaining, repairing, or reconstituting the parallel geometry of the spinal cord white matter. In this review, we focus on environmental factors that have been implicated as putative inhibitors of axonal regeneration and the evidence that their organization may be an important determinant in whether they inhibit or promote regeneration. Consideration of tissue geometry may be important for developing successful strategies to promote spinal cord regeneration.

Glial influence on nerve fiber formation from rat ventral mesencephalic organotypic tissue cultures

Rat fetal ventral mesencephalic organotypic cultures have demonstrated two morphologically different dopamine nerve fiber growth patterns, in which the initial nerve fibers are formed in the absence of astrocytes and the second wave is guided by astrocytes. In this study, the presence of subpopulations of dopamine neurons, other neuronal populations, and glial cells was determined. We used "roller-drum" organotypic cultures, and the results revealed that beta-tubulin-positive/tyrosine hydroxylase (TH)-negative nerve fibers were present as early as 1 day in vitro (DIV). A similar growth pattern produced by TH-positive neurons was present from 2 DIV. These neurites grew to reach distances over 4 mm and over time appeared to be degenerating. Thin, vimentin-positive processes were found among these nerve fibers. As the first growth was retracted, a second outgrowth was initiated and formed on migrating astrocytes. TH- and aldehyde dehydrogenase-1 (ALDH1)-positive nerve fibers formed both the nonglia-associated and the glia-associated outgrowth. In cultures with membrane inserts, only the glia-associated outgrowth was found. Vimentin-positive cells preceded migration of NG2-positive oligodendrocytes and Iba-1-positive microglia. Oligodendrocytes appeared not to be involved in guiding neuritic growth, but microglia was absent over areas dense with TH-positive neurons. In conclusion, in "roller-drum" cultures, nerve fibers are generally formed in two sequences. The early-formed nerve fibers grow in the presence of thin, vimentin-positive processes. The second nerve fiber outgrowth is formed on astroglia, with no correlation to the presence of oligodendrocytes or microglia. ALDH1-positive nerve fibers, presumably derived from A9 dopamine neurons, participate in formation of both sequences of outgrowth.

A Review and Rationale for the Use of Cellular Transplantation as a Therapeutic Strategy for Traumatic Brain Injury

Experimental research during the past decade has greatly increased our understanding of the pathophysiology of traumatic brain injury (TBI) and allowed us to develop neuroprotective pharmacological therapies. Encouraging results of experimental pharmacological interventions, however, have not been translated into successful clinical trials, to date. Traumatic brain injury is now believed to be a progressive degenerative disease characterized by cell loss. The limited capacity for self-repair of the brain suggests that functional recovery following TBI is likely to require cellular transplantation of exogenous cells to replace those lost to trauma. Recent advances in central nervous system transplantation techniques involve technical and experimental refinements and the analysis of the feasibility and efficacy of transplantation of a range of stem cells, progenitor cells and postmitotic cells. Cellular transplantation has begun to be evaluated in several models of experimental TBI, with promising results. The following is a compendium of these new and exciting studies, including a critical discussion of the rationale and caveats associated with cellular transplantation techniques in experimental TBI research. Further refinements in future research are likely to improve results from transplantation-based treatments for TBI.

Guidance of dopaminergic neuritic growth by immature astrocytes in organotypic cultures of rat fetal ventral mesencephalon

Astrocytes, with their many functions in producing and controlling the environment in the brain, are of great interest when it comes to studying regeneration after injury and neurodegenerative diseases such as in grafting in Parkinson's disease. This study was performed to investigate astrocytic guidance of growth derived from dopaminergic neurons using organotypic cultures of rat fetal ventral mesencephalon. Primary cultures were studied at different time points starting from 3 days up to 28 days. Cultures were treated with either interleukin-1 beta (IL-1 beta), which has stimulating effects on astrocytic proliferation, or the astrocytic inhibitor cytosine arabinoside (Ara-C). Tyrosine hydroxylase (TH)-immunohistochemistry was used to visualize dopaminergic neurons, and antibodies against glial fibrillary acidic protein (GFAP) and S100 beta were used to label astrocytes. The results revealed that a robust TH-positive nerve fiber production was seen already at 3 days in vitro. These neurites had disappeared by 5 days. This early nerve fiber outgrowth was not guided by direct interactions with glial cells. Later, at 7 days in vitro, a second wave of TH-positive neuritic outgrowth was clearly observed. GFAP-positive astrocytic processes guided these neurites. TH-positive neurites arborized overlying S100 beta-positive astrocytes in an area distal to the GFAP-positive astrocytic processes. Treatment with IL-1 beta resulted in an increased area of TH-positive nerve fiber network. In cultures treated with Ara-C, neither astrocytes nor outgrowth of dopaminergic neurites were observed. In conclusion, this study shows that astrocytes play a major role in long-term dopaminergic outgrowth, both in axonal elongation and branching of neurites. The long-term nerve fiber growth is preceded by an early transient outgrowth of dopamine neurites.

Disruption of spinal cord white matter and sciatic nerve geometry inhibits axonal growth in vitro in the absence of glial scarring

BACKGROUND

Axons within the mature mammalian central nervous system fail to regenerate following injury, usually resulting in long-lasting motor and sensory deficits. Studies involving transplantation of adult neurons into white matter implicate glial scar-associated factors in regeneration failure. However, these studies cannot distinguish between the effects of these factors and disruption of the spatial organization of cells and molecular factors (disrupted geometry). Since white matter can support or inhibit neurite growth depending on the geometry of the fiber tract, the present study sought to determine whether disrupted geometry is sufficient to inhibit neurite growth.

RESULTS

Embryonic chick sympathetic neurons were cultured on unfixed longitudinal cryostat sections of mature rat spinal cord or sciatic nerve that had been crushed with forceps ex vivo then immediately frozen to prevent glial scarring. Neurite growth on uncrushed portions of spinal cord white matter or sciatic nerve was extensive and highly parallel with the longitudinal axis of the fiber tract but did not extend onto crushed portions. Moreover, neurite growth from neurons attached directly to crushed white matter or nerve tissue was shorter and less parallel compared with neurite growth on uncrushed tissue. In contrast, neurite growth appeared to be unaffected by crushed spinal cord gray matter.

CONCLUSIONS

These observations suggest that glial scar-associated factors are not necessary to block axonal growth at sites of injury. Disruption of fiber tract geometry, perhaps involving myelin-associated neurite-growth inhibitors, may be sufficient to pose a barrier to regenerating axons in spinal cord white matter and peripheral nerves.

Myelin contributes to the parallel orientation of axonal growth on white matter in vitro

BACKGROUND

Brain and spinal cord white matter can support extensive axonal growth. This growth is generally constrained to an orientation that is parallel to the longitudinal axis of the fiber tract. This constraint is presumably due to permissive and non-permissive substrates that are interleaved with each other and oriented in parallel within the tract.

RESULTS

Embryonic chick sympathetic neurons were cultured on cryostat sections of rat brain and the orientation of neurite growth on white matter was assessed. To determine if haptotaxis is sufficient to guide parallel neurite growth, neurons were cultured under conditions designed to interfere with interactions between growing neurites and factors that act as biochemical contact guidance cues but not interactions with haptotactic cues. Under these conditions, neurites extending on white matter were not exclusively oriented in parallel to the fiber tract, suggesting that biochemical cues are involved. To assess the role of myelin in guiding parallel neurite growth, neurons were cultured on myelin-deficient corpus callosum. These neurons also extended neurites that were not constrained to a parallel orientation. Moreover, preincubation with NGF and treatment with cAMP analogs, manipulations that attenuate overall myelin-mediated inhibition of neurite growth, also led to a reduced parallel orientation of neurite growth.

CONCLUSIONS

The present studies suggest that some of the relevant factors that constrain axonal growth on white matter are not haptotactic in nature and appear to be partly mediated by factors that are associated with myelin and may involve myelin-associated "inhibitors".

White matter of the CNS supports or inhibits neurite outgrowth in vitro depending on geometry

Axonal regeneration is normally limited within myelinated fiber tracts in the CNS of higher vertebrates. Numerous studies suggest that CNS myelin contains inhibitors that may contribute to abortive axonal growth. In contrast to the evidence of myelin-associated neurite inhibitors, embryonic neurons transplanted into the CNS can regenerate extensively within myelinated tracts in vivo. It has been speculated that embryonic neurons do not yet express the appropriate receptors for myelin-associated inhibitors. Recently, however, extensive regeneration from transplanted adult neurons has also been reported within myelinated tracts of the CNS, casting doubt on the role myelin-associated inhibitors play in abortive regeneration. The present study reexamined the potential of white matter to support neurite growth in vitro. By the use of Neurobasal medium, neurons were cultured onto unfixed cryostat sections of mature rat CNS tissue. As documented previously, robust neuronal attachment and neurite outgrowth occurred on gray matter but these neurites were sharply inhibited by white matter. In addition, however, increased rates of neuronal attachment directly to white matter occurred with neurite outgrowth comparable in length with that on gray matter but limited to directions parallel to the fiber tract. Frequently, the same section of white matter was found to inhibit neurite outgrowth from neurons on gray matter while supporting parallel neurite outgrowth from neurons on white matter. These results suggest that whether white matter supports or inhibits axonal growth depends on the geometric relationship between the axon and the fiber tract; more specifically, white matter supports parallel growth but inhibits nonparallel growth.

Fiber outgrowth from anterior hypothalamic and cortical xenografts in the third ventricle

Fetal grafts of the anterior hypothalamus (SCN/AH) containing the suprachiasmatic nucleus (SCN) restore circadian rhythms to SCN-lesioned host hamsters and rats following implantation into the third ventricle. Previous studies suggest that intraventricular SCN/AH grafts are variable in their attachment sites, the extent of their outgrowth, and the precise targets innervated in the host brain. However, the use of different methods to analyze graft outgrowth in this model has previously led to inconsistent results. We have reevaluated the outgrowth of fetal rat SCN/AH grafts implanted in the third ventricle of hamsters by using two methods: the carbocyanine dye, 1,1'dioctadecyl-3,3'-tetramethylindocarbocyanine percholate (DiI), was placed directly onto grafted tissue; and a donor-specific neurofilament marker was used in conjunction with xenografts. We examined the specificity of outgrowth by comparing SCN/AH xenografts with that of control cortical (CTX) xenografts. To evaluate whether SCN/AH graft efferents arise from the donor SCN, we used micropunch grafts that contained minimal extra-SCN tissue. The results show that the use of a donor-specific neurofilament marker reveals more extensive SCN/AH graft outgrowth than DiI. SCN/AH graft efferents project into areas normally innervated by the intact SCN. However, this outgrowth is variable among graft recipients, is not specific to SCN/AH tissue, and does not necessarily derive from the donor SCN. The precise functional role of neural efferents arising from SCN/AH grafts in the restoration of circadian clock function and the extent of SCN-derived efferents remain to be determined.

Characteristics of human fetal spinal cord grafts in the adult rat spinal cord: influences of lesion and grafting conditions

The present study evaluated the growth potential and differentiation of human fetal spinal cord (FSC) tissue in the injured adult rat spinal cord under different lesion and grafting conditions. Donor tissue at 6-9 weeks of gestational age was obtained through elective abortions and transplanted either immediately into acute resection (solid grafts) or into chronic contusion (suspension and solid grafts) lesions (i.e., 14-40 days after injury) in the thoracic spinal cord. The xenografts were then examined either histologically in plastic sections or immunocytochemically 1-3 months postgrafting. Intraspinal grafts in acute lesions demonstrated an 83% survival rate and developed as well-circumscribed nodules that were predominantly composed of immature astrocytes. Solid-piece grafts in chronic contusion lesions exhibited a 92% survival rate and also developed as nodular masses. These grafts, however, contained many immature neurons 2 months postgrafting. Suspension grafts in chronic contusion lesions had an 85% survival rate and expanded in a nonrestrictive, diffuse pattern. These transplants demonstrated large neuronally rich areas of neural parenchyma. Extensive neuritic outgrowth could also be seen extending from these grafts into the surrounding host spinal cord. These findings show that human FSC tissue reliably survives and differentiates in both acute and chronic lesions. However, both the lesion environment and the grafting techniques can greatly influence the pattern of differentiation and degree of host-graft integration achieved.

Morphological and morphometric analysis of serotonin-containing neurons in primary dissociated cultures of human rhombencephalon: a study of development

Primary dissociated cultures of rhombencephalon were prepared from 5-9-week-old human fetuses. Half of some cultures were treated by two non-competitive N-methyl-D-aspartate antagonists, namely 1-(2-thienyl)cyclohexylpiperidine (TCP) and cis-Pip/Mel-[1-(2-thienyl)-2-methyl-cyclohexyl]piperidine (GK11) in negative enantiomeric form, which enhance the survival of human fetal central nervous system cells in culture. At different days in vitro, the treated and the control cultures were processed for immunocytochemical detection of serotonin-containing neurons which were studied by morphological and morphometric analysis. Statistical analysis showed that the surface of the stained neurons increased as a function of two parameters of time, the gestational age of the cells and the duration of the cultures. The complexity of the shape of the serotonin neurons characterized by the shape factor, the number of bifurcations and the morphological feature (bipolar or multipolar) was found to increase with the gestational age. It appears that the in vitro development of the embryonic cells which represents stages of maturation and differentiation can be specifically evaluated. Such an analysis of fetal central nervous system cells improves the knowledge of factors important in grafting experiments. We verified that the two drugs do not appreciably alter the in vitro development of the treated cells; thus they may be considered as promising drugs for human neuroprotection.

Acute and chronic noradrenergic regulation of neurotrophin messenger RNA expression in rat hippocampus: evidence from lesions and organotypic cultures

Noradrenergic neurons from the locus coeruleus innervate several brain regions, such as hippocampus and cortex. The hippocampus exhibits the highest concentration of the neurotrophins nerve growth factor, brain-derived neurotrophic factor and neurotrophin-3 in the brain. To study the role of the noradrenergic system in the chronic regulation of neurotrophin messenger RNA expression, chemical [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, 6-hydroxydopamine] and mechanical (knife-cut axotomy) lesions were performed, in the rat, and neurotrophin messenger RNAs analysed after 14 and 35 days. The intensity of the lesion was verified by characterization of the noradrenergic system using immunohistochemistry and in situ hybridization for dopamine-beta-hydroxylase and the measurement of noradrenaline tissue levels. To study the acute regulation, hippocampal organotypic slice cultures were prepared and neurotrophin messenger RNAs analysed after incubation in different concentrations of noradrenaline. We report that the noradrenergic N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine depletion significantly increased nerve growth factor and brain-derived neurotrophic factor messenger RNAs but not neurotrophin-3 messenger RNA in hippocampal areas 35 days after the lesion, while the knife-cut axotomy had a less pronounced effect and the 6-hydroxydopamine lesion did not change the neurotrophins. When incubating the organotypic hippocampal cultures with different concentrations of noradrenaline, nerve growth factor and brain-derived neurotrophic factor messenger RNAs but not neurotrophin-3 messenger RNA were significantly reduced in the dentate gyrus. We conclude that nerve growth factor and brain-derived neurotrophic factor but not neurotrophin-3 expression are inhibited by noradrenaline, arising from the locus coeruleus.

Human fetal cortical tissue fragments survive grafting following one week storage at +4 degrees C

Grafting of human fetal tissue fragments has been used successfully in experimental and clinical trials. The development of techniques to store human fetal tissue fragments for longer time periods would allow to establish temporary tissue banks. We dissected several human cortical tissue fragments from one fetus and tested different storage conditions (cooling, freezing, culturing). After storage, the tissue fragments were transplanted into cavities in the cortex of host rats and the volume of the surviving grafts calculated. We report that human cortical tissue fragments grafted immediately after dissection (control group) or grafted after storage for 3 h in cryopreservation medium at room temperature survived grafting and resulted in graft sizes of 102 +/- 26 mm3 and 242 +/- 210 mm3, respectively, however, statistically not different. When the human cortical tissue fragments were slowly frozen and stored for 1 wk and/or when the fragments were cultured for 1 week in culture medium using a roller tube technique, grafts did not survive under our conditions. However, when the human cortical tissue fragments were stored for 1 week at +4 degrees C in cryopreservation medium, the graft size (48 +/- 24 mm3) was reduced but statistically not different from the control group. We conclude that human cortical tissue fragments can be stored at +4 degrees C for at least 1 wk without major loss of ability to survive grafting.