Transplantation of embryonic serotonin immunoreactive neurons into the transected spinal cord of adult monkey (Macaca fascicularis)

Altered Differentiation of Cns Neural Progenitor Cells after Transplantation into the Injured Adult Rat Spinal Cord

Denervation of CNS neurons and peripheral organs is a consequence of traumatic SCI. Intraspinal transplantation of embryonic CNS neurons is a potential strategy for reinnervating these targets. Neural progenitor cell lines are being investigated as alternates to embryonic CNS neurons. RN33B is an immortalized neural progenitor cell line derived from embryonic rat raphé nuclei following infection with a retrovirus encoding the temperature-sensitive mutant of SV40 large T-antigen. Transplantation studies have shown that local epigenetic signals in intact or partially neuron-depleted adult rat hippocampal formation or striatum direct RN33B cell differentiation to complex multipolar morphologies resembling endogenous neurons. After transplantation into neuron-depleted regions of the hippocampal formation or striatum, RN33B cells were relatively undifferentiated or differentiated with bipolar morphologies. The present study examines RN33B cell differentiation after transplantation into normal spinal cord and under different lesion conditions. Adult rats underwent either unilateral lesion of lumbar spinal neurons by intraspinal injection of kainic acid or complete transection at the T10 spinal segment. Neonatal rats underwent either unilateral lesion of lumbar motoneurons by sciatic nerve crush or complete transection at the T10 segment. At 2 or 6-7 wk postinjury, lacZ-labeled RN33B cells were transplanted into the lumbar enlargement of injured and age-matched normal rats. At 2 wk posttransplantation, bipolar and some multipolar RN33B cells were found throughout normal rat gray matter. In contrast, only bipolar RN33B cells were seen in gray matter of kainic acid lesioned, sciatic nerve crush, or transection rats. These observations suggest that RN33B cell multipolar morphological differentiation in normal adult spinal cord is mediated by direct cell-cell interaction through surface molecules on endogenous neurons and may be suppressed by molecules released after SCI. They also indicate that the fate of immortalized neural progenitor cell lines in injured CNS must be stringently characterized.

The role of the serotonergic system in locomotor recovery after spinal cord injury

Serotonin (5-HT), a monoamine neurotransmitter synthesized in various populations of brainstem neurons, plays an important role in modulating the activity of spinal networks involved in vertebrate locomotion. Following spinal cord injury (SCI) there is a disruption of descending serotonergic projections to spinal motor areas, which results in a subsequent depletion in 5-HT, the dysregulation of 5-HT transporters as well as the elevated expression, super-sensitivity and/or constitutive auto-activation of specific 5-HT receptors. These changes in the serotonergic system can produce varying degrees of locomotor dysfunction through to paralysis. To date, various approaches targeting the different components of the serotonergic system have been employed to restore limb coordination and improve locomotor function in experimental models of SCI. These strategies have included pharmacological modulation of serotonergic receptors, through the administration of specific 5-HT receptor agonists, or by elevating the 5-HT precursor 5-hydroxytryptophan, which produces a global activation of all classes of 5-HT receptors. Stimulation of these receptors leads to the activation of the locomotor central pattern generator (CPG) below the site of injury to facilitate or improve the quality and frequency of movements, particularly when used in concert with the activation of other monoaminergic systems or coupled with electrical stimulation. Another approach has been to employ cell therapeutics to replace the loss of descending serotonergic input to the CPG, either through transplanted fetal brainstem 5-HT neurons at the site of injury that can supply 5-HT to below the level of the lesion or by other cell types to provide a substrate at the injury site for encouraging serotonergic axon regrowth across the lesion to the caudal spinal cord for restoring locomotion.

C3 peptide enhances recovery from spinal cord injury by improved regenerative growth of descending fiber tracts

Functional recovery and regeneration of corticospinal tract (CST) fibers following spinal cord injury by compression or dorsal hemisection in mice was monitored after application of the enzyme-deficient Clostridium botulinum C3-protein-derived 29-amino-acid fragment C3bot154-182. This peptide significantly improved locomotor restoration in both injury models as assessed by the open-field Basso Mouse Scale for locomotion test and Rotarod treadmill experiments. These data were supported by tracing studies showing an enhanced regenerative growth of CST fibers in treated animals as visualized by anterograde tracing. Additionally, C3bot154-182 stimulated regenerative growth of raphespinal fibers and improved serotonergic input to lumbar α-motoneurons. These in vivo data were confirmed by in vitro data, showing an enhanced axon outgrowth of α-motoneurons and hippocampal neurons cultivated on normal or growth-inhibitory substrates after application of C3bot154-182. The observed effects were probably caused by a non-enzymatic downregulation of active RhoA by the C3 peptide as indicated by pull-down experiments. By contrast, C3bot154-182 did not induce neurite outgrowth in primary cultures of dorsal root ganglion cells. In conclusion, C3bot154-182 represents a novel, promising tool to foster axonal protection and/or repair, as well as functional recovery after traumatic CNS injury.

Astrocytes and oligodendrocytes reactions after a total section of the rat spinal cord

Regeneration after an injury in the Central Nervous System is dependent on intrinsic and extrinsic factors. Among the latter are the reactions of glial cells. Using the model of total section of adult rat spinal cord, we have studied the spatial and temporal responses of astrocytes and oligodendrocytes to the lesion of spinal cord axons. We studied at molecular and cellular levels the specific markers GFAP (glial fibrillary acidic protein) for the astrocytes, CNP (2'-3' cyclic 3' nucleotide phosphodiesterase) which is principally expressed by immature oligodendrocytes, and MBP (myelin basic protein) implicated later in the myelin compaction, and which is more specific of mature oligodendrocytes. After injury, all astrocytes, but more markedly those of the grey matter, reacted by an increase of GFAP messenger and protein. This increase was very rapid for messenger, and peaked at 3 days. This increase was more protracted for the protein and persisted after 3 weeks. Messenger increase is more marked and more protracted below than above the lesion. Oligodendrocytes also reacted quickly by an increase of CNP and MBP messengers. For CNP, both messenger and protein increased rapidly and returned to control level after 1 week. MBP showed the same time course of changes, with lower and slower decrease above the lesion. Counts of oligodendrocytes showed that the percentage of the less mature form (light oligodendrocytes) increased dramatically above and below the lesion. After 1 week, above the lesion, this percentage was well below that of the control, whereas below the lesion, it reverted to control value. These results indicate that, following a lesion, astrocytes react quickly and intensely, but more so below the lesion; oligodendrocytes resume a sequence of maturation which is eventually completed above the lesion where remyelinisation can occur and which is prematurely interrupted below the lesion. However, intact oligodendrocytes persist below the lesion, where they constitute a potential for remyelinisation of regenerated and/or transplanted axons.

Transplant therapy: recovery of function after spinal cord injury

Spinal cord injuries (SCI) result in devastating loss of function and altered sensation. Presently, victims of SCI have few remedies for the loss of motor function and the altered sensation often experienced subsequent to the injury. A goal in SCI research is to improve function in both acute and chronic injuries. Among the most successful interventions is the utilization of transplanted tissues toward improved recovery. The theory is that the transplanted tissue could (1) bridge the spinal lesion and provide chemical and/or mechanical guidance for host neurons to grow across the lesion, (2) bridge the spinal lesion and provide additional cellular elements to repair the damaged circuitry, (3) provide factors that would rescue neurons that would otherwise die and/or modulate neural circuits to improve function. A variety of tissues and cells have been added to the adult mammalian spinal cord to encourage restoration of function. These include Schwann cells, motor neurons, dorsal root ganglia, adrenal tissue, hybridomas, peripheral nerves, and fetal spinal cord (FSC) tissue en bloc or as disassociated cells. It is postulated that these tissues would rescue or replace injured adult neurons, which would then integrate or promote the regeneration of the spinal cord circuitry and restore function. In some instances, host-appropriate circuitry is supplied by the transplant and functional improvement is demonstrated. In this presentation, specific examples of recent work with transplanted tissue and cells that demonstrate improved behavioral outcome are presented. New recent work describing the in vitro propagation and characterization of human fetal spinal cord multipotential progenitor cells are also described in the context of a potential resource for transplantable cells. Additionally, data from transplantation experiments of human FSC cells into nonimmunosuppressed rat spinal cord are described, and the resultant improvements in behavioral outcome reported. Lastly, directions for future SCI research are proposed.

Primary dissociated cultures of human brainstem cells: a useful tool for their characterization and neuroprotection study

Dissociated cell cultures were prepared from brainstems of 5- to 10-week-old human fetuses. Catecholamine- as well as indolamine-containing cells were visualized using respectively dopamine (DA), noradrenaline (NA) and serotonin (5HT) as immunocytochemical markers. NA-, DA-, and 5HT-stained cells were characterized in the rhombencephalic cultures, representing respectively the fetal localization of the locus coeruleus and raphe nuclei. DA-stained cells were characterized in the mesencephalic cultures; these DA-cells originating from the substantia nigra presented morphological aspects different from the DA-rhombencephalic cells. Two types of GABA neurons and glial cells presenting glial fibrillary acidic protein (GFA-P) reactivity were also found in all the cultures. Two non-competitive N-methyl-D-aspartate antagonists, 1-[1-(2-thienyl)cyclohexyl]piperidine (TCP) and cis-Pip/Me 1-[1-(2-thienyl)-2-methylcyclohexyl]piperidine (GK11) in enantiomeric form (-), have been investigated for survival on rhombencephalic cultured cells. The number of 5HT-cells was found to be greater in the treated cultures than in the control ones. This in vitro system appears to be a useful tool for the investigation of the development of central nervous system (CNS) cells as well as the study of neuroprotection.

Patterning of the neocortical projections from the raphe nuclei in perinatal rats: investigation of potential organizational mechanisms

Serotoninergic (5-HT) fibers in the cerebral cortex of perinatal rats have a pattern that coincides with the boundaries of primary sensory areas and within the primary somatosensory cortex form the rattunculus. This patterned immunoreactivity (IR) appears about 60 hours after birth and disappears between postnatal days (P-) 12 and 15. Three experiments were carried out to evaluate mechanisms that might underlie the precise patterning of the 5-HT-IR. Retrograde labelling with fluorescent tracers in perinatal rats revealed only a coarse rostrocaudal topography in the raphe-cortical projection and the existence of raphe cells projecting to multiple cortical locations. Thus, a precise point-to-point, raphe-cortical projection does not underlie the patterned cortical 5-HT-IR. Ablation of the thalamus prior to the age at which patterned 5-HT-IR could be seen in the developing cortex caused a complete loss of patterned immunoreactivity. This suggests that 5-HT fibers may require the presence of thalamocortical axons to achieve the pattern observed in normal animals. Serotoninergic raphe neurons transplanted to the cortices of newborn rats exhibited extensive axonal outgrowth, but did not form a somatotopic pattern. This result also suggests that specific spatiotemporal interactions between growing 5-HT and thalamocortical axons may be necessary for the somatotopic patterning of the former fibers.

Migration and differentiation of PC12 cells transplanted into the rat spinal cord

To test the hypothesis that transplanted neuronal or neuronal-like cell lines, grown in vitro, might survive and differentiate in the mammalian spinal grey matter, adult male Sprague-Dawley rats (N = 5) were injected with a suspension of between 3 x 10(5) and 1.0 x 10(6) DiI labeled, undifferentiated rat pheochromocytoma (PC12) cells in sterile phosphate buffered saline. The PC12 cell line was chosen since, in certain in vitro conditions, this cell line serves as a model of neuronal differentiation, which includes the ability to conduct action potentials and form functional synapses. After a survival time of 7 or 8 days, the spinal cords were removed, cryosectioned longitudinally and examined for detection of DiI labeled PC12 cells using fluorescent microscopy. The number of DiI labeled profiles and the proportions of the DiI cells which were differentiated were counted per section in at least five non-contiguous sections per animal. Differentiation was defined as cells with neurite-like extension which exceeded twice the soma diameter. Results demonstrated the following: (1) from 2 to 15% of the transplanted PC12 cells survived; (2) migration within the spinal grey matter occurred since PC12 cells were found as much as 510 microns away from the injection site; (3) of the surviving PC12 cell population, a proportion of between 60 and 80% were differentiated, many with two or more neurite-like processes, in all of the rats; (4) no mitotic profiles were observed in DiI labelled cells; (5) undifferentiated PC12 cells were juxtaposed to the lumens of small blood vessels or within the lesion cavity. Although the specific factors remain to be elucidated, the observed PC12 migration and differentiation within the host spinal grey matter appears to be controlled by factors in the microenvironment. These data support the use of a homogeneous in vitro population of neuronal or neuronal-like cells, which are readily accessible to transfection with the appropriate genes, as transplant sources for the injured spinal cord.

Immunocytochemical demonstration of monoamine-containing cells in human fetal brain stem dissociated cultures

Primary dissociated cultures were prepared from the brain stems of 7- to 10-week-old human fetuses. Immunocytochemical detection of serotonin (5HT)-, dopamine (DA)-, noradrenaline (NA)- and tyrosine hydroxylase (TH)-containing cells was performed within 4 to 12 weeks in culture. We observed 5HT- and NA-stained neurons in the rhombencephalon. DA-stained cells were observed in the mesencephalon. TH-stained neurons were evidenced in both parts of the brain stem. Our in vitro system appears particularly appropriate for further investigation of grafts transplanted into the lesioned central nervous system (CNS).