Naomi Kleitman

A Combination of BDNF and NT-3 Promotes Supraspinal Axonal Regeneration into Schwann Cell Grafts in Adult Rat Thoracic Spinal Cord

We previously demonstrated that Schwann cells (SCs) in semipermeable guidance channels promote axonal regeneration in adult rat spinal cord transected at the mid-thoracic level. Propriospinal but not supraspinal axons grew into these channels. Here, we tested the ability of exogenous brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) to promote axonal regeneration in this novel model. The two neurotrophins were delivered simultaneously into the channel by an Alzet minipump at a rate of 12 micrograms/day for each neurotrophin for 14 of 30 days tested; phosphate-buffered saline, the vehicle solution, was used as a control. Significantly more myelinated nerve fibers were present in SC/neurotrophin grafts than in SC/vehicle grafts (1523 +/- 292 vs 882 +/- 287). In the graft, at least 5 mm from the rostral cord-graft interface, some nerve fibers were immunoreactive for serotonin, a neurotransmitter specific to raphe-derived axons in rat spinal cord. Fast blue retrograde tracing from SC/neurotrophin grafts revealed labeled neurons in 10 nuclei of the brain stem, 67% of these being in the lateral and spinal vestibular nuclei. The mean number of labeled brain stem neurons in the SC/neurotrophin group (92; n = 3) contrasted with the mean in the SC/vehicle group (6; n = 4). Our results clearly demonstrate that BDNF and NT-3 infusion enhanced propriospinal axonal regeneration and, more significantly, promoted axonal regeneration of specific distant populations of brain stem neurons into grafts at the mid-thoracic level in adult rat spinal cord.

Bridging Schwann cell transplants promote axonal regeneration from both the rostral and caudal stumps of transected adult rat spinal cord

Transplantation of cellular components of the permissive peripheral nerve environment in some types of spinal cord injury holds great promise to support regrowth of axons through the site of injury. In the present study, Schwann cell grafts were positioned between transected stumps of adult rat thoracic spinal cord to test their efficacy to serve as bridges for axonal regeneration. Schwann cells were purified in culture from adult rat sciatic nerve, suspended in Matrigel:DMEM (30:70), and drawn into polymeric guidance channels 8mm long at a density of 120×106 cells ml-1. Adult Fischer rat spinal cords were transected at the T8 cord level and the next caudal segment was removed. Each cut stump was inserted 1mm into the channel. One month later, a bridge between the severed stumps had been formed, as determined by the gross and histological appearance and the ingrowth of propriospinal axons from both stumps. Propriospinal neurons (mean, 1064±145 SEM) situated as far away as levels C3 and S4 were labelled by retrograde tracing with Fast Blue injected into the bridge. Near the bridge midpoint there was a mean of 1990±594 myelinated axons and eight times as many nonmyelinated, ensheathed axons. Essentially no myelinated or unmyelinated axons were observed in control Matrigel-only grafts. Brainstem neurons were not retrogradely labelled from the graft, consistent with growth of immunoreactive serotonergic and noradrenergic axons only a short distance into the rostral end of the graft, not far enough to reach the tracer placed at the graft midpoint. Anterograde tracing with PHA-L introduced rostral to the graft demonstrated that axons extended the length of the graft but essentially did not leave the graft. This study demonstrates that Schwann cell grafts serve as bridges that support (1) regrowth of both ascending and descending axons across a gap in the adult rat spinal cord and (2) limited regrowth of serotonergic and noradrenergic fibres from the rostral stump. Regrowth of monoaminergic fibres into grafts was not seen in an earlier study of similar grafts placed inside distally capped rather than open-ended channels. Additional intervention will be required to foster growth of the regenerated axons from the graft into the distal cord tissue.

Methylprednisolone administration improves axonal regeneration into Schwann cell grafts in transected adult rat thoracic spinal cord

Schwann cell (SC) grafts support the regeneration of axons of numerous spinal cord neurons when placed into transected adult rat midthoracic spinal cord. Clinically, methylprednisolone (MP) has been shown to be neuroprotective if administered within 8 h after spinal cord injury. We investigated whether axonal regrowth into SC grafts is enhanced when MP is administered at the time of spinal cord transection and SC implantation. SCs from adult rat sciatic nerves were purified in culture, suspended in Matrigel, and drawn into semipermeable polymeric channels. MP (30 mg/kg) or vehicle (control) was administered intravenously at 5 min, 2 h, and 4 h to adult Fischer rats after transection at T8 and removal of the next three caudal segments. The rostral cord stump was inserted 1 mm into the channel; the distal end of the channel was capped. Thirty to forty-five days later, the SC/MP group showed large tissue cables in the channels and host cord tissue retained in the rostral end of the channels. Significantly more myelinated axons (1159 +/- 308) were present at the 5-mm level in SC/MP grafts (n = 6) than in SC/vehicle cables (355 +/- 108, n = 5). More unmyelinated than myelinated axons (approximately 4:1, n = 3) were resolved in the cables by electron microscopy. In the SC/MP group, unlike the SC/vehicle group, serotonergic and noradrenergic fibers were detected immunocytochemically 2.5 and 2.0 mm respectively, into the graft; astrocytes were also identified at similar distances from the interface. Fast Blue retrograde tracing (SC/MP, n = 4; SC/vehicle, n = 3) showed that more spinal cord neurons (1116 +/- 113 vs 284 +/- 88, respectively) and spinal cord neurons more distant from the graft (C8 vs C5) responded by extending axons into the graft in the presence of MP. Also, very significantly, supraspinal brain stem neurons extended axons into the graft only when MP was administered (mean 46 vs 0, n = 3). These results indicate that MP improves axonal regenerationn from both spinal cord and brain stem neurons into thoracic SC grafts, possibly by reducing secondary host tissue loss adjacent to the graft.

Long-term effects of methylprednisolone following transection of adult rat spinal cord.

Clinically, high‐dose treatment with the glucocorticosteroid, methylprednisolone (MP), within 8 h after spinal cord injury, has been shown to improve neurological recovery. The current standard of care is to administer MP as a bolus of 30 mg/kg followed by a 23‐h infusion of 5.4 mg/kg/h to spinal cord injured patients. To better understand the role of MP in neuroprotection, we have studied how MP administration affects macrophage accumulation, tissue loss, and axonal dieback at 1, 2, 4 and 8 weeks after a complete transection of the eighth thoracic spinal cord in the adult rat. A 30 mg/kg dose of MP was administered intravenously at 5 min, and 2 and 4 h after injury. The number of ED1 (antibody against microglia/macrophages) ‐positive cells was quantified in a 500‐μm‐wide strip of tissue directly adjacent and parallel to the transection. At all time points, MP treatment led to a significant decrease in the number of ED1‐positive cells in both rostral and caudal stumps. Over the 2‐month post‐transection period, the average MP‐induced reduction in the number of ED1‐positive cells was 82% in the rostral cord stump and 66% in the caudal stump. Using a computerized image analysis system, it was observed that MP treatment resulted in a significant reduction in tissue loss in both cord stumps at 2, 4 and 8 week post‐injury. Over the 2‐month post‐lesion period, the average MP‐induced reduction in tissue loss in the caudal cord stump was higher than that in the rostral stump; 48 versus 37%, respectively. Immunostaining for neurofilaments and growth‐associated protein‐43 (GAP‐43) revealed the presence of numerous axons near and in the lesion site. Anterograde neuronal tracing with biotinylated dextran amine showed that, in MP‐treated animals, dieback of vestibulospinal fibres, but not of corticospinal fibres, was significantly diminished at all time points studied. In addition, with MP administration, 1 and 2 weeks after injury, an increase in the number of vestibulospinal fibres was found at 1 and 2 mm from the transection, suggesting transient regenerative sprouting of these fibres. The results demonstrate that treatment with MP shortly after spinal cord transection in the adult rat led to a long‐term reduction of ED1‐positive cells and spinal tissue loss, reduced dieback of vestibulospinal fibres, and a transient sprouting of vestibulospinal fibres near the lesion at 1 and 2 weeks post‐lesion. The possible relationships between the inflammatory changes, spinal tissue sparing, and axonal survival and sprouting are complex and need to be further explored.

Methylprednisolone and interleukin-10 reduce gray matter damage in the contused Fischer rat thoracic spinal cord but do not improve functional outcome.

The effects of two antiinflammatory and neuroprotective agents, methylprednisolone (MP) and interleukin-10 (IL-10), singly and in combination on tissue damage, axonal preservation and functional recovery were studied in the contused adult Fischer rat thoracic spinal cord 12 weeks after injury. MP (30 mg/kg at 5 min, and 2 and 4 h after injury) was administered intravenously and IL-10 (15 or 30 microg/kg at 30 min after injury), intraperitoneally. MP, IL-10, or the combination significantly reduced the volume of damaged tissue (including cavities) compared to control animals. The loss of spinal tissue (cavities) was reduced after treatment with MP alone or combined with IL-10, but not with IL-10 alone. The reduction in tissue damage was confined to spinal gray matter; at the level of the lesion epicenter, the thickness of the lateral white matter columns was similar in all groups. Retrograde tracing using fast blue revealed that the number of spared propriospinal and supraspinal projections was similar in all groups at 12 weeks after the contusion. The open-field BBB-test showed no significant difference in hindlimb locomotion between groups. Our results demonstrate that all tested antiinflammatory treatments significantly increase the volume of spared spinal gray matter 3 months after a moderate contusion of the Fischer rat thoracic spinal cord, but none of the treatments improved axonal preservation or functional recovery.

A combination of insulin-like growth factor-I and platelet-derived growth factor enhances myelination but diminishes axonal regeneration into schwann cell grafts in the adult rat spinal cord

Insulin‐like growth factor‐I (IGF‐I) promotes axonal regeneration in the peripheral nervous system and this effect is enhanced by platelet‐derived growth factor (PDGF). We decided, therefore, to study the effects of these factors on axonal regeneration in the adult rat spinal cord. Semipermeable polymer tubes, closed at the distal end, containing Matrigel mixed with cultured rat Schwann cells and IGF‐I/PDGF, were placed at the proximal stump of the spinal cord after removal of the thoracic T9‐11 segments. Control animals received implants of only Matrigel and Schwann cells or only Matrigel and IGF‐I/PDGF. Four weeks after implantation, electron microscopic analysis showed that the addition of IGF‐I/PDGF resulted in an increase in the myelinated:unmyelinated fiber ratio from 1:7 to 1:3 at 3 mm in the Schwann cell graft, and that myelin sheath thickness was increased 2‐fold. The reduced number of unmyelinated axons was striking in electron micrographs. These results suggested that IGF‐I/PDGF enhanced myelin formation of regenerated axons in Schwann cell implants, but there was a 36% decrease in the total number of myelinated axons at the 3 mm level of the graft. This finding and the altered myelinated:unmyelinated fiber ratio revealed that the overall fiber regeneration into Schwann cell implants was diminished up to 63% by IGF‐I/PDGF. Histological evaluation revealed that there were more larger cavities in tissue at the proximal spinal cord‐graft interface in animals receiving a Schwann cell implant with IGF‐I/PDGF. Such cavitation might have contributed to the reduction in axonal ingrowth. In sum, the results indicate that whereas the combination of IGF‐I and PDGF enhances myelination of regenerating spinal cord axons entering implants of Matrigel and Schwann cells after midthoracic transection, the overall regeneration of axons into such Schwann cell grafts is diminished. GLIA 19:247–258, 1997.

Common data elements for spinal cord injury clinical research: a National Institute for Neurological Disorders and Stroke project

Objectives:To develop a comprehensive set of common data elements (CDEs), data definitions, case report forms and guidelines for use in spinal cord injury (SCI) clinical research, as part of the CDE project at the National Institute of Neurological Disorders and Stroke (NINDS) of the US National Institutes of Health.Setting:International Working Groups.Methods:Nine working groups composed of international experts reviewed existing CDEs and instruments, created new elements when needed and provided recommendations for SCI clinical research. The project was carried out in collaboration with and cross-referenced to development of the International Spinal Cord Society (ISCoS) International SCI Data Sets. The recommendations were compiled, subjected to internal review and posted online for external public comment. The final version was reviewed by all working groups and the NINDS CDE team before release.Results:The NINDS SCI CDEs and supporting documents are publically available on the NINDS CDE website and the ISCoS website. The CDEs span the continuum of SCI care and the full range of domains of the International Classification of Functioning, Disability and Health.Conclusion:Widespread use of CDEs can facilitate SCI clinical research and trial design, data sharing and retrospective analyses. Continued international collaboration will enable consistent data collection and reporting, and will help ensure that the data elements are updated, reviewed and broadcast as additional evidence is obtained.

Incorporation of the International Spinal Cord Injury Data Set elements into the National Institute of Neurological Disorders and Stroke Common Data Elements.

Objectives:To develop consistent variable names and a common database structure for the data elements in the International Spinal Cord Injury (SCI) Data Sets.Setting:National Institute of Neurological Disorders and Stroke (NINDS) Common Data Elements (CDE) Project and The Executive Committee of the International SCI Standards and Data Sets committees (ECSCI).Methods:The NINDS CDE team creates a variable name for each defined data element in the various International SCI Data Sets. Members of the ECSCI review these in an iterative process to make the variable names logical and consistent across the data sets. Following this process, the working group for the particular data set reviews the variable names, and further revisions and adjustments may be made. In addition, a database structure for each data set is developed allowing data to be stored in a uniform way in databases to promote sharing data from different studies.Results:The International SCI Data Sets variable names and database specifications will be available through the web sites of the International Spinal Cord Society (http://www.iscos.org.uk), the American Spinal Injury Association (http://www.asia-spinalinjury.org) and the NINDS CDE project web site (http://www.CommonDataElements.ninds.nih.gov).Conclusion:This process will continue as additional International SCI Data Sets fulfill the requirements of the development and approval process and are ready for implementation.

Large animal and primate models of spinal cord injury for the testing of novel therapies

Large animal and primate models of spinal cord injury (SCI) are being increasingly utilized for the testing of novel therapies. While these represent intermediary animal species between rodents and humans and offer the opportunity to pose unique research questions prior to clinical trials, the role that such large animal and primate models should play in the translational pipeline is unclear. In this initiative we engaged members of the SCI research community in a questionnaire and round-table focus group discussion around the use of such models. Forty-one SCI researchers from academia, industry, and granting agencies were asked to complete a questionnaire about their opinion regarding the use of large animal and primate models in the context of testing novel therapeutics. The questions centered around how large animal and primate models of SCI would be best utilized in the spectrum of preclinical testing, and how much testing in rodent models was warranted before employing these models. Further questions were posed at a focus group meeting attended by the respondents. The group generally felt that large animal and primate models of SCI serve a potentially useful role in the translational pipeline for novel therapies, and that the rational use of these models would depend on the type of therapy and specific research question being addressed. While testing within these models should not be mandatory, the detection of beneficial effects using these models lends additional support for translating a therapy to humans. These models provides an opportunity to evaluate and refine surgical procedures prior to use in humans, and safety and bio-distribution in a spinal cord more similar in size and anatomy to that of humans. Our results reveal that while many feel that these models are valuable in the testing of novel therapies, important questions remain unanswered about how they should be used and how data derived from them should be interpreted.

Factors influencing the growth of regenerating nerve fibers in culture.

Publisher Summary This chapter discusses selected aspects of the influences of neuronal age, substratum, and nonneuronal cells on nerve fiber growth. Neurite growth from sympathetic ganglia removed from perinatal rats starts earlier and initially progresses faster than that from either embryonic or postnatal ganglia under identical conditions. These age dependent results reflect the morphology and behavior of individual growth cones. With increasing embryonic age, the chick sensory ganglion neurons increase in total axon length and complexity when cultured for equal periods. Age dependent growth is also expressed by some central nervous tissues, the olfactory bulb, and the retina. Collagen, laminin, and Schwann cell generated extracellular matrix all promote neurite outgrowth, but to varying degrees depending upon the type of neuron. Neurites from some types of central neurons grow faster on Schwann cells and/or their extracellular matrix than on two-dimensional collagen and faster on three-dimensional collagen than on laminin. Thus, the neurons of different age express differences in their intrinsic developmental program when placed in culture, but this program may be modified by environmental influences, such as the surface they contact.