SOX2 expression is upregulated in adult spinal cord after contusion injury in both oligodendrocyte lineage and ependymal cells.

The upregulation of genes normally associated with development may occur in the adult after spinal cord injury (SCI). To test this, we performed real-time RT-PCR array analysis of mouse spinal cord mRNAs comparing embryonic day (E)14.5 spinal cord with intact adult and adult cord 1 week after a clinically relevant standardized contusion SCI. We found significantly increased expression of a large number of neural development- and stem cell-associated genes after SCI. These included Sox2 (sex determining region Y-box 2), a transcription factor that regulates self-renewal and potency of embryonic neural stem cells and is one of only a few key factors needed to induce pluripotency. In adult spinal cord of Sox2-EGFP mice, Sox2-EGFP was found mainly in the ependymal cells of the central canal. After SCI, both mRNA and protein levels of Sox2 were significantly increased at and near the injury site. By 1 day, Sox2 was upregulated in NG2(+) oligodendrocyte progenitor cells (OPC) in the spared white matter. By 3 days, Sox2-EGFP ependymal cells had increased proliferation and begun to form multiple layers and clusters of cells in the central lesion zone of the cord. Expression of Sox2 by NG2(+) cells had declined by 1 week, but increased numbers of other Sox2-expressing cells persisted for at least 4 weeks after SCI in both mouse and rat models. Thus, SCI upregulates many genes associated with development and neural stem cells, including the key transcription factor Sox2, which is expressed in a pool of cells that persists for weeks after SCI.

GGF2 (Nrg1-ß3) treatment enhances NG2+ cell response and improves functional recovery after spinal cord injury.

The adult spinal cord contains a pool of endogenous glial precursor cells, which spontaneously respond to spinal cord injury (SCI) with increased proliferation. These include oligodendrocyte precursor cells that express the NG2 proteoglycan and can differentiate into mature oligodendrocytes. Thus, a potential approach for SCI treatment is to enhance the proliferation and differentiation of these cells to yield more functional mature glia and improve remyelination of surviving axons. We previously reported that soluble glial growth factor 2 (GGF2)- and basic fibroblast growth factor 2 (FGF2)-stimulated growth of NG2(+) cells purified from injured spinal cord in primary culture. This study examines the effects of systemic administration of GGF2 and/or FGF2 after standardized contusive SCI in vivo in both rat and mouse models. In Sprague-Dawley rats, 1 week of GGF2 administration, beginning 24 h after injury, enhanced NG2(+) cell proliferation, oligodendrogenesis, chronic white matter at the injury epicenter, and recovery of hind limb function. In 2',3'-cyclic-nucleotide 3'-phosphodiesterase-enhanced green fluorescent protein mice, GGF2 treatment resulted in increased oligodendrogenesis and improved functional recovery, as well as elevated expression of the stem cell transcription factor Sox2 by oligodendrocyte lineage cells. Although oligodendrocyte number was increased chronically after SCI in GGF2-treated mice, no evidence of increased white matter was detected. However, GGF2 treatment significantly increased levels of P0 protein-containing peripheral myelin, produced by Schwann cells that infiltrate the injured spinal cord. Our results suggest that GGF2 may have therapeutic potential for SCI by enhancing endogenous recovery processes in a clinically relevant time frame.

Increased expression of the close homolog of the adhesion molecule L1 in different cell types over time after rat spinal cord contusion.

The close homolog of the adhesion molecule L1 (CHL1) is important during CNS development, but a study with CHL1 knockout mice showed greater functional recovery after spinal cord injury (SCI) in its absence. We investigated CHL1 expression from 1 to 28 days after clinically relevant contusive SCI in Sprague-Dawley rats. Western blot analysis showed that CHL1 expression was significantly up-regulated at day 1 and further increased over 4 weeks after SCI. Immunohistochemistry of tissue sections showed that CHL1 in the intact spinal cord was expressed at low levels. By 1 day and through 4 weeks after SCI, CHL1 became highly expressed in NG2(+) cells. Hypertrophic GFAP(+) astrocytes also expressed CHL1 by 1 week after injury. The increase in CHL1 protein paralleled that of NG2 in the first week and GFAP between 1 and 4 weeks after injury. At 4 weeks, NG2(+) /CHL1(+) cells and GFAP(+) /CHL1(+) astrocytes were concentrated at the boundary between residual spinal cord tissue and the central lesion. NF200(+) spinal cord axons approached but did not penetrate this boundary. In contrast, CHL1(+) cells in the central lesion at 1 week and later colabeled with p75 and NG2 and were chronically associated with many NF200(+) axons, presumably axons that had sprouted in association with CHL1(+) Schwann cells infiltrating the cord after contusion. Thus, our study demonstrates up-regulation of CHL1 in multiple cell types and locations in a rat model of contusion injury and suggests that this molecule may be involved both in inhibition of axonal regeneration and in recovery processes after SCI.

Phosphatidylinositol 3-kinase/protein kinase Cdelta activation induces close homolog of adhesion molecule L1 (CHL1) expression in cultured astrocytes.

Upregulation of expression of the close homolog of adhesion molecule L1 (CHL1) by reactive astrocytes in the glial scar reduces axonal regeneration and inhibits functional recovery after spinal cord injury (SCI). Here, we investigate the molecular mechanisms underlying upregulation of CHL1 expression by analyzing the signal transduction pathways in vitro. We show that astrogliosis stimulated by bacterial lipopolysaccharide (LPS) upregulates CHL1 expression in primary cultures of mouse cerebral astrocytes, coinciding with elevated protein synthesis and translocation of protein kinase delta (PKCdelta) from cytosol to the membrane fraction. Blocking PKCdelta activity pharmacologically and genetically attenuates LPS-induced elevation of CHL1 protein expression through a phosphatidylinositol 3-kinase (PI3K) dependent pathway. LPS induces extracellular signal-regulated kinases (ERK1/2) phosphorylation through PKCdelta and blockade of ERK1/2 activation abolishes upregulation of CHL1 expression. LPS-triggered upregulation of CHL1 expression mediated through translocation of nuclear factor kappaB (NF-kappaB) to the nucleus is blocked by a specific NF-kappaB inhibitor and by inhibition of PI3K, PKCdelta, and ERK1/2 activities, implicating NF-kappaB as a downstream target for upregulation of CHL1 expression. Furthermore, the LPS-mediated upregulation of CHL1 expression by reactive astrocytes is inhibitory for hippocampal neurite outgrowth in cocultures. Although the LPS-triggered NO-guanylate cyclase-cGMP pathway upregulates glial fibrillary acid protein expression in cultured astrocytes, we did not observe this pathway to mediate LPS-induced upregulation of CHL1 expression. Our results indicate that elevated CHL1 expression by reactive astrocytes requires activation of PI3K/PKCdelta-dependent pathways and suggest that reduction of PI3K/PKCdelta activity represents a therapeutic target to downregulate CHL1 expression and thus benefit axonal regeneration after SCI.

Interaction of NG2(+) glial progenitors and microglia/macrophages from the injured spinal cord.

Spinal cord contusion produces a central lesion surrounded by a peripheral rim of residual white matter. Despite stimulation of NG2(+) progenitor cell proliferation, the lesion remains devoid of normal glia chronically after spinal cord injury (SCI). To investigate potential cell-cell interactions of the predominant cells in the lesion at 3 days after injury, we used magnetic activated cell sorting to purify NG2(+) progenitors and OX42(+) microglia/macrophages from contused rat spinal cord. Purified NG2(+) cells from the injured cord grew into spherical masses when cultured in defined medium with FGF2 plus GGF2. The purified OX42(+) cells did not form spheroids and significantly reduced sphere growth by NG2(+) cells in co-cultures. Conditioned medium from these OX42(+) cells, unlike that from normal peritoneal macrophages or astrocytes also inhibited growth of NG2(+) cells, suggesting inhibition by secreted factors. Expression analysis of freshly purified OX42(+) cells for a panel of six genes for secreted factors showed expression of several that could contribute to inhibition of NG2(+) cells. Further, the pattern of expression of four of these, TNFalpha, TSP1, TIMP1, MMP9, in sequential coronal tissue segments from a 2 cm length of cord centered on the injury epicenter correlated with the expression of Iba1, a marker gene for OX42(+) cells, strongly suggesting a potential regional influence by activated microglia/macrophages on NG2(+) cells in vivo after SCI. Thus, the nonreplacement of lost glial cells in the central lesion zone may involve, at least in part, inhibitory factors produced by microglia/macrophages that are concentrated within the lesion.

NG2 cell response in the CNP-EGFP mouse after contusive spinal cord injury.

NG2(+) cells in the adult CNS are a heterogeneous population. The extent to which the subpopulation of NG2(+) cells that function as oligodendrocyte progenitor cells (OPCs) respond to spinal cord injury (SCI) and recapitulate their normal developmental progression remains unclear. We used the CNP-EGFP mouse, in which oligodendrocyte lineage cells express EGFP, to study NG2(+) cells in the normal and injured spinal cord. In white matter of uninjured mice, bipolar EGFP(+)NG2(+) cells and multipolar EGFP(neg)NG2(+) cells were identified. After SCI, EGFP(+)NG2(+) cell proliferation in residual white matter peaked at 3 days post injury (DPI) rostral to the epicenter, while EGFP(neg)NG2(+) cell proliferation peaked at 7 DPI at the epicenter. The expression of transcription factors, Olig2, Sox10, and Sox17, and the basic electrophysiological membrane parameters and potassium current phenotype of the EGFP(+)NG2(+) population after injury were consistent with those of proliferative OPCs during development. EGFP(neg)NG2(+) cells did not express transcription factors involved in oligodendrogenesis. EGFP(+)CC1(+) oligodendrocytes at 6 weeks included cells that incorporated BrdU during the peak of EGFP(+)NG2(+) cell proliferation. EGFP(neg)CC1(+) oligodendrocytes were never observed. Treatment with glial growth factor 2 and fibroblast growth factor 2 enhanced oligodendrogenesis and increased the number of EGFP(neg)NG2(+) cells. Therefore, based on EGFP and transcription factor expression, spatiotemporal proliferation patterns, and response to growth factors, two populations of NG2(+) cells can be identified that react to SCI. The EGFP(+)NG2(+) cells undergo cellular and physiological changes in response to SCI that are similar to those that occur in early postnatal NG2(+) cells during developmental oligodendrogenesis.

Stem cells in spinal cord injury.

Traumatic injury to the adult spinal cord results in a massive loss of cells and permanent functional deficits. However, recent studies demonstrate that there is a proliferative response of endogenous glial precursors and progenitors and perhaps also pluripotent neural stem cells. These cells may prove to be an important new therapeutic target to improve recovery after injury to the spinal cord and brain.

Effect of injury severity on lower urinary tract function after experimental spinal cord injury.

Lower urinary tract dysfunction is a serious burden for patients following spinal cord injury. Patients are usually limited to treatment with urinary drainage catheters, which can lead to repeated urinary tract infections and lower quality of life. Most of the information previously obtained regarding lower urinary tract function after spinal cord injury has been in completely transected animals. After thoracic transection in the rat, plasticity of local lumbosacral spinal circuitry establishes a "reflex bladder," which results in partial recovery of micturition, albeit with reduced voiding efficiency. Since at least half of cord-injured patients exhibit neurologically incomplete injury, rat models of clinically relevant incomplete contusion injury have been developed. With respect to lower urinary tract function, recent anatomical and physiological studies have been performed after incomplete thoracic contusion injury. The results show greater recovery of lower urinary tract function that varies inversely with the severity of the initial trauma and is positively correlated with time after injury. Recovery, as measured by coordination of the bladder with the external urethral sphincter, occurs between 1 and 4 weeks after spinal cord injury. It is associated with normalization of: serotonin immunoreactivity and glutamate receptor subunit mRNA expression in the dorsolateral nucleus that innervates the external urethral sphincter muscle, the response to glutamatergic pharmacological probes administered at the lumbosacral spinal cord level, and c-Fos activation patterns in the lumbar spinal cord. Understanding the mechanisms involved in this recovery will provide a basis for enhancing lower urinary tract function in patients after incomplete spinal cord injury.

Phenotypic changes in NG2+ cells after spinal cord injury.

Following contusive spinal cord injury (SCI), 50% of oligodendrocytes in the residual white matter are lost within 24 h. NG2-expressing cell proliferation is maximal 3 days after SCI, and may be the source of mature oligodendrocytes and astrocytes that chronically replace those that were lost. We studied NG2(+) cells dissociated from the 3-day injured spinal cord for comparison with those from uninjured adult and early postnatal cords. After 24 h in serum-containing medium, we performed patch clamp analysis and immunocytochemistry for NG2 in combination with nestin (progenitors), and A2B5, O4, and O1 (oligodendrocyte lineage markers). We observed an NG2(+)/A2B5-/O4-/O1- population in both adult preparations. More than double the normal number of NG2(+) cells was isolated from the injured cord, but OX42(+) microglia/macrophages were the predominant cell type after injury. Most cells isolated at P7 were NG2-/A2B5(+), whereas those from the normal adult were NG2(+)/A2B5-. NG2(+) cells after SCI displayed altered voltage-gated potassium current profiles compared to normal adult and P7 animals. Additionally, less than 25% of adult cells (normal and injured) responded to GABA and glutamate, compared to 100% of P7 cells. Our results indicate that the adult NG2(+) cell pool is antigenically and physiologically different than the early postnatal pool, and that contusive injury induces changes in adult NG2(+) cells.

Serotonin 1A receptor agonists reverse respiratory abnormalities in spinal cord-injured rats.

Contusion spinal cord injury (SCI) at T8 produces respiratory abnormalities in conscious rats breathing room air and challenged with CO2. In seeking ways to improve respiration after SCI, we tested drugs that stimulate serotonin 1A (5-HT1A) receptors, based on our previous findings that these agents can counteract respiratory depression produced by morphine overdose. Respiratory function was measured with a head-out plethysmograph system in conscious rats. T8 SCI rats (n = 5) showed decreased tidal volume (Vt; 0.90 +/- 0.02-0.66 +/- 0.03 ml; p < 0.05) and increased respiratory rate (f;91 +/- 3.7-132 +/- 5.7 breaths/min; p < 0.05) with room air ventilation at 24 hr after injury. They also exhibited a diminished response to the respiratory stimulating effect of 7% CO2; minute ventilation increased to 250 +/- 17 ml/min before, but only to 162 +/- 15 ml/min at 24 hr after SCI (p < 0.05). Respiratory deficits during room air ventilation were also observed at 7 d after injury (n = 3). Treatment with the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylmino)tetralin (8-OH-DPAT; 250 microg/kg, i.p.) at 24 hr (n = 5) or 7 d (n = 3) after injury normalized Vt, f, and the respiratory response to 7% CO2. Identical results were obtained with another 5-HT1A receptor agonist, buspirone (1.5 mg/kg, i.p.; n = 3). In contrast, intraperitoneal saline vehicle administration (n = 5) showed no beneficial effects on SCI-impaired respiration. Finally, pretreatment with a specific antagonist of 5-HT1A receptors, 4-iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinyl-benzamide (3 mg/kg, i.p.; n = 3) given 20 min before 8-OH-DPAT, prevented 8-OH-DPAT from restoring respiration to normal. Our results demonstrate that drugs that stimulate 5-HT1A receptors counteract respiratory abnormalities in conscious rats after SCI.

Rapid functional recovery after spinal cord injury in young rats.

Responses to traumatic injury in the immature spinal cord may be different from those in adults. We modified an adult model of weight-drop injury to characterize the histopathology and functional recovery after spinal cord injury (SCI) in rat pups at postnatal day 14-15. A 10-g weight was dropped from 2.5 or 5.0 cm at T8-T9. Hindlimb function was evaluated at 24 h and 1, 2, 3, and 4 weeks after injury using the Combined Behavioral Score that estimates overall hind limb sensorimotor function, and the BBB scale for open field locomotion. Histopathology was examined at 15 min, 24 h, and 4 weeks after SCI. The initial hemorrhagic lesion was similar to that seen in adults, but the time course of secondary loss of ventral horn motor neurons was extended. By 4 weeks, only a partial rim of white matter surrounding a central cavity was seen. The 5.0 cm injury group exhibited significantly less recovery of function at 4 weeks than the 2.5 cm group. In the latter, the degree of hindlimb deficit at 4 weeks was similar to that previously described for adults with 10 g x 2.5 cm SCI. However, pups in both injury groups exhibited a significantly faster rate of recovery than adults. Recovery was maximal by 1 week after SCI in pups as compared to 3-4 weeks in adults. The more rapid functional recovery observed in the pups suggests that this new model may be useful for studying mechanisms of functional plasticity after SCI.

Increased growth factor expression and cell proliferation after contusive spinal cord injury.

The damage caused by traumatic central nervous system (CNS) injury can be divided into two phases: primary and secondary. The initial injury destroys many of the local neurons and glia and triggers secondary mechanisms that result in further cell loss. Approximately 50% of the astrocytes and oligodendrocytes in the spared white matter of the epicenter die by 24 h after spinal cord injury (SCI), but their densities return to normal levels by 6 weeks. This repopulation is largely due to the proliferation of local progenitors that divide in response of CNS injury. Previous studies indicate that the secondary events that cause cell death after SCI also increase the local levels of several growth factors that stimulate the proliferation of these endogenous progenitors. We compared the spatial pattern of the post-injury up-regulation of the pro-mitotic growth factors with that of 5-bromodeoxyuridine (BrdU) incorporation to determine if each could play a role in proliferation. Three days after a standard contusive SCI or laminectomy, animals received intraperitoneal BrdU injections to label dividing cells and were perfused 2 h after the last injection. Immunohistochemistry for BrdU and basic fibroblast growth factor (FGF2) and in situ hybridization for ciliary neurotrophic factor (CNTF) and glial growth factor (GGF2) mRNA were used to compare the number of dividing cells with growth factor levels in sections 2 and 4 mm from the epicenter. All three growth factors are significantly up-regulated 3 days after SCI, when cell proliferation is maximal. The increase in GGF2 and FGF2 levels is highest in sections 2 mm rostral to the epicenter, mimicking BrdU incorporation. Addition of rhGGF2 to cultured cells isolated from the spinal cord 3 days after SCI increased the number of NG2+ glial progenitors. These data suggest that FGF2 and GGF2 may contribute to the spontaneous recovery observed after SCI by stimulating the proliferation of local progenitors that help repopulate the injured cord.

Expression of tumor necrosis factor alpha and its mRNA in the spinal cord following a weight-drop injury.

The effect of traumatic spinal cord injury (SCI) on the expression of tumor necrosis factor (TNFalpha) and its mRNA was examined. Quantitative reverse transcription polymerase chain reaction assay showed TNFalpha mRNA level increased > 20-fold at the lesion site by 1 h after the injury compared to that in uninjured controls. The TNFalpha mRNA level was still significantly higher than in the controls 72 h after the injury. TNFalpha mRNA in the samples collected immediately caudal to the lesion site was also increased. Levels of TNFalpha protein, determined by a cytotoxic bioassay, were also significantly increased at the lesion site. The TNFalpha protein level was maximal 1 and 8 h after the injury and still significantly higher than in the controls 24 h post-injury. The present results demonstrate that TNFalpha is rapidly induced in the spinal cord after the injury, and it may play a significant role in secondary events in SCI.

Glutamate receptor subunit expression after spinal cord injury in young rats.

To investigate the possibility that glutamate receptor levels in the spinal cord are altered following injury to young rats, we used a previously characterized model of spinal cord contusion that produces a reliable injury in rats at postnatal day 14-15. Quantitative Western blot analysis was used to measure relative amounts of protein for several glutamate receptor subunits acutely (24 h) and chronically (28 days) after spinal cord injury (SCI). Acutely after injury significant decreases were observed in the GluR1, GluR2, and GluR4 subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionate (AMPA) receptor, and the NR2A and NR2B subunits, but not the NR1 subunit, of the N-methyl-d-aspartate (NMDA) receptor. However, 28 days after injury only one subunit (GluR4) was shown to be altered. These widespread changes that occur acutely in receptor subunit expression may be an attempt to protect cells from glutamate-induced death. The injured spinal cord in these young animals, however, appears to have the capacity to regulate receptor subunit levels to normal within a month of injury.

Quantitative measurement of glutamate receptor subunit protein expression in the postnatal rat spinal cord.

Glutamate is the major excitatory neurotransmitter in the CNS and its effects on neurons are dependent on the type and composition of glutamate receptors with which it interacts. In this study, the protein expression levels of several ionotropic glutamate receptor subunits (N-methyl-D-aspartate (NMDA) subunits NR1, NR2A, NR2B, and alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA) receptor subunits GluR1, GluR2, GluR4) were quantified in particulate preparations from rat spinal cord at various ages after birth. We found that all six subunits showed high expression in the early postnatal period, followed by a subsequent decline as the rats matured to adults. The levels of two subunits (NR2A and GluR4) were found to initially increase during the first postnatal week prior to the decline to adult levels. The high levels of expression observed of these subunits in the early postnatal period may have implications for mechanisms of neural injury and cell death in the immature nervous system that involve cation influx through ionotropic glutamate receptors.

Blast-related brain injury: imaging for clinical and research applications: report of the 2008 st. Louis workshop.

Blast-related traumatic brain injury (bTBI) and post-traumatic stress disorder (PTSD) have been of particular relevance to the military and civilian health care sectors since the onset of the Global War on Terror, and TBI has been called the "signature injury" of this war. Currently there are many questions about the fundamental nature, diagnosis, and long-term consequences of bTBI and its relationship to PTSD. This workshop was organized to consider these questions and focus on how brain imaging techniques may be used to enhance current diagnosis, research, and treatment of bTBI. The general conclusion was that although the study of blast physics in non-biological systems is mature, few data are presently available on key topics such as blast exposure in combat scenarios, the pathological characteristics of human bTBI, and imaging signatures of bTBI. Addressing these gaps is critical to the success of bTBI research. Foremost among our recommendations is that human autopsy and pathoanatomical data from bTBI patients need to be obtained and disseminated to the military and civilian research communities, and advanced neuroimaging used in studies of acute, subacute, and chronic cases, to determine whether there is a distinct pathoanatomical signature that correlates with long-term functional impairment, including PTSD. These data are also critical for the development of animal models to illuminate fundamental mechanisms of bTBI and provide leads for new treatment approaches. Brain imaging will need to play an increasingly important role as gaps in the scientific knowledge of bTBI and PTSD are addressed through increased coordination, cooperation, and data sharing among the academic and military biomedical research communities.

Mixed primary culture and clonal analysis provide evidence that NG2 proteoglycan-expressing cells after spinal cord injury are glial progenitors.

NG2(+) cells in the adult rat spinal cord proliferate after spinal cord injury (SCI) and are postulated to differentiate into mature glia to replace some of those lost to injury. To further study these putative endogenous precursors, tissue at 3 days after SCI or from uninjured adults was dissociated, myelin partially removed and replicate cultures grown in serum-containing or serum-free medium with or without growth factors for up to 7 days in vitro (DIV). Cell yield after SCI was 5-6 times higher than from the normal adult. Most cells were OX42(+) microglia/macrophages but there were also more than twice the normal number of NG2(+) cells. Most of these coexpressed A2B5 or nestin, as would be expected for glial progenitors. Few cells initially expressed mature astrocyte (GFAP) or oligodendrocyte (CC1) markers, but more did at 7 DIV, suggesting differentiation of glial precursors in vitro. To test the hypothesis that NG2(+) cells after SCI express progenitor-like properties, we prepared free-floating sphere and single cell cultures from purified suspension of NG2(+) cells from injured spinal cord. We found that sphere cultures could be passaged in free-floating subcultures, and upon attachment the spheres clonally derived from an acutely purified single cell differentiated into oligodendrocytes and rarely astrocytes. Taken together, these data support the hypothesis that SCI stimulates proliferation of NG2(+) cells that are glial progenitor cells. Better understanding the intrinsic properties of the NG2(+) cells stimulated by SCI may permit future therapeutic manipulations to improve recovery after SCI.

Glial cell loss, proliferation and replacement in the contused murine spinal cord.

Studies in the rat have shown that contusive spinal cord injury (SCI) results in devastating pathology, including significant loss of mature oligodendrocytes and astrocytes even in spared white matter. Subsequently, there is increased proliferation of endogenous NG2(+) cells, postulated to contribute to replacement of mature glia chronically, which is important for functional recovery. Studies of mechanisms that stimulate endogenous progenitor cells would be facilitated by using mouse models with naturally occurring and genetically engineered mutations. To determine whether the murine response is similar to that in the rat, we performed contusive SCI on adult female C57Bl/6 mice at the T8-9 level. Animals received bromodeoxyuridine injections in the first week following injury and were killed at 1, 3, 4, 7 or 28 days postinjury (DPI). The overall loss of macroglia and the temporal-spatial response of NG2(+) cells after SCI in the (C57Bl/6) mouse was very similar to that in the (Sprague-Dawley) rat. By 24 h after SCI nearly half of the macroglia in spared ventral white matter had been lost. Cell proliferation was increased at 1-7 DPI, peaking at 3-4 DPI. Dividing cells included NG2(+) cells and Cd11b(+) macrophages and microglia. Furthermore, cells dividing in the first week expressed markers of mature glia at 28 DPI. The similarities in endogenous progenitor cell response to SCI in the mouse and rat suggest that this is a fundamental injury response, and that transgenic mouse models may be used to further probe how this cellular response to SCI might be enhanced to improve recovery after SCI.

Up-regulation of 5-HT2 receptors is involved in the increased H-reflex amplitude after contusive spinal cord injury.

The amplitude of the H-reflex increases chronically after incomplete SCI and is associated with the development of exaggerated hindlimb reflexes. Although the mechanism for this increased H-reflex is not clear, previous studies have shown that pharmacological activation of the 5-HT2 receptors (5-HT2R) can potentiate the monosynaptic reflex. This study tested the hypothesis that increased expression of 5-HT2R on motoneurons is involved in increased H-reflex amplitude after a standardized clinically relevant contusive SCI. Adult female rats were subjected to contusion, complete surgical transection, or a T8 laminectomy only. At 4 weeks after surgery, H-reflex recordings from the hindpaw plantar muscles of contused rats showed twice the amplitude of that in laminectomy controls or transected rats. To probe the role of 5-HT2R in this increased amplitude, dose-response studies were done with the selective antagonists mianserin or LY53857 and the 5-HT2R agonist (+/-)-1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI). The drugs were intrathecally infused into the lumbar cord while recording the H-reflex. Mianserin did not have any significant effects on the H-reflex after transection, consistent with the loss of distal serotonergic innervation. After contusion, both 5-HT2R antagonists reduced the H-reflex reflex amplitude with a significantly higher ID50 compared to the uninjured controls. The 5-HT2R agonist DOI significantly increased reflex amplitude in contused but not control rats. Furthermore, while 5-HT immunoreactivity was similar, contused rats displayed increased 5-HT2AR immunoreactivity in plantar muscle motoneurons compared to uninjured controls. We conclude that increased expression of 5-HT2R is likely to be involved in the enhanced H-reflex that develops after contusive SCI.