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Biomedical subjects

J R Wrathall

Publications and source records attributed to J R Wrathall.

At least 37 records · Page 2Linked to original sources
PubMed1997

Local blockade of sodium channels by tetrodotoxin ameliorates tissue loss and long-term functional deficits resulting from experimental spinal cord injury.

Although relatively little is known of the mechanisms involved in secondary axonal loss after spinal cord injury (SCI), recent data from in vitro models of white matter (WM) injury have implicated abnormal sodium influx as a key event. We hypothesized that blockade of sodium channels after SCI would reduce WM loss and long-term functional deficits. To test this hypothesis, a sufficient and safe dose (0.15 nmol) of the potent Na+ channel blocker tetrodotoxin (TTX) was determined through a dose-response study. We microinjected TTX or vehicle (VEH) into the injury site at 15 min after a standardized contusive SCI in the rat. Behavioral tests were performed 1 d after injury and weekly thereafter. Quantitative histopathology at 8 weeks postinjury showed that TTX treatment significantly reduced tissue loss at the injury site, with greater effect on sparing of WM than gray matter. TTX did not change the pattern of chronic histopathology typical of this SCI model, but restricted its extent, tripled the area of residual WM at the epicenter, and reduced the average length of the lesions. Serotonin immunoreactivity caudal to the epicenter, a marker for descending motor control axons, was nearly threefold that of VEH controls. The increase in WM at the epicenter was significantly correlated with the decrease in functional deficits. The TTX group exhibited a significantly enhanced recovery of coordinated hindlimb functions, more normal hindlimb reflexes, and earlier establishment of a reflex bladder. The results demonstrate that Na+ channels play a critical role in WM loss in vivo after SCI.

Animals↗
PubMed1997

Delayed antagonism of AMPA/kainate receptors reduces long-term functional deficits resulting from spinal cord trauma.

Excitatory amino acid (EAA) receptors play a significant role in delayed neuronal death after ischemic and traumatic injury to the CNS. Focal microinjection experiments have demonstrated that 2,3-dihydro-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX), a highly selective and potent antagonist of non-N-methyl-D-aspartate ionotropic EAA receptors, i.e., those preferring alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) or kainate, can reduce histopathology and functional deficits when administered at 15 min after traumatic spinal cord injury (SCI). Similarly, intravenous infusion of NBQX, beginning at 15 min postinjury (p.i.), results in a significant amelioration of the functional deficits produced by experimental SCI. However, if antagonists of AMPA/kainate receptors were to be used therapeutically for patients with SCI, administration would likely be delayed for several hours after injury. We therefore examined the effects of NBQX administered at 4 h after SCI on functional deficits and histopathology in a standardized rat model of contusive SCI. An incomplete SCI was produced in Sprague-Dawley rats at T8 with a weight-drop device (10 g x 2.5 cm). NBQX (15 nmol), or vehicle alone, was microinjected into the injury site 4 h later. Recovery of hind limb reflexes, postural control, and locomotor function was determined by a battery of behavioral tests performed for 8 weeks. Spinal cord tissue was then fixed by perfusion and used for morphometric and immunocytochemical analyses. Previous studies with acute NBQX treatment showed significant functional improvement by 1 week; the effects of delayed NBQX treatment on functional deficits were not discernible until 3-4 weeks after SCI. Thereafter, significant reductions in hindlimb deficits were demonstrated in two independent studies. The nature and magnitude of the reductions in chronic deficits were similar to those observed previously when NBQX was administered acutely at 15 min after SCI. Morphometric analyses showed that delayed treatment with NBQX resulted in sparing of gray matter adjacent to the injury site but no significant effect on the area of white matter at the epicenter. However, serotonin immunoreactivity below the lesion, used as a marker for preservation of one supraspinal pathway, was significantly higher in the NBQX-treated group. These results support a therapeutic potential for NBQX, and presumably other AMPA antagonists, in SCI by demonstrating effectiveness in a clinically relevant time frame. They indicate the importance of assessing chronic functional deficits in evaluating the therapeutic potential of a treatment paradigm. Further, they suggest the intriguing hypothesis that mechanisms underlying early functional recovery after SCI are, at least in part, distinct those from those involved in reducing chronic functional deficits.

Animals↗
PubMed1997

Quantitative analysis of acute axonal pathology in experimental spinal cord contusion.

The major sensorimotor deficits that result from traumatic spinal cord injury (SCI) are due to loss of axons in ascending and descending pathways of the white matter (WM). Experimental treatments administered after a standardized SCI can reduce WM loss and long-term functional deficits. Thus, a significant proportion of WM loss occurs secondary to the mechanical injury and may be a target for therapeutic intervention. Presently, we know little of how and when secondary injury mechanisms operate in the WM after SCI. We therefore used a standardized rat model of clinically relevant contusion injury to examine axonal pathology over the first 24 h by light and electron microscopy. Based on qualitative evaluation of tissue at 15 min, 4 h, and 24 h after a "mild" SCI produced with a weight-drop device (10 g x 2.5 cm), we selected areas from the ventromedial WM at the lesion epicenter for quantitative analyses. We compared axon number and the proportion of axons with various axoplasmic and myelin abnormalities over time after SCI, as well as the effect of axon size on degree of pathology and loss. We found by 4 h postinjury (pi) axonal pathology was more severe than at 15 min and that a significant loss of large diameter axons had occurred; no significant additional loss of axons was seen by 24 h pi. When we compared axonal pathology after a more severe contusion (10 g x 17.5 cm), we found a greater loss of axons at 4 h. In addition, a higher proportion of the remaining axons demonstrated pathological alterations. We developed a semi-quantitative Axonal Injury Index (AII) as an overall measure of axonal pathology that was sensitive to the effects of injury severity at 4 h pi. The AII has greater statistical power than our individual measures of axonal pathology. Our results suggest that it may be possible to use the AII at 4 h pi to assess effects of potential therapeutic agents on acute axonal pathology after SCI.

Animals↗
PubMed1996

Evaluation of cardiorespiratory parameters in rats after spinal cord trauma and treatment with NBQX, an antagonist of excitatory amino acid receptors.

2,3-Dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX), a selective antagonist of amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate receptors, ameliorates functional deficits and tissue loss after experimental contusive spinal cord injury (SCI). Data suggest that NBQX acts via local receptors at the injury site. However, potential systemic effects of NBQX could also modify consequences of SCI. We therefore examined effects of therapeutic doses of NBQX on cardiorespiratory parameters (CRP) including: mean arterial pressure, heart rate, respiratory rate and arterial blood gas. We found no significant effect on these CRP of either focal microinjection or intravenous administration of NBQX at doses that are therapeutic for SCI, in either uninjured rats, or rats after SCI. The results support the hypothesis that NBQX affects SCI by acting locally rather than through systemic effects and demonstrate NBQX treatment paradigms without adverse effects on CRP.

Animals↗
PubMed1996

Amelioration of functional deficits from spinal cord trauma with systemically administered NBQX, an antagonist of non-N-methyl-D-aspartate receptors.

Excitatory amino acid (EAA) receptors play a significant role in delayed neuronal death after ischemic and traumatic injury to the CNS. Recent data based on focal microinjection experiments have demonstrated that 2,3-dihydro-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX), a highly selective and potent antagonist of non-N-methyl-D-aspartate ionotropic EAA receptors, i.e., those preferring alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) or kainate, can reduce histopathology and functional deficits after traumatic spinal cord injury (SCI). Thus, non-NMDA receptors at or near the injury site appear to be important in secondary injury processes that contribute significantly to the consequences of SCI. We have now examined the effects of systemic NBQX, using intravenous infusion, the most commonly used and temporally efficient clinical mode of drug administration. Standardized contusive SCI was produced at the T8 vertebral level in Sprague-Dawley rats. Beginning at 15 min postin-jury, NBQX was administered intravenously at 1 mg/kg/min for 30 min. Behavioral tests of hindlimb functional deficits were performed at 1 day and weekly for 1 month after SCI. Spinal cord tissue was then examined morphometrically to compare lesion size and amount of spared tissue. We found that intravenous administration of NBQX significantly reduced functional impairment after SCI. The effects included more rapid and extensive recovery of hindlimb reflexes, more rapid establishment of a reflex bladder, and a more rapid and greater degree of recovery of coordinated use of hindlimbs in open field locomotion, swimming, and maintaining position on an inclined plane. The profile of effects was similar to that seen with focal microinjection of NBQX, suggesting that even with systemic administration, the drug acts mainly at the injury site. Further, the results support a therapeutic potential for NBQX, or similar drugs that antagonize non-NMDA receptors and inhibit secondary injury processes after SCI.

Animals↗
PubMed1996

Increased basic fibroblast growth factor expression following contusive spinal cord injury.

Neurotrophic factors appear to be crucial for the survival and potential regeneration of injured neurons. We have previously demonstrated that contusive spinal cord injury (SCI) increases the levels of mRNA for basic fibroblast growth factor (FGF2). To determine whether FGF2 protein levels also increase, Western blot analysis was performed on extracts of spinal cord tissue after a standardized SCI and compared to laminectomy controls. In spinal cord extracts, a monoclonal antibody to FGF2 recognized various molecular forms of FGF2 (18-24 kDa) and some characteristic proteolytic fragments. Extracts of spinal cords 1 day after SCI showed a slight increase in the levels of these polypeptides. By 4 days, a significant increase (two-fold) was detected in the levels of the 18-kDa and higher molecular weight forms as well as the proteolytic fragments. Immunohistochemical analyses on spinal cord tissue sections confirmed an increased cellular (glial) FGF2 as well as interstitial immunoreactivity surrounding neurons and along blood vessels. Heparinpurified spinal cord extracts from tissue 4 days after SCI showed increased biological activity as indicated by their ability to (i) increase [3H]thymidine incorporation in cultures of Balb/c 3T3 cells and (ii) induce phosphorylation of suc-associated neurotrophic factor-induced tyrosine-phosphorylated target, a FGF2 target protein. These data suggest that SCI induces increased FGF2 expression and support the hypothesis that FGF2 may play a role in the partial recovery of function seen following SCI.

Animals↗
PubMed1995

Neurotrophic factors in central nervous system trauma.

Although regeneration of injured neurons does not occur after trauma in the central nervous system (CNS), there is often significant recovery of functional capacity with time. Little is currently known about the molecular basis for such recovery, but the increased trophic activity in injured CNS tissue and the known properties of neurotrophic factors in neuronal growth and maintenance suggest that these polypeptides are probably involved in recovery of function. Members of the neurotrophin family, including nerve growth factor (NGF), brain-derived neurotrophic factors (BDNF), and neurotrophin 3 (NT-3), are capable of supporting survival of injured CNS neurons both in vitro and in vivo. They also stimulate neurite outgrowth, needed for reorganization of the injured CNS, and the expression of key enzymes for neurotransmitter synthesis that may need to be upregulated to compensate for reduced innervation. The effects of the neurotrophins are mediated through specific high affinity trk receptors (trk A, B, C) as well as a common low affinity receptor designated p75NGFR. Another class of neurotrophic polypeptides also provides candidate recovery-promoting molecules, the heparin-binding growth factors' acidic and basic fibroblast growth factor (aFGF, bFGF). FGFs not only sustain survival of injured neurons but also stimulate revascularization and certain glial responses to injury. Both the neurotrophins and the FGFs, as well as their respective receptors, have been shown to be upregulated after experimental CNS injury. Further, administration of neurotrophins or FGF has been shown to reduce the effects of experimental injury induced by axotomy, excitotoxins, and certain other neurotoxins. The cellular basis for the potential therapeutic use of neurotrophic molecules is discussed as well as new strategies to increase neurotrophic activity after CNS trauma based on the recently obtained information on pharmacological and molecular control of the expression of these genes.

Animals↗
PubMed1994

Increased basic fibroblast growth factor mRNA following contusive spinal cord injury.

Neurotrophic factors appear to be crucial for the survival and potential regeneration of injured neurons. Injury of the peripheral nervous system results in the induction of a number of neurotrophic molecules. Less is known about the response of central nervous tissue to injury. We have examined changes in levels of mRNA for three trophic factors, basic and acidic fibroblast growth factor (bFGF, aFGF), and nerve growth factor (NGF), after a standardized incomplete thoracic contusive spinal cord injury (SCI). RNase protection assays showed a rapid increase (3-fold) in the content of bFGF mRNA by 6 hours after SCI in tissue that included the injury site. No effect of injury was seen in segments of cervical or lumbar cord. bFGF mRNA at the injury site remained significantly increased at 1 and 7 days after SCI. Further, at 7 days, the increase was anatomically restricted to the rostral portion of the injury site suggesting the involvement of specific pathways in the maintenance of high levels of bFGF mRNA. No change in the levels of aFGF mRNA was seen after SCI. Similarly, no difference in the expression of the mRNA for NGF or its high affinity receptor (trkA), were observed at 6 h, 1 or 7 days following SCI. Our observation of a specific effect of SCI on bFGF mRNA expression supports a speculative hypothesis that bFGF may play a role in the partial recovery of function seen following incomplete contusive spinal cord injury.

Animals↗
PubMed1994

Dose-dependent reduction of tissue loss and functional impairment after spinal cord trauma with the AMPA/kainate antagonist NBQX.

Initial studies on the role of glutamate receptors in traumatic spinal cord injury (SCI) implicated the NMDA subclass of ionotropic glutamate receptors in contributing to functional deficits. Recently we obtained evidence suggesting that non-NMDA ionotropic receptors may participate in producing a portion of the behavioral impairment after SCI. To test this hypothesis we have conducted a dose-response experiment, focally injecting 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX; 1.5, 5, or 15 nmol), a highly selective antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate receptors, or vehicle alone, into the injury site beginning at 15 min after a standardized contusive SCI. Behavioral tests of hindlimb reflex and coordinated sensorimotor function were performed 1 d after injury and weekly thereafter. At 4 weeks, spinal cord tissue was examined using quantitative histopathological and immunocytochemical techniques. We found a dose-dependent reduction in tissue loss at the thoracic injury site, with greater residual amounts of both gray matter and myelinated white matter. The maximum dose (15 nmol) significantly reduced the average length of the lesions and doubled the area of residual white matter at the epicenter. Serotonin immunoreactivity caudal to the lesion, used as a marker for descending motor control axons, was also increased in a dose-related manner and nearly tripled with the highest dose of NBQX as compared to controls. Most importantly, the reduced tissue loss in NBQX-treated groups was correlated with reduced functional deficits. There was a dose-dependent enhancement of speed and degree of recovery of both reflex and coordinated hindlimb motor activity, and reduction in the time required for establishing a reflex bladder. The long-term functional deficits at 4 weeks after SCI were reduced in a dose-related manner. Further, regression analyses demonstrated a significant correlation between the increase in amount of residual tissue and improvement in hindlimb function. Our results suggest that in this type of incomplete contusive SCI, a large and functionally important proportion of the tissue loss appears to be due to secondary injury mediated by local AMPA/kainate receptors.

Animals↗
PubMed1992

Effect of kynurenate on functional deficits resulting from traumatic spinal cord injury.

The potential role of excitatory amino acid (EAA) receptors in spinal cord trauma was examined in a standardized rat model of contusive injury. EAA antagonists were administered in a split-dose protocol with half given 5 min prior to and the remainder 15 min after contusion produced at the T8 vertebral level. Hindlimb function was assessed using a battery of tests of reflex and more complex behaviors at 1 day after injury and weekly thereafter through 4-8 weeks. Functional deficits were compared for groups administered intravenous MK 801 (1 mg/kg), dextromethorphan (10 mg/kg) and kynurenate (300 mg/kg) or the vehicle, saline, alone. In addition, possible effect of the drugs themselves on hindlimb function were assessed in uninjured controls. None of the drugs produced more than transient effect on uninjured rats. In contused rats, only kynurenate produced significant reductions in functional deficits as compared to saline controls. Significant improvement of hindlimb function was also observed when the thoracic cord was locally perfused with kynurenate via intrathecal cannulas and when kynurenate was directly infused into the contusive injury site by stereotaxic microinjection. Using the latter route of administration, a dose-dependent effect of kynurenate (100, 200 and 400 nmol) on the ability of contused rats to use their hindlimbs in locomotion was demonstrated. The highest dose also resulted in a significant reduction in overall functional deficits from 1 week through 1 month and at 2 months after injury. Our results support the hypothesis that EAA receptors at or near the injury site are involved in producing a proportion of the overall functional deficits stemming from traumatic injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1992

Evidence that local non-NMDA receptors contribute to functional deficits in contusive spinal cord injury.

To investigate the role of non-N-methyl-D-aspartate (non-NMDA) types of excitatory amino acid (EAA) receptors in traumatic spinal cord injury, we administered 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(F)-quinoxaline (NBQX), a potent and specific antagonist of non-NMDA receptors, to rats with a standardized contusive spinal cord injury. Focal infusion of NBQX into the injury site significantly reduced long-term hindlimb functional deficits as well as decreasing the time required for the rats to establish a reflex bladder. The results suggest that non-NMDA receptors at or near the injury site are involved in producing a portion of the functional deficits that result from contusive spinal cord injury.

Animals↗
PubMed1992

Spinal cord injury models.

Spinal cord injury models continue to be used to learn more about the pathophysiology of injury as well as potential therapeutic interventions. Most researchers now rely on rat models of injury with injury produced by impact, compression, or even photochemical techniques. A number of laboratories have confirmed that reproducible and graded injury can be produced in the rat with outcome monitored by behavioral, neurophysiologic, and morphologic analyses. Biochemical, physiologic, and pharmacologic studies with these models are being used to further define factors that contribute to chronic injury and thus may be the subject of therapeutic intervention. In addition, a new approach to therapy is being explored via implantation of cells into the injured spinal cord. Cell suspensions can be implanted in clinically relevant injury models without exacerbating the effects of injury and with some indications of beneficial effect. The potential usefulness of such an approach is just beginning to be evaluated.

Animals↗
PubMed1991

Localization of nerve growth factor receptor mRNA in contused rat spinal cord by in situ hybridization.

Northern blot analysis using a probe for the low-affinity nerve growth factor receptor (NGFR) revealed that a mild contusive injury induces the expression of NGFR mRNA in rat spinal cord with a maximal expression at 7 days post-injury. We have now localized this induction using in situ hybridization and found the highest concentration of NGFR mRNA at the lesion epicenter. The location and pattern of autoradiographic grains were compared with that of various cell types at the injury site as determined by immunocytochemical studies. The results suggest that cells associated with blood vessels at the epicenter are induced to express NGFR mRNA at 7 days post-injury.

Animals↗
PubMed1991

Increase in nerve growth factor-like immunoreactivity and decrease in choline acetyltransferase following contusive spinal cord injury.

We have previously described a graded spinal cord injury model in the rat. Mild contusive injury results in an initially severe functional deficit that is attenuated over time to reveal the mild chronic deficits that characterize this injury. In this study, we have shown that mild contusive injury also results in a significant decrease in choline acetyltransferase (ChAT) activity during the first week after injury. At 1 week ChAT activity is maximally reduced at the site of the contusion and is also significantly lowered throughout the spinal cord. ChAT activity then rebounds during the following 3 weeks, partially at the injury site where there is considerable loss of gray and white matter, and completely in rostral and caudal cord segments. The rebound in ChAT activity is temporally associated with the partial recovery of function. Further, the changes in ChAT activity after injury are mirrored by changes in nerve growth factor-like immunoreactivity (NGF-LI) as determined by a specific two-site ELISA. NGF-LI increases significantly after injury, reaching a maximum at 7 days after contusion and at the injury site. However, levels of NGF-LI are also significantly increased throughout the spinal cord. NGF-LI then decreases at 2 and 4 weeks as ChAT activity rebounds. Further experiments will be needed to examine the possibility of a role for NGF in promoting the recovery of function after spinal cord injury.

Animals↗
PubMed1991

Implantation of neuronal suspensions into contusive injury sites in the adult rat spinal cord.

Implants of various types of neuronal and nonneuronal tissue have shown promise for the amelioration of certain disorders of the adult mammalian brain. Implants may also have therapeutic potential for some lesions of the spinal cord. To examine the feasibility of implantation for clinically relevant spinal cord injuries, we have implanted cells into injury sites produced by a well-characterized and standardized rat model of contusive injury. To reduce the possibility of the implantation procedure itself causing damage to the spinal cord, the tissue was dissociated and a suspension of cells introduced into the cord via a small bore needle. To test the implantation procedure, dissociated adult rat dorsal root ganglia were used because of the ease with which these neurons could be distinguished after implantation. The extent to which functional deficits were produced or exacerbated by the implantation procedure was assessed by behavioral tests of groups of rats that had been implanted (implant controls), contused (injury only) or contused and implanted (injury-implant). Survival of the implanted neurons was assessed by quantitative morphological analysis of histological sections taken through the injury/implant sites at different times following injury. In addition, the histopathology of the contusive injury sites was compared for rats that had or had not received immediate or delayed implants. Results indicated that cell suspensions could be implanted into the spinal cord without causing a functional deficit in an otherwise uninjured animal or exacerbating a standardized incomplete contusive injury. Implanted neurons survived for at least 4 weeks in all contusion sites whether implantation was performed immediately following injury or after a delay of 1 week.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Increased nerve growth factor receptor mRNA in contused rat spinal cord.

Peripheral nerve injury induces the expression of nerve growth factor receptor (NGFR). To determine whether a similar induction results from injury of the spinal cord, NGFR mRNA content was determined using Northern blot hybridization analysis of total RNA from spinal cords of rats contused in the mid-thoracic region. By four days after contusion NGFR mRNA was significantly increased in the thoracic segments that included the injury site. The induction was maximal at 7 days, about 5- to 7-fold the level of uninjured controls, and remained 4 times higher than controls at 14 and 28 days after injury. These results suggest that axotomy in the CNS may also trigger the molecular mechanism(s) leading to up-regulation of NGFR expression.

Animals↗
PubMed1989

Distribution and time course of protein extravasation in the rat spinal cord after contusive injury.

We have previously characterized a graded, spinal cord contusive injury in the rat. We have now used this reproducible model to examine vascular permeability to horseradish peroxidase (HRP) after injury. The relationship between severity of injury and distribution of protein extravasation was evaluated at 3 h after injury. After mild injury, tracer was primarily confined to central gray matter and the ventral part of the dorsal columns. After moderate injury, protein extravasation was similar to that observed after mild injury, with the exception that the central hemorrhage included pericentral while matter and occasionally extended to the pial surface. After severe injury, reaction product (RP) was more densely distributed within the central cord and peripheral white matter. The axial extent of tracer at sites proximal and distal to the impact site increased with severity of injury. At 2.0 cm from the injury, no leakage of tracer was noted after mild injury. In contrast, after moderate and severe injury limited microvascular leakage of HRP was noted. Furthermore, after severe injury, in addition to local sites of microvascular leakage, intense RP was present in the dorsal columns up to at least 2.0 cm from the injury. The time course for re-establishment of the blood-spinal cord barrier to protein was evaluated from 3 h to 14 days after moderate injury. At 3 h to 1 day, protein leakage was maximal and coincided with sites of extravasated blood components, although was consistently more extensive. By 7 days, despite resolution of the initial hemorrhage, there remained scattered evidence for protein extravasation at the injured site and at sites along the axis of the cord. The blood-spinal cord barrier to HRP was reestablished by 14 days after injury.

Animals↗