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W Young

Publications and source records attributed to W Young.

At least 91 records · Page 5Linked to original sources
PubMed1994

Dynamics of extracellular calcium activity following contusion of the rat spinal cord.

The role of Ca2+ in cellular injury has received particular attention in studies of acute spinal cord trauma. In this context, the spatial and temporal distribution of extracellular Ca2+ ([Ca2+]e) may have an important bearing on the development of secondary tissue injury. We therefore studied the spatial-temporal distribution of [Ca2+]e following moderate (25 g-cm) contusive injury to the rat thoracic (T9-T11) spinal cord. Double-barreled, Ca(2+)-selective microelectrodes were used to measure the magnitude and time course of [Ca2+]e at increasing depths from the dorsal spinal cord surface. After 2 h, the tissue was frozen and later analyzed for total Ca concentration using atomic absorption spectroscopy. [Ca2+]e fell at all depths, but the decrease was maximal at 250 and 500 microns from the dorsal surface, where, at 0-10 min after injury, [Ca2+]e averaged 0.09 +/- 0.03 and 0.06 +/- 0.03 mM respectively. By 2 h postinjury, [Ca2+]e recovered to nearly 1 mM across all depths. Over this time, total tissue calcium concentration ([Ca]t) was 4.54 +/- 0.16 mumol/g in injured cords vs 2.75 +/- 0.1 mumol/g in sham-operated controls. These data place emphasis on the dorsal gray matter as a principal site of ionic derangement in acute spinal cord injury. The implications of these findings are discussed with reference to secondary injury processes.

Animals↗
PubMed1994

Workshop on intraspinal transplantation and clinical application.

The following general conclusions were reached at the workshop: 1. Laboratory studies suggest a potential benefit of cellular transplant therapy for SCI. 2. Some evidence supporting the safety of human fetal transplants is available from clinical studies of transplants in Parkinson's disease and SCI. 3. Assessment criteria and methodology are available, including imaging approaches, validated neurologic scoring systems, detailed electrophysiologic studies of conduction and spinal cord reflexes, and functional scoring approaches. 4. More controlled animal studies are needed (a) to demonstrate efficacy and to evaluate the necessity for immunosuppressive therapy and the overall safety of intraspinal transplantation, (b) to obtain more supporting evidence (e.g., electrophysiologic, histopathologic, MRI, molecular) that would provide insights into ways that transplanted tissue could mediate function, (c) to provide guidance for the procurement, harvesting, preparation, storage, and other logistics related to the use of human cells for transplantation into the spinal cord, (d) to define more thoroughly the cell type(s) that would be most likely to have benefit and the conditions that affect their viability, migration, gene expressions, and proliferation after transplantation, (e) to determine the most optimal time after injury for transplantation, and (f) to clarify patient selection characteristics that might optimize success (i.e., complete vs incomplete injuries, spinal level involved, age of recipient).

Animals↗
PubMed1994

The effects of arterial blood gas values on lesion volumes in a graded rat spinal cord contusion model.

The detrimental effects of extreme blood gas values are well documented. However, the range of normal values has not been rigorously defined. There is an ongoing debate concerning the need for ventilation and tight control of blood gas values in spinal cord injury models. Consequently, we performed a retrospective study of 84 rats using a graded rat spinal cord contusion model. Spinal cord ionic lesion volumes were calculated from Na and K shifts at 24 h after injury. Blood gas measurements were obtained 5 min before contusion. For pH values of 7.31-7.46, systemic acidosis was associated with a small but significant decrease in ionic lesion volumes in the 12.5 and 25 g.cm contusion groups (p < 0.05 and p < 0.03, respectively). pH had no effect on ionic lesion volumes in the 50 g.cm contusion group (p > 0.5). PaCO2 values from 23 to 53 mm Hg showed an effect only at 25 g.cm (p < 0.05). PaO2 values of 46-138 mm Hg and calculated HCO3 values of 13-28 mEq/L had no effect on ionic lesion volumes. Two conclusions may be derived from these data. First, mild systemic acidosis is associated with a small reduction in ionic lesion volumes after mild and moderate injury but not after severe injury. This suggests that secondary mechanisms play a greater role in mild injuries. Second, variations in arterial blood gases within clinically normal ranges do not strongly influence 24-h ionic lesion volumes in a graded spinal cord injury model. The effects of blood gas values on ionic lesion volumes are not statistically significant unless the data are adjusted for injury severity. Although blood gas values must be carefully monitored, ventilation may not be needed routinely in rat spinal cord injury models. We recommend maintaining pH values between 7.35 and 7.40, PaCO2 between 35 and 41 mm Hg, and PaO2 greater than 71 mm Hg.

Acidosis↗
PubMed1994

The effects of methylprednisolone and the ganglioside GM1 on acute spinal cord injury in rats.

Recent clinical trials have reported that methylprednisolone sodium succinate (MP) or the monosialic ganglioside GM1 improves neurological recovery in human spinal cord injury. Because GM1 may have additive or synergistic effects when used with MP, the authors compared MP, GM1, and MP+GM1 treatments in a graded rat spinal cord contusion model. Spinal cord injury was caused by dropping a rod weighing 10 gm from a height of 1.25, 2.5, or 5.0 cm onto the rat spinal cord at T-10, which had been exposed via laminectomy. The lesion volumes were quantified from spinal cord Na and K shifts at 24 hours after injury and the results were verified histologically in separate experiments. A single dose of MP (30 mg/kg), given 5 minutes after injury, reduced 24-hour spinal cord lesion volumes by 56% (p = 0.0052), 28% (p = 0.0065), and 13% (p > 0.05) in the three injury-severity groups, respectively, compared to similarly injured control groups treated with vehicle only. Methylprednisolone also prevented injury-induced hyponatremia and increased body weight loss in the spine-injured rats. When used alone, GM1 (10 to 30 mg/kg) had little or no effect on any measured variable compared to vehicle controls; when given concomitantly with MP, GM1 blocked the neuroprotective effects of MP. At a dose of 3 mg/kg, GM1 partially prevented MP-induced reductions in lesion volumes, while 10 to 30 mg/kg of GM1 completely blocked these effects of MP. The effects of MP on injury-induced hyponatremia and body weight loss were also blocked by GM1. Thus, GM1 antagonized both central and peripheral effects of MP in spine-injured rats. Until this interaction is clarified, the authors recommend that MP and GM1 not be used concomitantly to treat acute human spinal cord injury. Because GM1 modulates protein kinase activity, protein kinases inhibit lipocortins, and lipocortins mediate anti-inflammatory effects of glucocorticoids, it is proposed that the neuroprotective effects of MP are partially due to anti-inflammatory effects and that GM1 antagonizes the effects of MP by inhibiting lipocortin. Possible beneficial effects of GM1 reported in central nervous system injury may be related to the effects on neural recovery rather than acute injury processes.

Animals↗
PubMed1993

Non-synaptic modulation of dorsal column conduction by endogenous GABA in neonatal rat spinal cord.

GABAA receptor activation can modulate axonal conduction in the isolated dorsal column of the neonatal rat spinal cord in vitro. However, it is not known whether axonal conduction in the dorsal column can be modulated by endogenous GABA in the developing spinal cord. We consequently compared the effects of GABA, a GABAA agonist, and a GABA uptake inhibitor on axonal conduction in the dorsal column of hemisected neonatal (0- to 9-day-old) rat spinal cords in vitro. Extracellular compound action potentials evoked by supramaximal stimuli were recorded at two points with glass microelectrodes. GABA (10(-4) to 10(-3) M) reversibly decreased the compound action potential amplitude and the population conduction velocity. At 10(-4) M, compound action potential amplitudes fell by 45.0 +/- 6.5% of control while the conduction velocity slowed by 11.8 +/- 4.3% (n = 5). The GABAA receptor agonist, isoguvacine, mimicked the effects of GABA on the dorsal column compound action potential. In contrast, while GABA at 10(-5) M decreased the amplitude by 7.7 +/- 3.1%, it increased conduction velocity by 9.7 +/- 1.3% (n = 5). The GABA uptake inhibitor, nipecotic acid (10(-3) M), consistently decreased the compound action potential amplitude by 17.7 +/- 6.5% (n = 6) but the conduction velocity slowed in four out of six preparations. In two instances, nipecotic acid decreased the amplitude and increased the conduction velocity. The effects of nipecotic acid on the dorsal column compound action potential were blocked in the presence of the GABAA antagonist bicuculline.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1993

A role of GABAA receptors in hypoxia-induced conduction failure of neonatal rat spinal dorsal column axons.

GABA (gamma-aminobutyric acid) depresses axonal conduction in neonatal dorsal columns. GABA released by injured spinal neurons may diffuse to white matter and contribute to secondary axonal damage. We studied the effects of hypoxia and GABAA receptor blockade on dorsal column conduction in vitro. The experiments compared the effects of hypoxia on longitudinally hemisected spinal cords and isolated neonatal dorsal columns. Before hypoxia, electrical stimulation elicited robust conducted compound action potentials in both isolated dorsal columns and hemicords. The tissues were superfused for 120 min with a hypoxic Ringer's solution saturated with 95% N2 and 5% CO2, followed by oxygenated Ringer's solution for 90 min. Isolated dorsal columns were remarkably insensitive to hypoxia. Response amplitudes fell by only 11 +/- 7% (n = 5) during hypoxia. In hemicords, however, hypoxia reduced response amplitudes by 56 +/- 16% (n = 5, mean +/- S.E.M.) and re-oxygenation did not restore response amplitude. We applied bicucullin (10(-5) M) to block GABAA receptors in the hemicords during hypoxia. Response amplitudes in bicucullin-treated hemicords fell by only 3 +/- 9% (n = 5) during hypoxia but declined 31 +/- 5% during re-oxygenation. These results suggest that endogenous GABA released from gray matter contributes to hypoxia-induced dorsal-column conduction failure.

Action Potentials↗
PubMed1993

Interaction of hypoxia and hypothermia on dorsal column conduction in adult rat spinal cord in vitro.

Trauma reduces both action potential amplitudes and conduction velocities, as well as the ability of axons to follow high-frequency stimulation, in spinal cord dorsal columns. Since white matter blood flow falls after spinal cord injury, hypoxia may play a role in post-traumatic axonal dysfunction. We examined the effects of hypoxia on action potential conduction in isolated adult rat dorsal columns under normothermic (37 degrees C) and hypothermic (25 degrees C) conditions. After stabilization in oxygenated Ringer's solution (95% O2 and 5% CO2), the isolated dorsal columns were superfused with hypoxic Ringer's solution (95% N2 and 5% CO2) for 120 min, followed by 90 min of reoxygenation. At 37 degrees C, hypoxia markedly depressed response amplitudes to 25 +/- 9% (mean +/- SEM, n = 7) of prehypoxic levels but paradoxically increased population conduction velocity to 133 +/- 6%. Reoxygenation restored response amplitudes to 57 +/- 11% and population conduction velocities returned to prehypoxic levels. At 25 degrees C, the dorsal columns were significantly less sensitive to hypoxia. Response amplitudes fell to 50 +/- 6% (n = 7) after hypoxia and recovered to 77 +/- 6% after reoxygenation. Normothermic dorsal columns responded to 500-Hz stimuli with minimal amplitude changes before (-9 +/- 3%, n = 7) and after hypoxia (-13 +/- 2%). In hypothermic preparations, 500-Hz stimulation depressed response amplitudes before (-40 +/- 8%, n = 7) and after hypoxia (-56 +/- 8%); they were not significantly different from each other.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1993

GABA and potassium effects on corticospinal and primary afferent tracts of neonatal rat spinal dorsal columns.

The neurotransmitter GABA markedly depresses action potential conduction in neonatal rat spinal dorsal columns. However, GABA sensitivity of the dorsal columns declines with maturation and myelination. At seven to 14 days after birth, the corticospinal tract component of the dorsal columns is immature and unmyelinated compared to the cuneate-gracilis fasciculi. GABA and isoguvacine (a GABAA receptor agonist) were applied to isolated neonatal (seven to 14 days old) dorsal columns during recordings of conducted cuneate-gracilis fasciculi and corticospinal tract action potentials. GABA (10(-4) to 10(-3) M) significantly reduced amplitudes (-28.9% to -69.7%) and increased latencies (+4.8% to +23.9%) of cuneate-gracilis fasciculi responses but had less effect on corticospinal tract response amplitudes (-1.1% to -14.7%) and latencies (+0.9% to +6.2%). Likewise, isoguvacine (10(-5) to 10(-4) M) reduced amplitudes (-26.7% to -37.5%) and increased latencies (+11.2% and +24.0%) of cuneate-gracilis fasciculi responses but had little or no effect on corticospinal tract response amplitudes (-6.2% to -3.8%) or latencies (-0.8% to +1.5%). At 10(-4) and 10(-3) M, GABA rapidly increased extracellular K+([K+]e) from baseline levels of 3.0 mM to 3.7 +/- 0.4 and 6.6 +/- 1.4 mM in cuneate-gracilis fasciculi and increased corticospinal tract [K+]e to 3.9 +/- 0.4 and 4.4 +/- 0.4 mM (mean +/- S.D.). [K+]e declined during drug application and fell below baseline after drug washout. Cuneate-gracilis fasciculi responses, however, did not recover until several minutes after [K+]e returned to baseline. In separate experiments, increasing bath [K+]e concentrations to 3.7 and 6.6 mM reduced cuneate-gracilis fasciculi response amplitudes by only -7.6% and -29.6%. Latencies increased by +1.3% and +3.6% respectively. The results indicate that the cuneate-gracilis fasciculi are more sensitive to GABA than the corticospinal tract and that the GABA effect is not entirely due to [K+]e changes.

Afferent Pathways↗
PubMed1993

The DNA-binding domain of simian virus 40 tumor antigen has multiple functions.

The DNA-binding domain of simian virus 40 tumor antigen has been previously shown to participate in a number of different activities. Besides being involved in binding to sequences at the viral replication origin, this domain appears to be required for nonspecific DNA binding, for structurally distorting origin DNA (melting and untwisting), and possibly for oligomerization of the protein into hexamers and double hexamers. We now provide evidence that it also takes part in unwinding origin DNA sequences, contributes a function specifically related to in vivo DNA replication, and perhaps supports the assembly of the virus or release of the virus from the cell. This 100-amino-acid domain appears to be an excellent model system for studying how a small region of a protein could have a number of distinct activities.

Antigens, Viral, Tumor↗
PubMed1993

Biochemical analysis of mutants with changes in the origin-binding domain of simian virus 40 tumor antigen.

The role of the origin-binding domain of simian virus 40 large tumor antigen (T antigen) in the initiation of virus DNA replication was investigated by analyzing the biochemical activities of a series of mutants with single-site substitutions in this region. These activities include origin-specific and nonspecific DNA binding, melting of the imperfect palindromic sequence, untwisting of the AT-rich region, unwinding of origin-containing DNA, helicase activity, and the ability to oligomerize normally in response to ATP. Three classes of T-antigen mutants that are unable to support virus replication in monkey cells are described. Class 1 mutants are unable to bind to the origin of DNA replication but are able to bind to DNA nonspecifically. Class 2 mutants exhibit defective binding to both types of DNA. As expected, mutants in these first two classes are unable to unwind origin DNA. Surprisingly, however, these mutants possess significant levels of melting and untwisting activities, suggesting that these reactions may not be solely dependent on the ability of the protein to recognize origin sequences. Most class 1 mutants oligomerize normally in response to ATP, indicating that their DNA-binding defects are not due to structural alterations but probably to a failure to directly recognize origin sequences. In contrast, class 2 mutants exhibit defective oligomerization. Class 3 mutants bind to origin and nonorigin DNA at near wild-type levels and melt and untwist origin DNA normally but exhibit defective oligomerization and unwinding. These mutants are, however, perfectly able to carry out the helicase reaction, indicating that their unwinding defect is at some step after melting but before a nonspecific helicase is used to separate parental strands during replication. These results therefore suggest that proper oligomerization to correctly position the molecules on the DNA may be more important in initiating unwinding than in bringing about efficient DNA binding, inducing structural changes in the DNA, or carrying out the helicase reaction.

Antigens, Polyomavirus Transforming↗
PubMed1993

Polyunsaturated fatty acid supplementation in peripheral neuropathy.

This study is an attempt to assess the role of dietary supplementation in the treatment and prevention of diabetic peripheral neuropathy. The authors developed an animal model system to study this problem. Animals given streptozotocin to induce a type I diabetic state showed elevated glucose levels and decreased body weight. Analysis of the sciatic nerve revealed a decrease in nerve conduction velocity and Na(+)-K(+)-ATPase activity. The activity of protein kinase C, another component of the nerve transmission process, was also affected by the diabetic state. The dietary intervention of polyunsaturated fatty acids seemed to revert some of these changes toward normal.

Animals↗
PubMed1993

Secondary injury mechanisms in acute spinal cord injury.

Experimental studies in animal spinal cord injury models suggest that preservation of a relatively small number of spinal axons can support neurological recovery. The second National Acute Spinal Cord Injury Study (NASCIS 2) was the first clinical trial to demonstrate that a treatment given after injury can enhance neurological recovery. In this trial, patients treated with high-dose methylprednisolone within 8 hours of spinal cord injury recovered more sensory and motor function than did those treated with placebo. In addition to demonstrating the first effective pharmacological intervention in central nervous system injury, NASCIS 2 identified several critical issues that must be investigated in future preclinical and clinical research. These include drug dose, initiation time, and duration of treatment, as well as combination therapy and injury severity. Addressing these issues systematically will require more reproducible animal models and more accurate outcome measures.

Animals↗
PubMed1992

Ricin and lentil lectin-affinity chromatography reveals oligosaccharide heterogeneity of thyrotropin secreted by 12 human pituitary tumors.

Some patients with thyrotropin (TSH)-producing pituitary tumors are more hyperthyroid than others despite similar TSH levels in serum, suggesting that qualitatively different TSH molecules with differing bioactivities may be secreted by different tumors. We used ricin and lentil lectin-affinity chromatography to test whether the TSH oligosaccharides varied among 12 patients with TSH-producing tumors. We found that each tumor secreted heterogeneous isoforms of TSH that differed in their extents of exposed galactose (Gal) residues, and their degrees of sialylation and core fucosylation. These biochemical parameters also varied markedly for TSH secreted by different tumors. Isoforms appeared to reflect poor sialyltransferase activity in two tumors and efficient sialyltransferase in the remainder. TSH secreted by tumors was more fucosylated than TSH secreted by control euthyroid persons. There was an inverse relationship between the sialylation and fucosylation of tumor TSH. No simple relationship between TSH oligosaccharide structures and bioactivity was evident, although mixtures of isoforms having the least and most sialylated TSH seemed to be the most bioactive clinically. In three patients from whom serum and medium TSH were both available, TSH in serum was more sialylated than TSH secreted by the tumor in vitro, perhaps reflecting slow clearance of sialylated isoforms from the circulation. Core fucosylation of serum TSH was less than that of medium TSH. These data prove that human tumors secrete TSH with heterogeneous oligosaccharide structures.

Adult↗
PubMed1992

Fetal cortical cells survive in focal cerebral infarct after permanent occlusion of the middle cerebral artery in adult rats.

Fetal rat cortical cells have been shown previously to survive at the periphery of cerebral infarction. The present study was designed to examine the ability of fetal cells to survive at the edge of the central core of ischemia. In three groups of 8 adult Sprague-Dawley rats, fetal cortical cells from ED 16 were stereotactically transplanted at 3 h, 24 h, and 7 days after unilateral middle cerebral artery occlusion. In 6 rats, fetal cells were transplanted by using the same coordinates, without arterial occlusion, for control. In the ischemic groups, overall graft survival was 85%, and in the control group, all grafts survived. Graft survival was determined by light microscopy. No significant difference was found in the survival of grafts transplanted at different intervals after middle cerebral artery occlusion. It is concluded that fetal cortical cells can survive in cerebral tissue undergoing severe ischemic change.

Animals↗