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Biomedical subjects

G L Clifton

Publications and source records attributed to G L Clifton.

At least 19 recordsLinked to original sources
PubMed1997

A calpain inhibitor attenuates cortical cytoskeletal protein loss after experimental traumatic brain injury in the rat.

The capacity of a calpain inhibitor to reduce losses of neurofilament 200-, neurofilament 68- and calpain 1-mediated spectrin breakdown products was examined following traumatic brain injury in the rat. Twenty-four hours after unilateral cortical impact injury, western blot analyses detected neurofilament 200 losses of 65% (ipsilateral) and 36% (contralateral) of levels observed in naive, uninjured rat cortices. Neurofilament 68 protein levels decreased only in the ipsilateral cortex by 35% relative to naive protein levels. Calpain inhibitor 2, administered 10 min after injury via continuous arterial infusion into the right external carotid artery for 24 h, significantly reduced neurofilament 200 losses to 17% and 3% relative to naive neurofilament 200 protein levels in the ipsilateral and contralateral cortices, respectively. Calpain inhibitor administration abolished neurofilament 68 loss in the ipsilateral cortex and was accompanied by a reduction of putative calpain-mediated neurofilament 68 breakdown products. Spectrin breakdown products mediated by calpain 1 activation were detectable in both hemispheres 24 h after traumatic brain injury and were substantially reduced in animals treated with calpain inhibitor 2 both ipsilaterally and contralaterally to the site of injury. Qualitative immunofluorescence studies of neurofilament 200 and neurofilament 68 confirmed western blot data, demonstrating morphological protection of neuronal structure throughout cortical regions of the traumatically injured brain. Morphological protection included preservation of dendritic structure and reduction of axonal retraction balls. In addition, histopathological studies employing hematoxylin and eosin staining indicated reduced extent of contusion at the injury site. These data indicate that calpain inhibitors could represent a viable strategy for preserving the cytoskeletal structure of injured neurons after experimental traumatic brain injury in vivo.

Animals↗
PubMed1997

Mechanisms of calpain proteolysis following traumatic brain injury: implications for pathology and therapy: implications for pathology and therapy: a review and update.

Much recent research has focused on the pathological significance of calcium accumulation in the central nervous system (CNS) following cerebral ischemia, spinal cord injury (SCI), and traumatic brain injury (TBI). Disturbances in neuronal calcium homeostasis may result in the activation of several calcium-sensitive enzymes, including lipases, kinases, phosphatases, and proteases. One potential pathogenic event in a number of acute CNS insults, including TBI, is the activation of the calpains, calcium-activated intracellular proteases. This article reviews new evidence indicating that overactivation of calpains plays a major role in the neurodegenerative cascade following TBI in vivo. Further, this article presents an overview from in vivo and in vitro models of CNS injuries suggesting that administration of calpain inhibitors during the initial 24-h period following injury can attenuate injury-induced derangements of neuronal structure and function. Lastly, this review addresses the potential contribution of other proteases to neuronal damage following TBI.

Animals↗
PubMed1996

Liposome-mediated NGF gene transfection increases ChAT activity in CNS cell cultures.

Liposome-mediated NGF transfection has been shown to increase the expression and secretion of NGF in primary rat septo-hippocampal cell cultures. Here we report that along with increased NGF expression, the activity of choline acetyltransferase, the synthetic enzyme for acetylcholine, is increased by 18% within 2 days, by 41% within 4 days and by 32% within 8 days after NGF gene transfection in septo-hippocampal cell cultures. This result further confirms that biologically active NGF is functionally expressed in septo-hippocampal cells when transfected with cDNA for NGF completed with liposomes.

Animals↗
PubMed1996

Liposome-mediated BDNF cDNA transfer in intact and injured rat brain.

We examined the temporal profile of the expression of brain-derived neurotrophic factor (BDNF) cDNA containing a viral promotor following the injection of liposome cDNA complexes into the intact and traumatically injured rat brain. In situ hybridization and PCR confirmed the presence of injected BDNF cDNA for at least 6 days after injection. A similar profile of BDNF cDNA was observed when it was injected following cortical impact injury. mRNA was also localized around the injection areas. These results suggest that liposome-mediated delivery of neurotrophin cDNA may be a practical gene transfer method for treating traumatic brain injury.

Animals↗
PubMed1996

Omental transposition in chronic spinal cord injury.

The results of omental transposition in chronic spinal cord injury have been reported in 160 patients operated upon in the United States, Great Britain, China, Japan, India and Mexico, with detailed outcomes reported in few studies. Recovery of function to a greater degree than expected by natural history has been reported. In this series, 15 patients with chronic traumatic spinal cord injury (> 1.5 years from injury) underwent transposition of pedicled omentum to the area of the spinal cord injury. Of the first series of four patients who were operated upon in 1988, one died, one was lost to follow-up and two were followed with sequential neurological examinations and Magnetic Resonance Imaging (MRI) scans preoperatively, at 1 year post injury and 4 1/2 years post injury. Another 11 patients were operated in 1992 and underwent detailed neurological and neurophysiological examinations and had MRI scans preoperatively and every 4 months for at least 1 year after surgery. All patients completed a detailed self-report form. Of the total of 13 operated patients in both series followed for 1-4 1/2 years, six reported some enhanced function at 1 year and five of these felt the changes justified surgery primarily because of improved truncal control and decreased spasticity. MRI scans showed enlargement of the spinal cord as compared to preoperative scans in seven patients. Increased T2 signal intensity of the spinal cord was found by 1 year after surgery in eight of 13 operated patients. Neurophysiological examinations of 11 patients in the second series agreed with self-reports of increases or decreases in spasticity (r = 0.65, P < 0.03). Somatosensory evoked potentials and motor evoked potentials at 4 month intervals up to 1 year in these patients showed no change after surgery. Neurological testing, using the American Spinal Injury Association (ASIA) and International Medical Society of Paraplegia (IMSOP) international scoring standards, failed to show any significant changes when the 1-year post operative examination was compared to the first preoperative examination except for decreased sensory function after surgery which approached statistical significance. When the 11 patients in the second series were compared to eight non-operated matched patients, followed for a similar length of time, no significant differences were found. Complications encountered in the operated patients from both series included one postoperative death from a pulmonary embolus, one postoperative pneumonia, three chronic subcutaneous cerebrospinal fluid (CSF) fistulae requiring wound revision, and one patient who developed biceps and wrist extensor weakness bilaterally requiring graft removal. We conclude that the omental graft remains viable over time and this operation can induce anatomical changes in the spinal cord as judged by MRI. Some patients reported subjective improvement but this was not supported by objective testing. We, therefore, find no justification for further clinical trials of this procedure in patients who have complete or sensory incomplete lesions. Further testing in motor incomplete patients would seem appropriate only with compelling supportive data.

Adolescent↗
PubMed1996

mu-calpain activation and calpain-mediated cytoskeletal proteolysis following traumatic brain injury.

Increasing evidence suggests that excessive activation of the calcium-activated neutral protease mu-calpain could play a major role in calcium-mediated neuronal degeneration after acute brain injuries. To further investigate the changes of the in vivo activity of mu-calpain after unilateral cortical impact injury in vivo, the ratio of the 76-kDa activated isoform of mu-calpain to its 80-kDa precursor was measured by western blotting. This mu-calpain activation ratio increased to threefold in the pellet of cortical samples ipsilateral to the injury site at 15 min, 1 h, 3 h, and 6 h after injury and returned to control levels at 24-48 h after injury. We also investigated the effect of mu-calpain activation on proteolysis of the neuronal cytoskeletal protein alpha-spectrin. Immunoreactivity for alpha-spectrin breakdown products was detectable within 15 min after injury in cortical samples ipsilateral to the injury site. The levels of alpha-spectrin breakdown products increased in a biphasic manner, with a large increase between 15 min and 6 h after injury, followed by a smaller increase between 6 and 24 h after the insult. No further accumulation of alpha-spectrin breakdown products was observed between 24 and 48 h after injury. Histopathological examinations using hematoxylin and eosin staining demonstrated dark, shrunken neurons within 15 min after traumatic brain injury. No evidence of mu-calpain autolysis, calpain-mediated alpha-spectrin degradation, or hematoxylin and eosin neuronal pathology was detected in the contralateral cortex. Although mu-calpain autolysis and cytoskeletal proteolysis occurred concurrently with early morphological alterations, evidence of calpain-mediated proteolysis preceded the full expression of evolutionary histopathological changes. Our results indicate that rapid and persistent mu-calpain activation plays an important role in cortical neuronal degeneration after traumatic brain injury. Our data also suggest that specific inhibitors of calpain could be potential therapeutic agents for the treatment of traumatic brain injury in vivo.

Analysis of Variance↗
PubMed1996

Cytoskeletal derangements of cortical neuronal processes three hours after traumatic brain injury in rats: an immunofluorescence study.

Semiquantitative Western blot analyses have shown that traumatic brain injury (TBI) can produce significant loss of cytoskeletal proteins (neurofilament 68 [NF68], neurofilament 200 [NF200] and microtubule associated protein 2 [MAP2]) possibly by calpain-mediated proteolysis. Thus, we employed immunofluorescence (light and confocal microscopy) to study the histopathological correlates of acute neurofilament and MAP2 protein decreases observed 3 hours following unilateral cortical injury in rats. TBI induced dramatic alterations in NF68, NF200, and MAP2 immunolabeling in dendrites within and beyond contusion sites ipsilateral and contralateral to the injury site. Marked changes in immunolabeling were associated with but not exclusively restricted to regions of dark shrunken neurons labeled by hematoxylin and eosin staining, a morphopathological response to injury suggesting impending cell death. Light microscopic studies of NF200 immunofluorescence revealed a prominent fragmented appearance of apical dendrites of pyramidal neurons within layers 3 and 5, as well as a loss of fine dendritic arborization within layer 1. Confocal microscopy detected varying degrees of NF200 disassembly associated with these areas of neurofilament fragmentation. Light microscopic studies of NF68 immunofluorescence detected subtle and less severe structural changes including smaller breaks and focal vacuolization of apical dendrites. Light microscopic immunofluorescence of MAP2 revealed changes similar to those seen for NF200. Acute axonal alterations detected with NF68 were minimal compared to immunofluorescence changes seen in dendritic regions. Therefore, preferential dendritic cytoskeletal derangements may be an early morphological feature of experimental traumatic brain injury in vivo. In addition, these cytoskeletal derangements may not be exclusively restricted to sites of contusion and cell death.

Animals↗
PubMed1996

Calpain inhibitors protect against depolarization-induced neurofilament protein loss of septo-hippocampal neurons in culture.

We examined the effect of a 6 min depolarization with 60 mM KCl and 1.8, 2.8 or 5.8 mM extracellular CaCl2 on neurofilament proteins of high (NF-H), medium (NF-M) and low (NF-L) molecular weight in primary septohippocampal cultures. One day after depolarization, Western blot analyses revealed losses of all three neurofilament proteins. Increasing the extracellular calcium concentration from 1.8 to 5.8 mM CaCl2 in the presence of 60 mM KCl produced increased losses of all three neurofilament proteins to approximately 80% of control values in the absence of cell death. Calcium-dependent losses of the neurofilament proteins correlated with calcium-dependent increases in calpain 1-mediated breakdown products of alpha-spectrin. Calpain inhibitors 1 and 2, applied immediately after depolarization and made available to cultures for 24 h, reduced losses of all three neurofilament proteins to approximately 14% of control values. The protective effects of calpain inhibitors 1 and 2 were influenced by different levels of extracellular calcium. Qualitative immunohistochemical evaluations confirmed semiquantitative Western blot data on neurofilament loss and protection by calpain inhibitors 1 and 2. We propose that brief depolarization causes loss of neurofilament proteins, possibly due to calpain activation. Thus, calpain inhibitors could represent a viable strategy for preserving the cytoskeletal structure of injured neurons.

Animals↗
PubMed1996

Memory tests distinguish between patients with focal temporal and extratemporal lobe epilepsy.

We examined the ability of preoperative memory performance to distinguish between patients who had been diagnosed as having left (LTLE, n = 31), right (RTLE, n = 37), and extra-(ETLE, n = 17) temporal lobe focal epilepsy. All patients eventually underwent surgical resections. Analyses indicated that the ETLE group performed better than the RTLE group on nonverbal memory measures and better than the LTLE group on verbal memory measures. Discriminant function analyses indicated that use of a combination of measures that assess different aspects of memory were of significant value in distinguishing between patients with focal TLE and ETLE. This approach, as compared the use of single measures, improved classification rates of all three groups. The best single predictor of group membership, an index of verbal learning, yielded a 47% overall correct classification rate, with sensitivities ranging from 25 to 59%, and performed at worse than chance levels in classifying RTLE patients. A multivariate approach, which included an index of verbal and nonverbal learning, incidental nonverbal memory, and consolidation of organized and rote verbal material, yielded a 65% correct classification rate, with sensitivities ranging from 57 to 75%. This compares favorably with the other noninvasive techniques for lateralizing epileptogenic lesions.

Adolescent↗
PubMed1995

Basal and scopolamine-evoked release of hippocampal acetylcholine following traumatic brain injury in rats.

This study employed in vivo microdialysis in awake, freely-moving Sprague-Dawley rats to examine acetylcholine (ACh) release in the dorsal hippocampus at 14 days following lateral controlled cortical impact. Extracellular levels of ACh were measured prior to and after an intraperitoneal administration of scopolamine (1 mg/kg), which evokes ACh release by blocking autoreceptors. At 14 days post injury there were no differences in basal ACh levels. However, injury produced a significant reduction in scopolamine-evoked ACh release. The data suggest that cholinergic neurotransmission remains chronically compromised, and thus may contribute to previously documented post traumatic spatial memory deficits.

Acetylcholine↗
PubMed1995

Calpain inhibitors reduce depolarization induced loss of tau protein in primary septo-hippocampal cultures.

We studied the effects of a 6-min potassium depolarization injury produced by 60 mM KCl and 1.8 mM or 5.8 mM extracellular CaCl2 on tau protein levels in primary rat septo-hippocampal cultures. One day after injury, Western blot analyses revealed a calcium dependent loss of tau protein of approximately 50% of control values. Loss of tau protein was associated with calpain 1 mediated breakdown products to alpha-spectrin. Calpain inhibitors 1 and 2, applied immediately after depolarization injury and available to cultures for 24 h reduced depolarization induced degradation of tau protein to approximately 35% or 25% of control values, respectively. We propose that brief potassium depolarization causes degradation of tau protein, possibly due to calpain activation. Thus, calpain inhibitors could represent a viable strategy for preserving the cytoskeletal structure of injured neurons.

Animals↗
PubMed1995

Rescue of injury-induced neurofilament loss by BDNF gene transfection in primary septo-hippocampal cell cultures.

We employed primary septo-hippocampal cell cultures to determine the ability of liposome-mediated BDNF gene transfection to facilitate recovery of neurofilament loss caused by depolarization injury. After BDNF gene transfection in uninjured cultures, RT-PCR and immunohistochemical staining confirmed increases in BDNF mRNA and protein in transfected cells. Three days after depolarization injury, Western blot and immunohistochemical analyses detected significant loss of neurofilament proteins in non-transfected cultures, while BDNF transfection produced marked increases in neurofilament proteins following either pre-injury transfection or transfection 24 h following injury. Immunohistochemical studies also detected enhanced immunolabeling of BDNF and total neurofilament protein (phosphorylated and non-phosphorylated) in injured neurons following BDNF transfection or administration of exogenous BDNF protein, compared to untransfected, injured controls.

Animals↗
PubMed1995

Systemic hypothermia in treatment of severe brain injury: a review and update.

Laboratory studies of moderate hypothermia (30-33 degrees C) after injury show diminished neuronal loss after ischemia, diminished excessive neurotransmitter release after ischemia, prevention of blood-brain barrier disruption after ischemia and brain injury, and behavioral improvement after brain injury. Clinical literature suggests that brief periods of moderate hypothermia (> or = 30 degrees C) in humans are not associated with cardiovascular, hematologic, metabolic, or neurological toxicity. Clinical studies were, therefore, organized to investigate the potential application of moderate systemic hypothermia in patients after severe brain injury. A study of 21 elective craniotomy patients and 11 patients with severe brain injury led to the conclusion that 32 to 33 degrees C was the lowest safe temperature in patients with severe brain injury. A randomized study of moderate hypothermia in 46 patients with Glasgow Coma Score (GCS) 4-7 gave an indication of improved neurologic outcome in the hypothermia group. A multicenter, randomized protocol to test the effect of moderate systemic hypothermia in patients with severe brain injury is in progress. Funded by the National Institutes of Health, The National Acute Brain Injury Study: Hypothermia tests the hypothesis that systemic hypothermia to 32-33 degrees C if rendered within 6 h of injury improves Glasgow Outcome Scores (GOS) at 6 months after injury in patients with severe brain injury (GCS 3-8).

Animals↗
PubMed1995

Hypothermia and hyperbaric oxygen as treatment modalities for severe head injury.

Moderate systemic hypothermia has been shown to improve neurologic outcomes in both fluid-percussion and cortical contusion models of experimental brain injury. Based upon initial clinical work, it was concluded that at temperatures < 32 degrees C, patients with severe brain injury were at increased risk of ventricular arrhythmias, and that rapid rewarming immediately postinjury predisposed to intracranial pressure increases. Subsequent clinical studies of moderate hypothermia (32 degrees C) for 24- to 48-hr duration with slow rewarming in human brain injury showed indications of neurologic improvement and a low incidence of hypothermia-related complications. Based upon the strengths of both laboratory and clinical data, a multicenter (nine centers), randomized, prospective trial testing moderate systemic hypothermia in patients with severe brain injury has been organized. This trial, funded by National Institutes of Health, National Institute of Neurological Disorders and Stroke, began on October 20, 1994. Five hundred patients are to be treated in an intent-to-treat protocol using standard management at normothermia versus standard management at hypothermia. The trial is designed to detect an absolute shift of 12% in the percentage of patients achieving satisfactory outcome (good recovery/moderate disability) at a power of 85% at 6 months postinjury. The efficacy of hyperbaric oxygen administered every 8 hrs for 1-hr duration for a 2-wk period has also been tested in patients after severe brain injury. While the mortality rate was reduced in the treated group, the percentage of favorable outcomes was unchanged. Further studies are in progress.

Craniocerebral Trauma↗
PubMed1993

Hypothermia attenuates the loss of hippocampal microtubule-associated protein 2 (MAP2) following traumatic brain injury.

Traumatic brain injury (TBI) produces a tissue-specific decrease in protein levels of microtubule-associated protein 2 (MAP2), an important cross-linking component of the neuronal cytoskeleton. Because moderate brain hypothermia (30 degrees C) reduces certain neurobehavioral deficits produced by TBI, we examined the efficacy of moderate hypothermia (30 degrees C) in reversing the TBI-induced loss of MAP2 protein. Naive, sham-injured, and moderate (2.1 atm) fluid percussion-injured rats were assessed for MAP2 protein content 3 h post injury using quantitative immunoreactivity measurements. Parallel groups of sham-injured and fluid percussion-injured animals were maintained in moderate hypothermia (30 degrees C), as measured by temporalis muscle temperature, for MAP2 quantitation 3 h post injury. No difference in MAP2 levels was observed between naive and sham-injured normothermic animals. Hypothermia alone had no effect on soluble MAP2 levels in sham-injured animals compared with normothermic sham-injured controls (88.0 +/- 7.3%; p > 0.10). Fluid percussion injury dramatically reduced MAP2 levels in the normothermic group (44.3 +/- 5.9%; p < 0.0005) compared with normothermic sham-injured controls. No significant reduction of MAP2 was seen in the hypothermic injured group (95.2 +/- 4.6%; compared with hypothermic sham-injured controls, p > 0.20). Although it is premature to infer any causal link, the data suggest that the attenuation of injury-induced MAP2 loss by hypothermia may contribute to its overall neuroprotective action.

Animals↗
PubMed1993

A phase II study of moderate hypothermia in severe brain injury.

Forty-six patients with severe nonpenetrating brain injury [Glasgow Coma Scale (GCS) 4-7] were randomized to standard management at 37 degrees C (n = 22) and to standard management with systemic hypothermia to 32 to 33 degrees C (n = 24). The two groups were balanced in terms of age (Wilcoxon's rank sum test, p > 0.95), randomizing GCS (chi-square test, p = 0.54), and primary diagnosis. Cooling was begun within 6 h of injury by use of cooling blankets. Metocurine and morphine were given hourly during induction and maintenance of hypothermia. Rewarming was at a rate of 1 degree C per 4 h beginning 48 h after intravascular temperature had reached 33 degrees C. Muscle relaxants and sedation were continued until core temperature reached 35 degrees C. There were no cardiac or coagulopathy-related complications. Seizure incidence was lower in the hypothermia group (Fisher's exact text, p = 0.019). Sepsis was seen more commonly in the hypothermia group, but difference was not statistically significant (chi-square test). Mean Glasgow Outcome Scale (GOS) score at 3 months after injury showed an absolute increase of 16% (i.e., 36.4-52.2%) in the number of patients in the Good Recovery/Moderate Disability (GR/MD) category as compared with Severe Disability/Vegetative/Dead (SD/V/D) (chi-square test, p > 0.287). Based on evidence of improved neurologic outcome with minimal toxicity, we believe that phase III testing of moderate systemic hypothermia in patients with severe head injury is warranted.

Adolescent↗
PubMed1993

Relationship between Glasgow Outcome Scale and neuropsychological measures after brain injury.

The present study was conducted to further our understanding of the relationship between performance on neuropsychological tests and functional status after head injury and to provide information on the relative usefulness of neuropsychological tests as outcome measures in clinical trials of brain injury. We sought to select the fewest number of 19 neuropsychological tests administered to 110 patients that, in combination, were most closely related to outcome (as measured by the Glasgow Outcome Scale (GOS) and to the remaining neuropsychological measures. The relationship of memory and intellectual deficits to functional status was also considered. To address these questions, we analyzed 19 neuropsychological measures and GOS scores of 110 severely brain injured patients from the Traumatic Coma Data Bank. Of 19 neuropsychological measures compared with GOS at 3 and 6 months, four tests (Controlled Oral Word Association, Grooved Pegboard, Trailmaking Part B, and Rey-Osterrieth Complex Figure Delayed Recall) provided the closest relationship to GOS and to the remaining 15 tests. Similar analyses were performed on 30 moderately injured patients to test the generality of our findings across different levels of patient severity. The same four tests were found to be highly predictive of GOS. Grooved Pegboard, a test of fine motor coordination, accounted for 80% of the variation in GOS. Fifteen percent of 116 patients with severe brain injury could not complete a neuropsychological battery and 39% were excluded because of previous brain injury or known substance abuse.

Adolescent↗