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Biomedical subjects

M Walton

Publications and source records attributed to M Walton.

At least 37 records · Page 2Linked to original sources
PubMed1999

Activity and injury-dependent expression of inducible transcription factors, growth factors and apoptosis-related genes within the central nervous system.

This review primarily discusses work that has been performed in our laboratories and that of our direct collaborators and therefore does not represent an exhaustive review of the current literature. Our aim is to further discuss the role that gene expression plays in neuronal plasticity and pathology. In the first part of this review we examine activity-dependent changes in the expression of inducible transcription factors (ITFs) and neurotrophins with long-term potentiation (LTP) and kindling. This work has identified particular ITFs (Krox-20 and Krox-24) and neurotrophin systems (particularly the brain-derived neurotrophic factor (BDNF)/tyrosine receptor kinase-B, Trk-B system) that may be involved in stabilizing long-lasting LTP (i.e. LTP3). We also show that changes in the expression of other ITFs (Fos, Jun-D and Krox-20) and the BDNF/trkB neurotrophin system may play a central role in the development of hippocampal kindling, an animal model of human temporal lobe epilepsy. In the next part of this review we examine changes in gene expression after neuronal injuries (ischemia, prolonged seizure activity and focal brain injury) and after nerve transection (axotomy). We identify apoptosis-related genes (p53, c-Jun, Bax) whose delayed expression selectively increases in degenerating neurons, further suggesting that some forms of neuronal death may involve apoptosis. Moreover, since overexpression of the tumour-suppressor gene p53 induces apoptosis in a wide variety of dividing cell types we speculate that it may perform the same function in post-mitotic neurons following brain injuries. Additionally, we show that neuronal injury is associated with rapid, transient, activity-dependent expression of neurotrophins (BDNF and activinA) in neurons, contrasting with a delayed and more persistent injury-induced expression of certain growth factors (IGF-1 and TGFbeta) in glia. In this section we also describe results linking ITFs and neurotrophic factor expression. Firstly, we show that while BDNF and trkB are induced as immediate-early genes following injury, the injury-induced expression of activinA and trkC may be regulated by ITFs. We also discuss whether loss of retrograde transport of neurotrophic factors such as nerve growth factor following nerve transection triggers the selective and prolonged expression of c-Jun in axotomized neurons and whether c-Jun is responsible for regeneration or degeneration of these axotomized neurons. In the last section we further examine the role that gene expression may play in memory formation, epileptogenesis and neuronal degeneration, lastly speculating whether the expression of various growth factors after brain injury represents an endogenous neuroprotective response of the brain to injury. Here we discuss our results which show that pharmacological enhancement of this response with exogenous application of IGF-1 or TGF-beta reduces neuronal loss after brain injury.

Animals↗
PubMed1999

Population genetics of the yellow fever mosquito in Trinidad: comparisons of amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) markers.

Recent development of DNA markers provides powerful tools for population genetic analyses. Amplified fragment length polymorphism (AFLP) markers result from a polymerase chain reaction (PCR)-based DNA fingerprinting technique that can detect multiple restriction fragments in a single polyacrylamide gel, and thus are potentially useful for population genetic studies. Because AFLP markers have to be analysed as dominant loci in order to estimate population genetic diversity and genetic structure parameters, one must assume that dominant (amplified) alleles are identical in state, recessive (unamplified) alleles are identical in state, AFLP fragments segregate according to Mendelian expectations and that the genotypes of an AFLP locus are in Hardy-Weinberg equilibrium (HWE). The HWE assumption is untestable for natural populations using dominant markers. Restriction fragment length polymorphism (RFLP) markers segregate as codominant alleles, and can therefore be used to test the HWE assumption that is critical for analysing AFLP data. This study examined whether the dominant AFLP markers could provide accurate estimates of genetic variability for the Aedes aegypti mosquito populations of Trinidad, West Indies, by comparing genetic structure parameters using AFLP and RFLP markers. For AFLP markers, we tested a total of five primer combinations and scored 137 putative loci. For RFLP, we examined a total of eight mapped markers that provide a broad coverage of mosquito genome. The estimated average heterozygosity with AFLP markers was similar among the populations (0.39), and the observed average heterozygosity with RFLP markers varied from 0.44 to 0.58. The average FST (standardized among-population genetic variance) estimates were 0.033 for AFLP and 0.063 for RFLP markers. The genotypes at several RFLP loci were not in HWE, suggesting that the assumption critical for analysing AFLP data was invalid for some loci of the mosquito populations in Trinidad. Therefore, the results suggest that, compared with dominant molecular markers, codominant DNA markers provide better estimates of population genetic variability, and offer more statistical power for detecting population genetic structure.

Aedes↗
PubMed1999

CREB phosphorylation promotes nerve cell survival.

The cyclic AMP-responsive element binding protein (CREB) is a posttranslationally activated transcription factor that has been implicated in numerous brain functions including cell survival. In this study we investigated whether CREB overexpression using transient transfection of a pAAV/CMV-CREB plasmid altered neuronal cells' susceptibility to apoptosis. We found that elevated CREB protein inhibited apoptosis induced by okadaic acid. At least part of this effect is critically dependent on prolonged Ser133 phosphorylation, as a directed mutation at this site decreased CREB-induced protection. These results suggest that CREB is a survival factor for neuronal cells and that treatments aimed at augmenting CREB phosphorylation in the brain may be neuroprotective.

Animals↗
PubMed1998

ATF-2 phosphorylation in apoptotic neuronal death.

Activating transcription factor (ATF-2) is a basic region-leucine zipper transcription factor that can mediate a diverse range of transcriptional responses including those generated by various forms of cellular stress. Activation of ATF-2 in response to these stimuli requires post-translational modification, in particular the phosphorylation of Thr69 and Thr71. To investigate whether ATF-2 activation also has a role in neuronal apoptosis, immunocytochemistry using a phospho-specific ATF-2 (Thr71) antibody was carried out in the 21 day old rat brain following a unilateral hypoxic-ischemic (HI) insult and PC12 cells cultured in the presence of okadaic acid. In both models a dramatic increase in phosphorylated ATF-2 was found within cells undergoing apoptosis.

Activating Transcription Factor 2↗
PubMed1998

CCAAT-enhancer binding protein alpha is expressed in activated microglial cells after brain injury.

Microglial cells play important roles in brain injury and repair and are implicated in diseases such as Alzheimer's disease, Creutzfeldt-Jacob disease, multiple sclerosis, the Aids Dementia Complex and stroke. Despite their importance in neuropathology, the underlying molecular basis for the activation of microglia after brain injury is not understood. We show, using RT-PCR, in situ hybridisation, immunocytochemistry, and electrophoretic mobility shift assay, that the CCAAT-enhancer binding protein alpha (C/EBP alpha), a sequence specific DNA-binding protein, is induced in microglial cells, but not astrocytes or neurons, after hypoxic-ischemic brain injury. These results suggest that C/EBP alpha might regulate gene expression and consequentially have a role in the activation and/or proliferation of microglia following brain injury.

Animals↗
PubMed1998

Do c-Jun, c-Fos, and amyloid precursor protein play a role in neuronal death or survival?

A unilateral hypoxic-ischemic (HI) episode in immature rat brain was used to investigate the role of the immediate early genes c-fos and c-jun in delayed neuronal death and survival. This HI paradigm results in an apoptotic cell death in selectively vulnerable areas, in particular the hippocampal CA1 pyramidal cell layer. In susceptible regions undergoing delayed neuronal death there was a prolonged induction of both c-Jun and c-Fos (mRNA and protein). This expression occurred in parallel with a pronounced increase in AP-1 DNA binding activity but was not associated with either increased levels of Jun NH2-terminal kinase or phosphorylation of c-Jun (ser-63). In addition to changes in immediate early gene expression, the CA1 neurons showed a delayed increase in the expression of amyloid precursor protein (APP751) mRNA, suggesting that APP, which contains an AP-1 site, might be a down-stream gene regulated by the Jun transcription factor in neurons dying by apoptosis. The surviving dentate granule cells also showed an increase in Fos, Jun, and APP751 although this expression occurred earlier than in the CA1 neurons and declined rapidly. These results are discussed with respect to the role of these proteins in neuronal death and survival.

Amyloid beta-Protein Precursor↗
PubMed1997

Annexin V labels apoptotic neurons following hypoxia-ischemia.

The translocation of phosphatidylserine from the cytosol to the external surface of the plasma membrane has been documented as a characteristic feature of apoptosis in a number of cell types. Annexin V is a calcium-dependent phospholipid binding protein that has high affinity for phosphatidylserine. To investigate whether Annexin V provides a marker of apoptosis in the central nervous system we carried out histochemical analysis of its binding in the 21-day-old rat brain at various time-points following a moderate unilateral hypoxic-ischemic (HI) insult. The CA1 pyramidal neurons, which are selectively vulnerable to HI injury and that die by an apoptotic mechanism showed an increase in Annexin V binding 48-168 hours post-insult.

Animals↗
PubMed1997

Prostaglandin H synthase-2 and cytosolic phospholipase A2 in the hypoxic-ischemic brain: role in neuronal death or survival?

The breakdown of membrane phospholipids and subsequent arachidonic acid metabolism to prostanoids is a well-documented brain response to cerebral ischemia. To further elucidate the components of this signal transduction pathway, immunocytochemistry was used to determine the levels of two potentially important enzymes, cytosolic phospholipase A2 (cPLA2) and prostaglandin H synthase-2 (PGHS-2), in the immature rat brain following moderate unilateral hypoxic-ischemia (HI). The CA1 pyramidal cells of the hippocampus which undergo delayed neuronal death on the injured side following HI demonstrated a significant induction of PGHS-2 immunoreactivity 48 h post-insult. However, a consistent increase in PGHS-2 was also evident in the resistant dentate granule cells at an earlier time point. Although PGHS-2 is present in both susceptible and resistant cell populations following HI, the possibility remains that divergence further down-stream in the pathway is responsible for selective vulnerability. In contrast to the neuronal PGHS-2 expression, cPLA2 immunoreactivity appears to be of glial origin with increases in and around the CAI-2 pyramidal cell layer at the 72-168-h time points. These results suggest that prostanoids are likely to serve important roles in HI brain damage and repair in infant brain.

Animals↗
PubMed1997

Expression of Fos, Jun, and Krox family proteins in Alzheimer's disease.

Apoptosis is an active process of cell death characterized by distinct morphological features and is often the end result of a genetic program of events, i.e., programmed cell death (PCD). There is growing evidence supporting a role for apoptosis and/or PCD in Alzheimer's disease (AD), based on DNA fragmentation studies and recent findings of increased levels of inducible transcription factors (ITFs) such as c-Jun in AD brains. We have characterized the expression of a large range of ITFs (c-Fos, Fos B, Fos-related antigens, c-Jun, Jun B, Jun D, Krox20, and Krox24) using multiple antisera in AD postmortem hippocampi and compared this with human control hippocampi as well as Huntington's disease hippocampi and human epilepsy biopsy tissue. We found little evidence of nuclear expression of any ITF except c-Jun in the human postmortem tissue, compared with nuclear staining in biopsy tissue. We found some evidence for increased levels of c-Jun and Krox24 protein and krox24 mRNA in the CA1 region of AD hippocampi, suggesting that PCD may be involved in the pathogenesis of AD. In general, staining characteristics of ITFs varied with different antisera directed against the same protein, indicating the need for caution when interpreting results.

Adult↗
PubMed1997

Histopathologic analysis of interval appendectomy specimens: support for the role of interval appendectomy.

The treatment of appendiceal abscess is controversial. For patients initially treated "conservatively" with antibiotics with or without drainage, the role of interval appendectomy is an area of considerable debate. Without interval appendectomy, the true risks of recurrent disease and missed pathological findings are uncertain, and large, long-term, prospective studies are unavailable. To evaluate the role of interval appendectomy, the authors reviewed the histopathologic specimens from patients with presumed appendiceal abscess treated by interval appendectomy. Over a 7-year period, 162 children presented with a clinical diagnosis of perforated appendicitis. Eighteen patients had localized abscesses treated conservatively, followed by interval appendectomy. Standard histopathologic sections of 17 of the 18 appendices were examined by one pathologist who was blinded to the clinical data and to the interpretation of the original pathologist. Of the 11 boys and seven girls (mean age, 7.4 +/- 3.4 years), eight underwent percutaneous drainage and one underwent operative drainage. All received intravenous antibiotics for a mean of 8.6 +/- 3.2 days with a hospital stay of 10.4 +/- 8.3 days. Interval appendectomy was performed at a mean of 92.7 +/- 20.7 days after initial admission, with discharge at a mean of 2 +/- 1.3 days after surgery. There were no complications or deaths. Histopathologic review showed normal appendix (n = 4), normal appendix with mild serositis (n = 6), normal appendix with unsuspected resolved Meckel's diverticulitis (n = 1), appendiceal duplication (n = 1), granulomatous appendicitis (n = 3), and acute appendicitis (n = 2). All appendices had patent lumens, and 15 were documented to be present to the tip. There was no correlation between the histopathologic findings and the interval between abscess and interval appendectomy. Interval appendectomy was performed with no morbidity and a short hospital stay. Two patients had histopathologic recurrent acute appendicitis, five had unsuspected pathological findings (appendiceal duplication, Meckel's diverticulitis, granulomatous inflammation), and none of the appendices had an obliterated lumen, suggesting that all patients were at long-term risk for recurrent disease. These data support the role of interval appendectomy in cases of perforated appendicitis treated conservatively.

Abscess↗
PubMed1997

Assessment of the postoperative visit after routine inguinal hernia repair: a prospective randomized trial.

Treatment of pediatric patients undergoing routine inguinal hernia repair usually includes a postoperative clinic visit. We prospectively assessed the necessity for the traditional postoperative visit. One hundred patients undergoing a routine inguinal hernia repair were randomly selected to receive either a follow-up visit at 4 weeks or a detailed instruction sheet and no follow-up visit. Parents were given a telephone questionnaire to determine overall satisfaction with their child's care and the usefulness of the follow-up visit or instruction sheet. Forty-seven of 50 parents of patients randomly assigned to a follow-up clinic visit (FU) and all 50 parents in the no follow-up group (NFU) completed the questionnaire. Sixty-eight percent of the FU group found the follow-up visit "helpful" and 59% found it "necessary." Fifty-six percent would have been satisfied with a telephone call instead of a visit. In the NFU group only 4% thought a follow-up visit would have been "helpful" and 4% thought a visit was "necessary." Ninety-six percent found the postoperative instruction sheet "helpful." There was no difference between groups in overall satisfaction with the care received as assessed on a 5-point scale (4.7 FU group v 4.7 NFU group). Accurate postoperative instruction and open access to follow-up when required is as effective as the traditional postoperative clinic visit for patients who have undergone routine inguinal hernia repair.

Appointments and Schedules↗
PubMed1997

Loss of Ref-1 protein expression precedes DNA fragmentation in apoptotic neurons.

Ref-1 is a bifunctional protein that has been implicated in the transcriptional regulation of AP-1 elements and in DNA repair. To investigate whether Ref-1 is involved in programmed cell death its expression was measured in the 21-day-old rat brain at various time-points following a moderate unilateral hypoxic-ischemic (HI) insult. The CA1 pyramidal cells, which are selectively vulnerable to HI injury, showed a significant decrease in Ref-1 immunoreactivity 48 h-7 days post-insult. This loss of Ref-1 immunoreactivity may contribute to a decrease in endogenous repair activity and the development of apoptosis in the CA1 pyramidal cells.

Animals↗
PubMed1996

The role of the cyclic AMP-responsive element binding protein (CREB) in hypoxic-ischemic brain damage and repair.

The cyclic AMP-responsive element binding protein (CREB) is a basally expressed, post-translationally activated transcription factor that has been implicated in the trans-activation of a number of genes in response to cAMP and calcium signals. A unilateral hypoxic-ischemic (HI) injury in the 21 day old rat was used to examine a potential role for CREB (phosphorylated and unphosphorylated) in neuronal programmed cell death or cell survival. The selectively vulnerable CAI pyramidal cells, which undergo delayed neuronal death following mild HI, show a loss of CREB and phosphorylated CREB (pCREB) immunoreactivity on the injured side 48 and 72 h following HI. In contrast the resistant dentate granule cells and cortical cells produce a bimodal increase in pCREB immunoreactivity, peaking 6 and 48 h following HI. The fact that cells surviving the HI insult are showing increased activation of CREB suggests that this protein might be involved in the process of neuroprotection.

Animals↗
PubMed1996

Induction of clusterin in the immature brain following a hypoxic-ischemic injury.

A unilateral hypoxic-ischemic (HI) insult in the 21 day old rat has been used to assess the role of clusterin in nerve cell death. Both clusterin mRNA and protein levels were measured at various time points after moderate (15 min) and severe (60 min) HI insult using in situ hybridisation and immunocytochemistry respectively. The severe HI insult lead primarily to necrotic neuronal death and showed very little if any clusterin mRNA and protein induction on the ligated side of the brain. However, following the moderate HI insult there was a dramatic time-dependent accumulation of clusterin protein in neurons of the CA1-CA2 pyramidal cell layers in the hippocampus and cortical layers 3-5, regions undergoing delayed neuronal death. Clusterin mRNA expression, in contrast to neuronal protein accumulation, appeared to be glial in origin (probably astrocytes) with increases in mRNA in and around the hippocampal fissure and only a weak signal over the CA1-CA2 pyramidal cell layer. These results support the hypothesis that the clusterin protein is synthesised in the astrocytes, secreted and then taken up by dying neurons. Clusterin immunoreactivity and in situ DNA end-labelling performed on the same sections revealed that clusterin was accumulating in neurons destined to die by programmed cell death. However the relative time-courses of DNA fragmentation and clusterin immunoreactivity suggest that clusterin production was a result of the selective delayed neuronal death rather than being involved in the biochemical cascade of events that cause it.

Animals↗
PubMed1995

Button-pexy fixation for repair of ileostomy and colostomy prolapse.

Intestinal stomas are used in the surgical management of a number of congenital and acquired gastrointestinal conditions. Minor stomal complications are relatively common and are often well managed with nonoperative measures. Stomal prolapse may not represent a serious problem, but occasionally it requires surgical correction because of severe skin excoriation, bleeding, or incarceration of the bowel. The authors describe the treatment of stomal prolapse with the technique of button-pexy fixation, as originally described by C.W. Mayo.

Colostomy↗
PubMed1995

Testicular fate after incarcerated hernia repair and/or orchiopexy performed in patients under 6 months of age.

This study assessed testicular viability after 476 inguinal procedures performed in 338 infants under 6 months of age, between 1974 and 1993. One hundred twenty-one elective hernia repairs (contralateral explorations) were compared with 355 hernia repairs complicated by incarceration and/or orchiopexy. Clinical examination of 323 testes in the early postoperative period showed 20 atrophic testes. Since January 1994, 71 of the 338 patients have had testicular measurements obtained through ultrasonography (US). An additional 13 atrophic testes were found during US examination. Of these, nine were believed to be normal during early postoperative examination. Assuming that US examination will confirm atrophy in the 20 atrophic testes noted early in the postoperative clinical evaluation, and that all other testes not yet scanned are found to be normal, the minimal atrophy rate (MAR) would be 9.3% (33 of 355). Neither operative nor early postoperative testicular assessment correlates with ultimate testicular survival. Testicular pathology may become more evident after puberty, and the real incidence of atrophy may increase.

Atrophy↗