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M J Coleman

Publications and source records attributed to M J Coleman.

At least 19 recordsLinked to original sources
PubMed2002

Central mechanisms underlying short- and long-term regulation of the cardiovascular system.

1. Sympathetic vasomotor nerves play a major role in determining the level of arterial blood pressure and the distribution of cardiac output. The present review will discuss briefly the central regulatory mechanisms that control the sympathetic outflow to the cardiovascular system in the short and long term. 2. In the short term, the sympathetic vasomotor outflow is regulated by: (i) homeostatic feedback mechanisms, such as the baroreceptor or chemoreceptor reflexes; or (ii) feed-forward mechanisms that evoke cardiovascular changes as part of more complex behavioural responses. 3. The essential central pathways that subserve the baroreceptor reflex and, to a lesser extent, other cardiovascular reflexes, have been identified by studies in both anaesthetized and conscious animals. A critical component of these pathways is a group of neurons in the rostral ventrolateral medulla that project directly to the spinal sympathetic outflow and that receive inputs from both peripheral receptors and higher centres in the brain. 4. Much less is known about the central pathways subserving feed-forward or 'central command' responses, such as the cardiovascular changes that occur during exercise or that are evoked by a threatening or alerting stimulus. However, recent evidence indicates that the dorsomedial hypothalamic nucleus is a critical component of the pathways mediating the cardiovascular response to an acute alerting stimulus. 5. Long-term sustained changes in sympathetic vasomotor activity occur under both physiological conditions (e.g. a change in salt intake) and pathophysiological conditions (e.g. heart failure). There is evidence that the paraventricular nucleus in the hypothalamus is a critical component of the pathways mediating these changes. 6. Understanding the central mechanisms involved in the long-term regulation of sympathetic activity and blood pressure is a major challenge for the future. As a working hypothesis, a model is presented of the postulated central mechanisms that result in sustained changes in sympathetic vasomotor activity that are evoked by different types of chronic stimulation.

Animals↗
PubMed2001

Prediction of stable walking for a toy that cannot stand.

Previous experiments [M. J. Coleman and A. Ruina, Phys. Rev. Lett. 80, 3658 (1998)] showed that a gravity-powered toy with no control and that has no statically stable near-standing configurations can walk stably. We show here that a simple rigid-body statically unstable mathematical model based loosely on the physical toy can predict stable limit-cycle walking motions. These calculations add to the repertoire of rigid-body mechanism behaviors as well as further implicating passive dynamics as a possible contributor to stability of animal motions.

Animals↗
PubMed2000

The cardiovascular effects of angiotensin-(1-7) in the rostral and caudal ventrolateral medulla of the rabbit.

Previous studies in the rat have indicated that the heptapeptide angiotensin-(1-7) has an excitatory action on pressor neurons in the rostral ventrolateral medulla that is equipotent to that evoked by angiotensin II, but which is mediated by separate receptors. In this study we have compared the cardiovascular effects and mechanisms of action of angiotensin-(1-7) with angiotensin II in the rostral and caudal ventrolateral medulla of the rabbit, a species which, unlike the rat, contains a high density of angiotensin receptors, similar to that observed in humans. Microinjections of angiotensin-(1-7) into the rostral and caudal ventrolateral medulla evoked dose-dependent increases and decreases, respectively, in arterial pressure and renal sympathetic nerve activity, but in comparison to angiotensin II much higher doses (approximately 50-fold higher) were required to produce cardiovascular response of similar magnitude. The cardiovascular effects of angiotensin-(1-7) were blocked by prior injection of the selective antagonist [D-Ala(7)]-Ang-(1-7) but were also blocked by the selective AT(1) receptor antagonist losartan. The results demonstrate that in the rabbit angiotensin-(1-7) can excite pressor and depressor neurons in the ventrolateral medulla, but indicate that these effects are mediated by AT(1) receptors. The much lower potency of angiotensin-(1-7) as compared to angiotensin II may be explained as a consequence of it having a much lower affinity to AT(1) receptors. Thus, in contrast to the rat, the results do not indicate that angiotensin-(1-7) has a biologically significant action in the ventrolateral medulla of the rabbit.

Adrenergic Fibers↗
PubMed2000

Arabidopsis RelA/SpoT homologs implicate (p)ppGpp in plant signaling.

Arabidopsis RPP5 is a member of a large class of pathogen resistance genes encoding nucleotide-binding sites and leucine-rich repeat domains. Yeast two-hybrid analysis showed that RPP5 specifically interacts with At-RSH1, an Arabidopsis RelA/SpoT homolog. In Escherichia coli, RelA and SpoT determine the level of guanosine tetraphosphate (ppGpp) and guanosine pentaphosphate (pppGpp), which are the effector nucleotides of the bacterial stringent response. Functional analysis in E. coli and in Streptomyces coelicolor A3 (2) showed that At-RSH1 confers phenotypes associated with (p)ppGpp synthesis. We characterized two additional Arabidopsis RelA/SpoT homologs, At-RSH2 and At-RSH3. At-RSH genes may regulate a rapid plant (p)ppGpp-mediated response to pathogens and other stresses.

Arabidopsis↗
PubMed2000

The operative management of screen-detected breast cancers.

BACKGROUND: Mammographic screening for breast cancer not only reduces the overall mortality from breast cancer but allows greater opportunities for breast-conserving operations. The predicted degree of breast conservation is not being realized, but is increasing in centres that have published their results. METHODS: The operative management of breast cancers diagnosed by BreastScreen Central and Eastern Sydney Screening and Assessment Service were compared between two time periods: January 1988-December 1992 (group 1) and January 1993-December 1995 (group 2). The rate of breast conservation, and other data were compared between the two periods. An attempt was made with multivariate analysis to identify some of the factors that made mastectomy rather than conservation more likely. RESULTS: There were 723 cancers detected that were suitable for analysis (group 1, n = 273; group 2, n = 450). In group 1 the breast conservation rate was 42.9%; this increased significantly to 60.4% in group 2 (P < 0.001). The data were examined to determine if there was any other factor that had changed over the time periods which might account for the increased rate of breast conservation. The use of pre-operative diagnostic techniques such as fine needle aspirate cytology and core biopsy increased significantly. Multivariate analysis comparing the differences in patient age, diagnostic technique, tumour type, grade, size, location and lymph node status, both independently and compositely did not account for the increase in breast conservation in group 2. CONCLUSION: The increase in breast conservation is due to other factors such as the surgeons' approach and patient attitude. The use of pre-operative, minimally invasive tissue sampling techniques is increasing.

Adult↗
PubMed2000

GABA and responses to GABA in the stomatogastric ganglion of the crab Cancer borealis.

The multifunctional neural circuits in the crustacean stomatogastric ganglion (STG) are influenced by many small-molecule transmitters and neuropeptides that are co-localized in identified projection neurons to the STG. We describe the pattern of gamma-aminobutyric acid (GABA) immunoreactivity in the stomatogastric nervous system of the crab Cancer borealis and demonstrate biochemically the presence of authentic GABA in C. borealis. No STG somata show GABA immunoreactivity but, within the stomatogastric nervous system, GABA immunoreactivity co-localizes with several neuropeptides in two identified projection neurons, the modulatory proctolin neuron (MPN) and modulatory commissural neuron 1 (MCN1). To determine which actions of these neurons are evoked by GABA, it is necessary to determine the physiological actions of GABA on STG neurons. We therefore characterized the response of each type of STG neuron to focally applied GABA. All STG neurons responded to GABA. In some neurons, GABA evoked a picrotoxin-sensitive depolarizing, excitatory response with a reversal potential of approximately -40 mV. This response was also activated by muscimol. In many STG neurons, GABA evoked inhibitory responses with both K(+)- and Cl(-)-dependent components. Muscimol and beta-guanidinopropionic acid weakly activated the inhibitory responses, but many other drugs, including bicuculline and phaclofen, that act on vertebrate GABA receptors were not effective. In summary, GABA is found in projection neurons to the crab STG and can evoke both excitatory and inhibitory actions on STG neurons.

Animals↗
PubMed1999

Different proctolin neurons elicit distinct motor patterns from a multifunctional neuronal network.

Distinct motor patterns are selected from a multifunctional neuronal network by activation of different modulatory projection neurons. Subsets of these projection neurons can contain the same neuromodulator(s), yet little is known about the relative influence of such neurons on network activity. We have addressed this issue in the stomatogastric nervous system of the crab Cancer borealis. Within this system, there is a neuronal network in the stomatogastric ganglion (STG) that produces many versions of the pyloric and gastric mill rhythms. These different rhythms result from activation of different projection neurons that innervate the STG from neighboring ganglia and modulate STG network activity. Three pairs of these projection neurons contain the neuropeptide proctolin. These include the previously identified modulatory proctolin neuron and modulatory commissural neuron 1 (MCN1) and the newly identified modulatory commissural neuron 7 (MCN7). We document here that each of these neurons contains a unique complement of cotransmitters and that each of these neurons elicits a distinct version of the pyloric motor pattern. Moreover, only one of them (MCN1) also elicits a gastric mill rhythm. The MCN7-elicited pyloric rhythm includes a pivotal switch by one STG network neuron from playing a minor to a major role in motor pattern generation. Therefore, modulatory neurons that share a peptide transmitter can elicit distinct motor patterns from a common target network.

Animals↗
PubMed1999

A point-mass model of gibbon locomotion.

In brachiation, an animal uses alternating bimanual support to move beneath an overhead support. Past brachiation models have been based on the oscillations of a simple pendulum over half of a full cycle of oscillation. These models have been unsatisfying because the natural behavior of gibbons and siamangs appears to be far less restricted than so predicted. Cursorial mammals use an inverted pendulum-like energy exchange in walking, but switch to a spring-based energy exchange in running as velocity increases. Brachiating apes do not possess the anatomical springs characteristic of the limbs of terrestrial runners and do not appear to be using a spring-based gait. How do these animals move so easily within the branches of the forest canopy? Are there fundamental mechanical factors responsible for the transition from a continuous-contact gait where at least one hand is on a hand hold at a time, to a ricochetal gait where the animal vaults between hand holds? We present a simple model of ricochetal locomotion based on a combination of parabolic free flight and simple circular pendulum motion of a single point mass on a massless arm. In this simple brachiation model, energy losses due to inelastic collisions of the animal with the support are avoided, either because the collisions occur at zero velocity (continuous-contact brachiation) or by a smooth matching of the circular and parabolic trajectories at the point of contact (ricochetal brachiation). This model predicts that brachiation is possible over a large range of speeds, handhold spacings and gait frequencies with (theoretically) no mechanical energy cost. We then add the further assumption that a brachiator minimizes either its total energy or, equivalently, its peak arm tension, or a peak tension-related measure of muscle contraction metabolic cost. However, near the optimum the model is still rather unrestrictive. We present some comparisons with gibbon brachiation showing that the simple dynamic model presented has predictive value. However, natural gibbon motion is even smoother than the smoothest motions predicted by this primitive model.

Animals↗
PubMed1998

Cholecystectomy in cardiothoracic organ transplant recipients.

OBJECTIVES: To assess the risks associated with cholelithiasis and cholecystectomy in cardiothoracic organ transplant recipients at this hospital and to identify any differences with potential causal significance between the group with known gallstones and the transplant recipient group as a whole. DESIGN: Medical records survey. SETTING: Tertiary care university hospital. PATIENTS: Six hundred forty-five patients had cardiothoracic organ transplantation at this hospital between February 1, 1984, and May 31, 1996. Gallstones were detected in 37 (5.7%) of these patients and 32 patients underwent cholecystectomy, of which 29 operations were performed primarily for symptomatic gallstone disease. All cholecystectomies were performed after transplantation. MAIN OUTCOME MEASURES: Mortality, morbidity, postoperative biliary disease. RESULTS: Patients with gallstones were significantly older than the transplant patient group as a whole (Student t test, P=.001); they were more likely to be female (chi2 test, P=.05); and they had a higher body mass index (t test, P=.001). There were no significant differences in the maximum serum bilirubin level during the transplantation admission, incidence of diabetes mellitus, cholestyramine use, or cyclosporine dosage during the first 12 months after transplantation. Cholecystectomy was performed after a median 5-month symptomatic period, mostly by the minilaparotomy method. Forty-five percent of cholecystectomies were urgent or semi-urgent. One patient died of lung infection on the second postoperative day. The median postoperative stay was 3 days. At a median 33 months' follow-up, 4 patients have had further biliary problems (2 patients with common bile duct stones, 1 patient with intrahepatic stones, and 1 patient with biliary dyskinesia). Four other patients with asymptomatic gallstones who did not receive cholecystectomy have remained asymptomatic for between 15 and 67 months. CONCLUSIONS: Cholecystectomy by the minilaparotomy or laparoscopic methods, with routine operative cholangiography, is the preferred treatment for symptomatic gallstones in cardiothoracic organ transplant recipients. Although the optimum management of asymptomatic gallstones in these patients remains unclear, our favorable experience with a policy of reserving cholecystectomy for symptomatic cases seems noteworthy.

Adolescent↗
PubMed1998

Splenectomy for HIV-related immune thrombocytopenia: comparison with results of splenectomy for non-HIV immune thrombocytopenic purpura.

OBJECTIVE: To determine the effectiveness and safety of splenectomy for patients with human immunodeficiency virus (HIV)-related immune thrombocytopenia, using the results of splenectomy for patients with non-HIV immune thrombocytopenic purpura as a control group for comparison. DESIGN: Retrospective study. SETTING: Tertiary care university hospital. PATIENTS: Fourteen patients who underwent splenectomy for symptomatic, medically refractory HIV-related immune thrombocytopenia at this hospital from 1988 to 1997. During the same period, 20 patients had splenectomy for treatment of non-HIV immune thrombocytopenic purpura. INTERVENTION: Splenectomy. MAIN OUTCOME MEASURES: Platelet response, need for postsplenectomy medical therapy, progression of HIV disease, and complications. RESULTS: All patients with HIV-related thrombocytopenia had a complete early platelet response to splenectomy, with an elevation of the platelet count to greater than 100X10(9)/L. After a median follow-up of 26.5 months, all but 1 patient had a sustained complete remission with no need for medical therapy for thrombocytopenia. Splenectomy was more effective in the HIV-related thrombocytopenia group than in the non-HIV immune thrombocytopenic purpura group, with significantly higher platelet counts at 1 week and 1 month after splenectomy in the HIV group (t test, P=.02 and P=.009, respectively). There were significantly fewer patients needing medical therapy for thrombocytopenia after splenectomy in the HIV group (chi2 test, P=.02). There were no remarkable short- or long-term complications in the patients with HIV infection, including no overwhelming postsplenectomy infections. Three patients have died, and 2 patients have developed AIDS since operation. CONCLUSIONS: Splenectomy is effective treatment for patients with symptomatic HIV-related thrombocytopenia that is resistant to medical therapy. The effectiveness of this treatment suggests that the predominant mechanism of thrombocytopenia in HIV-infected patients is increased destruction of platelets because of platelet-associated immunoproteins.

Adolescent↗
PubMed1998

Incidence of deep vein thrombosis after laparoscopic vs minilaparotomy cholecystectomy.

OBJECTIVES: To determine the frequency of deep vein thrombosis (DVT) associated with minimally invasive cholecystectomy and to determine, using minilaparotomy cholecystectomy as a control operation, the influence of the laparoscopic pneumoperitoneum on DVT formation. DESIGN: Prospective nonrandomized control trial. SETTING: Tertiary care university hospital. PATIENTS: One hundred consecutive patients intended to undergo either laparoscopic cholecystectomy (59 patients) or minilaparotomy cholecystectomy (41 patients) with either of 2 surgeons were prospectively enrolled between April 1996 and April 1997. The minilaparotomy cholecystectomy group served as controls to isolate the effect of the pneumoperitoneum. Patient details, operative details, and any thromboembolic or bleeding complications were recorded. The same thromboprophylaxis regimen was prescribed for each group; namely, preoperative and postoperative subcutaneous low-molecular-weight heparin (LMWH), graduated compression stockings, and intraoperative intermittent calf compression. INTERVENTION: Minimally invasive cholecystectomy. MAIN OUTCOME MEASURE: Frequency of DVT. Bilateral lower limb venous color duplex scanning was used to detect DVT. Scans were performed on 3 occasions: (1) preoperatively on admission to hospital, (2) on the first postoperative day, and (3) between 2 and 4 weeks postoperatively. RESULTS: Three patients in the laparoscopic group and 2 patients in the minilaparotomy group underwent conversion to conventional open cholecystectomy. There were no significant differences between patients in the 2 groups for age, sex, body mass index, preoperative white blood cell count, platelet count, prothrombin time, or activated partial thromboplastin time. There were no significant differences between the 2 groups for elective vs emergency operations, public hospital vs private hospital admissions, or consultant vs resident surgeon. Macroscopic gallbladder pathology grades for both groups were not significantly different, and there was no significant difference in the duration of postoperative hospital stay. Operative cholangiography was performed in a significantly larger proportion of laparoscopic cases (86% vs 66% in the minilaparotomy group; chi(2) test, P=.002), and the duration of anesthesia was significantly longer for the laparoscopic operation (118 minutes vs 98 minutes; t test, P=.05). Ninety-seven patients received preoperative LMWH and all patients received graduated compression stockings, intraoperative intermittent calf compression, and postoperative LMWH. Two of the 100 patients had postoperative DVT, 1 after laparoscopic cholecystectomy and 1 after minilaparotomy cholecystectomy. Both DVTs were detected by duplex examination on the first postoperative day. The DVT found after laparoscopic cholecystectomy was in 1 of the 3 patients who did not receive preoperative LMWH. There were no DVTs in any of the 40 patients who had an additional duplex scan between 2 and 4 weeks after operation. CONCLUSIONS: Despite the theoretical risk of thromboembolic disease due to use of the laparoscopic pneumoperitoneum, the frequency of DVT after either laparoscopic cholecystectomy or minilaparotomy cholecystectomy is low if adequate thromboprophylaxis is provided.

Cholecystectomy, Laparoscopic↗
PubMed1998

Sympathoinhibition evoked from caudal midline medulla is mediated by GABA receptors in rostral VLM.

The present study was performed to determine whether the powerful depressor and sympathoinhibitory response that can be evoked from neurons in the caudal midline medulla is mediated by gamma-aminobutyric acidergic (GABAergic) inhibition of sympathoexcitatory neurons in the rostral part of the ventrolateral medulla (VLM). In anesthetized barointact and barodenervated rabbits, bilateral micro-injections of bicuculline into sympathoexcitatory sites in the rostral VLM resulted in a sustained increase in renal sympathetic nerve activity and abolished or reversed the depressor and sympathoinhibitory response evoked by glutamate micro-injection into the caudal midline medulla. By contrast, the sympathoinhibitory response evoked from the caudal midline medulla persisted when the background level of renal sympathetic nerve activity was reflexly raised by baroreceptor unloading. The results indicate that 1) the depressor and sympathoinhibitory response evoked by stimulation of neurons in the caudal midline medulla is mediated by a GABAergic synapse in the rostral VLM and 2) there are also sympathoexcitatory neurons in the caudal midline medulla whose presence is revealed by blockade of the more powerful sympathoinhibitory response.

Animals↗
PubMed1997

Autoradiography of [3H]alpha,beta-methylene-ATP binding sites in medulla oblongata and spinal cord of the rat.

Excitatory purinoceptors of P2x-type have long been known to exist on smooth muscle cells, but recently it has been shown that they are also involved in synaptic transmission in the CNS. We have used a P2x-specific agonist, alpha,beta-methylene-ATP, as a 3H-labelled radioligand, to study the distribution and characteristics of P2x receptor-binding sites in the spinal cord and medulla oblongata. Using auto-radiographic techniques, [3H]alpha,beta-methylene-ATP binding was found throughout the grey matter of the spinal cord with small areas of above-average density of binding sites in the marginal zone and substantia gelatinosa at all spinal levels and in the central grey matter of the thoracic spinal cord. In the medulla, [3H]alpha,beta-methylene-ATP binding was found to be strong in all cranial nerve nuclei, particularly those known to receive primary sensory fibres. We have found that the binding of [3H]alpha,beta-methylene-ATP in the spinal cord and medulla was inhibited by a broad-spectrum P2-receptor antagonist suramin (IC50 approximately 27 microM). This is in accordance with the data obtained previously in the forebrain and cerebellum. There was, however, no inhibition of [3H]alpha,beta-methylene-ATP binding by another close analogue of alpha,beta-methylene-ATP and P2x ligand beta,gamma-methylene-ATP (10 microM). The latter result is discussed in terms of possible involvement of Ca2+ in the binding of [3H]alpha,beta-methylene-ATP to P2x receptors in the CNS.

Adenosine Triphosphate↗
PubMed1997

Molecular intimacy between proteins specifying plant-pathogen recognition.

Disease resistance in plants is commonly specified by genetically paired plant resistance (R) and pathogen avirulence (Avr) proteins. Recent molecular analyses of several R-Avr protein interactions provide compelling evidence for a receptor-ligand mechanism in which specific binding of the Avr elicitor by its matching R protein leads to activation of the plant defence response. Direct R-Avr protein recognition precedes the function of an expanding battery of plant resistance signalling components.

Bacterial Proteins↗
PubMed1997

Map positions of 47 Arabidopsis sequences with sequence similarity to disease resistance genes.

Map positions have been determined for 42 non-redundant Arabidopsis expressed sequence tags (ESTs) showing similarity to disease resistance genes (R-ESTs), and for three Pto-like sequences that were amplified with degenerate primers. Employing a PCR-based strategy, yeast artificial chromosome (YAC) clones containing the EST sequences were identified. Since many YACs have been mapped, the locations of the R-ESTs could be inferred from the map positions of the YACs. R-EST clones that exhibited ambiguous map positions were mapped as either cleavable amplifiable polymorphic sequence (CAPS) or restriction fragment length polymorphism (RFLP) markers using F8 (Ler x Col-0) recombinant inbred (RI) lines. In all cases but two, the R-ESTs and Pto-like sequences mapped to single, unique locations. One R-EST and one Pto-like sequence each mapped to two locations. Thus, a total of 47 loci were identified in this study. Several R-ESTs occur in clusters suggesting that they may have arisen via gene duplication events. Interestingly, several R-ESTs map to regions containing genetically defined disease resistance genes. Thus, this collection of mapped R-ESTs may expedite the isolation of disease resistance genes. As the cDNA sequencing projects have identified an estimated 63% of Arabidopsis genes, a very large number of R-ESTs (approximately 95), and by inference disease resistance genes of the leucine-rich repeat-class probably occur in the Arabidopsis genome.

Arabidopsis↗
PubMed1997

The Arabidopsis downy mildew resistance gene RPP5 shares similarity to the toll and interleukin-1 receptors with N and L6.

Plant disease resistance genes operate at the earliest steps of pathogen perception. The Arabidopsis RPP5 gene specifying resistance to the downy mildew pathogen Peronospora parasitica was positionally cloned. It encodes a protein that possesses a putative nucleotide binding site and leucine-rich repeats, and its product exhibits striking structural similarity to the plant resistance gene products N and L6. Like N and L6, the RPP5 N-terminal domain resembles the cytoplasmic domains of the Drosophila Toll and mammalian interleukin-1 transmembrane receptors. In contrast to N and L6, which produce predicted truncated products by alternative splicing, RPP5 appears to express only a single transcript corresponding to the full-length protein. However, a truncated form structurally similar to those of N and L6 is encoded by one or more other members of the RPP5 gene family that are tightly clustered on chromosome 4. The organization of repeated units within the leucine-rich repeats encoded by the wild-type RPP5 gene and an RPP5 mutant allele provides molecular evidence for the heightened capacity of this domain to evolve novel configurations and potentially new disease resistance specificities.

Alleles↗
PubMed1997

Gastric cancer in the bypassed segment after operation for morbid obesity.

A case is reported in which two separate adenocarcinomas were detected in the bypassed distal stomach 13 years after gastric stapling with loop gastro-enterostomy was performed for the treatment of morbid obesity. Retrograde endoscopy via the afferent loop was used to establish the diagnosis. Although gastritis and metaplasia have been described in the bypassed stomach, only one case of carcinoma in this area has previously been reported.

Adenocarcinoma↗