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Biomedical subjects

J A O'Brien

Publications and source records attributed to J A O'Brien.

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

Disruption of the substance P receptor (neurokinin-1) gene does not prevent upregulation of preprotachykinin-A mRNA in the spinal cord of mice following peripheral inflammation.

The neuropeptide substance P is thought to play an important role in nociception, although the function of the peptide remains controversial. Following peripheral inflammation there is a pronounced upregulation of substance P expression both in sensory neurons and in postsynaptic neurons within the spinal cord. We have examined the levels of expression of mRNA encoding substance P and dynorphin following the development of inflammatory hyperalgesia in mice in which the substance P receptor gene, also known as the neurokinin-1 receptor gene, has been disrupted by homologous recombination. We show that inflammatory hyperalgesia following injection of complete Freund's adjuvant develops normally in animals that lack the neurokinin-1 receptor and that expression of mRNAs encoding substance P and the neuropeptide dynorphin are upregulated regardless of the genotype of the mouse. This suggests that substance P activity is not required for the development and maintenance of inflammatory hyperalgesia and that the upregulation of substance P expression is mediated by neurotransmitters other than substance P.

Animals↗
PubMed1999

Cotransmission of GABA and glycine to brain stem motoneurons.

Using whole cell patch-clamp recording in a rat brain stem slice preparation, we found that gamma-aminobutyric acid (GABA) and glycine act as cotransmitters to hypoglossal motoneurons (HMs). Focal application of GABA and glycine onto a single HM revealed that GABAA and glycine receptors are present on the same neuron. To demonstrate that HMs receive both GABAergic and glycinergic synaptic inputs, we simultaneously recorded GABAA- and glycine-receptor-mediated spontaneous miniature inhibitory postsynaptic currents (mIPSCs) in single HMs. GABAergic and glycinergic mIPSCs were differentiated based on their kinetics and modulation by pentobarbital. Specifically, GABAA-receptor-mediated events decayed more slowly than glycine-receptor-mediated events. GABAergic response decay kinetics were prolonged by pentobarbital, whereas glycinergic response decay kinetics remained unchanged. The distinct kinetics of the glycine- and GABAA-receptor-mediated synaptic events allowed us to record dual component mIPSCs, mIPSCs that are mediated by both receptor types. These data suggest that GABA and glycine are colocalized in the same presynaptic vesicle and are coreleased from presynaptic terminals opposed to motoneurons.

Animals↗
PubMed1999

Leukotriene B4 receptor transgenic mice reveal novel protective roles for lipoxins and aspirin-triggered lipoxins in reperfusion.

Polymorphonuclear neutrophil (PMN) activation is pivotal in acute inflammation and injury from reperfusion. To elucidate components controlling PMNs in vivo, we prepared novel transgenic mice with the human leukotriene (LT) B4 receptor (BLTR) for functional characterization. Overexpression of BLTR in leukocytes dramatically increased PMN trafficking to skin microabscesses and lungs after ischemia-reperfusion, whereas mice deficient in 5-lipoxygenase (5-LO) showed diminished PMN accumulation in reperfused lungs. Hence, both BLTR expression and LT biosynthesis are critical for PMN infiltration in reperfusion-initiated second-organ injury. Also, in BLTR transgenic mice, 5-LO expression and product formation were selectively increased in exudates, demonstrating that receptor overexpression amplifies proinflammatory circuits. Endogenous lipoxin (LX) A4 was produced in ischemic lungs and elevated by reperfusion. Because LXA4 and aspirin-triggered 15-epimeric LXA4 (ATL) selectively regulate leukocyte responses, they were tested in BLTR transgenic mice. Despite excessive PMN recruitment in BLTR transgenic mice, intravenous injection of ATL sharply diminished reperfusion-initiated PMN trafficking to remote organs, and topical application of LX was protective in acute dermal inflammation. These results demonstrate a direct role for BLTR with positive feedback, involving BLTR and 5-LO signaling in controlling PMNs. Moreover, LXA4 and ATL counter BLTR-amplified networks, revealing a novel protective role for LX and ATL in stress responses that has applications in perioperative medicine.

Animals↗
PubMed1998

Altered nociception, analgesia and aggression in mice lacking the receptor for substance P.

The peptide neurotransmitter substance P modulates sensitivity to pain by activating the neurokinin-1 (NK-1) receptor, which is expressed by discrete populations of neurons throughout the central nervous system. Substance P is synthesized by small-diameter sensory 'pain' fibres, and release of the peptide into the dorsal horn of the spinal cord following intense peripheral stimulation promotes central hyperexcitability and increased sensitivity to pain. However, despite the availability of specific NK-1 antagonists, the function of substance P in the perception of pain remains unclear. Here we investigate the effect of disrupting the gene encoding the NK-1 receptor in mice. We found that the mutant mice were healthy and fertile, but the characteristic amplification ('wind up') and intensity coding of nociceptive reflexes was absent. Although substance P did not mediate the signalling of acute pain or hyperalgesia, it was essential for the full development of stress-induced analgesia and for an aggressive response to territorial challenge, demonstrating that the peptide plays an unexpected role in the adaptive response to stress.

Aggression↗
PubMed1998

Migraine therapy: development and testing of a patient preference questionnaire.

OBJECTIVES: To develop and test a patient preference questionnaire in migraine. METHODS: A user-friendly, self-administered questionnaire was developed to assess the relative importance of aspects of migraine therapy to patients. It was tested in a convenience sample of 66 migraineurs. The questionnaire has five sections: patient preference, migraine history, demographics, usual behavior during an attack, and migraine impact on cognition and functionality. It employs a special reverse-ranking technique to quantify preferences. RESULTS: Sixty-six migraineurs participated: 86% were women, 53% had not consulted their doctor about migraine in the previous year; and only 51% took prescribed medication, the majority (52%) at the start of a migraine. "A medication that can be taken any time during a migraine attack" was ranked most important by 20% of the migraineurs, one that decreases pain from the unbearable level in 30 minutes by 17%, and one that relieves pain completely within 2 hours by 15%. Not being able to think or concentrate with severe symptoms was reported by 71%. Optional activities were impeded by migraine in 83% of subjects, but required activities in only 60%. CONCLUSIONS: The patient preference questionnaire is readily completed by subjects and reveals that the dimensions of relief preferred by patients can be addressed by a self-report questionnaire.

Analgesics↗
PubMed1998

Direct medical costs of complications resulting from type 2 diabetes in the U.S.

OBJECTIVE: To estimate direct medical costs of managing the complications of type 2 diabetes. RESEARCH DESIGN AND METHODS: Costs were estimated for 15 diabetic complications by applying unit costs to typical resource-use profiles. Resource used and unit costs were estimated from many sources, including acute care discharge databases, clinical guidelines, government reports, fee schedules, and peer-reviewed literature. For each complication, the event costs are those associated with resource use that is specific to the acute episode and any subsequent care occurring in the 1st year. State costs are the annual costs of continued management. All costs are expressed in 1996 U.S. dollars. RESULTS: As expected, the more severe or debilitating events, such as acute myocardial infarction ($27,630 event cost; $2,185 state cost), generate a greater financial burden than do early-stage complications, such as microalbuminuria ($62 event cost; $14 state cost). Yet, complications that are initially relatively low in cost (e.g., microalbuminuria) can progress to more costly advanced stages (e.g., end-stage renal disease, $53,659 state cost); therefore, minor complications should also be considered in any economic analysis of diabetes. CONCLUSIONS: The recent literature has lacked cost estimates that may be readily translated into patient-level cost inputs for an economic model. Emerging therapies that may reduce the incidence of some diabetic complications will need to be scrutinized economically in today's cost-conscious environment. The cost estimates from this study provide one piece of the economic analysis needed to evaluate these new interventional therapies.

Animals↗
PubMed1997

A Schwann cell mitogen accompanying regeneration of motor neurons.

Motor neurons are the only adult mammalian neurons of the central nervous system to regenerate following injury. This ability is dependent on the environment of the peripheral nerve and an intrinsic capacity of motor neurons for regrowth. We report here the identification, using a technique known as messenger RNA differential display, of an extracellular signalling molecule, previously described as the pancreatic secreted protein Reg-2, that is expressed solely in regenerating and developing rat motor and sensory neurons. Axon-stimulated Schwann cell proliferation is necessary for successful regeneration, and we show that Reg-2 is a potent Schwann cell mitogen in vitro. In vivo, Reg-2 protein is transported along regrowing axons and inhibition of Reg-2 signalling significantly retards the regeneration of Reg-2-containing axons. During development, Reg-2 production by motor and sensory neurons is regulated by contact with peripheral targets. Strong candidates for peripheral factors regulating Reg-2 production are cytokines of the LIF/CNTF family, because Reg-2 is not expressed in developing motor or sensory neurons of mice carrying a targeted disruption of the LIF receptor gene, a common component of the receptor complexes for all of the LIF/CNTF family.

Animals↗
PubMed1997

NMDA and non-NMDA receptors are co-localized at excitatory synapses of rat hypoglossal motoneurons.

We used whole-cell patch clamp recordings in a rat brainstem slice preparation to characterize the properties of miniature excitatory postsynaptic currents (mEPSCs) in hypoglossal motoneurons. The distinct kinetic characteristics of N-methyl-D-aspartate (NMDA) and non-NMDA receptor-mediated synaptic responses allowed us to study dual component mEPSCs mediated by the two receptor types. Using this approach, NMDA and non-NMDA receptors were found to be co-localized at the same synaptic locations. In addition, some sites contain only NMDA receptors since a large proportion of mEPSCs were apparently mediated by NMDA receptors only. Furthermore, the amplitudes of pharmacologically isolated NMDA receptor-mediated mEPSCs were highly variable in individual cells and their decay kinetics were modulated by membrane potential.

Animals↗
PubMed1997

Effects of albumin on the disposition of morphine and morphine-3-glucuronide in the rat isolated perfused liver.

1. The effect of albumin on the disposition of morphine and hepatically generated morphine-3-glucuronide (M3G) was investigated in the single-pass rat isolated perfused liver. 2. Using a balanced cross-over design, each of 10 livers was perfused at 30 mL/min with medium containing 2.7 mumol/L morphine in the presence and absence of 10 g/L bovine serum albumin (BSA). 3. Both bile flow rate and hepatic oxygen consumption were significantly higher (P < 0.005) when BSA was present in the perfusion medium, suggestive of a change in the functional performance of the perfused liver. 4. The binding of morphine and M3G was negligible in both BSA-free and -containing perfusate. 5. Outflow perfusate contained both morphine and M3G, while the metabolite but not morphine was found in bile. The recovery of the administered morphine was approximately 100% and was not altered (P > 0.05) by the presence or absence of BSA. 6. The fraction of morphine escaping heptic extraction in the absence of BSA (mean +/- SD; 0.41 +/- 0.14) was not altered significantly (P > 0.05) by the presence of the protein in perfusate (0.35 +/- 0.13), indicating no change in the intrinsic clearance or morphine despite the difference in oxygen consumption. 7. The fraction of hepatically generated M3G excreted in bile was significantly higher (P < 0.005) when BSA was present in the perfusate than when it was not (0.44 +/- 0.14 vs 0.38 +/- 0.16, respectively). 8. The results are consistent with the concept that BSA modifies the ability of solutes, including M3G, to move through the paracellular pathway from the canalicular to the vascular space. 9. It is concluded that because albumin may modify not only the unbound fraction of a ligand in perfusate, but also the functional performance of the liver, care is needed in the interpretation of studies examining the influence of the protein on the hepatic disposition of drugs and their metabolites.

Animals↗
PubMed1997

Quantitative analysis of firing properties of pyramidal neurons from layer 5 of rat sensorimotor cortex.

Quantitative aspects of repetitive firing evoked by injected current steps and ramps were studied in layer 5 pyramidal neurons in brain slices of rat sensorimotor cortex to answer the following questions. Do the tonic firing properties of burst-firing and regular-spiking (nonbursting) neurons differ significantly? Does burst firing denote a discrete class of neurons or represent a continuum of firing properties? Is firing rate during the burst of action potentials related to stimulus amplitude? What aspect of the stimulus might the initial firing rate code? How stable are a neuron's firing properties over time? All recorded neurons fired tonically to a long-lasting current above a minimum value, and the tonic firing properties of most neurons were quite similar irrespective of their initial response to a current step. Only a group of high-resistance neurons had significantly different tonic firing properties. When slow current ramps (rising between 0.5 and approximately 20 nA/s) were applied, the relation between firing rate and current during the ramp was very similar to the relation between tonic firing rate and current obtained from long-lasting current steps. Low-resistance cells exhibited three distinct initial responses to a current step: fast adaptation, high-threshold bursts, and low-threshold bursts, observed in 54, 28, and 10% of recorded cells, respectively. High-resistance cells exhibited a distinctive slow adaptation of firing rate. Slowly adapting, fast-adapting (FA), and high-threshold burster (HTB) neurons exhibited no adaptation near the minimum current that evoked repetitive firing (I(o)). FA and HTB cells exhibited two-spike adaptation to a fina tonic firing rate during currents up to 1.6 times I(o). Only a higher current (2.1 times I(o)) evoked a burst in HTB cells, whereas a burst was evoked at I(o) in the low-threshold burster cells. In most cells analyzed, the initial firing rate, whatever its nature, increased monotonically with current step amplitude. The response to fast current ramps indicated that firing rate during adaptation or bursting may code rate of change of current. Repeated measurements during long-duration impalements indicated that both transient and tonic firing properties are stable over time. We discuss how the different tonic firing properties of large and small pyramidal neurons could be more important functionally than the different transient responses (burst/nonburst) of the large neurons. We conclude that the large neurons would perform a better linear transduction of time-varying synaptic current that reaches their somata. We compare the responses evoked by somatically injected current with those evoked by dendritic glutamate iontophoresis in previous studies.

Animals↗
PubMed1996

The cytoplasmic tail of NSP4, the endoplasmic reticulum-localized non-structural glycoprotein of rotavirus, contains distinct virus binding and coiled coil domains.

The final steps in the assembly of rotavirus occur in the lumen of the endoplasmic reticulum (ER). Targeting of the immature inner capsid particle (ICP) to this compartment is mediated by the cytoplasmic tail of NSP4, a non-structural virus glycoprotein located in the ER membrane. To delineate structural and functional features of NSP4, soluble fragments of the cytoplasmic tail have been expressed and purified. Our analysis combines a functional assay for ICP binding with biochemical and CD spectroscopic studies to examine the secondary and quaternary structure. The ICP-binding domain is located within the C-terminal 20 amino acids of the polypeptide. A second region, distinct from this receptor domain, adopts an alpha-helical coiled coil structure and mediates the oligomerization of the virus binding domains into a homotetramer. The domain organization of the cytoplasmic fragments of NSP4 suggests a novel structure for an icosahedral virus receptor protein in which C-terminal binding sites for immature rotavirus particles are connected to an alpha-helical coiled coil stalk which projects from the ER membrane.

Biopolymers↗
PubMed1996

Pharmacology of L-744,453, a novel nonpeptidyl endothelin antagonist.

L-744,453 ((+/-)3-[4-(1-carboxy-1-(3,4-methylenedioxyphenyl)methoxy)-3,5-diprop ylphenyl methyl]-3H-imidazo[4,5-c]pyridine) is an endothelin (ET) receptor antagonist from a new structural class, the dipropyl-alpha-phenoxyphenylacetic acid derivatives. L-744,453 competitively and reversibly inhibits [125I]-ET-1 binding to Chinese Hamster Ovary cells expressing cloned human ET receptors (K(i)s: hET(A)=4.3 nM; hET(B)=232 nM), and is selective for endothelin receptors compared to other peptide receptors. It is an antagonist of ET-1 stimulated phosphatidyl inositol hydrolysis in rat uterine slices (IC50=220 nM) and exhibits no agonist activity. This compound also inhibits ET-1 stimulated contraction of rat aortic rings with a K(b) value of 50 nM. L-744,453 protects against ET-1 induced lethality in mice after i.v. (AD50=13 mg/kg i.v.) or oral administration. This compound also antagonizes ET-1 induced increases in diastolic blood pressure in conscious normotensive rats (AD50=0.67 mg/kg i.v.) and anesthetized ferrets (AD50=1.6 mg/kg i.v.). L-744,453 is a potent, selective, orally active endothelin antagonist which may be useful in elucidating the role of endothelin in normal and pathophysiological states.

Animals↗
PubMed1996

The disposition of morphine and morphine-3-glucuronide in the isolated perfused rat liver: effects of altered perfusate flow rate.

The rat single-pass isolated perfused liver preparation was used to study the effects of altered perfusate flow rate on the hepatic disposition of morphine and its polar metabolite morphine-3-glucuronide (M3G). Using a balanced, cross-over design, livers of female Sprague-Dawley rats (n = 6) were perfused at 15 and 30 mL min-1 with erythrocyte- and protein-free perfusion medium containing a constant concentration of morphine (2.7 microM). After reaching steady-state, inflow and outflow perfusate and bile samples were collected and morphine and M3G were measured by HPLC. Doubling of perfusate flow rate was associated with a significant increase (P < 0.05) in the availability of morphine (mean +/- s.d. of 0.19 +/- 0.06 at 15 mL min-1 and 0.29 +/- 0.08 at 30 mL min-1). The magnitude of the change in morphine availability was consistent with the predictions of the well-stirred model of hepatic elimination. The fate of hepatically generated M3G was assessed by the biliary extraction ratio of M3G; alterations in perfusate flow rate had no significant effect on this ratio (mean +/- s.d. of 0.49 +/- 0.14 at a perfusate flow rate of 15 mL min-1 and 0.47 +/- 0.22 at 30 mL min-1). A physiologically-based mathematical model, in which the vascular and intracellular spaces of the liver were represented by two well-mixed compartments, was utilized to derive an equation for the biliary extraction ratio of M3G. According to the model, the value of this extraction ratio will become insensitive to changes in perfusate flow rate when the permeability for M3G of the membrane separating the intracellular and vascular compartments is low compared with perfusate flow rate. Hence, the experimental results are consistent with the concept that the hepatic sinusoidal membrane represents a diffusional barrier to M3G.

Animals↗
PubMed1996

Quinoxapeptins: novel chromodepsipeptide inhibitors of HIV-1 and HIV-2 reverse transcriptase. I. The producing organism and biological activity.

Quinoxapeptin A and B are novel chromodepsipeptides which were isolated from a nocardioform actinomycete with indeterminant morphology. Quinoxapeptins A and B are potent inhibitors of HIV-1 and HIV-2 reverse transcriptase and almost equally active against two single mutants forms as well as a double mutant form of HIV-1 reverse transcriptase. Quinoxapeptin A and B are specific inhibitors of HIV-1 and HIV-2 reverse transcriptase because they did not inhibit human DNA polymerase alpha, beta, gamma and delta. Quinoxapeptin A and B are structurally similar to luzopeptin A which was also active against HIV-1 and HIV-2 reverse transcriptase.

Actinomycetales↗
PubMed1996

The cost of treating heart valve related complications.

BACKGROUND AND AIM OF THE STUDY: Heart valve replacement can result in serious complications. Therefore, it is important in decision making regarding the choice of valves to know the cost of such complications. METHODS: Complications were defined according to guidelines proposed by the Society of Thoracic Surgeons. They included valve thrombosis, embolism, hemorrhage due to anticoagulation, non-structural dysfunction, structural deterioration and endocarditis. The costs of the pre-admission assessment, acute inpatient stay, inpatient physician fees, post-discharge and out-patient physician fees were estimated for each complication to determine the average total cost in 1995 US dollars. Cost inputs were obtained from existing Massachusetts databases and Medicare fee schedules. RESULTS: The costs of managing valve thrombosis, endocarditis and non-structural dysfunction were all estimated to exceed $30,000 for a single event. The costs of acute management of embolism and anticoagulant-related hemorrhage were between $8,000 and $11,500. However, it is of note that managing the sequelae of an embolism was calculated to be greater than $70,000 over 15 years. The greatest contributor to the average cost of treating a complication was determined to be the in-patient facility cost. CONCLUSIONS: Complications related to heart valve replacement can be very costly to manage in both the short term and the long term.

Costs and Cost Analysis↗
PubMed1995

Impaired cell volume regulation in intestinal crypt epithelia of cystic fibrosis mice.

Cystic fibrosis is a disease characterized by abnormalities in the epithelia of the lungs, intestine, salivary and sweat glands, liver, and reproductive systems, often as a result of inadequate hydration of their secretions. The primary defect in cystic fibrosis is the altered activity of a cAMP-activated Cl- channel, the cystic fibrosis transmembrane conductance regulator (CFTR) channel. However, it is not clear how a defect in the CFTR Cl- channel function leads to the observed pathological changes. Although much is known about the structural properties and regulation of the CFTR, little is known of its relationship to cellular functions other than the cAMP-dependent Cl- secretion. Here we report that cell volume regulation after hypotonic challenge is also defective in intestinal crypt epithelial cells isolated from CFTR -/- mutant mice. Moreover, the impairment of the regulatory volume decrease in CFTR -/- crypts appears to be related to the inability of a K+ conductance to provide a pathway for the exit of this cation during the volume adjustments. This provides evidence that the lack of CFTR protein may have additional consequences for the cellular function other than the abnormal cAMP-mediated Cl- secretion.

Animals↗