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B Pearce

Publications and source records attributed to B Pearce.

At least 19 recordsLinked to original sources
PubMed2001

Regulatory role of nitric oxide over hippocampal 5-HT release in vivo.

Previous work has shown that N-methyl-D-aspartate (NMDA) receptor activation decreases 5-hydroxytryptamine (5-HT) release in the hippocampus of freely moving rats. Given the association between NMDA receptor function and nitric oxide (NO) production with the regulation of 5-HT release in other brain regions, we have studied this in rat hippocampus. NMDA (100 microM) decreased hippocampal 5-HT release by approximately 70% and this was reversed by the NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (AP5; 10 microM). The NO donor S-nitroso-N-acetylpenicillamine (SNAP) had an inverse concentration-dependent effect on 5-HT release. At 500 microM, SNAP elevated dialysate 5-HT by 55% over basal, while at 5 mM a 70% decrease was seen. The non-selective nitric oxide synthase (NOS) inhibitor N-nitro-L-arginine methyl ester (L-NAME) at 1 mM increased extracellular 5-HT, although a return to basal levels occurred despite the continued presence of the drug. At 1 mM L-NAME prevented the decrease in 5-HT elicited by NMDA (100 microM) infusion. 7-Nitroindazole (7-NI), a relatively selective neuronal NOS (nNOS) inhibitor, decreased extracellular 5-HT at 100 microM and 1 mM. When 100 microM 7-NI was infused for 60 min prior to NMDA, 5-HT levels were transiently increased above basal before returning to control levels. Following combined application of the two drugs, no decrease in dialysate 5-HT was seen. Our data support a role for NO in modulating both basal and NMDA-evoked changes in 5-HT release in the hippocampus, however, the association appears to be complex. It may be that the recorded changes in 5-HT release are secondary to changes in the release of amino acid transmitters which we have previously found to be dependent on the prevailing extracellular NO concentration.

2-Amino-5-phosphonovalerate↗
PubMed2000

Nitric oxide-mediated regulation of dopamine release in the hippocampus in vivo.

Infusion of N-methyl-D-aspartate (NMDA) into the hippocampus of freely moving rats produced a concentration-dependent decrease in the extracellular levels of dopamine, an effect which was reversed by D-2-amino-5-phosphonovaleric acid (D-AP5). To determine the involvement of nitric oxide (NO) in this response, two nitric oxide synthase (NOS) inhibitors, N-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI), were examined for their ability to modify both basal and NMDA-inhibited dopamine release. When infused alone both NOS inhibitors elicited an increase in extracellular dopamine concentration, moreover, when administered prior to the application of NMDA, the agonist failed to elicit a decrease in dopamine levels. Infusion of the NO donor S-nitroso-N-acetylpenicillamine (SNAP) over a 30 min period caused either an increase or a decrease in dopamine release depending upon the concentration used. At the lower concentration (0.5 mM) SNAP promoted dopamine release whilst at the higher concentration (5 mM), the donor elicited a long lasting reduction in basal dopamine levels. The effect of the lower concentration of SNAP was reversed by the prior application of D-AP5, but that of the higher concentration was unaffected by the antagonist.

Animals↗
PubMed1999

Glutamate toxicity in rat cultured neurones: effects on amyloid precursor-like protein 2.

Amyloid precursor protein, which gives rise to the A beta polypeptide found in senile plaques in the brains of patients with Alzheimer's disease, is a member of a family of proteins which includes amyloid precursor-like protein 2 (APLP2). To date, little is known of the involvement of this protein in Alzheimer's disease or any other neurodegenerative condition. The present study set out to determine whether APLP2 expression could be modified in cultured rat cortical neurones exposed to an excitotoxic insult. Treatment of cultures with glutamate (500 microM) for 30 min resulted in increased lactate dehydrogenase liberation into the bathing medium 24 h after removal of the insult indicating neuronal damage. This was accompanied by a decrease in APLP2 recovery in the medium but no change in its intracellular level. Both the increase in LDH release and APLP2 recovery were prevented by pretreatment with the N-methyl-D-aspartate receptor antagonist MK-801. These data show that neuronal APLP2 metabolism is altered in response to an excitotoxic insult.

Alzheimer Disease↗
PubMed1999

Novel quinolizidine salicylamide influenza fusion inhibitors.

A novel series of quinolizidine salicylamides was synthesized as specific inhibitors of the H1 subtype of influenza A viruses. These inhibitors inhibit the pH-induced fusion process, thereby blocking viral entry into host cells. Compound 16 was the most active inhibitor in this series with an EC50 of 0.25 microg/mL in plaque reduction assay. The synthesis and the SAR of these compounds are discussed.

Animals↗
PubMed1999

Restructuring asthma care in a hospital setting to improve outcomes.

STUDY OBJECTIVES: To restructure asthma care as the pilot program in hospital-wide redesign aimed at providing better and more standardized care. We chose asthma care to begin our reorganization because it is the highest-volume diagnosis at our hospital and it involves a broad spectrum of services. DESIGN: Key elements of our restructuring included the following: (1) establishing a pulmonary unit with expanded bed capacity from 8 to 22 beds for asthma patients; (2) standardized treatment protocols; (3) availability of direct admission by primary care physicians who maintained management of their patients with the option of consultation with a specialist; and (4) use of case managers who helped patients and their families overcome obstacles to optimum care. SETTING: A hospital serving a high proportion of Medicaid patients. PATIENTS/PARTICIPANTS: Children with asthma and their families. INTERVENTIONS: Standardized care for asthma; use of case managers to facilitate adherence to treatment. RESULTS: With the restructured asthma care program, parent satisfaction with treatment was sustained; the average length of stay and use of the emergency department (ED) were reduced; observation unit use increased; and there were fewer readmissions to both the inpatient unit and the ED. CONCLUSIONS: We conclude that an inner-city hospital can provide optimum care for asthma patients by standardizing treatment, aggregating asthma patients in one location, and providing education and follow-up through the use of case managers. The protocol shifts some costs from expensive services such as the pediatric ICU and the ED to less costly case management and outreach personnel. In the long run, this allocation of resources should help to lower costs as well as improve quality of care.

Asthma↗
PubMed1998

Pyrimidine nucleotide-stimulated thromboxane A2 release from cultured glia.

1. Uridine triphosphate (UTP), uridine diphosphate (UDP), cytidine triphosphate (CTP), and deoxythymidine triphosphate (TTP) caused concentration-dependent increases in the release of thromboxane A2 (TXA2) from cultured glia prepared from the newborn rat cerebral cortex. Although each of the pyrimidine nucleotides displayed similar potencies, CTP and TTP were considerably less effective than either UTP or UDP. The purine nucleotide ATP was equally as potent as the pyrimidine nucleotides but was marginally less effective than either UTP or UDP. 2. The ability of UTP, UDP, TTP, and CTP to promote TXA2 release from cultured glia was inhibited in a concentration-dependent manner by suramin and was markedly reduced when incubations were performed either in Ca(2+)-free medium or on cultures which had been maintained in serum-free growth medium for 4 days prior to experimentation. 3. Challenges with UTP and UDP in combination were found to elicit a response which was no different from the effects of these nucleotides alone; in addition, their effects were reversed by the phospholipase A2 inhibitor ONO-RS-082. A slight reduction in UTP- and UDP-stimulated TXA2 release was observed in cultures grown in the presence of leucine methyl ester, a treatment reported to limit microglial survival. 4. These results suggest that glia are targets for extracellular pyrimidine nucleotides and that their ability to release eicosanoids from these cells may be important in the brain's response to damage.

Aminobenzoates↗
PubMed1997

Peroxynitrite-induced toxicity in cultured astrocytes.

The exposure of cultured astrocytes to peroxynitrite (ONOO-) for 40 min resulted in a concentration-dependent increase in the release of lactate dehydrogenase from the cells into the bathing medium over the following 24 h. Control experiments showed that the breakdown products of ONOO- contribute, to some extent, to its ability to cause cell death but that the drug vehicle (0.3 M NaOH), which increased the pH of the bathing medium to 9.4, had little effect. The cytotoxic action of ONOO- was mimicked by 3-morpholinosydnonimine (SIN-1) which liberates both nitric oxide (NO) and superoxide but not by S-nitrosoglutathione which liberates only NO. SIN-1-induced cytotoxicity was reversed in a concentration-dependent manner by superoxide dismutase and attenuated by haemoglobin suggesting that the effect of SIN-1 is due, at least in part, to the formation of ONOO-.

Animals↗
PubMed1997

Glutamate toxicity in neuron-enriched and neuron-astrocyte co-cultures: effect of the glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylate.

Exposure of neuron-enriched cultures of the embryonic rat cerebral cortex to glutamate (Glu) resulted in a concentration-dependent (EC50 = 50 microM) increase in the release of lactate dehydrogenase (LDH) into the bathing medium. Glu-induced neurotoxicity appeared to be mediated predominantly by the activation of N-methyl-D-aspartate receptors because its effects were almost completely reversed by 1 microM (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine hydrogen maleate (MK-801). The potency of Glu was increased by ca eight-fold (EC50 = 6 microM) when neuronal cultures were incubated with Glu in the presence of the uptake inhibitor L-trans-pyrrolidine-2, 4-dicarboxylate (L-trans-PDC). Increased LDH release was also observed when neuron-enriched cultures were exposed to an ineffective concentration of Glu in the presence of increasing concentrations of L-trans-PDC, moreover, the uptake inhibitor itself became neurotoxic at concentrations above 100 microM. Glu also stimulated the release of LDH from neuron-astrocyte co-cultures in a concentration-dependent manner, however, it was found to be less potent (EC50 = 200 microM) in these cultures than it was in the neuron-enriched cultures. Incubation of the cocultures with Glu in the presence of the uptake inhibitor increased the potency of Glu (EC50 = 100 microM) but to a much lesser extent than that found in neuron-enriched cultures. Cultured astrocytes were found to be resistant to injury by Glu even in the presence of the uptake inhibitor.

Animals↗
PubMed1996

Outcome of cardiac transplantation in children. Survival in a contemporary multi-institutional experience. Pediatric Heart Transplant Study.

BACKGROUND: Meaningful analysis of survival and risk factors for death in children who undergo heart transplantation is problematic because of the small number of heart transplantations performed at individual institutions. METHODS AND RESULTS: To more accurately examine survival and risk factors for death in children undergoing heart transplantation, we analyzed 191 patients between 1 and 18 years old who received transplants at 22 centers in the Pediatric Heart Transplant Study between January 1, 1993, and December 31, 1994. Cardiac diagnosis was congenital heart disease in 74 patients (39%), dilated cardiomyopathy in 73 (38%), and other in 44 (23%). Actuarial survival was 93% at 1 month, 82% at 1 year, and 81% at 2 years after transplantation. The major causes of death (n = 31) were rejection (29% of deaths), early graft failure (19%), infection (16%), sudden death (13%), and other causes (23%). By multivariate analysis, risk factors for death were assist devices (P = .02), nonidentical ABO blood types (P = .05), and younger age (P = .10). CONCLUSIONS: Contemporary survival for pediatric heart transplant recipients > or = 1 year old is comparable to survival after adult heart transplantation. Risk factors for death are the need for assist devices, nonidentical ABO blood types, and younger age. Rejection is the most common cause of death after pediatric heart transplantation.

Adolescent↗
PubMed1996

Purine- and pyrimidine nucleotide-stimulated changes in intracellular calcium concentration in cultured astrocytes.

Cultured astrocytes prepared from the newborn rat cerebral cortex were challenged with a variety of purine and pyrimidine nucleotides and changes in intracellular Ca2+ concentration ([Ca2+]i) assessed. ATP, ADP, 2-methylthioadenosine triphosphate (2-MeSATP) and the pyrimidine nucleotide uridine triphosphate (UTP) produced Ca2+ transients which were characterized by an initial spike which decayed rapidly to a secondary plateau phase. Concentration response curves for these ligands gave the following rank order of potency: 2-MeSATP > ADP > ATP > UTP. Analysis of the number of cells responding to these nucleotides revealed that 2-MeSATP, ATP and ADP were effective in all cell fields examined whilst UTP generated a response in only 40%. In some experiments cells were challenged with various combinations of agonists. In those fields where ATP, 2-MeSATP and UTP were effective, the transients elicited by combined additions of these agonists were essentially the same as those produced by the agonists alone. Of the other nucleotides tested, uridine diphosphate was effective in only 24% of cell fields examined, moreover, its transient appeared to lack an initial spike phase. Guanosine triphosphate (GTP), cytidine triphosphate (CTP) and deoxythymidine triphosphate (TTP) were found to increase [Ca2+]i in 75%, 47% and 37% of cell fields respectively and the transients generated appeared to lack a secondary plateau phase. The responses to GTP, CTP and TTP also displayed rapid desensitization, a situation never encountered with ligands such as ATP.

Adenosine Diphosphate↗
PubMed1994

Purine- and pyrimidine-stimulated phosphoinositide breakdown and intracellular calcium mobilisation in astrocytes.

Phosphoinositide breakdown in cultured cortical astrocytes was assessed by measuring the accumulation of [3H]inositol phosphates (IP's) following incubations with various purines and pyrimidines. Dose-response relationships gave the following order of potency: 2-methylthioadenosine triphosphate (2-MeSATP) > uridine 5'-triphosphate (UTP) > ATP = ADP > inosine 5' triphosphate (ITP). However, 2-MeSATP and UTP were only half as effective as either ATP or ADP in stimulating [3H]IP production. Astrocytes were also challenged with combined additions of maximally effective concentrations of agonists. Responses to ADP plus UTP and 2-MeSATP plus UTP were essentially additive whilst ATP plus UTP evoked a response which was only partially additive. ATP-stimulated [3H]IP accumulation was markedly reduced in the presence of 2-MeSATP suggesting that the latter may be a partial agonist at these receptors. We also examined the ability of ATP and UTP to increase intracellular Ca2+ concentrations in these cells. Greater than 90% of all cells tested responded to ATP with a release from internal Ca2+ stores but less than half of these responded similarly when challenged with UTP. Our results indicate that astrocytes possess both P2Y-purinoceptors and a population of receptors which are also coupled to phosphoinositide metabolism and intracellular Ca2+ mobilisation but recognise ATP and the pyrimidine nucleotide UTP.

Adenine Nucleotides↗
PubMed1994

Ryanodine-induced intracellular calcium mobilisation in cultured astrocytes.

Changes in intracellular Ca2+ concentration were monitored in cultured cortical astrocytes challenged with ryanodine and ATP. Ryanodine elicited a modest, in comparison to ATP, increase in cytosolic Ca2+ concentration in approximately 60% of the cell fields examined. This effect was evident and, in fact, was augmented when incubations were performed in Ca(2+)-free bathing medium. In addition, ryanodine-evoked changes in intracellular Ca2+ concentration were dose dependent, desensitised rapidly, and could not be mimicked by caffeine. Exposure to ryanodine was without effect on eicosanoid release from these cells nor did it influence Ca2+ mobilisation and eicosanoid release in response to ATP. In contrast, caffeine attenuated part of the ATP-evoked increase in intracellular Ca2+ concentration in the majority of cells tested and abolished its effect on eicosanoid release.

Adenosine Triphosphate↗
PubMed1994

Phosphatidic acid promotes phosphoinositide metabolism and DNA synthesis in cultured cortical astrocytes.

The addition of exogenous phosphatidic acid (PA) to cultured cortical astrocytes prelabelled with [3H]inositol resulted in the accumulation of intracellular [3H]inositol phosphates (IP) in a concentration-dependent (EC50 = 20 microM) manner. Analysis of the individual IPs formed following a PA challenge revealed a rapid but transient generation of [3H]inositol trisphosphate (IP3) indicating the involvement of phosphatidylinositol 4,5-bisphosphate (PIP2) breakdown in this response a fact which was confirmed when the recovery of radiolabel in membrane phosphoinositides was assessed. PA's ability to stimulate IP3 accumulation was found to be dependent upon its acyl-chain length. Dioleoyl-PA (C18:1) was equally as effective as PA from egg yolk lecithin in this respect whilst dipalmitoyl-PA (C16:0) was less so and dimyristoyl-PA (C14:0) and dilauroyl-PA (C12:0) were without effect. In subconfluent, serum-deprived cultures, PA was found to increase DNA synthesis following a 48 h exposure period. This effect was observed over the same concentration range used to measure phosphoinositide breakdown and was found to be mediated by the activation of protein kinase C. As with its effect on phosphoinositide metabolism, PA's ability to promote DNA synthesis was correlated with its acyl-chain length. These data show that PA is capable of stimulating both phosphoinositide metabolism and DNA synthesis in cultured astrocytes possibly via the activation of specific membrane receptors. However, the precise relationship between these events remains to be elucidated.

Animals↗
PubMed1993

Training chicks on a passive avoidance task modulates glutamate-stimulated inositol phosphate accumulation.

The effects of glutamate, N-methyl-D-aspartate (NMDA), (+)-5-methyl-10,11-dihydro-5H-dibenzo-(a,d)-cyclo-hepten 5,10-imine maleate (MK801), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) and quisqualate on the accumulation of inositol phosphates (IP) from the breakdown of phosphoinositides in vitro have been studied in tissue prisms derived from a region of the chick forebrain, the intermediate medial hyperstriatum ventrale (IMHV). In prisms from the left IMHV, glutamate stimulated IP accumulation by 10-20%, AMPA by 55% and quisqualate by 650%. These effects were more marked in the right IMHV, where AMPA stimulated IP accumulation by 157% and quisqualate by 920%. MK801 and NMDA had no significant effect on IP accumulation in either hemisphere. The left IMHV is known to be the site of a biochemical cascade resulting in synaptic remodelling following training day-old chicks on a one-trial passive avoidance task. The effect of such training was to reduce glutamate-stimulated accumulation of IP by 27% (P < 0.05) in prisms taken 30 min after training. There was no effect on prisms taken at 5 or 180 min after training, and no effect at any time in the right IMHV. MK801, injected intraperitoneally before training at a concentration known to produce amnesia for the passive avoidance task, abolished the training-induced decrease without itself affecting IP accumulation. Taken in conjunction with pharmacological and autoradiographic evidence, these results indicate that memory formation for the passive avoidance task involves the activation of NMDA receptor channels, but not quisqualate or AMPA receptors, in the left IMHV of the chick 30 min after training.

Animals↗
PubMed1993

Protein kinase C down-regulation in astrocytes: differential effects on agonist-stimulated inositol phosphate accumulation.

Prolonged phorbol ester treatment abolished protein kinase C (PKC) activity for over 48 h in cortical astrocyte cultures. Receptor-stimulated inositol phospholipid breakdown in these cultures subsequent to PKC depletion produced either enhanced, depressed or unchanged responses depending upon the agonist used. Noradrenaline-, ATP-, histamine- and glutamate-evoked [3H]-inositol phosphate accumulations were potentiated to varying degrees in PKC-depleted cultures whilst those evoked by carbachol and NaF were reduced and unchanged respectively. Analysis of the individual metabolites of inositol phospholipid metabolism formed in response to noradrenaline in PKC-depleted astrocytes revealed potentiated accumulations of radiolabelled glycerophosphoinositol (GPI), inositol monophosphate (IP1) and inositol bisphosphate (IP2) but not inositol trisphosphate (IP3) when compared to controls. Under the same conditions, accumulations of radiolabelled IP1 and IP2 were reduced and those of GPI and IP3 unchanged in carbachol-treated cultures. These results suggest that astrocyte receptors coupled to inositol phospholipid metabolism are differentially regulated by PKC.

Adenosine Triphosphate↗