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Biomedical subjects

J M Sullivan

Publications and source records attributed to J M Sullivan.

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

Mechanism of cannabinoid effects on long-term potentiation and depression in hippocampal CA1 neurons.

Cannabinoids, the active constituents of marijuana, are known to impair learning and memory. Receptors for cannabinoids are highly expressed in the hippocampus, a brain region that is believed to play an important role in certain forms of learning and memory. To investigate the possible contribution of cannabinoid receptor-mediated deficits in hippocampal function to the learning and memory impairments produced by marijuana, we studied the effects of cannabinoid receptor activation on two models of learning and memory, long-term potentiation (LTP) and long-term depression (LTD), in hippocampal slices. Although LTP and LTD of CA1 field potentials were blocked by cannabinoid receptor activation in the presence of Mg(2+), they could be induced after Mg(2+) was removed. Similarly, LTP and LTD of whole-cell EPSCs were unimpaired in the presence of cannabinoid receptor agonist when the postsynaptic membrane was depolarized during the LTP or LTD induction protocol. Cannabinoid receptor activation also reduced EPSCs and enhanced paired-pulse facilitation, while having no effect on the amplitude of spontaneous miniature EPSCs. Finally, as with cannabinoid receptor activation, inhibition of LTP by adenosine receptor activation could be overcome by removal of Mg(2+) or depolarization of the postsynaptic membrane during tetanus. Our results indicate that cannabinoid receptor activation does not directly inhibit the molecular mechanisms responsible for long-term synaptic plasticity but instead impairs LTP and LTD by reducing presynaptic neurotransmitter release to a level below that required to depolarize the postsynaptic membrane to relieve Mg(2+) blockade of NMDA receptors.

Animals↗
PubMed1999

Eukaryotic initiation factor 2alpha kinase and phosphatase activity during postischemic brain reperfusion.

When ischemic brain is reperfused, there is in vulnerable neurons immediate inhibition of protein synthesis associated with a large increase in phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 [eIF2alpha, phosphorylated form eIF2alpha(P)]. We examined eIF2alpha kinase and eIF2alpha(P) phosphatase activity in brain homogenate postmitochondrial supernatants obtained from rats after 3 to 30 min of global brain ischemia (cardiac arrest), after 5 min of ischemia and 5 min of reperfusion (5R), and after 10 min of ischemia and 90 min reperfusion (90R). Because it has been suggested that PKR might be specifically responsible for producing eIF2alpha(P) during reperfusion, we also examined in brain homogenates from wild-type and PKR0/0 C57BL/6J x 129/SV mice the effect of 5 min of ischemia and 5 min of reperfusion on eIF2alpha(P). Cytosolic brain eIF2alpha(P) in the 5R and 90R rats was 18- and 23-fold that of nonischemic controls without any change in the rate of eIF2alpha(P) dephosphorylation. There was no change in eIF2alpha kinase activity between 3 and 30 min of ischemia but an 85% decrease in the 5R group; the 90R group was similar to controls. In wild-type and PKR0/0 mice total eIF2alpha was identical, and there was an identical 16-fold increase in eIF2alpha(P) at 5 min of reperfusion. Our observations contradict hypotheses that PKR activation, loss of eIF2alpha(P) phosphatase activity, or any general increase in eIF2alpha kinase activity are responsible for reperfusion-induced phosphorylation of eIF2alpha, and we suggest that the mechanism may involve regulation of the availability of eIF2alpha to a kinase.

Animals↗
PubMed1999

Time-resolved rhodopsin activation currents in a unicellular expression system.

The early receptor current (ERC) is the charge redistribution occurring in plasma membrane rhodopsin during light activation of photoreceptors. Both the molecular mechanism of the ERC and its relationship to rhodopsin conformational activation are unknown. To investigate whether the ERC could be a time-resolved assay of rhodopsin structure-function relationships, the distinct sensitivity of modern electrophysiological tools was employed to test for flash-activated ERC signals in cells stably expressing normal human rod opsin after regeneration with 11-cis-retinal. ERCs are similar in waveform and kinetics to those found in photoreceptors. The action spectrum of the major R(2) charge motion is consistent with a rhodopsin photopigment. The R(1) phase is not kinetically resolvable and the R(2) phase, which overlaps metarhodopsin-II formation, has a rapid risetime and complex multiexponential decay. These experiments demonstrate, for the first time, kinetically resolved electrical state transitions during activation of expressed visual pigment in a unicellular environment (single or fused giant cells) containing only 6 x 10(6)-8 x 10(7) molecules of rhodopsin. This method improves measurement sensitivity 7 to 8 orders of magnitude compared to other time-resolved techniques applied to rhodopsin to study the role particular amino acids play in conformational activation and the forces that govern those transitions.

Cell Fusion↗
PubMed1999

Normal and mutant rhodopsin activation measured with the early receptor current in a unicellular expression system.

The early receptor current (ERC) represents molecular charge movement during rhodopsin conformational dynamics. To determine whether this time-resolved assay can probe various aspects of structure-function relationships in rhodopsin, we first measured properties of expressed normal human rhodopsin with ERC recordings. These studies were conducted in single fused giant cells containing on the order of a picogram of regenerated pigment. The action spectrum of the ERC of normal human opsin regenerated with 11-cis-retinal was fit by the human rhodopsin absorbance spectrum. Successive flashes extinguished ERC signals consistent with bleaching of a rhodopsin photopigment with a normal range of photosensitivity. ERC signals followed the univariance principle since millisecond-order relaxation kinetics were independent of the wavelength of the flash stimulus. After signal extinction, dark adaptation without added 11-cis-retinal resulted in spontaneous pigment regeneration from an intracellular store of chromophore remaining from earlier loading. After the ERC was extinguished, 350-nm flashes overlapping metarhodopsin-II absorption promoted immediate recovery of ERC charge motions identified by subsequent 500-nm flashes. Small inverted R(2) signals were seen in response to some 350-nm flashes. These results indicate that the ERC can be photoregenerated from the metarhodopsin-II state. Regeneration with 9-cis-retinal permits recording of ERC signals consistent with flash activation of isorhodopsin. We initiated structure-function studies by measuring ERC signals in cells expressing the D83N and E134Q mutant human rhodopsin pigments. D83N ERCs were simplified in comparison with normal rhodopsin, while E134Q ERCs had only the early phase of charge motion. This study demonstrates that properties of normal rhodopsin can be accurately measured with the ERC assay and that a structure-function investigation of rapid activation processes in analogue and mutant visual pigments is feasible in a live unicellular environment.

Cell Line↗
PubMed1999

Insulin induces dephosphorylation of eukaryotic initiation factor 2alpha and restores protein synthesis in vulnerable hippocampal neurons after transient brain ischemia.

Brain reperfusion causes prompt, severe, and prolonged protein synthesis suppression and increased phosphorylation of eukaryotic initiation factor 2alpha [eIF2alpha(P)] in hippocampal CA1 and hilar neurons. The authors hypothesized that eIF2alpha(P) dephosphorylation would lead to recovery of protein synthesis. Here the effects of insulin, which activates phosphatases, were examined by immunostaining for eIF2alpha(P) and autoradiography of in vivo 35S amino acid incorporation. Rats resuscitated from a 10-minute cardiac arrest were given 0, 2, 10 or 20 U/kg of intravenous insulin, underwent reperfusion for 90 minutes, and were perfusion fixed. Thirty minutes before perfusion fixation, control and resuscitated animals received 500 microCi/kg of 35S methionine/cysteine. Alternate 30-microm brain sections were autoradiographed or immunostained for eIF2alpha(P). Controls had abundant protein synthesis and no eIF2alpha(P) in hippocampal neurons. Untreated reperfused neurons in the CA1, hilus, and dentate gyrus had intense staining for eIF2alpha(P) and reduced protein synthesis; there was little improvement with treatment with 2 or 10 U/kg of insulin. However, with 20 U/kg of insulin, these neurons recovered protein synthesis and were free of eIF2alpha(P). These results show that the suppression of protein synthesis in the reperfused brain is reversible; they support a causal association between eIF2alpha(P) and inhibition of protein synthesis, and suggest a mechanism for the neuroprotective effects of insulin.

Animals↗
PubMed1999

Mechanisms of cannabinoid-receptor-mediated inhibition of synaptic transmission in cultured hippocampal pyramidal neurons.

Cannabinoids, such as marijuana, are known to impair learning and memory perhaps through their actions in the hippocampus where cannabinoid receptors are expressed at high density. Although cannabinoid receptor activation decreases glutamatergic synaptic transmission in cultured hippocampal neurons, the mechanisms of this action are not known. Cannabinoid receptor activation also inhibits calcium channels that support neurotransmitter release in these cells, making modulation of these channels a candidate for cannabinoid-receptor-mediated effects on synaptic transmission. Whole cell patch-clamp recordings of glutamatergic neurons cultured from the CA1 and CA3 regions of the hippocampus were used to identify the mechanisms of the effects of cannabinoids on synaptic transmission. Cannabinoid receptor activation reduced excitatory postsynaptic current (EPSC) size by approximately 50% but had no effect on the amplitude of spontaneous miniature EPSCs (mEPSCs). This reduction in EPSC size was accompanied by an increase in paired-pulse facilitation measured in low (1 mM) extracellular calcium and by a decrease in paired-pulse depression measured in normal (2.5 mM) extracellular calcium. Together, these results strongly support the hypothesis that cannabinoid receptor activation decreases EPSC size by reducing release of neurotransmitter presynaptically while having no effect on postsynaptic sensitivity to glutamate. Further experiments were done to identify the molecular mechanisms underlying this cannabinoid-receptor-mediated decrease in neurotransmitter release. Cannabinoid receptor activation had no effect on the size of the presynaptic pool of readily releasable neurotransmitter-filled vesicles, eliminating reduction in pool size as a mechanism for cannabinoid-receptor-mediated effects. After blockade of Q- and N-type calcium channels with omega-agatoxin TK and omega-conotoxin GVIA; however, activation of cannabinoid receptors reduced EPSC size by only 14%. These results indicate that cannabinoid receptor activation reduces the probability that neurotransmitter will be released in response to an action potential via an inhibition of presynaptic Q- and N-type calcium channels. This molecular mechanism most likely contributes to the impairment of learning and memory produced by cannabinoids and may participate in the analgesic, antiemetic, and anticonvulsive effects of these drugs as well.

Animals↗
PubMed1999

Comparison of hepatic lesions in veal calves with concentrations of copper, iron and zinc in liver and kidney.

Veal calf producers in Indiana have reported condemnation of carcasses due to icterus as well as condemnation of livers because of yellow discoloration, hepatomegaly and fibrosis. This study assessed the degree of hepatic injury in affected veal calves and correlated it with copper, iron and zinc concentrations in the liver and kidney. Tissues examined histopathologically were from slaughtered and necropsied veal calves. Hepatic lesions were divided into histopathologic categories of severity (minimal, moderate, marked or severe) based upon the degree of fibrosis, biliary epithelial hyperplasia, and inflammation. Hepatic copper levels decreased as the severity of lesions increased. The clinical observations and morphologic changes suggested initial hepatic damage before 9 w-of-age. The affected calves either died of acute copper toxicosis or survived to develop hepatomegaly, hepatic discoloration and/or fibrosis at the time of slaughter.

Age Factors↗
PubMed1998

Regulation of the readily releasable vesicle pool by protein kinase C.

Modulation of the size of the readily releasable vesicle pool has recently come under scrutiny as a candidate for the regulation of synaptic strength. Using electrophysiological and optical measurement techniques, we show that phorbol esters increase the size of the readily releasable pool at glutamatergic hippocampal synapses in culture through a protein kinase C (PKC)-dependent mechanism. Phorbol ester activation of PKC also increases the rate at which the pool refills. These results identify two powerful ways that activation of the PKC pathway may regulate synaptic strength by modulating the readily releasable pool of vesicles.

Electric Stimulation↗
PubMed1998

Apoptosis.

Apoptosis is a process of cell suicide, the mechanisms of which are encoded in the genomes of all higher eukaryotes. The mechanisms involved in apoptosis suggest that the process is based on a viral defense originally developed in primitive multicelled eukaryotes and that the fundamental execution platform of the process involves 1) inhibition of protein synthesis at the level of translation initiation, 2) proteolysis specifically involving degradation of DNA repair mechanisms, and 3) polynucleotide degradation. In mammals this execution platform is regulated by a complex molecular signaling system that includes feedback mechanisms tending toward activation of all elements of the execution platform if only one element is initially engaged. Tissue ischemia and reperfusion activate elements of the apoptosis system, which thus represents a therapeutic target for emerging treatment approaches to preserve cellular integrity in critical organs such as the heart and brain.

Animals↗
PubMed1998

Process modeling for health care organizations.

Process models can be useful tools for managers seeking to correct problems within their organization. This paper explores how two such process models can be utilized in a medical practice.

Humans↗
PubMed1997

Effect on survival of estrogen replacement therapy after coronary artery bypass grafting.

We examined the relation between postmenopausal estrogen placement therapy (ERT) and survival in 1,098 women who underwent coronary artery bypass grafting (CABG). Patients were selected for the study if their age was > or = 55 years at the time of preoperative coronary angiography or if they had previously undergone bilateral oophorectomy. Life-table analysis was used to compare survival after surgery in 92 women who received ERT and 1,006 women who did not. Five-year survival was 98.8% in the estrogen users and 82.3% in the non-users. Ten-year survival was 81.4% in the users and 65.1% in the nonusers (p = 0.0001 by Lee Desu test). The women who did not take estrogen were significantly older (p < 0.001), had more vessels with significant stenosis (p = 0.033), lower ejection fractions (p = 0.051), and more prior myocardial infarctions (p = 0.054). However, a Cox proportional-hazards model selected the number of coronary arteries narrowed (RR 1.43, p < 0.0001), estrogen use (RR 0.38, p = 0.001), left main coronary stenosis (RR 1.83, p = 0.001), and diabetes mellitus (RR 1.57, p = 0.003) as the significant independent predictors of survival. These data suggest that ERT improves survival significantly after CABG in postmenopausal women with coronary artery disease.

Case-Control Studies↗
PubMed1997

Effect of brain ischemia and reperfusion on the localization of phosphorylated eukaryotic initiation factor 2 alpha.

Postischemic brain reperfusion is associated with a substantial and long-lasting reduction of protein synthesis in selectively vulnerable neurons. Because the overall translation initiation rate is typically regulated by altering the phosphorylation of serine 51 on the alpha-subunit of eukaryotic initiation factor 2 (eIF-2 alpha), we used an antibody specific to phosphorylated eIF-2 alpha [eIF-2(alpha P)] to study the regional and cellular distribution of eIF-2(alpha P) in normal, ischemic, and reperfused rat brains. Western blots of brain postmitochondrial supernatants revealed that approximately 1% of all eIF-2 alpha is phosphorylated in controls, eIF-2(alpha P) is not reduced by up to 30 minutes of ischemia, and eIF-2(alpha P) is increased approximately 20-fold after 10 and 90 minutes of reperfusion. Immunohistochemistry shows localization of eIF-2(alpha P) to astrocytes in normal brains, a massive increase in eIF-2(alpha P) in the cytoplasm of neurons within the first 10 minutes of reperfusion, accumulation of eIF-2(alpha P) in the nuclei of selectively vulnerable neurons after 1 hour of reperfusion, and morphology suggesting pyknosis or apoptosis in neuronal nuclei that continue to display eIF-2(alpha P) after 4 hours of reperfusion. These observations, together with the fact that eIF-2(alpha P) inhibits translation initiation, make a compelling case that eIF-2(alpha P) is responsible for reperfusion-induced inhibition of protein synthesis in vulnerable neurons.

Animals↗
PubMed1997

Doctorally-prepared nurses: different practice settings, different views.

Nurse researchers in academic and clinical settings have the ultimate goal of improving nursing care while balancing the demands of education, their institution, research, and nursing service. The setting shapes the focus of research, the choice of research models, and the parameters of the position. The setting also influences available resources and the services rendered to the institution and the community. The functions of doctorally-prepared nurses in academic and clinical settings are compared. A better understanding of the functions of nurses in each setting could lead to better informed employment choices and improved collaborative efforts.

Education, Nursing, Graduate↗
PubMed1996

Estrogen replacement therapy.

For decades, observers have noted that women lose their natural resistance to coronary disease following menopause. It is now known that this increase in coronary risk is due to the loss of the protective effect of estrogen. Although still somewhat controversial, estrogen replacement therapy appears to offer significant cardioprotective benefits to postmenopausal women. These benefits extend to women with a history of coronary artery disease as well as to those without. The exact mechanism by which estrogen confers protection is not known, although the primary focus has been on estrogen's effect on serum lipids. Estrogen reduces total cholesterol levels and low-density-lipoprotein cholesterol levels and increases levels of high-density lipoproteins. Recent data suggest that estrogen may also have a beneficial effect on lipoprotein (a), a less studied lipid fraction, and may affect lipid metabolism in the blood-vessel wall. Numerous studies are under way to define better the risks and benefits of estrogen replacement therapy. Until more is known, the decision to recommend estrogen replacement therapy must be made on an individual basis.

Coronary Disease↗
PubMed1996

The clinical aspects of estrogen and the cardiovascular system.

Extensive epidemiologic and postmortem studies have identified a link between menopause and cardiovascular disease. The relation is especially strong in surgically menopausal women who do not receive estrogen replacement. More than 30 observational studies and one small randomized, controlled clinical trial have provided evidence that estrogen replacement reduces cardiovascular risk by approximately 50%. Four studies that used coronary arteriography to document the presence of coronary atherosclerosis have provided some of the most compelling evidence that estrogen replacement reduces cardiovascular risk in postmenopausal women. One study of survival in women undergoing coronary arteriography found that the greatest improvement in total mortality took place in those women with substantial coronary stenosis; less benefit was observed in those without disease. Angiographic studies have also confirmed the importance of high-density lipoprotein cholesterol in mediating the effect of estrogen and the beneficial effect of estrogen on endothelial function. Although the addition of progestins to estrogen attenuates estrogen's effect on high-density lipoprotein cholesterol, limited observational daa have suggested that the cardioprotective effect is not reduced.

Cardiovascular Diseases↗
PubMed1996

Estrogens, menopause, and coronary artery disease.

The incidence of cardiovascular disease increases after menopause as women age. Estrogen-replacement therapy has been found to reduce cardiovascular risk by about 50% in over 30 observational studies. Part of the beneficial effect appears to be due to a reduction of LDL cholesterol and an increase in HDL cholesterol. Another important mechanism is related to the effect of estrogen on endothelial function. In making a decision to use estrogen-replacement therapy, the benefits must be weighed against the risks of endometrial and breast cancer.

Aged↗