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L Vachon

Publications and source records attributed to L Vachon.

At least 37 records · Page 2Linked to original sources
PubMed1987

GTPase and adenylate cyclase desensitize at different rates in NG108-15 cells.

The time course of opioid receptor binding disappearance and loss of responsiveness of the opioid-controlled GTPase and adenylate cyclase were compared in membranes derived from NG108-15 cells pretreated with the opioid peptide agonist [D-Ala2,D-Leu5]enkephalin (DADLE). Upon pretreatment with DADLE, a rapid desensitization of the opioid-stimulated GTPase occurred with a time course distinguishable as two exponential components having respective half-lives of 5-9 and 60-80 min. Opioid receptor binding activity, as assessed using [3H]diprenorphine, also decayed as two exponential components whose half-lives were similar to those for GTPase desensitization (7 and 120 min). However, when [3H]diprenorphine binding was measured in the presence of sodium and GTP, only the second, slow component was apparent. In contrast, desensitization of the opioid-controlled adenylate cyclase occurred as only one exponential decaying process, displaying a half-life of 57 min. Whereas the loss of responsiveness of GTPase to DADLE was entirely accounted for by a reduction in the maximal stimulation produced acutely by DADLE, desensitization of adenylate cyclase was characterized by both a decrease in maximal inhibition and a shift to the right of the EC50 of the agonist in inhibiting acutely the enzyme. In addition, after 1 hr of pretreatment with DADLE, the opioid-stimulated GTPase was desensitized by 65%, whereas 80% of maximal inhibition of adenylate cyclase could still be achieved. We suggest that: the rapid loss of responsiveness of the opioid-GTPase system results from an uncoupling between the receptor and the nucleotide-binding regulatory protein (N); the fast decaying GTPase activity appears to be not directly related to the opioid-mediated inhibition of adenylate cyclase; and the slow decaying GTPase activity, as well as the desensitization of the opioid-adenylate cyclase, is most likely accounted for by down-regulation of the opioid receptor. These findings may indicate that part of the opioid-stimulated GTPase in the membrane is not involved in inhibition of the cyclase and could reflect the activity of a regulatory protein which couples opioid receptors to another membrane effector. Alternatively, they might be interpreted on the basis of a model which involves a tight coupling between receptor activation and N protein and a large amplification mechanism between N protein and adenylate cyclase.

Adenylyl Cyclase Inhibitors↗
PubMed1986

Negative ion chemical ionization mass spectrometry of 2,4-dinitrophenyl amino acid esters.

We report the negative ion chemical ionization mass spectra of 2,4-dinitrophenyl (DNP) amino acid methyl esters. For the common amino acids, these derivatives exhibit very simple mass spectra; the molecular anion is the base peak in all cases. The electrophilicity of the DNP group allows selective and sensitive ionization. Amino acids can be identified singly or in mixtures by their molecular weights, and picomole detection is possible. Chromatography is only needed for Leu/Ile differentiation. Amino-terminal analysis of proteins is demonstrated.

Amino Acids↗
PubMed1986

Percutaneous drainage of hepatic abscesses in children.

Ultrasound guided percutaneous drainage of seven hepatic abscesses in five pediatric patients was performed. Abscesses were pyogenic in four of the patients and amebic in one. All patients recovered completely without surgical intervention. Methodology necessary in the pediatric patient is stressed.

Adolescent↗
PubMed1986

Pelvic lesion simulated by asymmetric marrow uptake following umbilical artery injection of technetium-99m sulfur colloid.

There is avid first-pass extraction of Tc-99m sulfur colloid by bone marrow. This factor must be considered when injection of the isotope is made via an unusual route. Tc-99m sulfur colloid was injected via an umbilical artery catheter into an infant's left iliac artery, causing marked marrow uptake in the left pelvis. The paucity of uptake on the right side of the pelvis simulated metastatic replacement of the marrow. A repeat study done via the jugular vein demonstrated no abnormalities of pelvic marrow uptake.

Bone Marrow↗
PubMed1986

Differential sensitivity of basal and opioid-stimulated low Km GTPase to guanine nucleotide analogs.

In membranes derived from NG108-15 cells, the opioid peptide [D-Ala2,D-Leu5]enkephalin (DADLE) stimulates a low Km GTPase. The nucleotide analogs guanosine 5'-O-(2-thio)diphosphate (GDP beta S), guanosine 5'-(beta,gamma-imido)triphosphate [Gpp(NH)p] and guanosine 5'-O-(3-thio)-triphosphate (GTP gamma S) inhibit the basal enzymatic activity with the order of potency GTP gamma S greater than Gpp (NH)p greater than GDP beta S. In the presence of DADLE, the inhibition isotherms of GDP beta S and Gpp(NH)p are shifted to the right five- and fourfold, respectively, compared to the inhibition observed in the absence of DADLE. In contrast, the IC50 of GTP gamma S for inhibiting the enzyme is reduced by 55% in the presence of the opioid. Both Gpp(NH)p and GTP gamma S produce a concentration-dependent increase in the Km(app) of GTPase, without affecting its Vmax, indicating a competitive inhibition. However, the replots of Km(app) versus inhibitor concentration are hyperbolic, suggesting a partial type of inhibition. Both Gpp(NH)p and GTP gamma S, but not GTP, induce an increase in the EC50 of DADLE for stimulating GTPase. These findings indicate that the basal and the opioid-stimulated low Km GTPase differ in their respective sensitivities to inhibition by guanine nucleotide analogs.

Animals↗
PubMed1986

Ossification centre of the hyoid bone in DiGeorge syndrome and tetralogy of Fallot.

The incidence of radiographic visibility of the ossification centre of the body of the hyoid bone in radiographs taken during the first month of life was analysed for 34 autopsied infants: 16 with DiGeorge syndrome (DGS), 14 with tetralogy of Fallot (TOF), four with interrupted aortic arch (IAA) and a further 13, surviving infants with non-DGS TOF or non-DGS IAA. The incidence of visible hyoid ossification centre (HOC) was 75.7% in a control series of infants with neither congenital heart disease (CHD) nor DGS. Autopsied patients with DGS, TOF without DGS, and IAA without DGS showed a significantly low incidence of visible HOC. Infants with TOF (and possibly those with IAA) who did not have DGS and who did not die during infancy showed a normal incidence of visible HOC in radiographs taken during the first post-natal month. Radiological visibility of the HOC in the first post-natal month appears useful in the diagnosis of DGS and forms of CHD often seen in association with DGS and in assessing prognosis of neonates with certain types of CHD.

Age Factors↗
PubMed1985

Desensitization of opioid-stimulated GTPase in neuroblastoma x glioma hybrid cells.

NG108-15 cells were pretreated with the opioid peptide [D-Ala2, D-Leu5]enkephalin and the opioid-dependent low Km GTPase was assayed in membranes. Pretreatment resulted in a small decrease in basal GTPase activity and led to a concentration-dependent reduction in opioid-mediated stimulation of the enzyme. These effects were observed whether the agonist was present or absent throughout all the experimental procedures, but, in the second condition, the desensitization was smaller. The addition of naloxone had no effect on basal GTPase activity, in either control or pretreated cell membranes. Both Na+ and Mg++ were required for the opioid-induced stimulation of the GTPase. Mg++ enhanced basal enzymatic activity in controls, whereas in membranes from pretreated cells, it produced an inhibition. Thus, desensitization of the opioid-dependent low Km GTPase occurs upon chronic opioid treatment and a Mg++ regulatory site might be altered in the course of this process.

Animals↗
PubMed1984

Chlordiazepoxide, go-nogo successive discrimination and brain biogenic amines in cats.

Chlordiazepoxide (CDP; 0.4 mg/kg/day, per os) was administered to cats during either the acquisition (CDP 21-22 days) of a go-nogo successive discrimination task (SD) or the performance (CDP 10 days) of the previously learned SD task. Endogenous levels of serotonin, 5-hydroxyindoleacetic acid, noradrenaline and dopamine were assayed in 12 brain areas, in trained as well as in untrained cats. This study has shown that (1) CDP strongly impaired the acquisition but not performance of the SD task, revealing a dissociation of the effects of CDP on these two stages of training; (2) the CDP administration, as well as the SD training, produced regional changes in brain levels of biogenic amines, suggesting the involvement of particular monoaminergic neurons in the behavioral effects of CDP and in operant behavior; and (3) in particular brain areas, interactions were observed between the effects of the SD training and those of the CDP administration on monoamines, indicating that the behavioral state may interfere with the neurochemical effects of CDP.

Animals↗
PubMed1983

Effects of chlordiazepoxide administration on biogenic amines in cat brain.

Cats underwent treatment with chlordiazepoxide hydrochloride (0.4, 10.0, and 20.0 mg/kg per os), for 7 consecutive days, and were killed 18 h after the last administration. The endogenous levels of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), noradrenaline (NA), and dopamine (DA) were assayed in 12 brain areas. Few effects on 5-HT, 5-HIAA, and NA content and on the 5-HT:5-HIAA ratio were observed with a 0.4 mg/kg treatment. These changes were localized in the piriform lobe (amygdala), hippocampus, mesencephalon, and mesencephalon raphe nuclei. Moreover, the DA concentration was not affected. The changes produced by 10.0 and 20.0 mg/kg chlordiazepoxide treatments were extended to many more structures, including the limbic system, brainstem, diencephalon, and neostriatum with respect to 5-HT, 5-HIAA, and NA content and also to DA levels. The changes observed after the three doses generally included an increased 5-HT content, a decreased 5-HIAA level, a high 5-HT:5-HIAA ratio, and increased NA and DA concentrations. However, in some structures, a decreased NA content and an increased 5-HIAA level were found. The present results suggest that administration of chlordiazepoxide for 7 consecutive days in cats produces regional changes in the content of endogenous biogenic amines in the central nervous system (CNS) at low doses; much more extended effects are produced at high doses. These findings are in agreement with a reducing effect of benzodiazepines on the turnover and release of biogenic amines in the CNS, but also suggest that certain discrete areas are more involved in these changes, thus dissociating them from the rest of the brain.

Animals↗
PubMed1982

Effects of chlordiazepoxide on acquisition and performance of a go-no go successive discrimination task, and on brain biogenic amines in cats.

1. Normal and chlordiazepoxide (0.4 mg/kg/day, per os) treated cats were trained on a symmetric go-no go successive discrimination task with positive reinforcement. 2. The treatment impaired the acquisition, but not the performance once the task was learned. 3. Serotonin, 5-hydroxyindoleacetic acid and noradrenaline were assayed in 12 brain areas in trained cats, and in normal and treated cats which did not undergo the training. 4. The treatment produced localized changes in the serotonin: 5-hydroxyindoleacetic acid ratio and the noradrenaline level; these effects were modified by the training. 5. The drug induced an acquisition deficit rather than a general behavioral disinhibition, and produced neurochemical effects which were dependent upon the brain area, the treatment duration and the behavioral state.

Animals↗
PubMed1977

Propranolol effects on acute marihuana intoxication in man.

To investigate the possible interaction of a beta adrenergic blocking agent and marihuana, six healthy experienced marihuana smokers received the two drugs separately and in combination. Propranolol (120 mg per os) reduced resting HR and BP; there were no changes in performance on tasks designed to test psychomotor speed, attention, memory and learning. Marihuana (10 mg delta9-THC), administered in smoke, induced the typical subjective state ("high") with marked increases in HR, BP and conjunctival injection; it impaired performance on a learning test without significantly affecting attention. Pre-treatment with propranolol blocked effectively the cardiovascular effects of marihuana; it prevented the learning impairment and, to a lesser degree, the characteristic subjective experience.

Adolescent↗