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Biomedical subjects

M R Vasko

Publications and source records attributed to M R Vasko.

11 recordsLinked to original sources
PubMed1992

Prostaglandin E2 increases calcium conductance and stimulates release of substance P in avian sensory neurons.

Prostaglandins are known to lower activation threshold to thermal, mechanical, and chemical stimulation in small-diameter sensory neurons. Although the mechanism of prostaglandin action is unknown, agents known to elevate intracellular calcium produce a sensitization that is similar to that produced by prostaglandins. Consistent with the idea of prostaglandin-induced elevations in calcium, prostaglandins might also stimulate the release of neurotransmitter from sensory neurons. We therefore examined whether prostaglandin E2 (PGE2) could enhance the release of the putative sensory transmitter substance P (SP) from isolated neurons of the avian dorsal root ganglion grown in culture. Utilizing the whole-cell patch-clamp recording technique, we also examined whether PGE2 could alter calcium currents in these cells. Exposure of sensory neurons to PGE2 produced a dose-dependent increase in the release of SP. One micromolar PGE2 increased release approximately twofold above basal release, whereas 5 and 10 microM PGE2 increased release by about fourfold. The release evoked by these higher concentrations of PGE2 was similar in magnitude to the release induced by 50 mM KCl. Neither arachidonic acid (10 microM), prostaglandin F2 alpha (10 microM), nor the lipoxygenase product leukotriene B4 (1 microM) significantly altered SP release. The addition of 1 microM PGE2 increased the peak calcium currents by 1.8-fold and 1.4-fold for neurons held at potentials of -60 and -90 mV, respectively. The action of PGE2 was rapid with facilitation occurring within 2 min. As with release studies, arachidonic acid, prostaglandin F2 alpha, and leukotriene B4 had no significant effect on the amplitude of the calcium current. These results suggest that PGE2 can stimulate the release of SP through the activation or facilitation of an inward calcium current. The capacity of PGE2 to facilitate the calcium current in these sensory neurons may be one mechanism to account for the ability of prostaglandins to sensitize sensory neurons to physical or chemical stimuli.

Animals↗
PubMed1991

Inhibitory effects of clonidine and tizanidine on release of substance P from slices of rat spinal cord and antagonism by alpha-adrenergic receptor antagonists.

Effects of clonidine and tizanidine, which have antinociceptive and alpha 2-agonistic actions, were studied on the release of substance P from slices of spinal cord from the rat. Veratridine-evoked depolarization induced a 2-3-fold increase in the release of substance P from the slices of spinal cord. Exposure of the cord tissue to 10 microM clonidine and tizanidine significantly reduced the release of substance P. The inhibitory effects of clonidine and tizanidine were attenuated by pre-exposure of the tissue to 10 microM piperoxane, which has alpha 2-antagonistic activity and the inhibitory effect of clonidine was attenuated by 10 microM yohimbine. Moreover, the inhibitory effects of clonidine and tizanidine were also blocked by a small dose of prazosin, an antagonist for alpha 1- and alpha 2B-receptors. None of the antagonists had any effect on release of substance P, when given alone. These results suggest that alpha 2B-adrenoceptors are involved in the inhibitory effects of clonidine and tizanidine on the release of substance P.

Adrenergic alpha-Antagonists↗
PubMed1991

A controlled trial of the cost benefit of computerized bayesian aminoglycoside administration.

We studied the effect of a bayesian pharmacokinetic dosing program on the outcome of aminoglycoside therapy in patients with clinical infections. Patients were randomized to a control (dosing based on physician choice; n = 75) or experimental group (dosing based on the bayesian program; n = 72). Both groups used serum aminoglycoside concentration data when making dosing decisions. Improved response rates were seen in the experimental (60%; 42/68) compared with the control group (48%; 36/68). A higher, but not statistically significant, incidence of toxicity was found in the control (7/75; 9.7%) versus the experimental group (4/72; 5.1%). Mean length of total hospital stay was significantly longer for patients in the control group (20.3 days) compared with the experimental group (16.0 days) (p = 0.028). The variables from multivariate analysis with a significant impact on length of stay were patient group and length of aminoglycoside therapy. On the basis of a reduced length of stay, a potential cost savings of $1311 per patient can be achieved.

Aminoglycosides↗
PubMed1991

In vitro release of endogenous dopamine from the striatum of the weaver mutant mouse.

The weaver mutant mouse has a genetically determined defect in the nigrostriatal dopaminergic system. The present study was undertaken to test the hypothesis that in the weaver mutant mouse, striatal nerve terminals undergo compensatory changes in response to this deficiency. To test this hypothesis, we studied the basal and stimulated release of dopamine from striatal slices of weaver mutant mice and matched controls. By using a superfusion system and concentrating the superfusate by passage over alumina, resting dopamine release could be determined in the weaver mutant despite the fact that striatal tissue content of dopamine in these mice is reduced by greater than 75% compared with control mice. Fractional resting release of dopamine in weaver striatal slices was significantly elevated compared with that in controls, suggesting that the release mechanisms in the weaver may be adapting to overcome the dopamine deficit. Potassium-evoked release (24 and 48 mM potassium) was not significantly different between the two genotypes. In contrast, amphetamine-evoked release (1 microM) was significantly greater in the weaver mice than in controls. In both genotypes, release evoked by amphetamine was completely inhibited by cocaine, implicating the dopamine uptake carrier in this release process. These findings suggest that fundamental differences in dopamine release mechanisms exist between weaver and control mice and support the hypothesis that compensatory mechanisms may develop in neurons in response to dopamine deficits.

Amphetamine↗
PubMed1990

gamma-Aminobutyric acid inhibits the potassium-stimulated release of somatostatin from rat spinal cord slices.

Evidence supports the idea that somatostatin (SO) is a neurotransmitter or neuromodulator of primary afferent neurons involved in nociception. Since gamma-aminobutyric acid (GABA), norepinephrine, and morphine alter nociception at the level of the spinal cord, we examined whether these agents could alter the potassium-stimulated release of somatostatin from rat spinal cord slices. Male Sprague-Dawley rats were decapitated and a 2 cm segment of the lumbar spinal cord removed and chopped into 0.5 x 0.5 mm pieces and perfused at 37 degrees C in individual perfusion chambers with a modified Krebs-bicarbonate buffer at a flow rate of 0.5 ml/min. Perfusates were collected at 2 min intervals and assayed for SO using radioimmunoassay. Exposure of spinal cord tissue to 50 mM KCl resulted in a 3-fold increase in release of SO from a basal level of approximately 0.2 to 0.6 pg/mg tissue/min. This evoked release was calcium dependent. Pre-exposure of tissue to GABA at 10(-4) and 10(-5) M significantly inhibited the potassium-stimulated release of SO, but did not alter basal release. The GABA receptor antagonist, bicuculline methiodide, at 10(-5) but not 10(-6) M attenuated the GABA-induced inhibition of somatostatin release. Bicuculline methiodide alone did not significantly alter either basal or stimulated release. Neither baclofen (10(-5) M, 5 x 10(-5) M), norepinephrine (10(-5) M), nor morphine (10(-5) M) had any significant effect on basal or stimulated release of SO from spinal cord tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Adenosine analogs do not inhibit the potassium-stimulated release of substance P from rat spinal cord slices.

Adenosine agonists produce antinociception when injected directly onto the spinal cord of rats and mice. One mechanism to account for this effect could be inhibition of neurotransmitter release from nociceptive sensory neurons. Consequently, we studied whether these agents could inhibit the potassium stimulated release of one such transmitter, substance P, from rat spinal cord slices. A 2 cm section of lumbar spinal cord was dissected from male Sprague-Dawley rats, chopped into 0.5 x 0.5 mm sections and perfused at 37 degrees C with a modified Krebs bicarbonate buffer containing either 3.5 mM, 30 mM, or 50 mM KCl in the presence and absence of various adenosine analogs. Perfusates, collected every 2 min, were assayed for substance P by radioimmunoassay. Exposure of tissue to 50 mM KCl produced an approximate three-fold increase in the release of substance P over basal release. This increase in release was calcium dependent. Perfusion of spinal cord tissues with either adenosine (10(-3) M). N6-cyclohexyladenosine (10(-5) M or 5 x 10(-5) M), 5'-N-ethylcarboxamide adenosine (10(-5) M) or L-N6-phenylisopropyladenosine (10(-5) M) did not significantly alter basal or potassium-stimulated release of SP when compared to controls. In contrast to the adenosine agonists, exposure of the spinal cord tissue to 10(-5) M morphine significantly reduced the potassium-stimulated release of substance P. Pretreatment of the slices with 10(-5) M theophylline or 8-phenyl-theophylline did not significantly attenuate the inhibition of substance P release produced by morphine. Theophylline alone (10(-5) M) had no significant effect on either basal or potassium-stimulated release of SP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine↗
PubMed1979

Lorazepam in status epilepticus.

Lorazepam, a dichloro-3-hydroxy-1,4-benzodiazepine, has been shown to be a potent anticonvulsant in animal models of epilsepsy and has minimal depressant effects on respiration and circulation in humans. The effects of this compound were studied in status epilepticus. Twenty-five patients were given intravenous lorazepam during status epilepticus of varying cause. Four or 8 mg of the drug controlled status in 22 of the 25 patients. Although single seizures recurred in 5 of the 22 patients, none experienced recurrence of status during a prolonged follow-up period. Transient respiratory arrest occurred in 1 patient, but no other significant complications were observed. Studies of plasma drug levels suggest that most patients attain good seizure control at concentrations between 30 and 100 ng per milliliter. Clinical observations indicate that repetitive injections are not required for continuing control of seizures in patients whose seizures are initially controlled. Lorazepam appears to be an effective and safe drug for treatment of status epilepticus, with a duration of control longer than that achieved with diazepam.

Adolescent↗
PubMed1979

Barbitone-induced tolerance to the effects of sedative-hypnotics and related compounds on operant behaviour in the rat.

1 Pretreatment doses of barbitone, pentobarbitone, ethanol, and phenytoin (diphenylhydantoin) in non-tolerant rats produced increases in operant responding at low doses and at higher doses resulted in decreases in responding.2 Daily barbitone injections (100 mg/kg, i.p.) resulted in the development of functional tolerance to both the stimulant and depressant effects of barbitone on responding.3 Barbitone tolerance development did not result in any change in the brain or plasma pharmacokinetics of barbitone.4 Barbitone-tolerant rats were cross-tolerant to the behavioural effects of pentobarbitone, ethanol, and phenytoin. The dose-effect curves for all of these drugs were shifted to the right in tolerant rats, compared to non-tolerant rats.5 Comparison of the brain and plasma levels of these drugs in non-tolerant and tolerant rats provided a means of separating functional cross-tolerance from dispositional cross-tolerance. Barbitone-tolerant rats appeared to be functionally cross-tolerant to ethanol in that there was no change in the brain and blood ethanol levels at times when the degree of behavioural impairment was substantially reduced. In contrast to ethanol, cross-tolerance to phenytoin appeared to be due to a decrease in the brain and plasma levels (dispositional tolerance). Cross-tolerance to pentobarbitone appeared to be comprised of both functional and dispositional cross-tolerance.6 The usefulness of a multidisciplinary approach in the analysis of sedative hypnotic tolerance and cross-tolerance is discussed. It is concluded that without the concurrent determination of both brain and plasma drug levels it would not be possible to distinguish between functional and dispositional tolerance.

Animals↗
PubMed1978

Tolerance development to the biphasic effects of morphine on locomotor activity and brain acetylcholine in the rat.

The development of tolerance to the depressant and stimulant actions of morphine on locomotor activity and brain acetylcholine (ACh) utilization (indirect turnover) was investigated in the rat. When administered to nontolerant rats, 1.0 mg/ kg s.c. of morphine produced an increase in locomotor activity and a concomitant increase in ACh utilization. Larger doses produced biphasic effects on locomotor activity, but only 10 mg/kg s.c. resulted in both an initial decrease and subsequent increase in ACh utilization in whole rat brain. The depressant and stimulant actions of morphine on both endpoints were antagonized by 1.0 mg/kg i.p. of naloxone administered 30 min before the maximum effect. Tolerance to morphine was produced by t.i.d. injections of increasing doses. Rapid tolerance developed to the locomotor depressant actions of morphine and to the decrease in brain ACh utilization. Tolerance to the depressant effects resulted in an enhanced stimulant action. Tolerance also developed to the stimulant actions of morphine but only when large doses of drug were administered daily. Biphasic effects of 10 mg/kg of morphine on brain ACh utilization were also observed in the hippocampus, thalamus and hypothalamus. Only a decrease in ACh utilization was observed in the caudate nucleus. Tolerance developed to the decreases and increases in ACh utilization in these discrete brain regions. This study demonstrates that tolerance development to the depressant and stimulant actions of morphine is complex and involves different dose and time schedules. It is not possible therefore to study tolerance to the actions or morphine without specifying the precise endpoint studied and the tolerance schedule utilized.

Acetylcholine↗
PubMed1977

The use of filtration techniques for the lysis and study of red blood cells.

A filtration technique for the gentle lysis of erythrocytes has been developed using cellulose triacetate membranes. When cell suspensions are filtered under nitrogen pressure, lysis occurs at the surface of the filter in such a way that the cell ghosts are retained on the filter. The contents of the cell are extruded through the pores of the filter without mixing with the cell suspension. Cell ghosts and intact erythrocytes have been collected on membranes and examined by electron microscopy. These preparations have the advantage of being free of the structural artifacts that result from centrifugation. In addition, the filter facilitates preparation for electron microscopy by providing a support for the sample during fixation and then dissolving during the dehydration of the sample.

Animals↗