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At least 1,189 records · Page 66Linked to original sources
PubMed1991

Temperature dependence of carbachol-induced modulation of miniature end-plate potential frequency in rats.

In the rat soleus, the frequency of miniature end-plate potentials (MEPP) did not change after application of 10(-5) M of the cholinomimetic drug carbachol between 18 degrees C and 34 degrees C but decreased by 40% at physiological temperatures of 37-38 degrees C. The carbachol-induced decrease in MEPP frequency was not eliminated by 10(-7) to 10(-8) M atropine or 3 x 10(-7) (+)-tubocurarine similarly as had been previously found at frog neuromuscular junction.

Animals↗
PubMed1995

Effect of veratridine on miniature endplate current amplitudes at the rat neuromuscular junction and acetylcholine uptake by Torpedo synaptic vesicles.

Veratridine produces a marked elevation in spontaneous quantal release from nerve endings through its ability to enhance sodium-channel activity, leading to sustained membrane depolarization. In the course of an electrophysiological investigation into the effects of vesamicol, an inhibitor of the synaptic vesicle acetylcholine transporter, on veratridine-induced acetylcholine release from rat motor nerve terminals we observed that veratridine itself has an effect on miniature endplate current amplitude distributions suggestive of an effect of the compound on the filling of cholinergic synaptic vesicles with acetylcholine. This effect of veratridine is release-dependent, being inhibited by either removal of extracellular calcium ions or by the addition of the sodium channel blocking toxin, tetrodotoxin. Biochemical studies using synaptic vesicles isolated from Torpedo electroplaque confirmed the ability of veratridine to directly inhibit the vesicular transport of acetylcholine. This appears to be a consequence of its ability to dissipate the trans-vesicular membrane proton gradient, which normally drives the active transport of acetylcholine into synaptic vesicles. We discuss how such an action of veratridine could lead to the observed release-dependent effects of the compound on electrophysiologically monitored spontaneous quantal acetylcholine release. The action of veratridine on cholinergic synaptic vesicles could be of considerable import when using this agent to elicit neurotransmitter release from either peripheral or central nerve endings.

Acetylcholine↗
PubMed1994

TNF-alpha increases the frequency of spontaneous miniature synaptic currents in cultured rat hippocampal neurons.

Tumor necrosis factor-alpha (TNF-alpha) is a cytokine secreted by activated astrocytes and is known to alter evoked synaptic activity in slices of adult rat hippocampus. In this paper we show that TNF-alpha increases the frequency of spontaneous miniature synaptic currents in cultured hippocampal neurons, acting at nanomolar concentrations. In addition, we show that the mRNA for the 55 kDa TNF-alpha receptor (TNF-R1) is detected in embryonic rat hippocampal cultures, as well as in acutely dissected embryonic and adult rat hippocampi. Possible transduction pathways mediating the TNF-alpha effect are discussed.

Animals↗
PubMed1994

Factors governing the appearance of small-mode miniature endplate currents at the snake neuromuscular junction.

At the snake neuromuscular junction, following a short period of high frequency motor nerve stimulation, a population of 'small-mode' miniature endplate currents (MEPCs) is seen. These small-mode MEPCs are believed to be due to the release of acetylcholine from incompletely refilled recycling synaptic vesicles [Searl et al., Neuroscience, 35 (1991) 145-156]. This study determines the role of the trans-vesicular membrane proton gradient in the generation of small-mode MEPCs. Preserving the trans-vesicular membrane proton gradient during synaptic vesicle exocytosis by exposure of snake nerve/muscle preparations to an extracellular pH approximately equal to the intravesicular pH, leads to an augmentation of the amplitude of the stimulation-induced small-mode MEPCs. Conversely, pretreatment of snake neuromuscular preparations with 10 mM ammonium ions, to buffer intravesicular protons and hence dissipate the trans-vesicular membrane proton gradient, leads to an inhibition of the stimulation-induced appearance of small-mode MEPCs. The data are consistent with the theory that the reduced acetylcholine content of recycled synaptic vesicles in the snake is a consequence of an incomplete restoration of the trans-vesicular membrane proton gradient following synaptic vesicle exocytosis. Thus, in recycling synaptic vesicles the limiting step in the refilling process appears to be generation of the trans-membrane proton gradient and not the transport of acetylcholine into the vesicle.

Ammonium Chloride↗
PubMed1991

Stimulation of miniature end-plate potential frequency by fluoride may involve activation of protein kinase C.

NaF caused a dose-dependent rise in miniature end-plate potential (MEPP) frequency at the frog neuromuscular junction. The effects on MEPP frequency of both NaF and the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) were rapidly reversed by the protein kinase C (PKC) inhibitor polymyxin B (2 microM). Theophylline augmented the response of MEPP frequency to TPA. It is concluded that the effect of fluoride on MEPP frequency may be through activation of phospholipase C and consequent PKC stimulation, and that the synergistic interaction of NaF and theophylline is consistent with such a mode of action.

Animals↗
PubMed1992

Rhodopsin levels in the central retinas of normal miniature poodles and those with progressive rod-cone degeneration.

Visual pigment in normal miniature poodles and those with progressive rod-cone degeneration (prcd), a late-onset autosomal recessive photoreceptor degeneration, has been studied using imaging fundus reflectometry (IFR). The stage to which the disease had advanced in the animals with prcd was assessed with electroretinography (ERG). Measurements were carried out on seven affected, two heterozygous and three homozygous normal animals. The IFR measurements showed that the in situ difference spectrum of visual pigment measured in the central retina of the normal poodle is typical of vertebrate rhodopsin, with a maximum at about 510 nm. Rhodopsin regeneration following extensive bleaches continues for up to 70 min. In poodles with prcd, rhodopsin is spectrally normal and regenerates at normal rates. In young affected animals under 1 year of age, the final levels of rhodopsin could already be substantially reduced. Serial measurements of visual pigment in these dogs showed differences in the degree and spatial pattern of pigment loss and rate of progression between animals. The extent of visual pigment loss also differed among the older (greater than 4.5 years) affected animals: while in one animal no pigment could be detected, in another a central band of retina was relatively spared, and significant levels of visual pigment were measured within it. Pigment levels measured within the central 25 degrees of the retinas of poodles heterozygous for prcd were lower than those in normal animals, even though their ERGs were within the normal range.

Animals↗
PubMed1983

Reduction of miniature end-plate potential amplitude in extraocular and limb muscles in an animal model of myasthenia gravis.

Miniature end-plate potential (MEPP) amplitudes of the superior oblique extraocular muscle (EOM) and forelimb flexor digitorum longus muscle (FDL) of rats with experimental autoimmune myasthenia gravis (EAMG) were expressed as reductions from mean MEPP amplitudes of the respective muscles of pair-matched control animals. Postjunctional blockade of neuromuscular transmission at EOM end-plates was no greater than at limb muscle end-plates. In contrast, the amount of reduction measured in EAMG-affected FDLs (52.3%) was marginally, but significantly, greater than that in EOMs (38.3%). A weak correlation was present between the MEPP reduction observed in an animal's FDL and that recorded in its EOM.

Acetylcholine↗
PubMed1984

Neurotrophic influences are not affected by miniature end-plate potentials.

We investigated whether or not miniature end-plate potentials (MEPPs) play a part in neurotrophic influences. The sciatic nerve of mice, which supplies the extensor digitorum longus muscles, was cut either close to, or far from, the muscle. Denervation changes were evaluated using the resting membrane potential and dose-response curves obtained by plotting acetylcholine-induced contractures of muscles denervated 3 days earlier. The cessation of MEPPs and the manifestation of denervation changes occurred significantly later in muscles with long nerve stumps than in those with short nerve stumps. A single administration of ethidium bromide, a specific inhibitor of mitochondrial protein synthesis, accelerated the cessation of MEPPs in muscles with long nerve stumps without affecting the manifestation of denervation changes. We therefore conclude that MEPPs do not have neurotrophic effects.

Acetylcholine↗
PubMed1977

Inverse effect of chronically elevated blood flow on atherogenesis in miniature swine.

The effect of chronically elevated blood flow on the development of atherosclerosis in miniature swine was studied. Fistulas connecting the right external iliac artery and vein were surgically created in four swine, while three were not fistulated. Pulsed Doppler velocity detection cuffs placed around the abdominal aorta and both iliac arteries of all pigs permitted chronic measurements of blood velocity, blood velocity distributions, and blood flow. All swine were fed an atherogenic diet consisting of 20% beef tallow, 3% cholesterol, and 5% cholic acid for 6 months. This diet elevated the serum cholesterol to values exceeding 500 mg/100 ml. Creation of the arteriovenous fistula (AVF) markedly elevated blood velocity and flow in the abdominal aorta and in the shunted iliac artery. In the shunted animals the aortic blood flow was 42.1 +/- 2.0 ml/sec compared with 17.3 +/- 1.4 ml/sec in the unshunted swine. The velocity distribution pattern across the vessel was also indicative of an elevated wall shear stress. After 6 months, the animals were killed and the arterial vessels examined macroscopically and microscopically for the presence of atherosclerotic lesions. In the shunted pigs, 17 +/- 15% of the lumenal surface was occupied by sudanophilic lesions, whereas 80 +/- 8% of the surface was covered by lesions in the unshunted (control) pigs. From these studies, it is apparent that mechanical factors related to blood flow rates can influence the development of atherosclerotic lesions in swine.

Animals↗
PubMed1978

A miniaturized in vitro diffusion culture system.

A miniaturized diffusion culture apparatus holding 24 individual cultures and utilizing 1/10 the cells and volume of standard Marbrook-type cultures is described. This system was evaluated by studying the anti-sheep erythrocyte response of spleen cells from unprimed or primed and boosted mice. Compared to parallel Mishell--Dutton plate cultures memory responses in mini-diffusion cultures rise more slowly, peak 1--2 days later and thereafter decline less rapidly. Moreover, the diffusion cultures give a pronounced IgG response peaking at 6 days, while the abortive IgG response evident in plate cultures at 4 days rapidly disappears. While viability in the two systems is equivalent, cell recovery on days 7 and 8 is markedly higher in the diffusion cultures. Of 4 cell concentrations tested, 2 million cells are found to produce the optimum anti-sheep erythrocyte plaque-forming cell response. A 0.2 micron nucleopore membrane is preferable to a dialysis membrane and yields up to a 2-fold higher response. Replacement of the reservoir medium on day 4 impairs rather than improves the response. The culture system was also found to support an excellent primary response. This response is dependent on the presence of 2-mercaptoethanol and does not require rocking.

Animals↗
PubMed1986

Miniaturization of the standard 51Cr release assay for long term follow-up of NK activity of individual mice.

Two modifications for miniaturizing the standard 51chromium release assay have been described. Using peripheral blood lymphocytes (PBL) as effectors and very few target cells, this permits longitudinal studies on NK cell activity of individual mice to be performed. The modifications are based on methods to increase the chromium uptake by the target cell. Firstly, chromium uptake by the YAC-1 target cells was enhanced to such an extent that appreciable activity could be detected against as little as 750 cells/well at an E/T ratio of 50:1. Secondly, the uptake was increased even further by labelling the target cells in the presence of isotonic sucrose, thus permitting the use of only 125 target cells/well at an E/T of 25:1. The long term pattern of NK activity in individual BALB/c mice was studied by repeated bleedings over a period of 8 months. Considerable fluctuations with time were observed in the pattern of NK activity of individual mice. However, the NK activity averaged over a large number of mice did not show a significant decrease with age. These methods may allow the study of the long term pattern of NK activity in individual mice and the response of this activity to physiological and environmental factors.

Age Factors↗
PubMed1988

Miniaturization of the immunoblot technique. Rapid screening for the detection of monoclonal and polyclonal antibodies.

A miniaturization of the immunoblot technique permitting the use of as little as 50 microliters of antibody is described. This method does not require any special equipment and the whole experimental procedure (incubation, washing, detection) can be performed in the same chamber, with economy of reagents at all steps and no prenumbering of blotted strips. This method has been applied for screening the presence of antibodies in hybridoma culture supernatants and is of special interest for testing any scarce material (immune sera or antigens).

Animals↗
PubMed1982

Development of a new miniature method for the study of wound healing in human subjects.

A new miniaturized method for evaluation of healing potential in human subjects has been developed. A small, standardized, subcutaneous wound is made in a standard location. Expanded PTFE tubing is placed in the wound and removed at specific intervals. The ingrowth of connective tissue is evaluated by histology and by measurement of hydroxyproline accumulation. Beginning on the fifth day, hydroxyproline accumulation correlates with visual accumulation of tissue in the tubing. Preliminary results show decreased hydroxyproline accumulation in the wounds of patients with preoperative debility. This is to be expected on the basis of previous clinical experience and laboratory studies. This method has the further advantage that the catheters may be placed with local anesthesia in outpatients and therefore may be applied systematically to populations, as well as for observation in patients requiring operation.

Animals↗
PubMed1980

The effects of alloxan diabetes on Yucatan miniature swine and their progeny.

Alloxanization as a method to induce diabetes has been successfully undertaken in several laboratory animal models. The genetic transmissibility of the alloxan-diabetic condition has been investigated and confirmed by several studies in rodents. The Yucatan miniature pig is a potential laboratory animal model for diabetes. Studies were conducted to investigate the possibility that alloxan diabetes could be transmitted to subsequent generations in these animals. Diabetic pigs were produced directly with alloxanization, but the genetic transmissibility of this trait was not substantiated through the F2 generation. On the basis of these data, alloxan diabetes is not transmissible in Yucatan pigs in the same way that it is in rats.

Alloxan↗
PubMed1975

Genetic instability in Drosophila melanogaster: Mutable miniature (mu).

A new mutable gene, mutable miniature wing (mu), is described. This mutable gene mutates spontaneously at an inordinate rate both germinally and somatically. Two classes of reversions of mu have been found in approximately equal frequency: those to an allele with an intermediate phenotype (mi) and those to a subliminal allele (ms) equivalent to wild type in phenotype. Reversions appear to be mutationally stable. The chronology of genetic events leading to the discovery of mu implicates, but does not prove, the insertion of a "foreign" DNA segment as the basis of mutability.

Alleles↗
PubMed1985

Verapamil alters the amplitude and time course of miniature endplate current.

The effect of verapamil on neuromuscular transmission was examined by recording miniature endplate currents (mepcs) in voltage-clamped frog sartorius muscle fibres. In the presence of 100 microM verapamil, the amplitude and time constant of decay of the mepcs (tau D) were reduced to 68% and 55% of control respectively, and the normal voltage dependency of tau D was decreased. Part of the decrease in amplitude of the mepc was independent of changes in tau D because, on washout, recovery of tau D was more rapid than that of amplitude, and in some cells smaller concentrations of verapamil (1 and 10 microM) decreased amplitude without affecting tau D. Evidence of open and closed channel blockade by verapamil (5-20 microM) was obtained from ionophoretic end-plate current trains and it is proposed that these effects are mediated via an allosteric mechanism.

Animals↗
PubMed1979

Trypanosoma brucei: Miniature anion-exchange centrifugation technique for detection of low parasitaemias: Adaptation for field use.

The miniature anion-exchange/centrifugation (AEC) method, originally developed for the detection of submicroscopic trypanosomaemias in laboratory rodents, has been adapted for the diagnosis of trypanosomiasis in man in the field using blood samples obtained by finger-prick. It has been tested in a survey in The Gambia. The method is shown to be highly sensitive and to fulfil the first essential criteria for exploitation in the field, namely, that it can be operated in the open air under tropical conditions, and that an adequate number of subjects can be examined in a normal working day at an acceptable cost. The method also offers two advantages over the other highly sensitive method applicable to small blood samples, the microhaematocrit buffy-coat microscopy (MBCM) method, namely, that it minimized the requirements for highly critical microscopy and provides, in the same operation, samples of diluted plasma which can be used for serological study.

Animals↗