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At least 1,135 records · Page 63Linked to original sources
PubMed1994

The timing of channel opening during miniature endplate currents at the frog and mouse neuromuscular junctions: effects of fasciculin-2, other anti-cholinesterases and vesamicol.

Fluctuation analysis was used to estimate the mean single-channel conductance and the mean channel duration of opening. Miniature endplate currents (MEPCs) were measured with the voltage-clamp technique. The timing of endplate channel opening during the generation of the MEPC was estimated by a deconvolution method. Often all of the channels opened during the rise of the MEPC, but in about half of the examples some 10% of the channels opened after the peak. We studied the effects of acetylcholinesterase (AChE) inhibition with neostigmine, diisopropyl fluorophosphate (DFP) and fasciculin-2. With AChE largely inhibited, the number of channels opening increased as much as fourfold, largely by channels opening in the "tail" that follows the peak of the MEPC. The results were compared to models of MEPC generation. Models did not account well for the pattern of channel opening, particularly after AChE inhibition. In the presence of fasciculin-2, the addition of 2 microM (-)-vesamicol reduced the number of channels opening and shortened the period over which channels were open. One interpretation is that quantal ACh release is not almost instantaneous, but that some of the ACh is released over a period of a millisecond or more and that some of the release is blocked by (-)-vesamicol.

Acetylcholine↗
PubMed1981

Analysis of miniature spontaneous inhibitory postsynaptic currents (sIPSCs) from current noise in crayfish opener muscle.

Deviating from the normal situation, some crayfish muscle fibres showed spontaneous inhibitory activity: discharge of large inhibitory postsynaptic currents, IPSCs, alternating with long lasting bursts of current noise. Analysis of the bursts of current noise revealed that they are composed of spontaneous miniature unit currents, sIPSCs. In the burst periods the sIPSCs occurred with an average rate of 3.5--10 k Hz and had an amplitude of about alpha = 90 pA at a driving force delta E = 10 mV. The peak conductance gamma alpha = alpha/delta E of the sIPSCs was gamma alpha = 9.2 nS +/- 0.5 (S.D., n = 5) for membrane potentials between E = --60 mV and E = --80 mV. gamma alpha seemed to decrease when the membrane was hyperpolarized. The time constants of decay, tau of the sIPSCs were identical with tau of the IPSCs. Further, tau and its potential dependence agreed with the mean lifetimes of inhibitory postsynaptic channels operated by gamma-aminobutyric acid (GABA) [Dudel et al. 1977, 1980]. Synchronized opening of about 750 inhibitory synaptic channels generates a sIPSC. Analysis of this anomalous bursting inhibitory activity thus yields the size of the inhibitory quantum of transmission, which could not be obtained from IPSCs.

Animals↗
PubMed1976

Miniature end-plate potentials and sensitivity to acetylcholine in the fast and slow limb muscles of hibernating golden hamsters.

During hibernation reduction of frequency of the miniature end-plate potential (m.e.p.p.) was observed. This parameter was reduced in the extensor digitorum longus (EDL) muscle to 16% and in the soleus muscle to 7% of values found in awake animals. The ACh-sensitive area of the individual muscle fibres in both types of muscle increased about three times during hibernation.

Acetylcholine↗
PubMed1988

Characteristics of Schwann-cell miniature end-plate currents in denervated frog muscle.

End-plates in denervated frog sartorius muscles were investigated, under voltage clamp, to determine the characteristics of miniature endplate currents (mepc) caused by the release of acetylcholine (ACh)-quanta from Schwann-cells. Staining for acetylcholinesterase ascertained that in most cases Schwann-cell mepc had been recorded focally from the end-plate. The mean amplitude of Schwann-cell mepc (about 1 nA) was smaller than the amplitude (3-4nA) of normal nerve evoked mepc. The amplitude distribution of Schwann-cell mepc was skewed, as were also the distributions of decay time constants and of rise times. Some Schwann-cell mepc appeared to be of composite nature, as shown by an inflexion on either the rising of falling phase. The decay time constant tau of both fast and slowly decaying Schwann-cell mepc increased with membrane hyperpolarization suggesting an exponential correlation. The potential dependence was 118 +/- 37 mV (means +/- SD from 6 experiments) for an e-fold change of tau, which does not differ significantly from that for neural mepc (98 mV). The cholinesterase inhibitor neostigmine increased the amplitude and prolonged the time course of Schwann-cell mepc to a similar degree after short and long term denervation, which indicates that cholinesterase was still functional after 3-4 months of denervation. The results show that the characteristics of Schwann-cell mepc resemble in many respects those of neural mepc but are more variable in shape and amplitude.

Acetylcholine↗
PubMed1978

Dual effect of external calcium on the frequency of miniature synaptic potentials in frog sympathetic ganglion cells.

The effect of calcium on spontaneous transmitter release and on the release induced by tetanic stimulation and by raising the external potassium concentration ([K]0) was studied in sympathetic ganglion cells of Rana esculenta. 1. In standard Ringer's solution the frequency of miniature excitatory postsynaptic potentials (mepsp) ranged from 0.05--2.0 s-1 (0.05 +/- 0.09 s-1, n = 37) at room temperature. 2. At a [K]0 of 2.5 mM mepsp frequency was approximately linearly related to the logarithm of the external calcium concentration (log [Ca]0) (0.1 mM less than or equal to [Ca]0 less than or equal to 20 mM). 3. Duration and amplitude of the potentiation of transmitter release after tetanic preganglionic stimulation increased depending on [Ca]0. 4. Mepsp frequency was strongly dependent on [K]0 between 10 and 20 mM; the frequency being increased to about 40 times control level at a [K]0 of 20 mM. 5. Raising [Ca]0 up to 1.8 mM in high K solutions resulted in an increase in mepsp frequency followed by a decrease at higher [Ca]0. 6. These results are consistent with the idea that the effect of calcium on mepsp frequency depends on: (a) the driving force for calcium entry, (b) the effect of Ca ions on the potential gradient within the nerve membrane.

Animals↗
PubMed1987

Two classes of spontaneous miniature excitatory junction potentials and one synaptic vesicle class are present in the ray electrocyte.

Cross sections (1-2 mm thick) of the ray (Raja) tail were secured to a dish and immersed in elasmobranch saline. Spontaneous miniature excitatory junction potentials (MEJPs) were recorded by advancing a 50 k omega, KCl filled electrode into the electric organ (20 microV peak-to-peak baseline noise). Data were filmed, and/or recorded on magnetic tape for computer analyses. Intracellularly recorded MEJP amplitude histograms showed a peak at 60 microV and had a right-hand skew with MEJPs up to 0.5 mV. The small peak amplitude and the skewed amplitude distribution of intracellularly recorded MEJPs result from the relatively low input resistance and the short space constant of the electrocyte coupled with the dispersed synapses on the electrocyte. At 23 degrees C the intracellularly recorded MEJP frequency ranged from 1-10 MEJPs/s. The MEJPs became larger and became focally recorded as the electrode was advanced against the intracellular surface of the innervated membrane of the electrocyte. Focal extracellular MEJPs (reversed polarity) were also recorded with the electrode positioned against the outside surface of the innervated side of the electrocyte. The frequency of focally recorded intracellular MEJPs was increased (up to 40/s) when the electrode was pushed against the membrane. Focal MEJP frequencies decreased to a few/min within 5-10 min but the mean amplitude of 3-5 mV remained constant. Decreases in amplitude and frequency in focally recorded intracellular MEJPs are attributed to changes in electrode pressure against the membrane. Amplitude histograms were constructed from focally recorded intracellular or extracellular MEJPs which showed the same time characteristics. The focal MEJP amplitude histograms have two distinct classes, each forming a bell-shaped distribution. It is concluded that both classes are generated at the electrode tip. The smaller class of MEJPs has a mean 1/10th that of the larger class and composes about 2% of the MEJPs. The small class is analogous to the sub-MEPP class found in the frog sartorius (Kriebel and Gross 1974) and mouse diaphragm (Kriebel et al. 1976, 1982). Distributions of synaptic vesicle diameters are slightly log normal (right hand skew) such that the mean diameter (57 nm) is slightly larger than the modal value (52 nm). Vesicles touching the membrane were of the same size and diameter distribution as the entire vesicle population. The profiles of the distributions are smooth and suggest only 1 class of synaptic vesicle based on diameter.

Action Potentials↗
PubMed1986

A comparison of miniature end-plate potentials at normal, denervated, and long-term botulinum toxin type A poisoned frog neuromuscular junctions.

The effects of denervation and long-term botulinum toxin type A (BoTx) poisoning on miniature end-plate potentials (m.e.p.p.s) in the frog were studied with intracellular microelectrode recording. BoTx reduced the frequency of m.e.p.p.s to less than 1% of the level seen in untreated frogs, leaving a large percentage of tiny m.e.p.p.s and slow-rising m.e.p.p.s (slow m.e.p.p.s). Unlike what is observed in the rat, the frequency of slow m.e.p.p.s never increased above the low rate measured in the untreated controls, and in fact slightly but significantly decreased after BoTx. A comparison of the m.e.p.p.s seen after BoTx poisoning (BoTx m.e.p.p.s) and m.e.p.p.s seen after denervation (Schwann m.e.p.p.s) revealed many similarities between the two including amplitude and time-to-peak distributions, temperature Q10 values and responses to several drugs and procedures. However, it was concluded that BoTx m.e.p.p.s do not originate from the Schwann cells because denervation of BoTx-paralysed frogs abolishes all m.e.p.p.s and the drug 4-aminoquinoline affects BoTx m.e.p.p.s and Schwann m.e.p.p.s in opposite ways, increasing the frequency of the former while almost eliminating the latter. BoTx m.e.p.p.s and Schwann m.e.p.p.s probably represent similar processes of secretion which are non-specific in nature, having a lower energy barrier than for normal release and not originating from specialized areas of transmitter release.

Aminoquinolines↗
PubMed1988

A study of cerebellar and cerebral cortical degeneration in miniature poodle pups with emphasis on the ultrastructure of Purkinje cell changes.

In a litter of three Miniature Poodles, a normal female pup contrasted with two males which displayed severe equilibrium and postural disturbances soon after birth. In the male pups diffuse cerebral cortical degeneration accompanied cerebellar cortical atrophy, which was characterized by extensive loss and degeneration of Purkinje neurons. As in some prior histological descriptions of canine cerebellar atrophies, degenerating Purkinje cells appeared either pale, swollen and vacuolated or shrunken and hyperchromatic. Swollen vacuolated cell bodies and condensed necrotic neurons were scattered through the cerebral cortex. Ultrastructural studies revealed that the vacuolar degeneration in Purkinje and cerebral neurons was referable to marked dilation of endoplasmic reticulum and loss of ribosomes. In shrunken Purkinje neurons, increased cytoplasmic eosinophilia was associated with a decline in Nissl bodies and accumulations of mitochondria and especially lamellar bodies. The latter, stacked derivatives of endoplasmic reticulum, were not encountered in shrunken cerebral perikarya. Lamellar bodies reached giant proportions in the dendritic stems of degenerating Purkinje neurons. In Purkinje axons, however, these bodies often were overshadowed by aggregates of axoplasmic tubules. The cytological changes in these Poodle pups were notably different from those reported in earlier ultrastructural studies of canine inherited cerebellar degenerations.

Animals↗
PubMed1990

Class II genes of miniature swine. II. Molecular identification and characterization of B (beta) genes from the SLAc haplotype.

Genomic clones corresponding to class II beta genes of the SLAc haplotype of miniature swine have been isolated and characterized. These genes have been grouped into seven non-overlapping clusters on the basis of restriction mapping. Ordering of exons within each cluster was accomplished by hybridization of Southern blots of restriction fragments with exon-specific probes. The two clusters (clusters 2 and 3) encoding the DRB and DQB genes were identified on the basis of hybridization with locus-specific 3' untranslated cDNA probes. Cluster 4 contained exons of both DOB and DQB genes, the basis for which remains to be determined. The remaining four clusters (1, 5, 6, 7) were identified as containing DP, DR, and DO coding sequences, respectively, on the basis of sequence analysis. The porcine class II region appears very similar to that of man in number and nature of the class II genes identified and in the intron/exon organization of corresponding genes.

Animals↗
PubMed1994

A microtiter plate assay for total glutathione and glutathione disulfide contents in cultured/isolated cells: performance study of a new miniaturized protocol.

The microtiter plate technique reported by Baker and colleagues for the glutathione reductase-DTNB recycling assay of total glutathione (GSx) and glutathione disulfide (GSSG) has been modified according to Anderson's recommendations, in order to improve the reliability and accuracy of this miniaturized method for the measurement of glutathione status in cultured/isolated cells. Dilute HCl (10 mmol/L) has been used to lyse cells, before protein removal by centrifugation in the presence of 1.3% sulfosalicylic acid. The final DTNB, GSSG-reductase and NADPH concentrations in the reaction mixture have been increased to 0.7 mmol/L, 1.2 IU/ml and 0.24 mmol/L, respectively. The procedure specificity has been tested by spiking and dilution assays, showing that about 90% of the expected GSx amounts could actually be recovered, while no changes of GSSG concentrations were caused in the cells. Accuracy has been assessed by analysis of within-series precision as well as of intra- and interassay reproducibility, showing coefficient variation of < 10%. Glutathione changes measured either in control rat hepatocytes or in primary cultures treated with paracetamol or menadione were in good agreement with well-known literature data. These data suggest that the experimental conditions reported in this paper are suitable for the analysis of total glutathione and glutathione disulfide concentrations in cultured/isolated cells.

Acetaminophen↗
PubMed1992

Rapid transport of the acidic phosphoproteins of Plasmodium berghei and P. chabaudi from the intraerythrocytic parasite to the host membrane using a miniaturized fractionation procedure.

A miniaturized procedure for the separation of the host erythrocyte membrane from malarial parasites based on saponin lysis and density-gradient centrifugation with Percoll is described. The procedure requires only 20-35 microliters packed infected erythrocytes, is simple to perform, needs no sophisticated equipment, and can be completed in less than 2 h. Analysis of the isolated erythrocyte membranes and parasites using marker enzymes and electron microscopy revealed that both the purity and the yield of these fractions were relatively high. Erythrocyte membrane proteins, including spectrin, ankyrin, and band 4.1, were not found on the parasitophorous vacuolar membrane, which remained associated with some but not all of the isolated parasites. Application of this method to pulse-chase experiments indicated that the acidic phosphoproteins of Plasmodium berghei and P. chabaudi were rapidly transported from the parasite to the erythrocyte membrane immediately after their synthesis. The rapid export of these acidic phosphoproteins from the parasite distinguishes them from other proteins exported by the malarial parasite.

Animals↗
PubMed1989

[Determination of the endotoxin content of egg products using a miniaturized chromogenic Limulus test].

A chromogenic Limulus amoebocyte lysate assay was applied to monitor endotoxin concentration in egg products. Analysis of differently contaminated whole egg probes revealed a strong correlation of endotoxin concentration to total bacterial count 6 x 10(4) cfu x ng-1, where cfu = colony-forming unit) as well as to number of Enterobacteriaceae (1 ng/7 x 10(2) cfu). Similar relations were also found for egg white and egg yolk probes. A significant influence of heat pretreatment of egg probes (65 degrees C, 60 min) on endotoxin detection could be excluded. Up to a concentration of 10 mg x ml-1 endotoxin-free whole egg material did not interfere with the test system. A miniaturized version of the chromogenic Limulus test, which can be carried out in microtiter plates, is described.

Animals↗
PubMed1984

New concepts on the structure of the neuronal networks: the miniaturization and hierarchical organization of the central nervous system. (Hypothesis).

The hypothesis is introduced that miniaturization of neuronal circuits in the central nervous system and the hierarchical organization of the various levels, where information handling can take place, may be the key to understand the enormous capability of the human brain to store engrams as well as its astonishing capacity to reconstruct and organize engrams and thus to perform highly sophisticated integrations. The concept is also proposed that in order to understand the relationship between the structural and functional plasticity of the central nervous system it is necessary to postulate the existence of memory storage at the network level, at the local circuit level, at the synaptic level, at the membrane level, and finally at the molecular level. Thus, memory organization is similar to the hierarchical organization of the various levels, where information handling takes place in the nervous system. In addition, each higher level plays a role in the reconstruction and organization of the engrams stored at lower levels. Thus, the trace of the functionally stored memory (i.e. its reconstruction and organization at various levels of storage) will depend not only on the chemicophysical changes in the membranes of the local circuits but also on the organization of the local circuits themselves and their associated neuronal networks.

Aging↗
PubMed1984

Pathogenesis of rotavirus-induced diarrhea. Preliminary studies in miniature swine piglet.

The pathogenesis of diarrhea caused by rotavirus infection was studied in miniature swine piglets. The animals were inoculated orally with 2 X 10(7) plaque-forming units of porcine rotavirus (OSU strain). During the height of diarrhea, intestinal function was investigated by in vivo perfusion of a 30-cm segment of proximal jejunum and a 30-cm segment of distal ileum. Absorption of Na+ and water decreased and 3-O-methylglucose transport was markedly reduced, P less than 0.01 compared to control animals. Mucosal lactase and sucrase levels were depressed in both the jejunum and ileum, P less than 0.001. Na+,K+-ATPase activity was significantly depressed only in the ileum, P less than 0.001. These changes were associated with a marked reduction in villous height, suggesting that the diarrhea could be an osmotic diarrhea due to nutrient (carbohydrate) malabsorption. Fresh stool samples were obtained and analyzed immediately for NA+,K+, osmolarity, glucose, and lactose; the osmotic gap was also determined. Stool osmolarity continually increased from 248 +/- 20 mosm/liter prior to inoculation to 348 +/- 20 mosm/liter at 75 +/- 1 hr postinoculation (P less than 0.005); the majority of the fecal osmotic gap could be accounted for by the amount of lactose present in the stools. Stool sodium increased from 34 +/- 6 mM prior to inoculation to a maximum of 65 +/- 4 mM at 53 +/- 1 hr postinoculation, P less than 0.001. There was no significant change in potassium concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Miniature equipment for the perfusion of rat limbs.

A simple, reliable and efficient miniaturized extracorporeal circulation system for the use in small animals, especially for the perfusion of rat hind limbs, has been described. The system consists of a newly devised bubble oxygenator and heat exchanger and of commercially available roller pumps, polyethylene cannulas and silicone tubes. The minimal and maximal priming volume of the entire system is 4.7 and 16.7 ml, respectively. The efficiency of the system is reflected in a high value of oxygen uptake in the range of 0.061 ml O2 X min-1 X ml-1 blood, a heat transfer coefficient ranging from 0.96 to 0.31 at flow rates between 1 and 20 ml X min-1, a low pulsation amplitude of the roller pump, a constant flow resistance at the arterial cannula, which implies optimal flow conditions, and in a low blood trauma with plasma hemoglobin concentrations of 47.5 +/- 5 mg dl-1 after 60 min of in vitro perfusion.

Animals↗
PubMed1975

[Streptozotocin diabetes in a miniature pig (author's transl)].

The intravenous application of 60 mg streptozotocin/kg body weight to a Hanford miniature pig 8 days after a first dose of 30 mg/kg led to a diabetes with loss of insulin response to glucose, hyperglycaemia, glucosuria and a considerable increase of triglycerides and cholesterol. The application of 40 mg streptozotocin/kg to a second pig had no effect.

Animals↗
PubMed1975

[The Goettingen miniature swine as an experimental animal. 1. Review of literature, breeding and handling, cardiovascular parameters].

The miniature swine is steadily gaining prominence as a laboratory animal. This paper attempts to survey the existing literature concerning the Göttinger Minipig and to give some information about breeding, growth-rate and handling. Further studies dealing with the circulation (ECG, blood pressure and heart-rate) of conscious minipigs are reported. In this regard, the Göttinger Minipig is shown, to display a more favorable ratio between diastole and systole than normal swine.

Animals↗
PubMed1987

Two-hour miniaturized system for detection of enteropathogenic bacteria in stool cultures.

A miniaturized 2-h system for detection of lactose-negative potentially enteropathogenic bacteria on the basis of nine enzymatic tests was evaluated. The system was challenged with 210 strains of lactose-negative and lactose-positive species grown on MacConkey agar. Specific and constant patterns were found for Salmonella, Shigella A-C, Yersinia enterocolitica, Aeromonas spp. and Vibrio cholerae. Shigella sonnei and Hafnia alvei had an identical pattern, likewise Plesiomonas shigelloides, halophilic vibrios and Pseudomonas aeruginosa.

Bacteria↗