Search PubMed⌕ Search

Biomedical subjects

C B Gundersen

Publications and source records attributed to C B Gundersen.

At least 73 records · Page 4Linked to original sources
PubMed1982

Capture immunoglobulin M system for rapid diagnosis of La Crosse (California encephalitis) virus infections.

A capture immunoglobulin M (IgM) enzyme immunoassay was developed to diagnose La Crosse virus infections by the detection of specific IgM in acutephase serum specimens. IgM was detected by the capture IgM system in the serum of 24 of 29 (83%) of the patients studied. In comparison, IgM was detected in 19 of 29 (66%) of the patients by an indirect immunofluorescence technique. Specific IgM was detected in 83% (20 of 24) of patient serum specimens by day 3 after the onset of clinical symptoms.

Encephalitis, Arbovirus↗
PubMed1981

The reduction of endplate responses by botulinum toxin.

Endplate responses were recorded in frog muscle fibres during an advanced stage of botulinum (BoTX) paralysis, when transmitter release had fallen to a very low level. By simultaneous recording from two points, it was found that, even when the quantal responses had been reduced to less than 0.01 per impulse (that is, four to five orders of magnitude below normal), the release continued to be spatially dispersed along the terminal arborization. These observations make it very unlikely that whole "active zones' could be eliminated, as has been suggested, in all-or-none fashion by local action of BoTX molecules, and they suggest a more graded, indirect mechanism by which the toxin molecules interfere with the sites of transmitter release.

Acetylcholine↗
PubMed1981

Choline uptake and acetylcholine synthesis in synaptosomes: investigations using two different labeled variants of choline.

Using sequential incubations in media of different K+ composition, we investigated the dynamics of choline (Ch) uptake and acetylcholine (ACh) synthesis in rat brain synaptosomal preparations, using two different deuterated variants of choline and a gas chromatographic-mass spectrometric (GC-MS) assay for ACh and Ch. Synaptosomes were preincubated for 10 min in a Krebs medium with or without high K+ and with 2 micrometer-[(2)H(9)]Ch. At the end of the preincubation al variants of ACh and Ch were measured in samples of the pellet and medium. In the second incubation (4 min) samples of synaptosomes were resuspended in normal or high K+ solutions containing [(2)H(4)]Ch (2 micrometer) and all variants of ACh and Ch were measured in the pellet and medium at the end of this period. This protocol allowed us to compare the effects of preincubation in normal or high K+ solution on the metabolism during a second low or high K+ incubation of a [(2)H(9)]Ch pool accumulated during the preincubation period. Moreover, we were able to compare and contrast the effects of this protocol on [(2)H(9)]Ch metabolism versus [(2)H(4)]Ch metabolism. The most striking result we obtained was that [(2)H(9)]Ch that had been retained by the synaptosomes after the preincubation was not acetylated during a subsequent incubation in normal or high K+ media. This result suggests that if an intraterminal pool of Ch is involved in ACh synthesis, the size of this pool is below the limits of detection of our assay. We have confirmed the observation that a prior depolarizing incubation results in an enhanced uptake of Ch during a second incubation in normal K+ Krebs. Moreover, Ch uptake is stimulated by prior incubation under depolarizing conditions relative to normal preincubation when the second incubation is in a high K+ solution. These results are discussed in terms of current models of the regulation of ACh synthesis in brain.

Acetylcholine↗
PubMed1981

Alterations of acetylcholine and choline metabolism in mammalian preparations treated with beta-bungarotoxin.

We have studied the effects of beta-bungarotoxin on acetylcholine and choline metabolism in central and peripheral cholinergic preparations using a gas chromatographic-mass spectrometric assay for acetylcholine and choline. In contrast with previous reports, beta-Bungarotoxin did not inhibit the high-affinity uptake of labeled choline or the synthesis of acetylcholine in rat brain synaptosomal fractions. However, the toxin did cause a significant increase of medium choline when it was incubated with synaptosomal fractions. This increase of endogenous choline in the medium may account for the previously reported inhibition of choline uptake because of a dilution of the specific activity of the labeled choline in the medium. Several experiments are reported in which a further characterization was made of the effect of beta-bungarotoxin on medium choline. beta-Bungarotoxin was also shown to cause a large increase of acetylcholine release from rat brain minces and a depletion of the acetylcholine content of minces. A similar phenomenon was found in diaphragm preparations that were exposed continuously to beta-bungarotoxin. However, diaphragms that were treated for only 30 min with toxin showed the previously reported increase of acetylcholine content. beta-bungarotoxin did not have any measurable effect on acetylcholine turnover in smooth muscle preparations from guinea pig ileum. These results help to explain certain inconsistencies in the literature regarding the action of beta-bungarotoxin.

Acetylcholine↗
PubMed1981

Studies of the effects of agents which alter calcium metabolism on acetylcholine turnover in the rat diaphragm preparation.

1 We measured the effects of agents, which are thought to alter the Ca2+ concentration in cells, on tissue and released acetylcholine and choline of rat diaphragm using a gas chromatographic mass spectrometric assay for acetylcholine and choline. 2 Lanthanum and ouabain increased the resting output of acetylcholine, while 4-aminopyridine enhanced the evoked output of acetylcholine. 3 Guanidine first increased and then depressed acetylcholine release. 4 Theophylline, dinitrophenol and the ionophore, A-23187, had no measurable effect on acetylcholine release and tetraethylammonium inhibited the release of acetylcholine. 5 Dinitrophenol caused a highly significant increase of the tissue and released choline. 6 None of these agents increased the tissue acetylcholine content. Tetraethylammonium caused a large decline of tissue acetylcholine while ouabain and guanidine caused smaller reductions of acetylcholine in diaphragm. 7 These results are discussed in relation to the hypothesis that intraterminal Ca2+ activity regulates the synthesis of acetylcholine in diaphragm nerve endings.

4-Aminopyridine↗
PubMed1981

Beta-bungarotoxin stimulates the synthesis and accumulation of acetylcholine in rat phrenic nerve diaphragm preparations.

1. The effects of beta-bungarotoxin on acetylcholine (ACh) synthesis, tissue content and release have been studied in the rat diaphragm. A gas chromatographic mass spectrometric assay was used to measure ACh and choline. 2. Within 30 min, beta-bungarotoxin (0.14 or 1.4 micrograms/ml.) caused a significant increase in tissue ACh content. This increase was apparent prior to the final inhibition by beta-bungarotoxin of evoked (10 Hz) ACh release. 3. The toxin enhanced the incorporation of [2H4]Ch into [2H4]ACh in both resting and stimulated preparations. 4. Hemicholinium-3 blocked the rise in diaphragm ACh normally produced by beta-bungarotoxin. 5. Beta-Bungarotoxin did not directly activate choline acetyltransferase in muscle homogenates. 6. The toxin-induced rise in tissue ACh was largely absent in Ca2+-free solutions which contained either EGTA (1 mM) or SrCl2 (2 or 10 mM). 7. Non-neurotoxic phospholipases A2, fatty acids and the neurotoxic phospholipase A2, notexin, did not cause ACh accumulation in the diaphragm. 8. Beta-Bungarotoxin did not stimulate ACh synthesis in denervated muscle. 9. The extra ACh which accumulated after beta-bungarotoxin did not contribute to enhanced release by nerve impulses even when 4-aminopyridine was added to the medium. High K+ solution and black widow spider venom were also ineffective in increasing output from toxin-treated diaphragms relative to controls that had not been treated with beta-bungarotoxin. 10. Prior injection of a rat with botulinum toxin prevented the accumulation of ACh due to beta-bungarotoxin. Tubocurarine, however, did not antagonize beta-bungarotoxin. 11. These data indicate that beta-bungarotoxin has a unique capacity to inhibit ACh release and stimulate ACh synthesis in diaphragm nerve endings. The results are discussed in terms of a possible action of beta-bungarotoxin to raise the level of ionized Ca in the nerve terminal cytosol.

Acetylcholine↗
PubMed1981

Diminished response to beta-bungarotoxin in neonatal rat diaphragm.

1. The effects of beta-bungarotoxin on acetylcholine turnover were studied in neonatal rat diaphragms using a gas chromatographic mass spectrometric assay to measure acetylcholine and choline. 2. Injection of neonatal rats (1-15 days old) with a fixed dose of beta-bungarotoxin resulted in a shorter time to death in the older animals. 3. This increased lethal potency of beta-bungarotoxin in the older rats was correlated with an enhancement of the stimulatory effect of the toxin on acetylcholine synthesis in diaphragm in vivo and in vitro. 4. The reduced effect of beta-bungarotoxin in promoting the accumulation of acetylcholine in new-born rat diaphragms was not due to an enhancement by the toxin of acetylcholine output from these preparations. 5. These results demonstrate that the stimulatory effect of beta-bungarotoxin on acetylcholine synthesis in diaphragm is a function of the age of the rat. Thus, beta-bungarotoxin may be valuable as a probe of the maturation of presynaptic function in rat skeletal muscle.

Acetylcholine↗
PubMed1981

Notexin preferentially inhibits the release of newly synthesized acetylcholine from rat brain synaptosomal fractions.

An investigation was made of the effects of the snake venom neurotoxin, notexin, on acetylcholine turnover in rat brain P2 fractions using a gas chromatographic mass spectrometric assay for acetylcholine and choline. In contrast to earlier reports, we found a stimulation of the uptake and acetylation of labeled choline by toxin-treated P2 fractions. More significantly, notexin inhibited the release of this newly synthesized transmitter. These effects were found to be dependent on the dose of the toxin and the time of exposure of the P2 fraction to notexin. Longer exposure to notexin or experiments involving resuspension of notexin-treated P2 fractions appeared to result in considerable lysis of the transmitter-containing particles. Thus, notexin may alter acetylcholine compartmentation in the nerve ending and thereby affect acetylcholine synthesis.

Acetylcholine↗
PubMed1980

Oxotremorine does not enhance acetylcholine release from rat diaphragm preparations.

We have reinvestigated the dramatic effect of oxotremorine on acetylcholine release from the rat diaphragm reported by Das, Ganguly & Vedasiromoni (1978), using a rigorous gas chromatographic mass spectrometric/isotope dilution method for identification and measurement of acetylcholine and choline. Oxotremorine (10 microM) causes no significant change in the spontaneous or evoked (1 or 10 Hz) release or in the tissue levels of acetylcholine or choline.

Acetylcholine↗
PubMed1977

Energy utilization in the uptake of catecholamines by synaptic vesicles and adrenal chromaffin granules.

Several inhibitors of energy metabolism decreased the ATP-stimulated uptake of catecholamines by isolated synaptic vesicles from rat brain and by chromaffin granules from bovine adrenal medulla. Catecholamine uptake was inhibited by dinitrophenol, S-13 and oleic acid, which are known to block active transport by dissipating trans-membrane proton gradients. Thus a proton gradient appears to be involved in catecholamine transport. Both catecholamine uptake and vesicle-associated Ca2+/Mg2+-ATPase were inhibited by dicyclohexylcarbodiimide and tributyltin, which had previously been shown to inhibit the Ca2+/Mg2+-ATPase of mitochondria. However, mitochondrial ATPase was not involved in catecholamine uptake as oligomycin and aurovertin, more specific inhibitors of mitochondrial ATPase, did not affect catecholamine uptake. It is suggested that ATP stimulates catecholamine uptake by serving as a substrate for the ATPase. Activity of this enzyme causes translocation of protons across the vesicle membrane establishing a trans-membrane proton gradient. The proton gradient drives the transport of catecholamines.

Adenosine Triphosphate↗
PubMedDate not supplied

Messenger RNA from human brain induces drug- and voltage-operated channels in Xenopus oocytes.

Sodium channels and receptors to serotonin and kainate were 'transplanted' from human brain into frog oocytes, by isolating messenger RNA from a fetal brain, and injecting it into Xenopus laevis oocytes. The mRNA was translated by the oocyte and induced the appearance of functional receptors and channels in its membrane. This approach renders drug- and voltage-operated channels of the human brain more amenable to detailed study.

Animals↗
PubMedDate not supplied

Giant synaptosomes.

Investigations using synaptosomes, pinched-off nerve ending particles from brain, have greatly improved our knowledge of presynaptic function. However, these structures, like most nerve endings, are too small to be penetrated with microelectrodes. We have treated synaptosomal preparations from rat brain with a neutral protease and obtained fused structures large enough to be recorded from directly with microelectrodes; we report here that these particles (30-250 microM in diameter) contain mitochondria and structures resembling synaptic vesicles, morphological features characteristic of synaptosomes. These 'giant synaptosomes' have resting membrane potentials in the range -45 to -76 mV, are depolarized by increasing concentrations of K+, show responses to a variety of neuroactive substances and exhibit active membrane responses to depolarizing current pulses. These results suggest that this preparation will be of value in further studies of nerve terminal function.

Animals↗