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Biomedical subjects

C B Gundersen

Publications and source records attributed to C B Gundersen.

At least 55 records · Page 3Linked to original sources
PubMed1985

A transient inward current elicited by hyperpolarization during serotonin activation in Xenopus oocytes.

Activation of serotonin, glutamate or muscarinic receptors, incorporated into the membrane of Xenopus oocytes following injection of messenger RNA from rat brain, caused the development of a transient inward (Tin) current when the membrane was hyperpolarized. A detailed study was made of the Tin current induced during serotonin activation. The current is due principally to efflux of chloride ions, and is presumably activated by an influx of calcium ions, because it was blocked by removal of calcium from the bathing medium, by addition of manganese, cobalt or lanthanum, or by intracellular injection of EGTA. During application of serotonin, the amplitude of the Tin current increased slowly, and after washing it persisted for longer than the direct serotonin-induced current. The amplitude of the Tin current was sensitive to temperature and pH, and was abolished at pH 6.5 or by cooling to 12 degrees C. The Tin current may be of importance in regulating the excitability of neurons in the central nervous system.

Animals↗
PubMed1985

Intracellular Ca2+-dependent and Ca2+-independent responses of rat brain serotonin receptors transplanted to Xenopus oocytes.

Xenopus oocytes injected with messenger RNA extracted from rat brain are induced to acquire a variety of neurotransmitter receptors and voltage-operated membrane channels. Activation of the receptors to serotonin, acetylcholine (muscarinic) and glutamate elicits oscillatory membrane currents carried by chloride ions. These currents are not abolished by removing external calcium, but are completely abolished after EGTA is injected into the oocytes to chelate intracellular calcium. A smooth current response to serotonin remained in EGTA-loaded oocytes, indicating that this response does not require intracellular calcium. In contrast to the oscillatory chloride currents, the chloride currents activated by GABA or glycine are not abolished by intracellular injection of EGTA. Thus, there appear to be two classes of chloride channels one of which requires intracellular calcium to open.

Animals↗
PubMed1985

Choline acetyltransferase and acetylcholine in Xenopus oocytes injected with mRNA from the electric lobe of Torpedo.

Xenopus oocytes were injected with poly(A)+ mRNA obtained from the electric lobes of Torpedo marmorata and Torpedo ocellata, which contain the cell bodies of the neurons that innervate the electric organs. The electric lobe mRNA preparation induces the oocytes to synthesize a catalytically active form of the enzyme choline acetyltransferase (EC 2.3.1.6). Enzymatic activity is found almost exclusively in the cytoplasmic fraction of injected, but not control, oocytes. Evidence is presented that distinguishes between the induced choline acetyltransferase activity and an intrinsic carnitine acetyltransferase activity present in the oocytes. This latter enzyme is associated principally with particulate fractions of the oocyte. The level of acetylcholine, which accumulates in mRNA-injected oocytes, is relatively insensitive to pharmacological manipulations that alter the acetylcholine content of other cells. These results show that Xenopus oocytes may be used advantageously to study functional properties of polypeptides associated with presynaptic elements in the nervous system.

Acetylcholine↗
PubMed1985

Rapid diagnosis of LaCrosse encephalitis: detection of specific immunoglobulin M in cerebrospinal fluid.

An immunoglobulin M (IgM) antibody capture enzyme immunoassay (MAC-EIA) was developed for the rapid and early diagnosis of LaCrosse (LAC) virus infections. The MAC-EIA was a sensitive and specific technique for the detection of IgM antibodies to LAC virus in cerebrospinal fluid specimens and in acute-phase serum specimens. In a retrospective study, cerebrospinal fluid and acute-phase serum paired samples from 108 patients were tested by the MAC-EIA and by an IgM immunofluorescence assay. The results were compared with the original diagnosis, which was made by using a variety of classical serological tests including serum neutralization, hemagglutination inhibition, and complement fixation. Thirty patients were confirmed as having LAC virus infections; of these, 30 (100%) were diagnosed as positive by serum MAC-EIA, and 27 (90%) were positive by cerebrospinal fluid MAC-EIA. The MAC-EIA was more sensitive than the IgM immunofluorescence assay. Two patients who were not previously confirmed as positive cases were diagnosed as having LAC virus infections by the MAC-EIA. One patient who was subsequently diagnosed as having a Jamestown Canyon virus infection and two patients who were previously infected with Jamestown Canyon virus were not falsely identified as having LAC virus infections by the MAC-EIA.

Antibodies, Viral↗
PubMed1984

Glutamate and kainate receptors induced by rat brain messenger RNA in Xenopus oocytes.

Xenopus laevis oocytes injected with poly(A)+ mRNA extracted from rat brain became sensitive to serotonin, glutamate, kainate, acetylcholine and gamma-aminobutyrate. Application of these substances to mRNA-injected oocytes elicited membrane currents. The glutamate- and acetylcholine-induced currents usually showed oscillations, while the kainate current was smooth. The current oscillations during glutamate application reversed direction at about the chloride equilibrium potential (-24 mV), but the reversal potential for the kainate current was close to 0 mV. The current-voltage relation for the glutamate-induced current oscillations showed strong rectification at hyperpolarized potentials, while that for the kainate current was nearly linear. In some oocytes, glutamate elicited smooth membrane currents, with oscillations either absent, or appearing after a delay. The reversal potential of this component was close to 0 mV, and was clearly different from that of the oscillatory component. The appearance of glutamate and kainate sensitivity in the oocyte membrane is due to the translation of the foreign messenger RNA, and not to activation of the oocytes' own genome, because oocytes still become sensitive when transcription is prevented by enucleation or by treatment with actinomycin D. It appears that mRNA from rat brain contains translationally active messengers which code for various neurotransmitter receptors. When this mRNA is injected into Xenopus oocytes, the messengers are translated and receptors are inserted into the oocyte membrane, where they form functionally active receptor-channel complexes.

Animals↗
PubMed1984

Properties of human brain glycine receptors expressed in Xenopus oocytes.

Glycine and gamma-aminobutyric acid (GABA) receptors from the foetal human brain were 'transplanted' into the Xenopus oocyte membrane by injecting the oocytes with poly(A)+-mRNA extracted from the cerebral cortex. Activation of both glycine and GABA receptors induced membrane currents carried largely by chloride ions. However, unlike the GABA-activated current, the glycine current was blocked by strychnine, and was not potentiated by barbiturate. At low doses, the glycine current increased with concentration following a 2.7th power relation, suggesting that binding of three molecules of glycine may be required to open a single membrane channel. The current induced by steady application of glycine decreased with hyperpolarization beyond about -60 mV.

Animals↗
PubMed1984

Slowly inactivating potassium channels induced in Xenopus oocytes by messenger ribonucleic acid from Torpedo brain.

Poly(A+) messenger RNA was extracted from the electric lobe and medulla of Torpedo and injected into oocytes of Xenopus laevis. The synthesis and processing of proteins coded by the injected messenger RNA led to the incorporation of voltage-activated channels in the oocyte membrane. A large, well maintained outward current was recorded from injected oocytes in response to depolarization. Non-injected oocytes did not show this current. The reversal potential of the current varied according to the Nernst equation with external potassium concentration, indicating that it was largely carried by potassium ions. The maintained potassium current was not reduced by manganese (5 mM) or lanthanum ions (0.1 mM). Tetraethylammonium and aminopyridines blocked the potassium current. The block produced by 3,4-diaminopyridine was enhanced by previous activation, but diminished by strong depolarization. The amplitude of the potassium current increased over the approximate voltage range -30 to +50 mV, but reduced at more positive potentials. The decline of the current during maintained depolarization became slower as the membrane potential was made more positive, and the rate of onset of the current became faster. Estimates from noise analysis indicated that the slow potassium current passes through channels with a mean lifetime of about 14 ms and conductance of 14 pS (at -10 mV and room temperature). Injection of the messenger RNA also induced the formation of fast sodium and potassium channels activated by voltage, and channels activated by kainate.

4-Aminopyridine↗
PubMed1984

Electrophysiological and neurochemical investigations of the action of presynaptic neurotoxins.

Previous experiments have suggested that hemicholinium-3 might directly antagonize certain actions of beta-bungarotoxin at the neuromuscular junction. Data presented here show that, on the contrary, hemicholinium-3 neither inhibits the phospholipase activity of beta-bungarotoxin nor does it affect the characteristic pattern of transmitter release observed at end plates exposed to the toxin. Lanthanum ions were found to promote the release of acetylcholine from sartorius nerve-muscle preparations that had been paralyzed by botulinum toxin. However, the acceleration of transmitter release by lanthanum was not nearly as great as in control preparations as monitored either electrophysiologically or by chemical measurement of ACh.

Acetylcholine↗
PubMed1983

Voltage-operated channels induced by foreign messenger RNA in Xenopus oocytes.

Poly(A)+ messenger RNA (mRNA) extracted from rat brains or from cat muscles was injected into Xenopus laevis oocytes. This led to the incorporation of voltage-operated Na+ and K+ channels into the oocyte membrane. These channels are not normally present in the oocyte and presumably result from the synthesis and processing of proteins coded by the injected mRNA. Tetrodotoxin blocked the Na+ channels induced by mRNA derived from either innervated or denervated muscle.

Animals↗
PubMed1983

Serotonin receptors induced by exogenous messenger RNA in Xenopus oocytes.

When poly(A)+-mRNA, extracted from rat brain, was injected into Xenopus laevis oocytes, it induced the appearance of serotonin receptors in the oocyte membrane. Application of serotonin to injected oocytes elicited, after a long delay, oscillations in membrane current. The equilibrium potential of this current corresponded with the chloride equilibrium potential. It appears that rat brain mRNA encodes the translation of serotonin receptors into the oocyte membrane. The combination of serotonin with these receptors leads to the opening of membrane channels.

Animals↗
PubMed1983

The effect of beta-bungarotoxin on acetylcholine and choline content of vertebrate tissues.

We have investigated the effects of intraventricularly or i.p. administered beta-bungarotoxin on the tissue content of acetylcholine and choline in three vertebrate species. A gas chromatographic mass spectrometric assay was used to measure acetylcholine and choline. Intraventricular administration of beta-bungarotoxin (1 microgram, 105 min) in rats raised the acetylcholine content of hippocampus and striatum but not of cortex. Choline was significantly increased in all three brain regions. Injection of the toxin i.p. (5 micrograms, 90 min) in rats caused variable increases of the acetylcholine content of diaphragm, tongue, temporalis muscle and adrenal gland, but no significant change was seen in heart atrium, eye, ileum or superior cervical ganglion. Significant increases of choline content were seen in heart and adrenal. The toxin caused the same degree of increase of acetylcholine in mouse diaphragm as in the rat. No alteration of sartorius muscle or tongue acetylcholine was observed after i.p. injection of beta-bungarotoxin (5 micrograms) in frog. Results with 125I-labelled beta-bungarotoxin (rats, i.p.) suggest that the observed differences in response to beta-bungarotoxin cannot be accounted for by the distribution of toxin alone. From these data we make suggestions regarding the variable effects of beta-bungarotoxin on tissue acetylcholine and choline content and the implication of these findings for the mechanism of action of the toxin.

Acetylcholine↗
PubMed1983

Acetylcholinesterase activity of Xenopus laevis oocytes.

The cholinesterase activity of Xenopus laevis oocytes was assessed using [3H]acetylcholine in a simple radiometric procedure. The cholinesterase activity of mature (stage V-Vl) oocytes was very sensitive to inhibition by the specific acetylcholinesterase inhibitor, BW284-C5l, and relatively insensitive to an inhibitor of non-specific, or butyrylcholinesterase. The Km and Vmax of the acetylcholinesterase measured in homogenates of oocytes were 312 microM and 4.6 nmol-oocyte 1-h 1, respectively. Triton X-100 increased the enzyme activity of homogenates four- to five-fold while collagenase treatment displaced into the medium none of the acetylcholinesterase activity from either homogenates or intact oocytes. Cations were found generally to diminish the acetylcholinesterase activity of oocyte homogenates, and lanthanum ions inhibited acetylcholine hydrolysis with an IC50 of 0.63 mM. Subcellular fractionation of oocytes revealed that the bulk of enzyme activity was associated with particulate fractions. Acetylcholinesterase activity was also detected on the surface, and in homogenates, of immature oocytes. Peak enzyme activity resided in stage IV oocytes. Eggs obtained from females induced to spawn were found to have acetylcholinesterase activity in homogenates but little or no hydrolytic activity was detected on the egg surface. These results provide a point of departure for further investigations of the functional significance of this enzyme in Xenopus oocytes.

Acetylcholine↗
PubMed1983

Peripheral resistance to thyroid hormone in a family: heterogeneity of clinical presentation.

We describe a family with thyroid hormone resistance. Juvenile Graves disease was diagnosed in the propositus, an 8-month-old boy. He was initially given propylthiouracil, and at 22 months of age underwent subtotal thyroidectomy. A diagnosis of hyperthyroidism was made in a younger sister at 3 months of age. Because of the unusual occurrence of juvenile Graves disease in two siblings, we evaluated the parents. The mother was euthyroid on physical examination and by thyroid hormone measurements. The father, although clinically euthyroid, had markedly elevated thyroid hormone values. In the three affected members, serum thyrotropin concentrations and results of thyrotropin-releasing hormone infusion tests were inappropriate for the elevated serum thyroid hormone levels. The father was given increasing doses of triiodothyronine. Complete suppression of TRH-induced TSH release did not occur until a daily dose of 300 micrograms triiodothyronine was administered. Furthermore, this large dose of T3 did not produce clinical evidence of hyperthyroidism or result in changes in his systolic ejection time intervals. This family therefore had the unusual feature of clinical heterogeneity. The two children had mainly pituitary resistance to thyroid hormone and were hyperthyroid; the euthyroid father, on the other hand, had generalized tissue resistance to thyroid hormone.

Adult↗
PubMed1983

Spontaneous output of acetylcholine from rat diaphragm preparations declines after treatment with botulinum toxin.

A gas chromatographic spectrometric assay was used to measure tissue and released acetylcholine and choline in diaphragm preparations of rats previously injected with botulinum toxin type A. Botulinum intoxication was found not to alter the acetylcholine content of rat diaphragms in vivo or in fully paralyzed muscles in vitro. This result provides direct support for the hypothesis that botulinum toxin blocks transmitter release without affecting acetylcholine synthesis. However, in diaphragm preparations in vitro, this toxin was found to inhibit not only the evoked release of acetylcholine but also the spontaneous "leakage" of acetylcholine that is measured at rest. Additional experiments were performed to characterize this action of the toxin. The magnitude of the decline in resting acetylcholine output appears to be too large to be accounted for solely by the known effect of botulinum toxin to reduce the frequency of miniature endplate potentials. The mechanism of this action of botulinum toxin remains an enigma.

Acetylcholine↗
PubMed1983

La Crosse encephalitis: occurrence of disease and control in a suburban area.

Fifteen (6.4%) of 233 residents sampled in State Road Coulee (SRC) during 1972-73 had antibodies neutralizing La Crosse (LAC) virus, 9 (3.9%) trivittatus (TVT), 12 (5.2%) Jamestown Canyon (JC) and 2 (0.9%) Bunyamwera serogroup virus. Six of seven youths who had antibodies to LAC virus had been ill: three were serologically confirmed as cases of LAC encephalitis and three had possibly related illnesses. The other reported no illness. Possibly related illnesses were reported by 1 of 10 adults with antibody to LAC; also by 3 of 6 youths who had antibodies to TVT or JC viruses, and by 4 of 39 youths who did not have these antibodies. In prospective studies, 4 of 132 sampled again during 1977 had acquired antibodies, including 2 to LAC and 2 to JC virus. The LAC disease-infection rate was 50%. One of those with antibody to LAC virus was a girl with encephalitis who had a serologically confirmed infection a year after she had moved away from SRC. Her exposure to mosquitoes was not in SRC. The other was a boy who remained a resident but did not have encephalitis or other severe illness. The two who had acquired antibody to JC virus were boys who reported histories of undiagnosed febrile illnesses while attending summer camps in central Wisconsin. Control measures, including closure of treeholes, removing old tires and education, were applied. LAC infections in SRC were reduced from six during 1965 thru 1972, to only one during 1973 thru 1977. No cases have been found in SRC since 1977. Following expansion to a county-wide control program, LAC encephalitis in La Crosse County has been reduced from seven and eight cases during 1978 and 1979 to only one and two during 1980 and 1981. No cases have been found in La Crosse County so far during 1982.

Adolescent↗
PubMed1982

The antagonism between botulinum toxin and calcium in motor nerve terminals.

The effects of tetraethylammonium and manganese, which modify calcium entry into motor nerve terminals, have been studied during advanced stages of botulinum paralysis. Evidence has been obtained that the voltage-activated calcium current in the nerve endings is not significantly reduced by botulinum toxin. The depression of transmitter release that the toxin produces must arise at a later stage, at an intracellular site of the release mechanism.

Acetylcholine↗
PubMed1982

Indirect fluorescent-antibody technique for serological diagnosis of La Crosse (California) virus infections.

A clinically relevant indirect fluorescent-antibody technique (IFA) was developed for the serological diagnosis of La Crosse virus infections. The IFA (67%) was as sensitive as the hemagglutination inhibition (58%) and neutralization (58%) tests in the detection of antibodies in acute-phase specimens. Immunoglobulin M antibodies were detected by the IFA test in 48% (11 of 23) of these specimens. Diagnostically significant increases in IFA titer were detected in 86% (19 of 22) of the paired samples. Antibodies were detectable in some patients 7 years after infection; however, the IFA test was not as sensitive as the other two tests in the detection of previous infections.

Child↗