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Biomedical subjects

C A Colton

Publications and source records attributed to C A Colton.

48 records · Page 3Linked to original sources
PubMed1986

The action of oxygen and oxygen at high pressure on inhibitory transmission.

The effect of 100% oxygen at ambient pressure, 100% oxygen at 1.7 Atmospheres Absolute (ATA), 100% oxygen at 5.1 ATA, helium at 1.7 ATA and helium at 5.1 ATA on inhibitory synaptic transmission was studied using the lobster walking leg neuromuscular preparation. Exposure to 100% oxygen at ambient pressure, at 1.7 ATA or at 5.1 ATA produced a decrease in inhibitory transmission manifest as a fall in inhibitory synaptic conductance (Ginh). The largest decrease in Ginh was seen in 100% oxygen at ambient pressure, while a progressively smaller decrease was seen in 100% oxygen at 1.7 ATA and 5.1 ATA, respectively. Also associated with 100% oxygen at ambient pressure was the disappearance of inhibitory junction potentials. Pressurization with helium produced a fall in Ginh at 5.1 ATA but no change or a slight increase at 1.7 ATA. The action of either 100% oxygen at ambient and at 1.7 or 5.1 ATA or helium at 1.7 or 5.1 ATA was shown to be on presynaptic parameters since the percent decrease in Ro induced by exogenous application of gamma-aminobutyric acid (GABA), the inhibitory transmitter, was the same in either 100% oxygen at ambient pressure, 100% oxygen or helium at 1.7 ATA and 5.1 ATA. The similarity in action of oxygen to the action of isoniazid, a known glutamic acid decarboxylase (the enzyme that catalyzes the production of GABA) inhibitor in the same preparation suggests that one possible site of oxygen action is on GABA production.

Animals↗
PubMed1986

Changes in synaptic transmission produced by hydrogen peroxide.

The effect of hydrogen peroxide (H2O2) on excitatory and inhibitory synaptic transmission was studied at the lobster neuromuscular junction. H2O2 produced a dose dependent decrease in the amplitude of the junction potential (Vejp). This decrease was due to changes in both presynaptic transmitter release and the postsynaptic response to the neurotransmitter. Observed presynaptic changes due to exposure to H2O2 were a decrease in the amount of transmitter released, that is, quantal content, as well as a decrease in the fast facilitation, that is, the amplitude increase of successive excitatory junction potentials at a rate of 3 Hz. To discern postsynaptic changes, glutamate, the putative excitatory neurotransmitter for this preparation was applied directly to the bathing medium in order to bypass the presynaptic release process. H2O2 produced a decreased response of the glutamate receptor/ionophore. The action of H2O2 was not selective to excitatory (glutamate-mediated) transmission because inhibitory (GABA-mediated) transmission was also depressed by H2O2. This effect was primarily presynaptic since H2O2 produced no change in the postsynaptic response to applied GABA.

Animals↗
PubMed1985

Blockade of hyperbaric oxygen induced seizures by excitatory amino acid antagonists.

The effectiveness of several excitatory amino acid antagonists to delay or block seizures induced by oxygen at high pressure was examined in mice. Of the antagonists tested, namely, L-proline, DL-alpha-aminoadipate, DL-2-amino-5-phosphonovalerate, and L-glutamic acid diethyl ester, DL-2-amino-5-phosphonovalerate was the most effective in delaying or preventing seizures. L-Glutamic acid diethylester was also effective but at significantly higher doses, which were also associated with marked sedation.

2-Amino-5-phosphonovalerate↗
PubMed1982

An electrophysiological analysis of oxygen and pressure on synaptic transmission.

The effect of oxygen at high pressure (OHP), helium at 150 PSIG and 100% oxygen at ambient pressure on excitatory synaptic transmission was studied using the lobster walking leg neuromuscular preparation. Both 100% oxygen at 150 PSIG (7135 mm Hg oxygen) and helium at 150 PSIG (7000 mm Hg helium plus 135 mm Hg oxygen) produced a significant decrease in the amplitude of the junction potential (Vejp). The decrease in Vejp induced by OHP, however, was greater than with pressure alone. OHP also produced a significant decrease in short term facilitation. Exposure to 100% oxygen at ambient pressure produced a transient increase in Vejp and a large increase in frequency of miniature junction potentials. In each case the change in Vejp was due to changes in presynaptic release of transmitter since quantal content per fiber (M') was shown to decrease for OHP and helium at 150 PSIG and to transiently rise with 100% oxygen at ambient pressure. In addition, the response to exogenously applied glutamate (the putative neurotransmitter) was not affected by OHP, 150 PSIG helium or 100% oxygen at ambient pressure. This further indicates a presynaptic site of action.

Action Potentials↗
PubMed1982

Effects of a thioreactive agent, diamide, on neuromuscular transmission in lobster.

Diamide[diazine-dicarboxylic acid-bis(dimethylamide)], a thiol-oxidizing agent, has both pre- and postsynaptic actions on the glutaminergic neuromuscular junction of the lobster walking leg. Postsynaptically, diamide produced an increase in the response to exogenously applied glutamate, whereas the effect of diamide on presynaptic transmitter release involved two major changes: 1) a decrease in excitatory junction potential amplitude and 2) an increase in miniature junction potential frequency. Short-term facilitation also decreased. Equilibration with 1,4-dithiothreitol (a sulfhydryl-reducing agent) reversed the decline in excitatory junction potential frequency, and the fall in short-term facilitation. The miniature junction potential frequency increase induced by diamide was independent of external Ca2+, as diamide in a Ca2+-free solution produced a similar response to that in a Ca2+-containing solution. We propose that the action of diamide on transmitter release is similar to the action of polyvalent cations, i.e., diamide has two sites of action, a blockade of inward Ca2+ flux and an increased release of Ca2+ inside the terminal.

Action Potentials↗
PubMed1979

Evaluation of a life support module used for air transport of critically ill infants.

To accomplish the safe transport of ill newborns, various infant transport systems have been developed. One such unit, produced by Airborne Life Support Systems, has been tested by the authors. The parameters used to evaluate the system were: (1) temperature stability at 2 degrees C and -28 degrees C ambient; (2) rate of internal temperature fall-off when all power to the unit was interrupted; (3) degree of CO2 accumulation, and (4) internal sound levels. Without heat shield, temperature decrease at 2 degrees C ambient was 12 degrees C/h; with head shield, 2 degrees C/h for the first hour and 0.9 degrees C in the second hour. At -28 degrees C ambient, temperature decrease was 6.1 and 2.2 degrees C/h for the first and second hour, respectively. The rate of temperature fall-off was 15.6 degrees C in 45 min. Average CO2 accumulation was 0.24% after 2 h. Sound level for heater and fan was 16.5 dB. An additional 1 dB of noise was contributed to the system when air and oxygen were turned on.

Aircraft↗
PubMed1978

Effect of oxygen at high pressure on spontaneous transmitter release.

The effect of oxygen at high pressure (OHP) on resting membrane properties (effective membrane resistance (Reff) and membrane potential (Vm)) and the spontaneous release of excitatory transmitter were examined at the lobster neuromuscular junction. Pressurization with 100% oxygen to 150 pounds per square inch gauge pressure (psig) or with nitrogen to 150 psig (7,000 mmHg nitrogen and 135 mmHg oxygen) produced a decrease in Reff associated with a hyperpolarization of Vm. These changes, however, returned to control values within 20--30 min after completion of pressurization. Spontaneous release of excitatory transmitter was shown to increase dramatically in the presence of 100% oxygen at 150 psig. The increase in miniature end-plate potential (MEPP) frequency persisted beyond the transient changes seen with Reff and Vm. This effect was selective to oxygen, as pressurization with nitrogen did not produce an increase in MEPP frequency. No change in average MEPP amplitude was seen with either OHP or pressure alone. An OHP-induced increase in MEPP frequency was also seen at the frog neuromuscular junction. The results indicate that both glutamate-mediated and acetylcholine-mediated synaptic transmission are altered by OHP.

Animals↗
PubMed1977

Depression of glutamate-mediated synaptic transmission by benzyl alcohol.

The data obtained from this study suggest that the nonionizable anesthetic benzyl alcohol has two prominent actions on GABA- and glutamate-mediated synaptic transmission at the lobster neuromuscular junction. They are as follows: (1) depression of the excitatory end-plate potential and the postsynaptic membrane response to applied glutamate, and (2) a hyperpolarization of the postsynaptic resting membrane potential associated with a decrease in effective membrane resistance. No change in amplitude of the inhibitory end-plate potential or inhibitory reversal potential was seen. Excitatory miniature end-plate potential frequency was also unaffected. The depression of excitatory synaptic transmission appears to be due to a decreased responsiveness of the postsynaptic receptor-ionophore complex.

Action Potentials↗
PubMed1976

Aminopyridines and sparteine as inhibitors of membrane potassium conductance: effects on Myxicola giant axons and the lobster neuromuscular junction.

The effects of the compounds 2-, 3- and 4-aminopyridine and sparteine on membrane conductance changes were examined using both voltage-clamped Myxicola axons and the lobster neuromuscular junction. In Myxicola axons, the aminopyridines very specifically inhibited the potassium conductance when applied at concentrations of 0.1 mM to 5 mM without any apparent effect of resting membrane potential. Concentrations in excess of 5 mM were needed to inhibit noticeably the sodium conductance. Potassium conductance-voltage curves were shifted in the depolarized direction along the voltage axis with no significant change in shape. There were only minor changes in the kinetics of potassium activation. In high potassium solutions, both inward and outward potassium currents were equally sensitive to the aminopyridines. Sparteine was, in general, found to be a more potent, but somewhat less specific, inhibitor of the potassium conductance. In contrast to the aminopyridines, sparteine was more effective when applied at basic pH and in addition tended to produce a noticeable degree of potassium inactivation. When applied to the lobster neuromuscular junction, 2-aminopyridine and sparteine dramatically increased the amplitude of both excitatory and inhibitory postjunctional potentials, with little or no change in resting potential, resting input conductance, reversal potential, or miniature end plate potential amplitude or frequency. Quantal content per fiber was increased by approximately a factor of 3 for the excitatory responses.

Animals↗
PubMed1976

Oxygen microelectrode response to oxygen pressures up to 15 ATA.

Polarographic measurements of oxygen at high pressures were made at 21-22 degrees C with open-type Wood's metal microelectrodes with tip diameter about 5 mu. Although the sensitivity of the individual electrodes ranged from 3.1 x 10(-10) to 8.8 x 10(-12) amps/mm Hg of O2, the oxygen current was always a straight line function of Po2 from 21% O2 at ambient pressure (Po2 = 160 mm Hg) to 100% O2 at 200 psig (Po2 = 11,102 mm Hg). Compression to 200 psig with 100% nitrogen produced no significant change in microelectrode current, showing that the microelectrodes are insensitive to pressure alone.

Microelectrodes↗