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D Gardner

Publications and source records attributed to D Gardner.

At least 91 records · Page 5Linked to original sources
PubMed1980

Rate-limiting step of inhibitory post-synaptic current decay in Aplysia buccal ganglia.

1. In neurones BL and BR 3, 6, 8, 9, 10 and 11 of Aplysia buccal ganglia, cholinergic inhibitory post-synaptic potentials are produced by activity in either of two presynaptic cells. In order to analyse the synaptic conductance change, neurones were voltage-clamped inhibitory post-synaptic currents (i.p.s.c.) recorded. 2. The synaptic conductance change rises to an average peak value of 0.65 micromho and decays exponentially with single time constant tau of 19 msec. 3. We have attempted to identify the rate-limiting step responsible for i.p.s.c. decay from among the following possibilities: (1) acetylcholine (ACh) supply, (2) ACh removal by diffusion, (3) ACh removal by hydrolysis or (4) a slow unbinding or conformational change closing open synaptic current channels. 4. Cooling prolongs tau, with Q10 of 5.2. Cooling and eserine treatment together produce greatly prolonged, exponentially decaying i.p.s.c.s with tau > 150 msec. These results suggest that ACh removal, either by diffusion or hydrolysis, is not the rate-limiting step. 5. Prolonging synaptic action potential time course with intracellular injection of tetraethylammonium broadens the i.p.s.c. peak but does not affect the decay tail, suggesting that the rate-limiting step is not ACh release. 6. The spectrum of ACh-induced current fluctuations is fitted by a double Lorentzian with cut-off frequencies of 7.8 and 47 Hz. The frequency of the slower component corresponds to the macroscopic i.p.s.c. decay tau. 7. We conclude that a slow conformational change closing open synaptic current channels is likely to determine i.p.s.c. decay. We cannot, however, exclude either delayed diffusion or a late tail of slow ACh release as possibilities.

Acetylcholine↗
PubMed1980

Membrane-potential effects on an inhibitory post-synaptic conductance in Aplysia buccal ganglia.

1. Inhibitory post-synaptic currents (i.p.s.c.s) were recorded under voltage clamp using two electrodes placed in neuronal somas of the buccal ganglia of Aplysia, in order to study the effects of membrane potential (Vm) on decay time constant (tau). 2. From -175 to -40 mV, tau did not vary with Vm. At Vm more depolarized than -40 mV, tau decreased. Also at depolarized Vm, cell input resistance (Rin) decreased and many cells showed non-exponential i.p.s.c. decay, including undershoot. These results suggest that the apparently faster tau is an artifact of remote membrane poorly clamped at the low Rin of depolarized levels, rather than a Vm-dependent i.p.s.c. relaxation. 3. Injected current pulses produced voltage relaxations which decayed faster including undershoot, when Vm was depolarized beyond -40 mV. 4. Step commands across the reversal potential were delivered during i.p.s.c.s. Currents reversed direction, relaxing consistent with the new Vm, thus showing that recorded current decay repressants the true time course of i.p.s.c. relaxation, rather than uncontrolled slow axonal charging from a fast remote synaptic current. 5. I conclude that clamp control is poor at depolarized Vm, due to decreased Rin, and the faster, non-exponential decay seen includes a superimposed nonsynaptic current. Tetraethylammonium injected into the presynaptic neurone produces only slight effect on the i.p.s.c. decay time constant, suggesting that the non-synaptic current is unlikely to be due to a voltage-dependent K conductance.

Animals↗
PubMed1980

Time integral of synaptic conductance.

1. Inhibitory post-synaptic currents (i.p.s.c.s) were recorded under voltage clamp from neurones of Aplysia buccal ganglia. 2. The synaptic charge, Q, transferred by each i.p.s.c. was calculated as the time integral of the synaptic current, approximated by numerical integration. For typical i.p.s.c.s recorded at or near resting potential, Q = -100 to -500 pC. The majority of the charge is transferred during the interval between the peak and a time one time constant later. 3. In order to characterize an alternative measurement of synaptic efficacy, the slope of the Q vs. membrane potential curve was calculated and defined as the time integral of conductance, b. Values of b ranged from 2.6 to 51 pC/mV, averaging 14 pC/mV. For i.p.s.c.s recorded in thirty-one cells at room temperature, b was well correlated with Gpeak, the peak synaptic conductance (r = 0.86). 4. In most synapses, the time integral of conductance, which incorporates both amplitude and duration, may be a more revealing measure of synaptic efficacy than peak conductance. 5. Size of synaptic response was determined as a function of temperature, T. While Gpeak decreases with decreasing temperature over the range 9-22 degrees C, b peaks at 12-18 degrees C and decreases at higher and lower values of T. The data permit the speculation that lengthening average channel lifetime, and therefore time constant of decay, with decreasing temperature, may have adaptive significance in maintaining synaptic efficacy.

Animals↗
PubMed1980

The family meeting in critical care settings.

A routine, carefully planned meeting with families of patients in a trauma unit or critical care setting can improve coping and enhance patient care. Even though staffs in intensive care units realize that families may profoundly influence a patient's psychologic state, or may themselves be severely stressed, few units systematically address the needs of families in crisis. Common needs of families of acutely injured patients are the need to be with the patient, to learn about his condition, to feel useful, to express feeling about the situation, and to obtain emotional support. Besides addressing these needs, a family meeting can reduce family turmoil, help dispel family-staff conflict, and provide a format for educating staff about psychologic responses to life-threatening illness. The experience with eight patients in an ICU is described, and guidelines given for family meetings. Factors assuring a successful family meeting include careful attention to leadership, timing, communication, and clear priorities.

Adolescent↗
PubMed1979

Continuing education: an attitudinal survey of physical therapists.

A descriptive study of 903 physical therapists located primarily in southeastern United States was undertaken to determine their attitudes toward continuing education and the types of course offerings they desired. A majority of physical therapists kept themselves up-to-date in professional practice, mainly through discussion with colleagues, study groups, and inservice training sessions. The continuing education courses they preferred were comparatively recent topics in physical therapy education--such as musculoskeletal assessment and mobilization--specific neurophysiological approaches to treatment of adults and children, and administration. The study also revealed the preferred schedule, length, type, and cost of continuing education courses, as well as the amount of advance notice preferred and willingness to complete preassigned readings. The main problem that respondents had in participating in continuing education was that courses did not fit into their schedules. A majority of respondents favored mandatory continuing education for relicensure.

Attitude↗
PubMed1978

[Method of studying the functional state of pulmonary alveolar macrophages during exposure to atmospheric pollutants].

On the basis of experimental research results a method to assess the functional state of pulmonary alveolar macrophages in rabbits and rats has been proposed as a criterion of the biological effect of chemical atmospheric pollutants. The test involves a cytological assay, determination of the viable cells quantity and of the phagocytic competence, and also the biochemical study of alveolar macrophages enzymes activity (acid phosphatase, beta-glucuronidase, lysozyme, beta-galactosidase, beta-glucosidase, N-acetyl-beta-D-glucosaminidase). It has been shown that this method is informative and reliably reproducible, and that it was reasonable to use it in environmental health and other branches of experimental biology and medicine.

Acid Phosphatase↗
PubMed1977

The absorption of protons with alpha-methyl glucoside and alpha-thioethyl glucoside by the yeast N.C.Y.C. 240. Evidence against the phosphorylation hypothesis.

1. When yeast N.C.Y.C. 240 was grown with maltose in a complex medium based on yeast extract and peptone, washed cell preparations fermented alpha-methyl glucoside much more slowly than maltose. 2. The yeast absorbed alpha-methyl[14C]glucoside from a 10mM solution in the presence of antimycin and iodoacetamide, producing [14C]glucose, which accumulated outside the cells. The yeast itself contained hexose phosphates, trehalose, alpha-methyl glucoside and other products labelled with 14C, but no alpha-methyl glucoside phosphate. 3. About 1 equiv. of protons was absorbed with each equivalent of alpha-methylglucoside, and 1 equiv. of K+ ions left the yeast. 4. alpha-Thioethyl glucoside was also absorbed along with protons. Studies by g.l.c. showed that the yeast concentrated the compound without metabolizing it. 5. The presence of trehalose, sucrose, maltose, L-sorbose, glucose or alpha-phenyl glucoside in each case immediately stimulated proton uptake, whereas fructose, 3-O-methylglucose and 2-deoxyglucose failed to do so. 6. The observations support the conclusion that alpha-thioethyl glucoside, alpha-methyl glucoside and maltose are substrates of one or more proton symports, whereas they seem inconsistent with the notion that the absorption of alpha-methyl glucoside involves the phosphorylation of the carbohydrate [Van Stevenick (1970) Biochim. Biophys. Acta 203, 376-384].

Carbohydrate Metabolism↗
PubMed1977

Voltage-clamp analysis of a self-inhibitory synaptic potential in the buccal ganglia of Aplysia.

1. In cholinergic neurones BL4, BL5, BR4, and BR5 of Aplysia buccal ganglia, each action potential is followed, in the same cell, by a curare- and high-Mg-sensitive hyperpolarizing after-potential which is enhanced by Ca. 2. In voltage-clamped neurons, substracting currents recorded in curare from currents recorded in sea water reveals that this potential is due to curare-sensitive currents which rise to a peak, then decay exponentially with an apparently voltage-independent time constant of 43 msec. Currents are produced by a voltage-independent, Ca-enhanced, conductance change with a 0-26 mumho peak and a -64 mV reversal potential. The curare-sensitive conductance is also sensitive to high Mg. 3. Both after-potential and curare- or Mg-sensitive current follow each action potential without failures, even in threshold-raising 80 mM-Ca-144-mM-Mg solutions. 4. Both after-potential and current decrease with repetitive firing or short inter-spike interval, possibly due to receptor desensitization. 5. The Mg- and curare-sensitive conductance is also blocked by 1 mM-ACh. 6. The data are consistent with the hypothesis that the hyperpolarization following action potentials in each of these four neurones is produced by a self-inhibitory synaptic mechanism.

Action Potentials↗
PubMed1977

Physiological and kinetic properties of cholinergic receptors activated by multiaction interneurons in buccal ganglia of Aplysia.

1. Neurons of Aplysia buccal ganglia contain three types of acetylcholine (ACh) receptors, each of which has been characterized by its sensitivity to inhibitors and kinetics of desensitization and by the properties of the conductance change it controls, including reversal potential, major ion, and functional consequence. The receptors are classified as depolarizing, slowly decrementing hyperpolarizing, and rapidly decrementing hyperpolarizing. Identified neurons are innervated by identified cholinergic multiaction interneurons; the form of the postsynaptic potential produced depends on the number and class of receptor found on each cell. 2. Interneuronal action potentials produce monosynaptic IPSPs by activating slowly decrementing hyperpolarizing receptors on seven cells in each ganglion. The IPSP reversal potential of 75 mV is shifted 42 mV in a depolarizing direction in Cl = free seawater. The ACh response has a reversal potential identical to that of the PSP; the PSP is blocked by 10(-4) g/ml curare but unaffected by hexamethonium. Interneuronal action potentials also produce monosynaptic EPSPs with a -14 mV extrapolated reversal potential by activating depolarizing receptors on one cell in each ganglion. This PSP is blocked by 10(-4) g/ml hexamethonium and mimicked by a Na-dependent ACh response. 3. Each interneuronal action potential also produces a diphasic depolarizing-hyperpolarizing synaptic potential in one cell in each ganglion as a result of released ACh acting on two classes of postsynaptic receptor on the same cell. One of these receptors is depolarizing; the other is a rapidly decrementing hyperpolarizing receptor. The two differ in their sensitivity to inhibitors, and the conductance changes they produce differ in their reversal potential, duration, and functional consequences. Both components can be mimicked by iontophoretic application of ACh. 4. Although the hyperpolarizing receptors on the inhibitory and diphasic follower cells have similar sensitivity to inhibitors and control similar conductance changes, they differ in their kinetics of desensitization. The hyperpolarizing receptor on the diphasic cell shows marked decrement to repeated presynaptic action potentials and to repeated iontophoretic application of ACh. This decrement is greater than that seen in either the hyperpolarizing receptor on the inhibitory follower cell or the depolarizing receptor on the dual follower cell. The shape of the PSP in the diphasic follower and its effect on firing of the cell are thus functions of both membrane potential and the degree of desensitization of the receptor. 5. Rate of desensitization is, therefore, an additional criterion for characterizing otherwise similar receptors for neurotransmitters.

Acetylcholine↗
PubMed1977

Interconnections of identified multiaction interneurons in buccal ganglia of Aplysia.

1. The 26 identified neurons of Aplysia buccal ganglia include 4 interneurons and their follower cells. Each interneuron makes cholinergic synaptic connections on eight identified ipsilateral follower neurons. Each interneuronal action potential also produces a zero-latency, Mg-intensitive electrotonic coupling potential in one cholinergic and electrotonic input from the interneurons. Electrotonic connections are bidirectional and nonrectifying. 2. Ipsilateral pairs of interneurons receive extensive common synaptic input from several unidentified neurons: each interneuron also receives some input not received by the other. These pairs are linked by bidirectional nonrectifying electronic coupling which is insensitive to high Mg. As a consequence of this organization, ipsilateral interneuron pairs can fire a) independently, or b) synchronously, or c) one active interneuron can depolarize the other. 3. Each follower receiving synaptic input from one ipsilateral interneuron also receives similar input from the other interneuron. Common follower cells thus receive a) asynchronous PSPs, or b) large summated PSPs, or c) an increased number of PSPs from each interneuron. The latter two modes constitute feed-forward summation of interneuronal action. 4. Interneuronal output is confined to ipsilateral neurons. Symmetric pairs of interneurons are coordinated by common inputs and are not directly interconnected by either chemical or electrotonic synapses. Synchrony of firing of symmetric pairs is, therefore, looser than that of ipsilateral pairs.

Action Potentials↗