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D G Stuart

Publications and source records attributed to D G Stuart.

116 records · Page 7Linked to original sources
PubMedDate not supplied

Electrophysiological and morphological properties of neurons in the ventral horn of the turtle spinal cord.

In this report, we present recent findings on the electrophysiological and morphological properties of spinal motoneurons (MNs) and interneurons (INs) of the adult turtle which were studied in slices of the spinal cord. The range of values for the measured electrophysiological parameters in 96 tested cells included: resting potential, -57 to -83 mV; input resistance, 2.5-344 M omega; time constant, 2.5-63 ms; rheobase current, 0.04-5.3 nA; after-hyperpolarization (AHP) duration, 72-426 ms; AHP half-decay time; 11-212 ms; and, slope of the stimulus current-spike frequency relationship, 3.4-235 Hz/nA. For another 20 cells, we made both morphological and electrophysiological measurements (the latter values within the above ranges). Their ranges in morphological properties included: soma diameter, 20-54 microm; soma surface area, 299-2045 microm2; soma volume, 2.3-45 microm3 x 10(4); rostro-caudal dendritic projection distance, 150-1200 microm; and, sum of dendritic lengths, 1.5-16 microm x 10(3). The emphasized findings include: 1) the quality and robustness of the intracellular recordings, which enabled accurate measurement of the action potential's shape parameters (spike, afterhyperpolarization [AHP]); 2) the substantial AHP of the INs' AP; 3) no single action-potential shape parameter (nor combination of parameters) being cardinal for its (or their combined) changes matching the profile of the initial and later phases of spike-frequency adaptation; 4) the utility and flexibility of a cluster analysis (using varying combinations of passive, transitional and active cell properties) for providing a provisional classification of low (like cat S) and high (like cat F) threshold MNs, and groups of INs with non-spontaneous versus spontaneous discharge; 5) the clear-cut morphological confirmation of the provisional classification strategy; 6) the basis for testing the possibility that one of the provisionally classified MN types innervates non-twitch muscle fibers; and 7) the heuristic value of comparing the properties of MNs versus INs across vertebrate species, with an emphasis on the lamprey, turtle, and cat.

Action Potentials↗
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Associations between force and fatigue in fast-twitch motor units of a cat hindlimb muscle.

Associations were quantified between the control force and fatigue-induced force decline in 22 single fast-twitch-fatigable motor units of 5 deeply anesthetized adult cats. The units were subjected to intermittent stimulation at 1 train/s for 360 s. Two stimulation patterns were delivered in a pseudo-random manner. The first was a 500-ms train with constant interpulse intervals. The second pattern had the same number of stimuli, mean stimulus rate, and stimulus duration, but the stimulus pulses were rearranged to increase the force produced by the units in the control (prefatigue) state. The associations among the control peak tetanic force of these units, 3 indices of fatigue, and total cumulative force during fatiguing contractions were dependent, in part, on the stimulation pattern used to produce fatigue. The associations were also dependent, albeit to a lesser extent, on the force measure (peak vs. integrated) and the fatigue index used to quantify fatigue. It is proposed that during high-force fatiguing contractions, neural mechanisms are potentially available to delay and reduce the fatigue of fast-twitch-fatigable units for brief, but functionally relevant, periods. In contrast, the fatigue of slow-twitch fatigue-resistant units seems more likely to be controlled largely, if not exclusively, by metabolic processes within their muscle cells.

Animals↗
PubMedDate not supplied

The research career of Richard B. Stein (1940-).

This report reviews the research and mentoring career of Richard B. Stein (1940-). In 1962, he completed a B.S. degree in physics at the Massachusetts Institute of Technology, USA, and thereafter an M.A. (1964), Ph.D. (1966), and postdoctoral training (1966-68) at the University of Oxford, UK. He subsequently assumed a faculty position at the University of Alberta (Canada), where he is currently an active researcher and mentor. To this point in 2004, Stein has trained and collaborated closely with over 160 scientists, largely neuroscientists and biomedical engineers, from 27 countries. He and his former trainees and collaborators have made important contributions on topics that span the cellular-to-behavioral spectrum of movement and rehabilitation-prosthetics neuroscience. His mentors, trainees, and collaborators include scientists whose countries of origin are: Australia, 2; Austria, 1; Belgium, 1; Bulgaria, 1; Canada, 64; China, 6; Denmark, 1; Germany, 1; Great Britain, 16; Hong Kong, 4; India, 5; Iraq, 2; Italy, 2; Japan, 10; Kenya, 1; New Zealand, 4; Pakistan, 1; Palestine, 1; Poland, 1; Romania, 1; South Africa, 1; Sri Lanka, 1; The Netherlands, 1; Turkey, 1; Uruguay, 1; USA, 21; and Yugoslavia, 6. In all instances, Stein's research collaborations and mentoring have advanced the careers of his trainees and junior collaborators, a well-deserved and important compliment to a stellar movement neuroscientist.

Animals↗
PubMedDate not supplied

Electromyographic responses of mammalian motor units to a fatigue test.

Evidence is presented that marked changes in the electromyographic (EMG) activity of single motor units often occur during a fatigue-test paradigm (12) widely used for the classification of mammalian motor units into fast-fatigable (FF), fast-intermediate-fatigable, fast-fatigue-resistant and slow categories (11), particularly in type FF units. Force output and EMG activity were measured in single motor units of the tibialis posterior muscle of anasthetized cats, while each unit was subjected to a fatigue test consisting of 4 min of motor-axon stimulation, using 1 Hz 330 ms trains of 0.1 ms shocks at 40 Hz. As a measure of the temporal characteristics of the EMG waveform, the reciprocal of the interval between first positive and subsequent negative peak was measured. For parameters of EMG magnitude, peak-to-peak amplitude and area were measured. The fatigue test was shown to produce, on average, significantly greater alterations in the values of the EMG parameters of FF units than of the other unit types. There were no significant EMG alterations among the other unit types. The results are discussed in relation to the interpretation of EMG depression as an indication of excitation failure and the relative fatigability and EMG depression of different motor unit types.

Animals↗