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Biomedical subjects

D G Stuart

Publications and source records attributed to D G Stuart.

At least 73 records · Page 4Linked to original sources
PubMed1983

Localization of monosynaptic Ia excitatory post-synaptic potentials in the motor nucleus of the cat biceps femoris muscle.

Evidence is presented for the existence of a localization of monosynaptic Ia excitatory post-synaptic potentials (e.p.s.p.s) in the motor nucleus of a cat hind limb muscle. Intracellular recordings from biceps femoris motoneurones were made in anaesthetized low spinal cats of the effects of stimuli to the nerve branches supplying the anterior, middle, and posterior portions of the biceps femoris muscle. Recordings were also made during stimulation of nerves to semimembranosus and semitendinosus in order to provide a means of categorizing middle biceps cells as 'extensors' (middle biceps-extensor; i.e. like anterior biceps cells) or as 'flexors' (middle biceps-flexor; like posterior biceps). Homonymous nerve-branch (i.e. from anterior, middle or posterior biceps) monosynaptic Ia e.p.s.p.s were compared within unifunctional (flexor or extensor) groups of motoneurones. In three of four comparisons (anterior biceps nerve branch onto anterior and middle biceps-extensor cells, middle biceps onto middle biceps-flexor and posterior biceps, posterior biceps onto middle biceps-flexor and posterior biceps) the anterior, middle and posterior biceps nerve branches contributed larger e.p.s.p.s to their 'own' motoneurones than to motoneurones supplying other 'compartments' of the muscle. In the fourth case, middle biceps's input appeared to have similar effects onto anterior biceps and middle biceps-extensor cells. A normalization was performed to eliminate the possibility that the differences in e.p.s.p. sizes were due to differences in cell type within the four cell groupings (i.e. differences in the number of cells supplying FF, F(int.), FR and S muscle units). This normalization confirmed that the localization in the first three comparisons was not a consequence of differences in motoneurone type and, in addition, suggested that middle biceps may indeed have greater effects on middle biceps-extensor than anterior biceps cells. In addition to the asymmetrical effects of anterior and middle biceps nerve branches onto anterior biceps and middle biceps-extensor motoneurones, it was shown that while semitendinosus and posterior biceps contributed larger e.p.s.p.s to middle biceps-flexor than to middle biceps-extensor cells, the anterior biceps nerve branch and semimembranosus nerve contributed equally to the two middle biceps groups. Analysis of cell location in the spinal cord and rostro-caudal differences in group I volley sizes gave evidence of a topographic organization of the biceps femoris motor nucleus which could contribute to the observed localization. However, localization was also evident when comparing e.p.s.p. amplitudes in pairs of neighbouring cells of different category, indicating a role for neuronal recognition factors.

Action Potentials↗
PubMed1983

Distribution of monosynaptic Ia excitatory post-synaptic potentials in the motor nucleus of the cat semitendinosus muscle.

Evidence is presented for a lack of localization of monosynaptic Ia excitatory post-synaptic potentials (e.p.s.p.s) in the motor nucleus supplying the atypical cat hind limb muscle semitendinosus, which has anatomically distinct in-series compartments. Recordings were made from dorsal root filaments containing functionally isolated Ia, spindle group II and Ib axons from the proximal and distal compartments of semitendinosus. Twitch of either of these in-series compartments resulted in accelerated discharge of Ia and spindle group II fibres in the other compartment. Ib fibres of either compartment showed an in-series response to twitch of a single compartment which was weaker than twitch of the whole muscle, a finding which was consistent with the diminished force produced by twitch of either compartment alone. In addition, intracellular recordings were made from semitendinosus motoneurones in anaesthetized low-spinal cats during electrical stimulation of the nerve branches to proximal semitendinosus and distal semitendinosus. Comparison of proximal semitendinosus and distal semitendinosus motoneurones failed to reveal any difference between the two cell groups with respect to the average Ia e.p.s.p. amplitude produced by either the proximal or distal semitendinosus nerve branch. However, e.p.s.p.s due to stimulation of distal semitendinosus were approximately 65% larger, on average, than those due to stimulation of proximal semitendinosus in either motoneurone group. Analysis of cell location along the rostro-caudal axis of the spinal cord indicated that the proximal and distal semitendinosus cell groups are largely co-extensive. Recordings of volleys in the proximal and distal semitendinosus nerve branches in response to stimulation of the L6, L7 and S1 dorsal roots showed that group I afferents from the proximal semitendinosus compartment tend to have a more rostral entry point to the spinal cord than do distal semitendinosus afferents. E.p.s.p. amplitude in either cell group due to stimulation of either nerve branch showed little dependence on cell location in the spinal cord. The results are discussed with respect to the relation between muscle function and the distribution of monosynaptic Ia connexions.

Action Potentials↗
PubMed1981

Intramuscular localization of monosynaptic Ia reflex effects in the cat biceps femoris muscle.

Intracellular recordings form biceps femoris (BF) motoneurons were made in anesthetized low spinal cats during periods of electrical stimulation of the nerve branches supplying the anterior, middle and posterior portions of the BF muscle and the nerves to semimembranosus and semitendinosus. Measurements were made of each cell's composite intrahomonymous and heteronymous monosynaptic Ia-EPSP responses to stimulation of the test nerves (branches). We have found evidence for an intramuscular localization of these monosynaptic Ia reflex effects not only when comparing responses between the two functional components of the BF muscle as is well established [6] but, in addition, when comparing responses between different parts of each functional (hip extensor and knee flexor) component as well. It is argued that both somatotopic and neuronal recognition factors may contribute to the localization of these monosynaptic reflex effects.

Animals↗
PubMed1980

A commentary on muscle unit properties in cat hindlimb muscles.

A broad survey of muscle unit properties in 14 muscles of the cat hind limb is presented which emphasizes some general features of unit properties in mammalian muscles. A more detailed analysis of muscle unit properties in three muscles of the posterior compartment of the lower leg is then presented using Burke's tetrapartite (FF, FI or F (Int.), FR, and S) unit classification scheme. Our data on the properties of motor units in cat tibialis posterior (TP) have been compared to those generated by Burke and colleagues on units in flexor digitorum longus (FDL) and medial gastrocnemius (MG). In all three muscles, twitch contraction time was distinctly slower for type S units and specific tension outputs were substantially greater for type FF units than for type S units. The innervation ratios of type FR units were slightly lower than for type S units but the specific tension of the FR units was closer to FF units than to type S units. The FF units controlled 70-74% of the cumulative force output of each muscles, indicating a substantial capacity for powerful rapid contractions of all three of these muscles despite their differences in "size," action, and force generation. Distinctive features of the three muscles included differences in the unit types' force producing capabilities and in the relative representation of "nonfatigable" type FR and S units in each muscle. In particular, TP is endowed with some unusually powerful type FF units and a high percentage (42%) of type S units. In contrast, FDL has units that develop relatively little force and an unusually high representation (56%) of type FR units. The possible relationships between these muscle features and their presumed role in posture and locomotion is discussed.

Animals↗
PubMed1980

Motor unit--muscle spindle interactions in active muscles of decerebrate cats.

Single muscle spindle afferent and motor unit EMG spike trains have been recorded simultaneously during periods of spontaneous motor activity in triceps surae muscles of decerebrate cats. The approximate time course and magnitude of the motor unit contractions were extracted from the whole muscle force record by spike-triggered averaging, and the functional interactions between motor unit contractions and spindle discharge were assessed by cross-correlating their respective spike trains. We have found that both spindle group Ia and II afferents are responsive to the contractions of single motor units in the presence of spontaneous motor activity, being strongly coupled to the activity of some motor units and indifferent to the contractions of others. Moreover, the cross-correlation analysis revealed modulation of a single motor unit's discharge pattern by the input of a single Ia afferent.

Action Potentials↗
PubMed1980

Responses of Ia and spindle group II afferents to single motor-unit contractions.

1. The responses of deefferented Ia and spindle group II afferents to electrically activated twitch contractions of randomly selected motor units of the cat tibialis posterior muscle have been studied. Each afferent was paired with from 8 to 20 of the muscle's 60 motor units, and each afferent-motor unit interaction was recorded to two muscle lengths. 2. Cross-correlation histograms were compiled for each afferent-motor unit interaction studied as well as the average twitch tension produced by the motor unit. A numerical "coupling index" was computed for the histogram distributions to quantitate the extent of mechanical coupling between the receptor and the single motor units. 3. Qualitatively, no consistent differences were noted in the responses of Ia and spindle group II afferents to single motor-unit contractions. However, Ia afferents were responsive to a higher percentage of motor units with which they were tested (89%) and, on the average, displayed a significantly larger magnitude of response (mean coupling index, 0.72 +/- 0.04 SE) than the spindle group II afferents (66% of motor units; mean coupling index, 0.51 +/- 0.03). 4. The extent to which a motor-unit contraction altered the discharge pattern of a spindle afferent was not strictly related to the amount of force generated by the unit, nor to its contraction time. 5. Muscle length exerted a strong influence on both the qualitative and quantitative features of many of the motor unit-muscle receptor interactions. 6. These results suggest that the degree of "mechanical coupling" between a receptor and a motor unit is largely dependent on anatomical arrangements and reinforce the possibility that muscle receptors generate a "sensory partitioning" of the motor-unit population within a muscle.

Animals↗
PubMed1980

Tetrapartite classification of motor units of cat tibialis posterior.

The results of this study and its precedents suggest that the tetrapartite classification scheme might have universal applicability to at least the muscle units of cat hindlimb muscles and perhaps any mammalian muscle in which fiber typing reveals the presence of FG, FI, FOG, and type SO fibers. A possible exception to this generalization involves a small (n = 18) but thoroughly examined sample of muscle units from the first deep lumbrical muscle of the cat's foot, which led Kernell et al. (30) to conclude that the FF, FR, and S classification scheme was not directly applicable to that muscle. However, histochemical fiber typing is not yet available for that muscle. Furthermore, more extensive sampling, use of a different stimulation regime in the fatigue test, and a more detailed analysis of the sag property might well reveal that the tetrapartite classification scheme is indeed appropriate for units of cat foot muscles.

Animals↗
PubMed1979

The regularity of muscle spindle discharge in man.

1. The variability of discharge of thirty-nine muscle spindle afferents from the pretibial muscles of normal human subjects was determined for spike train sequences recorded with the ankle joint fixed in 25 degrees plantar flexion, during further stretch and during graded voluntary contractions of the receptor-bearing muscle. 2. In non-contracting muscles with the ankle joint in 25 degrees plantar flexion, a sustained discharge was maintained by twenty-four of the thirty-nine endings. The mean discharge frequency for the active endings was 11.1 Hz (range 4.8--22.1 Hz), the mean coefficient of variation 0.073 (range 0.021--0.183). With further stretch, the discharge of endings maintaining frequencies below 10--12 Hz became more regular. For endings maintaining higher frequencies, changes in the coefficient of variation were small and occurred in either direction. All secondary endings maintained a highly regular discharge, but, at these frequencies, there was no statistically significant difference in the variability of primary and secondary endings. 3. It is considered that these findings are comparable to those of Matthews & Stein (1969) for de-efferented feline spindle endings, and support the view that there is no functionally effective background fusimotor drive to non-contracting muscles of normal human subjects. 4. A voluntary contraction sufficient to accelerate a spindle ending invariably decreased the regularity of its afferent discharge. During voluntary contractions, coefficients of variation up to 0.345 were recorded. However, coefficients as low as 0.1 were not uncommon, and thus the absence of fusimotor drive cannot necessarily be inferred from a regular afferent discharge pattern. 5. With contractions of different strength, the increase in the coefficient of variation did not parallel the increase in discharge frequency. It is concluded that not all fusimotor influences acting on a spindle ending are translated into variability, and that measurements of the variability of discharge do not accurately reflect the level of fusimotor drive. 6. The discharge frequency of some spindle endings decreased slightly in some contractions and this was accompanied by an increase in the variability of discharge. It is suggested that contracting extrafusal muscle fibres can modulate the discharge pattern of spindle endings and contribute to the variability of discharge during a voluntary contraction. 7. In contracting muscles the irregular fusimotor-driven spindle discharge contained a 'hidden' periodicity, but this was not as extensive as has been reported for the cat. No such periodicity could be demonstrated for spindle endings in non-contracting human muscles.

Action Potentials↗
PubMed1978

Rapid determination of bacteriological water quality by using limulus lysate.

The Limulus lysate assay was used to measure the endotoxin content in stream water and was found to reflect the degree of bacterial contamination as measured by coliform, enteric, gram-negative, and heterotrophic bacteria. The firm-clot method was found to be a less sensitive and reproducible technique for the detection of endotoxin than was the spectrophotometric modification of the Limulus lysate assay. Bound endotoxin, as determined by the spectrophotometric modification of the Limulus lysate assay, was found to be a better measure of the endotoxin associated with bacterial cells than was total endotoxin.

Journal Article↗
PubMed1978

Speed-force relations in the motor units of the cat tibialis posterior muscle.

The neuro-mechanical properties and speed-force relations of 81 cat tibialis posterior motor units have been studied. Statistically significant correlations were found between alpha-axonal conduction velocity (CV) and average twitch tension (log10 TwT; r = 0.459, p less than 0.001), between CV and twitch contraction time (CT; r = -0.395, p less than 0.001) and between CT and log10 TwT (r = -0.277, p less than 0.02). The present correlations for the intermediate-sized tibialis posterior are stronger than those previously reported for large muscles such as soleus, medial gastrocnemius, plantaris and flexor hallucis longus. However, they are considerably weaker than those reported for the much smaller lumbrical muscles of the cat's foot. These findings support the contention that the spinal mechanisms governing an orderly recruitment of motor units according to the size of their muscle units must be more complex for large than for small muscles, at least in the cat hindlimb.

Animals↗
PubMed1977

The response of Golgi tendon organs to single motor unit contractions.

1. Cross-correlation analysis has been used to quantify the responses of cat soleus tendon organs to repetitive twitch contractions of: (a) different motor units within the muscle, (b) single motor units at different muscle lengths, and (c) single motor units when the pulse-train pattern of stimulation delivered to the motor unit axon was altered. 2. Ib afferents were observed which responded to each of several hundred successive motor unit twitches with identical numbers of spikes and with relatively invariant latencies. 3. The present results show that tendon organs are sensitive to subtle alterations in motor unit twitch wave form and amplitude, and that this sensitivity is reflected in the precise timings of their afferent discharge. 4. Examination of these tendon organ responses indicates that the forces produced by single motor units couples to the receptor capsule are well above threshold. Calculations based on these results, and earlier soleus motor unit and muscle fibre data, suggest that the absolute force threshold for tendon organs may be as little as 4 mg, which is less than the estimated minimum twitch force generated by individual soleus muscle fibres. 5. Considering the number of tendon organs in a muscle, and the likelihood that every motor unit is connected with at least one receptor, the sensitivity of tendon organs ensures that every twitch of every motor unit will be reflected in the population of afferent signals projecting to the spinal cord.

Action Potentials↗
PubMed1977

Evaluation of recovery methods to detect coliforms in water.

Various recovery methods used to detect coliforms in water were evaluated by applying the membrane filter chamber technique. The membrane filter chambers, containing pure-culture suspensions of Escherichia coli or natural suspensions of raw sewage, were immersed in the stream environment. Samples were withdrawn from the chamber at regular time intervals and enumerated by several detection methods. In general, multiple-tube fermentation techniques gave better recovery than plating or membrane filtration procedures. The least efficient method of recovery resulted when using membrane filtration procedures, especially as the exposure period of the organisms to the stream environment increased. A 2-h enrichment on a rich, nonselective medium before exposure to selective media improved the recovery of fecal coliforms with membrane filtration techniques. Substantially enhanced recoveries of E. coli from pure-culture suspensions and of fecal coliforms from raw-sewage suspensions were observed when compared with recoveries obtained by direct primary exposure to selective media. Such an enrichment period appears to provide a nontoxic environment for the gradual adjustment and repair of injured cells.

Journal Article↗
PubMed1977

Membrane filter technique for the quantification of stressed fecal coliforms in the aquatic environment.

A two-layer membrane filtration (MF) medium (injury-mitigating MF [IM-MF]) and a procedure for the enumeration of injured fecal coliforms are described. These procedures included the addition of glycerol and acetate plus reducing agents to both layers of a two-layer medium and rinsing of the filter with a rich resuscitation medium. Some changes in incubation time and temperatures were used. This method was compared with the multiple-tube fermentation most-probable-number procedure and the one-step M-FC agar-membrane filter method (direct M-FC) in terms of fecal coliform recovery from various aquatic environments that cause bacterial injury. With chlorinated sewage effluents, results of the IM-MF technique were equal to or greater than the most probable number in 9 of 18 trials and were 1.3 to 19 times greater than the M-FC method. When sewage samples were chlorinated in the laboratory, fecal coliform counts with IM-MF equaled or exceeded the most probable number in 7 of 15 trials and always exceeded the M-FC. M-FC was exceeded by IM-MF in 30 of 33 trials with clean mountain stream water. Fecal coliform bacteria that were exposed to low levels of an iodophore in the laboratory produced IM-MF counts 3 to 10 times greater than those with M-FC. A biochemical rationale for the formation of the IM-MF medium is discussed.

Bacteriological Techniques↗