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Biomedical subjects

D Burke

Publications and source records attributed to D Burke.

At least 271 records · Page 15Linked to original sources
PubMed1984

Saturation in human somatosensory pathways.

The relationship between the size of an afferent volley and the size of the short-latency cerebral potential produced by the volley is not linear for purely cutaneous afferents, mixed cutaneous and muscle afferents or purely muscle afferents. The cerebral potential approaches a maximum when the responsible afferent input is 50% of maximum, while cerebral potentials of about half maximal size require an afferent volley of about one fifth of maximum. The relationship for sural (cutaneous) afferents rises less steeply. This saturation probably results from the convergence of the most rapidly conducting components in each afferent volley at sequential subcortical relay nuclei. The present data is compared with published data from animal experiments.

Afferent Pathways↗
PubMed1984

The projection of muscle afferents from the hand to cerebral cortex in man.

This study provides direct evidence that muscle afferents from the human hand project to the cerebral cortex. Electrical stimulation within a purely muscle fascicle of the median nerve at the wrist produced a cerebral potential, the latency of which (to the initial negative deflection, N1) was the same as, or shorter than, the latency with stimulation of cutaneous fascicles. The average latencies to N1 for muscle afferent and cutaneous afferent inputs were 19.0 and 20.3 ms, respectively. This difference could not be accounted for by differences in peripheral conduction velocity. The site of the maximal initial negative deflection of the cerebral potential for muscle afferents was posterior to that for cutaneous afferents. This locus for muscle afferents corresponded to that for mixed afferent inputs. Muscle afferents contribute to, and may dominate, the cerebral potential produced by stimulation of the mixed median nerve at the wrist.

Afferent Pathways↗
PubMed1984

Differentiation of Brucella ovis from Brucella abortus by gas-liquid chromatographic analysis of cellular fatty acids.

The cellular fatty acid composition of Brucella ovis and Brucella abortus strains was determined by gas-liquid chromatography. Both species were characterized by the presence of fatty acids 16:0, 17:0, 17:0 cyclopropane, 18:0, 18:1, and 19:0 cyclopropane; B. ovis also contained some 15:0. There were differences in the relative proportions of the fatty acids present, and it was possible to differentiate B. ovis from B. abortus on the basis of the absence of 15:0, lower concentrations of 17:0 and 18:1, and higher concentrations of 19:0 cyclopropane in B. abortus. The data indicate that analysis of cellular fatty acid composition by gas-liquid chromatography can be used for the identification of B. ovis and its differentiation from B. abortus.

Brucella↗
PubMed1984

Reproducibility of the visual evoked potential using a light-emitting diode stimulator.

The intersubject and intrasubject reproducibility of the VEP was evaluated using two different methods of producing pattern reversal--a mirror/projector system and a light-emitting diode (LED) system. Intersubject reproducibility was determined in 100 normal subjects (50 males, 50 females). Ten subjects were studied on ten different occasions over 11 months to establish intrasubject reproducibility. The two methods gave comparable results. It is concluded that the mirror/projector system has no advantages over the LED system, which is cheaper, more robust and more convenient. Most of the intersubject variability was found to be due to subject variables and it is concluded that technical improvements are unlikely to reduce further the variability of the test. A variability in the latency of P100 of up to 7.7 ms was recorded in the serial studies on the ten subjects, indicating that in longitudinal studies on patients, changes in latency must exceed 9-10 ms to be significant. With both stimulus systems, there were significant sex-related differences in latency (P50 and P100 but not N70) and amplitude (N70-P100). The extent of the difference was such that the upper limit of normal latency for P100 (2.5-3 SD from the mean) was 4.2-4.7 ms longer for males than females-a value which exceeds 1 SD. Separate control values for males and females are advisable whichever method is used to produce pattern reversal.

Adolescent↗
PubMed1984

Absence of somatotopic projection of muscle afferents onto motoneurons of same muscle.

During weak voluntary contractions, muscle afferents from a restricted region of the tibialis anterior of humans were activated with mechanical or electrical stimuli while electromyographic recordings (EMG) were made from pairs of motor units. One motor unit of a pair was located in the region of muscle from which the afferents arose; the other was at least 10 cm distal. The territories of the motor units of each pair did not overlap. All motor units were of low threshold, recruited at less than 5% of maximal voluntary strength. Direct recordings of muscle afferent activity, using a microelectrode in the nerve fascicle innervating the tibialis anterior, showed that taps delivered to the muscle belly activated submaximally a discrete population of receptors, restricted to the site of the taps. The spread of the disturbance set up by the taps or by vibration at 100 Hz applied to the muscle belly was measured with an accelerometer and was also found to be restricted to the site of application of the vibrator tip. With each of 12 pairs of motor units, vibration at 100 Hz was applied to the muscle near the motor unit of higher threshold for recruitment in a voluntary contraction. The vibration produced detectable reflex effects but did not alter recruitment order within any pair of motor units. During voluntary contractions involving 10 pairs of motor units, taps were applied to the muscle belly near each motor unit of a pair. The taps produced, at short latency, an increase in the probability of discharge of each motor unit. This change in probability is related to a composite excitatory postsynaptic potential (EPSP) caused by dynamically responding mechanoreceptors near the tap site and is generated through monosynaptic/oligosynaptic pathways. Taps near one motor unit of a pair did not selectively or preferentially affect the discharge of that motoneuron. During a voluntary contraction of tibialis anterior, electrical stimuli just below threshold for efferent axons, and so probably above threshold for afferent axons, were delivered singly and in brief trains through a microelectrode in a nerve fascicle innervating that muscle. Such stimulation had no detectable effect on the discharge pattern of four pairs of motor units. These findings suggest that the feedback from a few receptors in the muscle has a negligible effect on the motoneuron pool, in comparison with the total excitatory drive present during a voluntary contraction.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1984

Monosynaptic and oligosynaptic contributions to human ankle jerk and H-reflex.

Studies were undertaken in normal subjects to determine whether it is possible for oligosynaptic reflex pathways to affect motoneuron discharge in the ankle jerk and H-reflex of the soleus. It is argued that if the rising phase of the increase in excitability of the soleus motoneuron pool produced by tendon percussion or by electrical stimulation of the peripheral nerve lasts more than a few milliseconds and if the increase in excitability takes several milliseconds to reach the threshold for motoneuron discharge, these reflexes are unlikely to be exclusively monosynaptic. In relaxed subjects, changes in excitability of the soleus motoneuron pool produced by tendon percussion and by electrical stimulation of the tibial nerve were examined using conditioning stimuli just below threshold and a test H-reflex just above threshold for a reflex response. The increase in excitability due to tendon percussion had an average rise time of 10.8 ms and a total duration of approximately 25 ms. With electrical stimulation the rising phase appeared shorter, but it could not be measured accurately due to afferent refractoriness. In single motor units, the rise times of the composite excitatory postsynaptic potentials (EPSPs) set up by subthreshold tendon percussion and by subthreshold electrical stimulation of the tibial nerve were estimated from changes in the probability of discharge of voluntarily activated single motor units. Rise times were significantly longer with tendon percussion (mean +/- SD, 7.1 +/- 2.3 ms; n = 34) than with electrical stimulation (2.4 +/- 1.4 ms; n = 32). In four experiments in which a number of motor units were studied using identical mechanical and identical electrical stimuli, the poststimulus time histograms (PSTHs) for each stimulus were pooled to provide an estimate of the rise time of the excitability change in the motoneuron pool. The mean rise times of these four samples were 10.5 ms with mechanical stimulation and 4.5 ms with electrical stimulation. The spontaneous variability in latency of reflexly activated single motor units was 0.8-3.1 ms (average SD, 0.34 ms) in the tendon jerk, and 0.6-1.4 ms (average SD, 0.19 ms) in the H-reflex. Comparison of these figures with the measurements of rise time given above suggests that the composite EPSPs are larger than the background synaptic noise. With six motor units, the timing of reflex discharge in the tendon jerk when the subject was relaxed was compared with the timing of the change in probability of discharge due to apparently identical percussion when the units were activated voluntarily.(ABSTRACT TRUNCATED AT 400 WORDS)

Achilles Tendon↗
PubMed1983

Expression of the human interferon-beta gene cloned in phage M13 mp7.

The single-stranded DNA phage, M13 mp7 was used in the construction of an expression vector containing the coding sequence for mature interferon-beta (IFN-beta). Two clones expressed a fused polypeptide showing the biological and physicochemical properties of IFN-beta, despite the fact that the N-terminal amino acid sequence had been changed; 10(6) I.U./l of culture were produced with a molecular weight of 20 000.

Amino Acid Sequence↗
PubMed1983

Convergence in the somatosensory pathway between cutaneous afferents from the index and middle fingers in man.

Average short-latency cerebral potentials were recorded from the parietal scalp to mechanical stimulation of the index and middle fingers and to electrical stimulation of the digital nerves in normal subjects. The early components of the cerebral potential, representing the arrival of the afferent volley at the sensorimotor cortex, were studied during stimulation of the fingers separately and together. When strong or moderate stimuli were used there was a suppressive interaction between the afferent input from the two fingers with either electrical or mechanical stimulation. During simultaneous stimulation of both fingers the size of the early component of the cerebral potential was less than predicted by simple addition of the potentials produced by stimulation of the fingers individually. When very weak stimuli, close to the level necessary for detection by the subject, the input from the two fingers produced additive or facilitatory interactions in the early components of the cerebral potential. These results suggest that there is convergence between the afferent inputs from the index and middle fingers along the somatosensory pathway. At levels of stimulation comparable to those which produced facilitation in the electrophysiological studies, simultaneous stimulation to both fingers was detected significantly more frequently than would be expected from the detection of stimulation to individual fingers.

Adult↗
PubMed1983

HeLa cell adhesion to microcarriers in high shear conditions: evidence for membrane receptors for collagen but not laminin or fibronectin.

HeLa-S3 cells were analyzed for their ability to attach and spread on cell culture microcarriers that were made either positively or negatively charged with polymeric plastics or were coated with BSA, gelatin, fibronectin or laminin. The cells stuck to all microcarriers under low shear, i.e. low stirring conditions with similar rates of attachment. Except in the case of gelatin microcarriers where cells fully spread, cells did not or only partially spread on the others. Under high shear, cells attached with the following rates: positive = negative = gelatin = BSA greater than laminin greater than fibronectin. Cells detached from all but the gelatin and BSA coated beads. However, the cells did not fully spread on BSA beads. The observation that cells not only attached but also spread on gelatin beads indicated that gelatin could be a specific substratum adhesion protein while the other surfaces were 'non-specific'. It should be noted that neither antibodies to laminin nor fibronectin interfered with attachment to gelatin. Protein synthesis inhibitors reduced the attachment and spreading on gelatin beads under high but not low shear conditions. With low shear, attachment and spreading appeared normal. We concluded that the density of the cell surface attachment proteins was reduced by the protein synthesis inhibitors and there were not enough present to facilitate attachment under high shear. The results also indicated that protein synthesis was not essential for cell spreading. Proteolysis of the cell surface with low concentrations of trypsin abolished the attachment of cells to gelatin-coated beads. The reappearance of attachment ability took several hours and was inhibited by actinomycin-D.

Cell Adhesion↗
PubMed1983

The afferent volleys responsible for spinal proprioceptive reflexes in man.

1. To define the neural volleys responsible for the Achilles tendon jerk and the H reflex, muscle afferent activity was recorded using micro-electrodes inserted percutaneously into appropriate fascicles of the tibial nerve in the popliteal fossa.2. The response of soleus muscle afferents to tendon percussion consisted of a dispersed volley, starting 3.5-7.0 ms after percussion, increasing to a peak over 6.5-11.0 ms, and lasting 25-30 ms, depending on the strength of percussion. Electrical stimuli to the sciatic nerve at a level adequate to evoke an H reflex but subthreshold for the M wave produced a more synchronized volley, the fastest fibres of which had conduction velocities of 62-67 m/s, and the slowest 36-45 m/s.3. The wave of acceleration produced by percussion subthreshold for the ankle jerk spread along the skin at over 150 m/s. Midway between the bellies of the gastrocnemii it consisted of a damped oscillation with four to five separate phases and maximum amplitude approximately one-twentieth of that recorded on the Achilles tendon.4. With ten primary spindle endings, tendon percussion subthreshold for the ankle jerk elicited two to five spike discharges per tap, the shortest interspike intervals being 4-7 ms. Tendon percussion elicited single discharges from two Golgi tendon organs, and altered the discharge pattern of a single secondary spindle ending. The degree of dispersion of the multi-unit muscle afferent volley can be explained by the pattern of discharge of primary spindle endings.5. Percussion on the Achilles tendon evoked crisp afferent volleys in recordings from nerve fascicles innervating flexor hallucis longus, tibialis posterior, the intrinsic muscles of the foot and the skin of the foot. Electrical stimuli delivered to the tibial nerve in the popliteal fossa at a level sufficient for the H reflex of soleus produced either a volley in muscle afferents from the intrinsic muscles of the foot or a volley in cutaneous afferents from the foot.6. For comparable stimuli in the two positions, the H reflex was inhibited but the Achilles tendon jerk enhanced when the ankle was dorsiflexed from 105 degrees to 90 degrees .7. The duration of the rise times of the excitatory post-synaptic potentials (e.p.s.p.s) produced in soleus motoneurones by electrical stimulation, and by tendon percussion subthreshold for the H reflex and the ankle jerk respectively, was estimated from post-stimulus time histograms of the discharge of voluntarily activated single motor units in soleus. The mean e.p.s.p. rise times were 1.9 ms for electrical stimulation and 6.6 ms for tendon percussion. There was evidence that the duration of the electrically evoked e.p.s.p. was curtailed by an inhibitory post-synaptic potential (i.p.s.p.) of only slightly longer latency than the e.p.s.p.8. The mechanically induced and electrically induced afferent volleys are not homogeneous volleys in group I a afferents from triceps surae. The afferent volleys differ in so many respects that it is probably invalid to compare the H reflex and tendon jerk as a measure of fusimotor activity. It is suggested that neither reflex can be considered a purely monosynaptic reflex.

Achilles Tendon↗
PubMed1983

Tarsal tunnel syndrome and peripheral neuropathy in rheumatoid disease.

Thirty patients with classical or definite rheumatoid disease (RD) with foot pain and radiologically demonstrated erosions were studied electrodiagnostically to ascertain the frequency of the tarsal tunnel syndrome and peripheral neuropathy. Four patients (13.3%) had evidence of the tarsal tunnel syndrome. The electrical abnormalities were mild and unassociated with specific clinical features. Two patients (6.6%) had evidence of sensory peripheral neuropathy. There may be an appreciable frequency of clinically unsuspected tarsal tunnel syndrome in RD.

Adult↗
PubMed1983

The effect of warning and prior instruction on short-latency cerebral potentials produced by muscle afferents in man.

This study examined the effect of a warning and of prior instruction on the early components of the cerebral potential produced by stimulation of the left posterior tibial nerve at the ankle. Early components of this potential are dominated by the activity in muscle afferents from the small muscles of the foot. In 50% of presentations, the stimulus to the posterior tibial nerve was preceded by an auditory cue. In some sequences subjects were required to move toes on the left foot immediately the stimulus was detected. Although subjects responded more rapidly to shocks which were preceded by a warning there was no statistically significant effect of the warning on the amplitude or latency of the early components of the muscle afferent cerebral potential. Prior instruction to respond to the stimulus also failed to change the cerebral potentials. This study suggests that the ability to respond more rapidly to "warned" stimuli is due to events "upstream" of the sensorimotor cortex rather than to enhancement of the volley arriving at the cortex.

Afferent Pathways↗
PubMed1983

Muscle spindle discharge in response to contraction of single motor units.

1. In human subjects, microelectrode recordings were made from 25 muscle spindle afferents and two tendon organ afferents coming from muscles innervated by the peroneal nerve. 2. Stimulation at low intensity through the recording microelectrode activated efferent axons innervating motor units in close proximity to the muscle spindle or tendon organ. There was a clear alteration in the discharge of 17 afferents (15 muscle spindle, 2 tendon organ) in response to twitch contractions that involved only one, two, or three motor units. With three other afferents there was a less overt but statistically significant alteration in discharge rate by the twitch contraction of a single motor unit. 3. The sensitivity of 21 receptors (20 spindles, 1 tendon organ) to twitch contractions of anatomically close motor units was contrasted with their sensitivity to twitches of more remote motor units in the muscle. In no instance was the sensitivity to the contraction of remote motor units greater than that to the contraction of local motor units stimulated through the microelectrode; with remote stimulation many units usually had to be activated before the resulting twitch contraction altered the discharge of an afferent. 4. It is concluded that muscle spindles as well as tendon organs can play a role in monitoring the activity of motor units anatomically close to the receptor.

Adult↗