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Biomedical subjects

O C Lippold

Publications and source records attributed to O C Lippold.

At least 19 recordsLinked to original sources
PubMed1987

Contralateral intramuscular acupuncture-like electrical stimulation differentially changes the short-latency responses to muscle stretch.

Measurements were made from the human first dorsal interosseous and extensor digitorum communis muscles of the surface electromyographic activity reflexly produced by brief stretch of the muscle. For the first dorsal interosseous muscle, reflex EMG activity was also produced by electrical stimulation of the ulnar nerve at the wrist. The procedures were carried out before, during, and after 25 min of nonspecific, low-frequency electrical stimulation to the contralateral arm delivered through intramuscular electrodes. Control stimulation was delivered subcutaneously. The EMG recorded during a maintained contraction was rectified, filtered, and averaged. Two reflex components (M1 and M2) of the EMG response to muscle stretch or ulnar nerve stimulation were investigated. During nonspecific intramuscular stimulation to the contralateral arm, M1 responses of the extensor digitorum communis were depressed, initially by 37%. The effect began to fade during stimulation but extended beyond it. Reflex responses were elicited alternately by brief stretch of the first dorsal interosseus muscle and by electrical stimulation of the ulnar nerve in the same experiment. Nonspecific intramuscular stimulation to the contralateral arm depressed the M1 response to stretch, but had no effect on the M1 response to electrical stimulation. It is concluded that nonspecific intramuscular electrical stimulation reduces the amplitude of the M1 component of the response to brief stretch of contralateral muscle, either through depression of fusimotor activity or inhibition of oligosynaptic pathways that contribute to the early reflex response.

Acupuncture Therapy↗
PubMed1986

Long-term potentiation and depression in hippocampal slices.

Antidromic stimulation of hippocampal CA 1 cells, in the presence of Mg2+ to eliminate synaptic transmission and with a pattern of impulses which when applied via a synaptic pathway produced long-term potentiation, was found to decrease the response of the CA 1 cells to subsequent synaptic activation. It was found that stimulation via synapses with the same pattern of stimuli caused long-term potentiation in normal conditions but not in the presence of 25 mM Mg2+.

Animals↗
PubMed1986

Reflex origin for the slowing of motoneurone firing rates in fatigue of human voluntary contractions.

During fatigue from a sustained maximal voluntary contraction (m.v.c.) the mean motoneurone discharge rates decline. In the present experiments we found no recovery of firing rates after 3 min of rest if the fatigued muscle was kept ischaemic, but near full recovery 3 min after the blood supply was restored. Since 3 min is thus sufficient time for recovery of any central changes in excitability, the results support the hypothesis that, during fatigue, motoneurone firing rates may be regulated by a peripheral reflex originating in response to fatigue-induced changes within the muscle.

Biomechanical Phenomena↗
PubMed1985

Intramuscular acupuncture-like electrical stimulation inhibits stretch reflexes in contralateral finger extensor muscles.

Electro-acupuncture is one of many physical measures used to relieve musculoskeletal pain and to improve the associated restricted range of motion. Experiments were designed to determine whether or not acupuncture-like stimulation inhibits stretch reflexes in an arm extensor muscle in human volunteers. Surface electromyographic recordings were made on the right extensor digitorum communis muscle and averaging techniques were used to study the reflex responses to brief deflection of the finger with a solenoid-driven probe. The ratio M1:M2 of two components of the reflex was reduced during continuous acupuncture-like stimulation of the contralateral first dorsal interosseus and extensor digitorum communis muscles near their motor points (acupuncture points LI 4 and LI 11). Concomitant changes in skin temperature were observed on the forehead and in the arm in which acupuncture-like stimulation was used. In control experiments, when the acupuncture needles were inserted subcutaneously and stimulated with the same current parameters at distinctly uncomfortable intensities, no change in the reflexes occurred. These findings show that acupuncture-like stimulation exerts physiologic effects on the central nervous system, mediated presumably by muscle afferent fibers. The effects may be relevant to relief of muscle spasm and musculoskeletal pain, and restoration of mobility.

Arm↗
PubMed1985

Long-latency spinal reflexes in humans.

Stretching human muscles with a mechanical device gave rise to multiple peaks in the rectified and averaged electromyogram. In the first dorsal interosseous the latency of the first peak (M1) was 32.4 +/- 2.4 ms (SD) and the latency of the second peak (M2) was 55.1 +/- 11.3 ms, in both cases measured from the time of the stimulus to the take-off point of the peak. Often a third peak (M3) was seen, having a considerably longer latency. The origin of peak M1 was considered to be in the stretch reflex arc because of its latency and its invariable association with muscle movement. Peak M2 was due to stimulation of afferent terminals in the skin and/or subcutaneous tissues by the mechanical device producing the muscle stretch. The conduction velocity of the pathway involved in the generation of the M1 component is the same as that for M2. This implies that central processing in the spinal cord delays the M2 response. The M2 mechanism does not involve a transcortical (long-loop) pathway because in foot muscles the M1-M2 delay remains the same as is found for hand muscles, although M1 latency is prolonged (to 39.4 +/- 6.2 ms for extensor digitorum longus). This indicates that there is not time for M2 impulses to traverse a pathway any longer than that passing to and from the spinal cord.

Afferent Pathways↗
PubMed1979

Prolonged changes in excitability of pyramidal tract neurones in the cat: a post-synaptic mechanism.

1. Prolonged changes in the excitability of cortical neurones can be produced by altering their firing rates for brief periods. In the anaesthetized cat, increased firing of pyramidal tract cells induced by trains of antidromic conditioning shocks led to increases in cell excitability, as measured by the size of the mass response at the medullary pyramid to test shocks applied to the cortical surface. We have shown in two ways that post-synaptic mechanisms could be responsible. 2. In one experimental design, MgCl2 solution (1 mole/l.) was applied to the cortical surface in order to block synaptic activity throughout the cortical depth. Following antidromic conditioning trains, cell excitability was increased; the size of the mass response was up to 30% larger than the control values. This persisted undiminished for up to 3 hr. 3. In the second experimental design, synaptic activity was not blocked, but we compared the effects of antidromic plus synaptic activation of pyramidal tract cells with the effects of synaptic activation alone. Antidromic plus synaptic activation was obtained by applying conditioning trains to the pyramidal tract at the medulla ipsilateral to the cortical test shock; prolonged increases in the ipsilateral response to the test shock were produced. Synaptic activation alone was obtained by the same conditioning trains, but in those cells whose axons projected into the contralateral pyramidal tract; prolonged increases in the contralateral response to the cortical test shock were never seen. In many instances prolonged decreases in excitability were found. 4. We conclude that prolonged increases in excitability of pyramidal tract cells can occur in the absence of any synaptic input, demonstrating that the underlying mechanism is post-synaptic; this does not preclude the action of synaptic mechanisms when synaptic transmission is not blocked.

Animals↗
PubMed1977

Long-lasting increases in the tremor of human hand muscles following brief, strong effort.

1. Long-lasting (up to 4 h) increases in finger tremor were produced by intense brief effort to contract the muscle. 2. Similar increases resulted from intense effort which did not contract the muscle because the motor nerve was blocked. 3. Comparable contractions induced electrically failed to give rise to increased tremor. 4. Power spectral analysis (1-15 HZ) revealed that all frequencies of tremor were approximately equally increased. 5. It is concluded that these long-lasting increases in tremor are of central nervous origin.

Action Potentials↗
PubMed1970

Oscillation in the stretch reflex arc and the origin of the rhythmical, 8-12 C-S component of physiological tremor.

1. A brief downward, stepwise displacement applied to the outstretched finger gives rise to a train of approximately sinusoidal movements of it, lasting often more than 1 sec. The frequency of these waves is the same, in any one subject, as that of physiological tremor.2. The oscillations are regular in form, and bear a constant phase relation to the applied displacement; they can be summated using an averaging computer (Biomac 1000) triggered by the mechanical stimulus.3. The oscillations are altered in the same way as is physiological tremor by a number of factors. Cooling the arm before recording lowers the frequency, warming raises it, while the application of an arterial cuff decreases the amplitude and tends to elevate the frequency. These factors have effects of similar magnitude on both the oscillations and the tremor. It thus appears highly likely that the waves produced by a mechanical input and physiological tremor waves are due to the same process, namely oscillation in an underdamped servo-system.4. The oscillation is not due simply to the mechanical, die-away resonance of the finger, because bursts of muscle action potentials can be recorded in phase with the finger movements both in the wave train evoked by the mechanical displacement and during normal tremor.5. It is concluded that physiological tremor in the 8-12 c/s band is due to oscillation in the stretch reflex servo-loop.

Action Potentials↗