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At least 793 records · Page 44Linked to original sources
PubMed1978

Stretch and Hoffmann reflexes during phasic voluntary contractions of the human soleus muscle.

Measurements were made of EMG responses in human soleus muscle, following torque disturbances of the foot during phasic voluntary plantarflexions. These were compared with measurements of the Hoffmann reflex during identical voluntary movements. We observe that stretch adequate to evoke a stretch reflex in the relaxed limb often fails to evoke any response during a phasic contraction until about 120 msec after the onset of the stimulus. During this period the H-reflex is facilitated. These findings are discussed in terms of the servo-theory of stretch reflex function and the concept of trans-cortical stretch reflexes.

Adult↗
PubMed1979

Hyperbaric hyperreflexia: tendon-jerk and Hoffmann reflexes in man at 43 bars.

Tendon jerk (TJR) and Hoffmann (H) reflexes of the soleus muscle were studied in two men during a 26-day simulated oxygenhelium dive to a maximum pressure of 43 bars. The amplitude of the TJR response was observed to increase markedly after compression and also at the end of decompression. This biphasic pattern of enhanced reflectivity was reproduced by synchronised but much smaller variations in H reflex response. The positive facilitatory effects of applying Jenkdrassik's manoeuvre were reduced and the negative effects increased during hyperbaric exposure. Excitability cycles (twin-pulses methods) revealed modifications in one subject similar to those observed in clinical hyperreflexia, namely a shortening of Phase III and an enhancement of Phase IV. The other subject exhibited a notable depression of Phase IV. Abnormal EMG recordings are described including randomly-triggered slow wave potentials with no mechanical effects, and fixed, long latency late responses of a reflex nature with a definite mechanical effect. The contention that alterations in vestibulo-spinal relations may result in the release from tonic presynaptic inhibitory control of myotatic reflex arc excitability is discussed as a partial explanation for these and related findings.

Adult↗
PubMed1980

Changes in excitability of tendon tap and Hoffmann reflexes following voluntary contractions.

The effects on the Hoffmann reflex and tendon tap responses in the human soleus and medial gastrocnemius muscles of a brief conditioning volitional contraction have been compared with the objective of distinguishing contributions from the central nervous system and the periphery. The H-wave on successive trials over a 50 sec period following contraction for the most part demonstrated a depression, especially upon the initial trial. The T-wave responses in the first few trials were greater than those in the control period. Using the assumption that responses to tendon taps had been reduced by the amounts reflected in the excitability curve for H-response, it was deducted that a marked enhancement in T-wave excitability had been present at the initial tendon tap and more moderate facilitation thereafter. This is consistent with the post-contraction discharge and increase in stretch sensitivity of spindle receptors seen after contraction of a muscle in experimental animals. It is concluded that such effects on spindles may occur in man, maybe of such force as to detectably influence dynamic movements.

Adult↗
PubMed1988

Recurrent inhibition of firing motoneurones in man.

The effects of antidromic stimulation of large motoneurones on firing small motoneurones of soleus muscle have been studied. Against the background of rhythmic firing of small motor units (MUs) activated during weak voluntary muscle contraction, thick efferents of the tibialis posterior nerve were selectively stimulated and an M response was evoked in which small MUs were not involved. This provided a means of avoiding antidromic stimulation of the motoneurone under study and, thus, analysing the effect of stimulation without its summation with after-hyperpolarization. The background firing rate of MUs was 4.5-9.2/sec. PSTHs revealed a distinct inhibitory effect with a latency of 35-40 msec (slightly exceeding the latency of monosynaptic reflex) and duration 5-30 msec. It was concluded that the short-latency inhibition could be identified as recurrent inhibition. The effectiveness of recurrent inhibition evaluated by the lengthening of the interspike interval was shown to depend on the arrival time of the volley in the interval and on the background firing rate of the motoneurone. When the inhibitory volley arrived at the beginning of the interspike interval it was ineffective. This indicates that in the investigated range of firing rates the motoneurone is unable to exert an inhibitory effect on its own firing via recurrent collaterals. The inhibitory volley became highly effective at the end of an interspike interval, when the membrane potential approached threshold. The lengthening of interspike interval was more marked at a lower firing rate of the motoneurone. An increase in the background firing rate reduced the extent of recurrent inhibition (at a rate above 10/sec up to its complete ineffectiveness).(ABSTRACT TRUNCATED AT 250 WORDS)

Electroencephalography↗
PubMed1993

The action of new potent GABAB receptor antagonists in the hemisected spinal cord preparation of the rat.

CGP 52432 (3-N-(3,4-dichlorobenzyl)aminopropyl-P-diethoxymethylphosphinic acid), CGP 54062 (3-N[1-(R,S)-(3,4-dichlorophenyl)ethyl]amino-2-(S)-hydroxypropyl-P-benzy l- phosphinic acid), CGP 54626 (3-N[[1-(S)-(3,4-dichlorophenyl)ethyl]amino-2-(S)- hydroxypropyl-P-cyclohexylmethylphosphinic acid) and CGP 55845 (3-N[1-(S)-(3,4-dichlorophenyl)ethyl]amino-2-(S)- hydroxypropyl-P-benzyl-phosphinic acid) are novel selective GABAB receptor antagonist. The apparent Kd values for the complex formed between the GABAB receptor and these compounds were determined using the monosynaptic reflex in the hemisected rat spinal cord preparation in vitro. CGP 55845 was found to be the most potent GABAB receptor antagonist tested (apparent Kd = 30 nM). On the same preparation 0.3 microM CGP 55845 was equipotent with 100 microM of CGP 35348 (P-(3-aminopropyl)-P-diethoxymethyl-phosphinic acid) for reversal of the depressant action of (R)-(-)-baclofen.

Animals↗
PubMed1994

Physiological and pharmacological characterization of the spinal tachykinin NK2 receptor.

The goal of these investigations was to study the role of tachykinin NK2 receptors in neonatal spinal cords using the selective NK2 receptor agonist [beta-Ala8]neurokinin A-(4-10) and the new NK2 receptor antagonist GR 94800. Experiments were performed with superfused hemisected rat and gerbil spinal cords. Dorsal roots were electrically stimulated and the synaptically elicited responses and the DC-potentials were recorded extracellularly from the corresponding ventral roots. [beta-Ala8]neurokinin A-(4-10) depolarized ventral roots (0.01-10 microM) and increased their spontaneous activity in a concentration-dependent manner. These effects of [beta-Ala8]neurokinin A-(4-10) were reduced by GR 94800. The action of GR 94800 was selective because the depolarizing effects of similar magnitude evoked by the NK1 receptor agonist [Sar9,Met(O2)11]substance P were not affected by GR 94800. The pA2 values of GR 94800 amounted to 6.0 +/- 0.4 in the rat and 5.4 +/- 0.3 in the gerbil. The NK2 receptor agonist was more potent in the rat than in the gerbil. The estimated EC50 (mean +/- S.E.M.) was found to be 3.9 + 6.0/-1.3 microM in the rat and 2.4 + 2.9/-1.3 microM in the gerbil spinal cord. The NK2 receptor agonist [beta-Ala8]neurokinin A-(4-10) potentiated the monosynaptic reflex evoked by dorsal root stimulation. The potentiation manifested itself as an increase in the amplitude of the early component of the response. The receptor type mediating this effect could not be elucidated. The potentiation ranged between 30 +/- 27 and 110 +/- 36% (0.3 and 10 microM), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1981

Analysis of conduction velocity in the H pathway. Part 1. Methodology and results in normal subjects.

An electrophysiological method is described for evaluating the conduction velocity in the different partial segments of the monosynaptic reflex pathway of the lower limbs in man. Using the latencies of M and H responses recorded from the soleus muscle elicited by stimulating the posterior tibial nerve at the popliteal fossa (pf) and the sciatic nerve at the upper thigh, the conduction velocities in the entire course (pf-to-spinal cord), in the proximal segment (upper thigh-to-spinal cord), and in the distal segment (pf-to-upper thigh) of the H circuit, were evaluated and expressed by mixed (sensory-motor) conduction indexes. The conduction distances were measured by using the Th11 spinal process as a reference point on the vertebral column. The conduction velocity of the 1a spindle afferent fibres and of the motor fibres was selectively determined in the pf-to-buttock segment. The results obtained in 50 healthy subjects are presented and the methodological problems related to the proposed technique are discussed.

Adolescent↗
PubMed1983

Actions of midazolam in the spinal cord of the cat.

Midazolam, which induces anaesthesia in humans at intravenous doses of 0.3 mg/kg, did not anaesthetize cats at doses of 20 mg/kg. Nevertheless, intravenous doses as small as 0.3 mg/kg enhanced spinal primary afferent depolarization and presynaptic inhibition of spinal monosynaptic reflexes, and both intravenous and microelectrophoretic administration of midazolam enhanced the inhibitory effect of GABA on spinal neurones and the depolarization of Ia afferent terminations by GABA and piperidine-4-sulphonate. Some degree of specificity was demonstrated for the inhibitory effect of GABA in relation to those of glycine and noradrenaline, and the enhancement by midazolam of inhibition by GABA was blocked by R015-1788, which alone was inactive. Although these results are consistent with proposals that depressant benzodiazepines enhance the effectiveness of GABA as a central transmitter, such an effect alone may not fully account for the anaesthesia produced by midazolam in humans.

Afferent Pathways↗
PubMed1985

Acrylamide neurotoxicity: altered spinal monosynaptic responses to quipazine, a serotonin agonist, in cats.

The effects of the serotonin agonist quipazine on the spinal monosynaptic reflex (MSR) were investigated in acrylamide-treated cats. Cats were administered 30 mg/kg acrylamide (ACR) for 10 days, and the MSR and spontaneous ventral root discharge (VRD) were recorded on the tenth day (ACR 10) or 10 days subsequent to the last injection (ACR 20). Cumulative doses of quipazine were administered to increase the MSR and VRD. It was found that the MSR in ACR 10 cats was significantly depressed by ACR while the ACR 20 cats showed increased MSRs with double peaks. Dose-response relationships between quipazine and the area-under-the-MSR showed a significant shift to the right in the ACR 10 from control and no significant change in the ACR 20 from control. Dose-response curves of quipazine vs VRD showed no significant difference in either group from control. These data suggest that the alpha-motoneuron in ACR-treated cats was responding normally to quipazine while the primary afferent terminal was not.

Acrylamide↗
PubMed1993

Activation of carotid baroreceptors inhibits spinal reflexes in man.

The present study was designed to investigate the effect of baroreceptors on a spinal reflex. The Achilles tendon reflex (T reflex), a monosynaptic spinal reflex, was chosen as an indicator of descending influences of central activation. The baroreceptors are stretch receptors which respond to extensions of the arterial wall. Carotid sinus baroreceptors can be manipulated non-invasively by means of a cuff around the neck. In this study, the phase-related external suction (PRES) neck cuff technique was used. PRES applies short changes in cuff pressure as a function of heart cycle phase, controlling for non-specific effects found in other baroreceptor manipulation methods. The T reflex was reduced when elicited during the highest levels of baroreceptor activation. Reflex amplitude was largest when elicited during the lowest levels of baroreceptor activation. These results are consistent with previous findings that baroreceptor activation reduces CNS excitability.

Adult↗
PubMed1989

A biphasic excitability change in hindlimb motoneurons evoked by stimulation of the nucleus raphes magnus in the cat.

1. The influence of electrical stimulation of the nucleus raphes magnus (RM) on spinal segmental systems were examined. 2. RM stimulation produced an initial increase and a subsequent suppression of the amplitude of both fiextor and extensor lumbar monosynaptic reflex potentials (MSRs). 3. Intracellular recordings were made from alpha-motoneurons of the common peroneal nerve (flexor) and the tibial nerve (extensor). RM stimulation evoked postsynaptic potentials with a time course similar to that of MSR facilitation. 4. RM stimulation inhibited the aggregate excitatory synaptic potential (EPSP) evoked by stimulation of group I afferent fibers without apparent changes in the motoneuronal membrane potential. 5. These data suggest that the RM-evoked biphasic effect on MSR consists of early facilitation due to EPSP, and late inhibition possibly due to presynaptic inhibition of group I afferent fibers.

Animals↗
PubMed1989

Modification of human spinal stretch reflexes: preliminary studies.

Modulation of the human spinal stretch reflex (SSR) may be important in treating hyperactive reflexes or may be a tool to enhance normal performance. Eight of 9 subjects given feedback of biceps brachii SSR amplitude and instructed to increase (uptrain) or decrease (downtrain) this response were able to do so in the appropriate direction. These results imply that, as in non-human primates, SSR amplitude can be modified.

Adult↗