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At least 73 records · Page 4Linked to original sources
PubMed1975

Studies on the receptor responsible for vibration induced inhibition of monosynaptic reflexes in man.

A further attempt has been made to define the receptor responsible for the inhibition of monosynaptic reflexes by vibration in man. Vibration of the tendo Achillis will produce inhibition of the H reflex even when the muscles of the anterior compartment of the leg are denervated or blocked with local anaesthetic, implying that there are receptors in the posterior compartment capable of producing this effect. However, there is evidence that vibration spreads through the limb. The inhibition is greater when the anterior compartment is innervated indicating that there is a contribution from receptors in this compartment. Stretching the muscles of the posterior compartment alone, or the muscles of the anterior and posterior compartments reciprocally does not influence the inhibition of the monosynaptic reflex by vibration. These observations support the contention that the reduction of the monosynaptic reflex by vibration in man is due to presynaptic inhibition resulting from activation of primary spindle endings.

Adult↗
PubMed2004

Plasticity of lumbosacral monosynaptic reflexes after a ventral root transection injury in the adult cat.

Injuries to spinal ventral roots may induce plastic changes in adjacent segmental reflex pathways. Earlier studies in the cat have demonstrated that a partial loss of target motoneurons, following a ventral root avulsion injury, induces a compensatory enhancement of monosynaptic reflexes in adjacent segments. Here, we studied electrophysiologically the effects of a primarily non-lethal motoneuron injury of lumbosacral ventral roots on monosynaptic reflexes in adjacent intact motoneurons in the adult cat. A unilateral L7 or a combined L7 and S1 ventral root transection was first performed. We next recorded bilaterally monosynaptic reflexes from the L6 and S1 ventral roots while stimulating the bilateral L6, L7 and S1 dorsal roots at 6 and 12 weeks postoperatively. We demonstrated a prominent strengthening of monosynaptic reflexes in the immediately adjacent spinal cord segments. The reflexes had almost doubled in size at 6 and 12 weeks postoperatively. Possible mechanisms and factors contributing to the reflex enhancement are discussed.

Animals↗
PubMed1990

The pharmacology of the spinal monosynaptic reflex following conditioning of a cutaneous and muscle nerve.

Conditioning of the spinal monosynaptic reflex from cutaneous or muscle afferents results in facilitation followed by inhibition. We administered a series of agents which have been shown to alter the monosynaptic reflex by blocking specific inhibitory pathways. We found that administration of mecamylamine and atropine, agents which affect recurrent inhibition had no effect on the facilitation or inhibition of the MSR by conditioning the sural or medial gastrocnemius nerve. Similarly, bicuculline, an agent which blocks pre-synaptic inhibition, had no effect on the conditioning of the MSR. However, strychnine, a glycine antagonist which blocks post-synaptic inhibition, did alter both the facilitation and inhibition of the MSR by conditioning pulses. Strychnine enhanced the facilitation and partially blocked the inhibition of the MSR by both sural and medial gastrocnemius conditioning. These data show that the flexor reflex afferents and the larger diameter afferents alter the MSR solely through glycine-mediated post-synaptic inhibition.

Afferent Pathways↗
PubMed1965

Parkinsonism: electromyographic studies of monosynaptic reflex.

Electromyographic studies of the monosynaptic reflex in 70 Parkinsonian patients and 12 normal subjects show four types of abnormal facilitation and recovery curves in the Parkinsonian group, types that correspond to variations in the clinical syndrome; Cryosurgical lesions in the, ventro-lateral and ventro-postero-lateral nuclei of the thalamus restore essentially normal curves.

Cryosurgery↗
PubMed1990

[The spinal monosynaptic reflexes elicited from the tibialis anterior muscle--standardization of the reflexes and diagnostic use in L5 radiculopathy].

The spinal monosynaptic reflexes evoked in the tibialis anterior muscle were investigated to establish a practical method for assessing L5 radiculopathy. Voluntary contraction and averaging technique made it possible to consistently obtain the H-and T-reflexes from the muscle in which these reflexes are normally unelicitable at rest. Based on the study of fifty normal subjects, formulae were produced by an analysis of the simultaneous regression of the latencies of these reflexes on height and age, because these latencies were highly correlated with them. A side-to-side latency difference of the H-and T-waves greater than 1.5 msec. and 2.3 msec. respectively, and/or low amplitude less than 26% and 39% of the amplitude of the contralateral side respectively, could be considered abnormal. According to these criteria, eight out of twelve patients (67%) with unilateral compressive L5 radiculopathy showed abnormalities.

Electrophysiology↗
PubMed2002

Capsaicin-sensitive muscle afferents modulate the monosynaptic reflex in response to muscle ischemia and fatigue in the rat.

The role of muscle ischemia and fatigue in modulating the monosynaptic reflex was investigated in decerebrate and spinalized rats. Field potentials and fast motoneuron single units in the lateral gastrocnemious (LG) motor pool were evoked by dorsal root stimulation. Muscle ischemia was induced by occluding the LG vascular supply and muscle fatigue by prolonged tetanic electrical stimulation of the LG motor nerve. Under muscle ischemia the monosynaptic reflex was facilitated since the size of the early and late waves of the field potential and the excitability of the motoneuron units increased. This effect was abolished after L3-L6 dorsal rhizotomy, but it was unaffected after L3-L6 ventral rhizotomy. By contrast, the monosynaptic reflex was inhibited by muscle fatiguing stimulation, and this effect did not fully depend on the integrity of the dorsal root. However, when ischemia was combined with repetitive tetanic muscle stimulation the inhibitory effect of fatigue was significantly enhanced. Both the ischemia and fatigue effects were abolished by capsaicin injected into the LG muscle at a dose that blocked a large number of group III and IV muscle afferents. We concluded that muscle ischemia and fatigue activate different groups of muscle afferents that are both sensitive to capsaicin, but enter the spinal cord through different roots. They are responsible for opposite effects, when given separately: facilitation during ischemia and inhibition during fatigue; however, in combination, ischemia enhances the responsiveness of the afferent fibres to fatigue.

Animals↗
PubMed1985

Electroneurographic correlates of the monosynaptic reflex: experimental studies and normative data.

The neurographic concomitants of the monosynaptic reflex, evoked either by electrical stimulation of the tibial nerve at the popliteal fossa or by percussion of the Achilles tendon, have been recorded from the sciatic nerve in the lower and middle thigh. Neurographic recordings were characterised by two travelling waves (P1 and P2), respectively increasing and decreasing in latency in the proximal direction, that showed the same chronological trend of the propagated action potentials concurrently recorded in the dorsal and ventral spinal roots at the lumbar level. At variance with P2, the speed of propagation of the P1 volley was stimulus-related, being faster on mechanical than on electrical stimulation, probably because in the latter case the latency of the fastest afferents is overestimated. The P2 volley is subserved by alpha-efferent fibres in either case as suggested, inter alia, by the strict parallelism between the P2 volley and the monosynaptic reflex under appropriate experimental conditions. Simultaneous recordings of spinal root and sciatic nerve action potentials allowed the direct assessment of afferent and efferent conduction velocities, both in the proximal (that is from the middle thigh to the spinal recording site and vice-versa) and in the distal (that is from the lower to the middle thigh recording site and vice versa) segments of the reflex arc. As expected, the speed of propagation of impulses was significantly higher in the proximal than in the distal segments, as well as in the afferent than in efferent limb of the monosynaptic pathway. The P1-P2 time interval was longer on mechanical than on electrical stimulation, probably due to the increased spinal delay of the T versus the H reflex. The present study provides a reliable method for the direct assessment of alpha-efferent as well as of Ia afferent group fibres conduction velocity, provided that in the latter case mechanical stimuli be used.

Adult↗
PubMed1983

Actions of guanidine hydrochloride on cat spinal monosynaptic reflex transmission.

The effects of a single intravenous dose of guanidine hydrochloride were examined on the function of the lumbar dorsal-ventral root and triceps surae nerve-ventral root monosynaptic reflex (MSR) in unanesthetized acute spinal (C-1 sectioned) cats. Guanidine, in a dose of 25 mg/kg, consistently depressed the amplitude of the monosynaptic reflex response while a dose of 200 mg/kg always exerted a facilitatory action. Intermediate doses of 50 or 100 mg/kg produced variable actions on the amplitude of the monosynaptic reflex from one preparation to another. The differential effects of guanidine on the evoked monosynaptic reflex are postulated to represent the ability of the drug to enhance both excitatory and inhibitory transmission, the latter predominating at smaller doses and the former becoming apparent with an increasing dose of guanidine. The facilitatory and the depressant effects of guanidine on the function of spinal reflexes were slow to develop, suggesting an intracellular site of action. These results may have significance for an understanding of the possible efficacy of guanidine in motor neuron disease in man.

Animals↗
PubMed1981

Excitability of the monosynaptic reflex pathway in the child from birth to four years of age.

The excitability of the monosynaptic reflex pathway was tested in infants and children from birth to four years of age during waking and sleeping. The H reflex, evoked in the soleus muscle, was used to calculate the ratio, maximal H to maximal M, construct recruitment curves and test reflex excitability by the paired stimulus method. The excitability of the monosynaptic reflex pathway during the waking state is greatest at birth; it diminishes gradually during the first years of life without reaching the average level observed in adults by the end of the fourth year of age. From birth, regardless of age, sleep always depresses excitability. The mechanism that underlie this change with age, and with waking or sleeping, are discussed.

Child Development↗
PubMed1999

The role of capsaicin-sensitive muscle afferents in fatigue-induced modulation of the monosynaptic reflex in the rat.

1. The role of group III and IV afferent fibres of the lateral gastrocnemious muscle (LG) in modulating the homonymous monosynaptic reflex was investigated during muscle fatigue in spinalized rats. 2. Muscle fatigue was induced by a series of increasing tetanic electrical stimuli (85 Hz, 600 ms) delivered to the LG muscle nerve. Series consisted of increasing train numbers from 1 to 60. 3. Potentials from the spinal cord LG motor pool and from the ventral root were recorded in response to proprioceptive afferent stimulation and analysed before and during tetanic muscle activations. Both the pre- and postsynaptic waves showed an initial enhancement and, after a '12-train' series, an increasing inhibition. 4. The enhancement of the responses to muscle fatiguing stimulation disappeared after L3-L6 dorsal root section, while a partial reflex inhibition was still present. Conversely, after section of the corresponding ventral root, there was only a reduction in the inhibitory effect. 5. The monosynaptic reflex was also studied in animals in which a large number of group III and IV muscle afferents were eliminated by injecting capsaicin (10 mM) into the LG muscle. As a result of capsaicin treatment, the fatigue-induced inhibition of the pre- and postsynaptic waves disappeared, while the response enhancement remained. 6. We concluded that the monosynaptic reflex inhibition, but not the enhancement, was mediated by those group III and IV muscle afferents that are sensitive to the toxic action of capsaicin. The afferents that are responsible for the response enhancement enter the spinal cord through the dorsal root, while those responsible for the inhibition enter the spinal cord through both the ventral and dorsal roots.

Animals↗
PubMed1978

Mechanism of monosynaptic reflex reinforcement during Jendrassik manoeuvre in man.

The facilitating effect of the Jendrassik manoeuvre on monosynaptic reflexes in man has been studied by comparing H and T reflexes of the soleus and by blocking the effects of spindle activation by ischaemia of the leg. The Jendrassik manoeuvre equally enhances H and T reflexes provided that the test reflexes are small. The H reflex remains facilitated when the spindle activation cannot affect the soleus alpha-motoneurones--that is, when the Ia afferent nerve fibres from the soleus are blocked by ischaemia. It is concluded that the facilitating effect of the Jendrassik manoeuvre on the alpha-motoneurones is not predominantly routed via the gamma-loop.

Achilles Tendon↗
PubMed1987

Effects of acetaldehyde on the monosynaptic reflex pathway in the cat spinal cord.

The effects of acetaldehyde on monosynaptic reflexes were investigated in the cat spinal cord. Intravenous injection of lower doses of acetaldehyde (0.1-0.5 mg/kg) increased the amplitude of the ventral root monosynaptic reflex potentials elicited by the dorsal root stimulation; the amplitude was decreased at higher doses (1.0-10.0 mg/kg). Acetaldehyde hyperpolarized the motoneuron at lower and depolarized it at higher doses. In some cells, however, acetaldehyde induced an initial, brief depolarization and subsequent hyperpolarization. Depolarization increased with increasing the dose of acetaldehyde. Hyperpolarization was always associated with an increased amplitude of the monosynaptically-induced action potentials. Depolarization was accompanied by a decreased amplitude or block of the action potentials. During aldehyde-induced depolarization, antidromic action potentials were more severely depressed than orthodromic ones. The present results suggest that acetaldehyde acts predominantly on the motoneuron membrane resulting in hyperpolarization at relatively lower doses and in depolarization at higher doses.

Acetaldehyde↗
PubMed1987

Morphological and physiological studies of development of the monosynaptic reflex pathway in the rat lumbar spinal cord.

1. The developmental process of the monosynaptic reflex pathway was investigated morphologically and electrophysiologically in isolated lumbar spinal cords of new-born and fetal rats. 2. Dorsal root fibres were stained with horseradish peroxidase in the fourth lumbar (L4) segment at different ages ranging from embryonic day (E) 15.5 to post-natal day (P) 0. At E15.5, several collaterals issued from axons in the dorsal funiculus and reached the dorsal part of the dorsal horn. At E16.5, the number of collaterals entering the grey matter increased. Also, a group of collaterals extended ventralwards forming a bundle, and reached the intermediate region. At E17.5, a small number of collaterals reached the motor nuclei. The number of collaterals entering the motor nuclei increased almost linearly with age: 0 at E15.5 and at E16.5, 27 at E17.5, 184 at E18.5, 432 at E19.5 and 746 at P0. 3. The tips of collaterals and their branches had growth cones, boutons (round or oval varicosities) or other varicosities. The mean number of branches with these structures per collateral in the motor nuclei was 1.2 at E17.5, 2.5 at E18.5, 3.6 at E19.5 and 5.8 at E20.5. 4. The percentage of collaterals having growth cones in the motor nuclei was 75% at E17.5, 70% at E18.5, 38% at E19.5 and 15% at E20.5. 5. The mean number of boutons per collateral in the motor nuclei was 0.6 at E17.5, 3.2 at E18.5, 4.9 at E19.5 and 10.7 at E20.5. This increase with age was caused by both branching of collaterals and the increase in the number of boutons of the en passant type. The estimated total number of boutons in the motor nuclei of the L4 segment steeply increased after E17.5: 16 at E17.5, ca. 600 at E18.5, ca. 2000 at E19.5 and ca. 8000 at E20.5-P0. 6. Stimulation of the L4 dorsal root evoked a reflex response in the L4 ventral root, recorded as the ventral root potential, in two out of nine preparations at E15.5 and in all preparations at and after E16.5. The onset of the ventral root potential indicated the onset of excitatory post-synaptic potentials in motoneurones. The segmental latency of the ventral root potentials was markedly shortened between E17.5 and E18.5 (from 12.5 to 7.2 ms) and essentially unchanged at the later stages. 7. The magnitude of monosynaptic reflex responses in the L4 segment gradually increased with age during prenatal stages, becoming maximal at P2-3 and then decreased at the following stages (P4-P8).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1996

[Effects of halothane, isoflurane, enflurane, and sevoflurane on the monosynaptic reflex response in the isolated spinal cord of newborn rats].

Monosynaptic reflex responses (MSRs) in the isolated spinal cord of newborn rats were elicited in the ventral root by stimulation of the ipsilateral dorsal root. MSRs were considered to be mediated by non-NMDA class glutamate receptors. We studied the depressant effects of halothane, isoflurane, enflurane, and sevoflurane on MSR amplitudes as a function of anesthetic concentration comparing with MAC value of each anesthetics. The spinal cord of newborn rats were rapidly dissected out, and placed in a chamber superfused with artificial cerebrospinal fluid (ACSF, pH 7.4, 34 degrees C) equilibrated with 95% O2 - 5% CO2. Anesthetic gases were delivered with specific vaporizers and bubbled in the ACSF. Each anesthetic concentration was determined by gas chromatography. Either of the anesthetics reversibly depressed MSR amplitudes in a concentration dependent fashion. Concentration-response curves for MSR amplitudes were constructed and the concentrations which produced a half-maximum inhibition (IC50) were 0.56, 0.65, 0.97 and 1.18 mM for halothane, isoflurane, enflurane, and sevoflurane, respectively. These IC50 values correlated well with those of MAC values (r = 0.999, P < 0.001) obtained from adult rats in an in vivo condition. The MSR response in the isolated spinal cord of newborn rats is considered as a useful model for analysis of potency of volatile anesthetics.

Anesthetics, Inhalation↗