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Results for “Reflex, Monosynaptic”

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PubMed1999

Value of homonymous and heteronymous monosynaptic reflexes in the diagnosis and follow-up of cervical spinal injuries.

Needle electromyographic examination constitutes the only neurophysiological test used routinely to assess the integrity of proximal nerve pathways. A heteronymous reflex, with a latency consistent with a monosynaptic pathway, can be evoked in the contracting biceps brachii muscle by stimulation of the median nerve at the elbow. This reflex response provides a complementary technique to the biceps and supinator jerks for accessing the C(5)/C(6)motoneuron pool because its afferent limb involves the median nerve and the C(5)/C(6)posterior roots. Three cases are described to illustrate the clinical value of this heteronymous monosynaptic reflex of biceps brachii and of conventional H reflexes in the diagnosis and follow-up of lesions involving the C(5)/C(6)segments. Reflex function can be assessed for most spinal segments innervating the upper and lower limbs, thus allowing both objective confirmation of the clinical findings and documentation of changes over time. Copyright 1999 Harcourt Publishers Ltd.

Journal Article↗

PubMed1991

Recurrent and reciprocal inhibition of the human monosynaptic reflex shows opposite changes following intravenous administration of acetylcarnitine.

A long-latency, long-lasting increase in the recurrent inhibitory effect on the soleus monosynaptic (Hoffmann, H) reflex was induced after intravenous administration of L-acetylcarnitine, a substance known to process central cholinergic activity. This effect was paralleled by disappearance of the H reflex inhibition (functionally disinhibition) induced by stimulation of Ia afferent fibres from the tibialis anterior (reciprocal inhibition) and gastrocnemius medialis muscle. Magnitude and time course of the L-acetylcarnitine-induced effects were significantly correlated. The data suggest that (1) the L-acetylcarnitine depression of the reciprocal inhibition is mediated by excitation of Renshaw cells impinging on Ia interneurones (INs), and (2) the inhibitory effect of GM Ia afferents onto Sol is mediated by INs subjected to Renshaw inhibition. The results point to the similarity in the wiring of the 'output stage' circuit between cat and humans, and provide a method for testing this network in man.

Acetylcarnitine↗

PubMed1973

The contingent negative variation and the excitability of the spinal monosynaptic reflex.

A method is described which permits simultaneous measurement of changes in slow electroencephalographic potentials (Contingent Negative Variation-CNV) and the excitability of the spinal monosynaptic arc (H reflex) during the foreperiod of a simple reaction time experiment. Data from 11 normal subjects show that during the development of the CNV there is an augmentation of the amplitude of the H-reflex. It is suggested that the two phenomena are controlled by a common subcortical structure.

Acoustic Stimulation↗

PubMed1977

Monosynaptic reflexes in falling man.

We have examined peripheral proprioceptive input during fall in man. The first 80 ms of unexpected free fall, both in a parachute harness and while seated, has been studied using the monosynaptic Hoffman (H) and Achilles tendon (T) reflexes. Facilitation of the H reflex begins about 30 to 40 ms after release, representing the onset of motor neurone facilitation before the electromyographic activity which begins about 80 ms after release. Earlier facilitation of the T reflex may represent spindle excitation due to change in muscle shape as suggested by Matthews and Whiteside (1960), but the T reflex inhibition described by these authors after 50 ms of seated fall is probably a purely mechanical phenomenon.

Achilles Tendon↗

PubMed1976

Monosynaptic reflexes in the superficial forearm flexors in man and their clinical significance.

Indirect motor responses with the characteristics of the H wave were recorded from the flexor carpi radialis and the palmaris longus muscles in normal adults. A series of experiments has been performed, constituting circumstantial arguments for the monosynaptic nature of these reflex responses. The findings in pathological conditions, which corroborated this point of view, are documented briefly.

Adolescent↗

PubMed1975

The effect of porphyrin precursors on monosynaptic reflex activity in the isolated hemisected frog spinal cord.

The porphyrin precursors beta-aminolevulinic acid (beta-ALA) and porphobilinogen (PBG) which accumulate, and are excreted in the urine in increased amounts during acute attacks of porphyria, were tested for their effects on reflex activity in the isolated hemisected spinal cords of Xenopus laevis. The two compounds were found to exert an inhibitory effect on monosynaptic ventral root responses, as well as on dorsal root responses (DRR) and dorsal root potentials (DRP). The latent period for inhibition of the monosynaptic response was longer than that for the DRR and DRP. The sensitivity of the preparations to the effect of the porphyrin precursors was subject to some seasonal variation. BETA-ALA and PBG did not effect conduction in isolated sciatic nerves at a concentration of 1 mg/ml.

Aminolevulinic Acid↗

PubMedDate not supplied

[Monosynaptic reflex responses of the spinal cord after the removal of the bones of the shin and thigh in white rats].

To analyse the mechanisms of the increase of excitability of the spinal cord neurons after division of a nerve, the author studied the character of changes of the monosynaptic responses (MSR) of the ventral spinal cord root in albino rats 5 days and 4 weeks after removal of the bones of one hind limb. The MSR did not change in 5 days but intensified significantly in 4 weeks as compared to the monosynaptic responses on the contralateral side. The possible mechanisms of the increase of MSR after osteotomy and division of a nerve are discussed.

Animals↗

PubMed1978

[Microiontophoretic study of the effect of acetylcholine and noradrenaline on the monosynaptic reflex activity of the spinal cord].

In anesthetized and spinal cats the influence of microionophoretic local injections of acetylcholine and noradrenaline into different layers of grey substance of lumbar segments of the spinal cord were studied with aid of monosynaptic EPSPs of motoneurons. Injections of ACH and NA in the surface layers of the grey substance of dorsal horn induced depression of monosynaptic reactions. In the area of 6--7 layers ACH induced a weak depression, while NA significantly increased the reflex responses. In the given arrangement of motoneurons NA depressed and ACH facilitated extensor and flexor monosynaptic reactions of motoneurons.

Acetylcholine↗

PubMed1968

The effects of prostaglandins E1, F1-alpha and F2-alpha on monosynaptic reflexes.

1. Experiments, using electrophysiological recording techniques, were carried out to confirm the report that prostaglandins affect spinal reflexes in cats.2. Ventral root potentials evoked by stimulation of the ipsilateral dorsal root were recorded. Those with a latent period corresponding to a monosynaptic pathway were used primarily in this investigation.3. Prostaglandin E(1) (3.5-17.8 mug/kg) injected into the aorta reduced the amplitude of monosynaptic responses in six out of ten cats. The effect began about 15 min after injection and lasted over 3 hr. In one cat E(1) caused potentiation of the reflex and in three cats there was no effect.4. Prostaglandin F(1alpha) (2.4-3.5 mug/kg) inhibited the monosynaptic response in four cats but in one of these a subsequent large dose (19.6 mug/kg) greatly potentiated the reflex.5. Prostaglandin F(2alpha) (1.4-17.8 mug/kg) injected into the aorta was followed by significant but variable changes in monosynaptic response. In one experiment an intravenous injection (30.3 mug/kg) was followed by a long-lasting potentiation of the reflex response.6. It is concluded that prostaglandins, two of which have previously been identified in cat brain extracts, have pronounced and long-lasting effects on monosynaptic spinal reflexes.

Animals↗

PubMed1999

Antidromic discharges of dorsal root afferents and inhibition of the lumbar monosynaptic reflex in the neonatal rat.

The in vitro brain stem-spinal cord preparation of neonatal (0- to five-day-old) rats was used to establish whether pathways descending from the brain stem are capable of modulating synaptic transmission from primary afferents to lumbar motoneurons within the first few days after birth. We stimulated the ventral funiculus of the spinal cord at the cervical (C1-C2) level. Single-pulse stimulations evoked both excitatory and inhibitory postsynaptic potentials in ipsilateral lumbar (L2-L5) motoneurons which were recorded intracellularly. Twin-pulse stimulations evoked bursts of action potentials in ventral roots. The amplitude of the monosynaptic dorsal root-evoked excitatory postsynaptic potential decreased when a conditioning stimulation was applied to the ventral funiculus 50-300 ms prior to the stimulation of the ipsilateral dorsal root. A decreased input resistance of the motoneurons during the early part (25-100 ms after the artifact) of the ventral funiculus-evoked postsynaptic potentials could account, at least partly, for the decreased amplitude of the dorsal root-evoked response. However, the duration of the inhibition of the dorsal root-evoked excitatory postsynaptic potential was longer than that of the decrease in input resistance. Ventral funiculus stimulation evoked antidromic discharges in dorsal roots. Recordings of dorsal root potentials showed that these discharges were generated by the underlying afferent terminal depolarizations reaching firing threshold. The dorsal root discharge overlapped with most of the time-course of the ventral funiculus-evoked inhibition of the response to dorsal root stimulation, suggesting that part of this inhibition may be exerted at a presynaptic level. The number of antidromic action potentials evoked in dorsal roots by ventral funiculus stimulation increased significantly in saline solution with chloride concentration reduced to 50% of control. Bursts of action potentials disappeared when chloride was removed completely. Antidromic discharges were therefore due to chloride conductance. The number of action potentials evoked in ventral roots was increased in low-chloride saline solutions. Removing chloride from the bathing solution resulted in an unstable ventral root activity. Bath application of the GABA(A) receptor antagonist, bicuculline (5-10 microM), blocked the ventral funiculus-evoked antidromic discharges in the dorsal roots. The increase in chloride conductance which generated the depolarizations underlying the dorsal root discharges was therefore mediated by an activation of GABA(A) receptors. In contrast, bursts of action potentials in the ventral roots were increased in both amplitude and duration under bicuculline. Our data demonstrate that pathways running in the ventral funiculus of the spinal cord exert a control on interneurons mediating presynaptic inhibition at birth.

Action Potentials↗

PubMed1966