SEARCH · PubMed Health

Results for “Reflex, Monosynaptic”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21Linked to original sources

PubMed1993

Is 5-hydroxytryptamine mediating descending inhibition in the neonatal rat spinal cord through different receptor subtypes?

The long-lasting descending inhibition of lumbar segmental reflexes in the neonatal rat spinal cord has been investigated in vitro by recording from lumbar ventral roots on stimulation of a single lumbar dorsal root. Descending inhibition was elicited by a single stimulus to the latero-ventral thoracic cord. A number of strategies were used to clarify the role of 5-hydroxytryptamine (5-HT) in inhibiting the monosynaptic reflex, the ipsilateral polysynaptic response and the contralateral fast response evoked on the opposite side of the lumbar cord. The 5-HT uptake inhibitor, citalopram (10 nM), potentiated both short-interval (0.5-2 s) inhibition and long-interval (5-100 s) inhibition of the monosynaptic reflex, and also inhibition of the polysynaptic response 10-100 s after the thoracic stimulus. Inhibition of the monosynaptic reflex was blocked by ketanserin (1 microM), spiperone (1 microM) and methiothepin (1 microM), but not by spiroxatrine (0.1 microM) or sulpiride (1 microM). Sumatriptan (20 nM) and methysergide (10 nM) enhanced inhibition of the monosynaptic reflex 0.2-1 s after the thoracic stimulus. It was concluded that 5-HT acting through 5-HT2A/2C receptors is the transmitter responsible for monosynaptic reflex inhibition, at intervals of 0.5-100 s, but a stronger stimulus to the thoracic cord may elicit a non-serotonergic component at intervals of 0.1-2 s. There was no unequivocal evidence that endogenous 5-HT activates 5-HT1 receptors to produce inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1975

Patterns of cortical projection to hindlimb muscle motoneurone pools.

This study was undertaken to examine the organization of the hindlimb area of the motor cortex. Two specific questions were posed. The first was: are the cortical neurones which control the excitability of a given motoneurone pool localized in a small zone of corjex or are they diffuse? The second question was: does microstimulation in the hindlimb area of the motor cortex activate spinal motoneurones in a reciprocal fashion, i.e., is cortically elicited facilitation of a muscle accompanied by inhibition of the antagonist? Intracortical microstimulation was used to condition monosynaptic reflexes of the cat hindlimb to study the organization of a cortical projection to lumbar motoneurone pools. Cortical neurones which produced facilitation or inhibition of a given monosynaptic reflex were localized within a small zone of the cortex. Facilitatory and inhibitory effective zones were found to have similar shape and size. Intracortical microstimulation elicited facilitation or inhibition of individual monosynaptic reflexes without eliciting reciprocal effects on the antagonists. The pyramidal tract was shown to play an important role in the mediation of cortically elicited facilitation as well as inhibition of the monosynaptic reflexes in the lumbar cord.

Animals↗

PubMed1991

Effect of muscle length on phasic stretch reflexes in humans and cats.

1. This is a report of the effects at different muscle lengths of the muscle's immediate history on the tendon jerk and Hoffman (H)-reflex in triceps surae of human subjects and cats. 2. In adult human subjects the size of the tendon jerk was measured as electromyogram (EMG) and torque in response to a tendon tap. Before each test tap the muscle was conditioned by a maximum voluntary contraction carried out with the foot either plantarflexed or dorsiflexed by 30 degrees from the test position. After a contraction with the foot dorsiflexed, the subsequent reflex response was smaller than after a contraction with the foot plantarflexed. 3. The same conditioning procedure was carried out with the H-reflex. The reflex was elicited by transcutaneous electrical stimulation of the tibial nerve in the popliteal fossa. Here the reflex after a contraction with the foot dorsiflexed was larger than after plantarflexion. In other words, the effects of conditioning were the opposite for the tendon jerk and H-reflex. 4. The effects of muscle conditioning were tested over a range of muscle lengths. As the test length was made progressively longer, that is, the foot more dorsiflexed, the difference in size of the tendon jerk following the two forms of conditioning became less, whereas for the H-reflex it remained the same. 5. These findings were confirmed in cats anesthetized with alpha-chloralose. The tendon jerk was elicited by a quick stretch applied to the triceps surae muscle group, and the H-reflex represented by the monosynaptic reflex recorded from the central, cut end of the ventral root in response to electrical stimulation of the triceps nerve. Muscle conditioning consisted of a 1-s period of stimulation at 20 pulses/s, at fusimotor strength, of the peripheral end of the cut ventral root at a muscle length 5 mm longer or shorter than the test length. In the cat, as in human subjects, the effect of conditioning on the tendon jerk reversed at long muscle lengths, whereas the monosynaptic reflex showed no reversal. 6. It had been proposed previously that the effects of conditioning on stretch reflexes could be explained by development of slack in the intrafusal fibers of muscle spindles after a contraction at a longer-than-test length. The presence of slack lowers the resting discharge of spindles and reduces the afferent response to a tendon tap.(ABSTRACT TRUNCATED AT 400 WORDS)

Achilles Tendon↗

PubMed1990

Low prevalence of cisplatin-induced neuropathy after 4-day continuous infusion in head and neck cancer.

The toxicity of cisplatin on peripheral nerves was studied using electrophysiologic recordings in 52 patients with head and neck squamous cell carcinoma. Induction chemotherapy (cisplatin: 25 mg/m2/day, days 1-4; 5-fluorouracil: 1 g/m2/day, days 1-4) was administered by continuous infusion every 3 weeks. Electrophysiologic recordings were performed before and after the completion of three courses of chemotherapy (cisplatin total dose: 250-300 mg/m2). The comparison between the recordings showed 14% of the patients had an increase in the latency of the soleus muscle monosynaptic reflex as studied by the Hoffman reflex and 9% showed a decrease in the conduction velocity of the cutaneous sensory fibers of the median nerve. These results indicated a low prevalence of cisplatin-induced neuropathy. The respective roles played by the continuous infusion of the drug and by the potentiation of neurotoxic effects resulting from the association of cisplatin with other neurotoxins is discussed to explain this low toxicity.

Adult↗

PubMedDate not supplied

Electrophysiologic properties of the cannabinoids.

The effects of the psychoactive cannabinoid delta 9-tetrahydrocannabinol (THC) and the nonpsychoactive cannabinoid cannabidiol (CBD) were investigated comparatively on electrically caused transcallosal cortical evoked responses, electrically induced limbic after discharges, photically evoked cortical afterdischarges, spontaneous cortical focal epileptic potentials, and spinal monosynaptic reflexes. In each system, THC produced central excitation; for example, the drug's responses ranged from enhancement of synaptic transmission to precipitation of frank convulsions. In addition to central nervous system stimulation, THC usually elicited depression; the qualitative character of the effect of the drug was dependent upon the dosage and the test system. In contrast to THC, cannabidiol generated no CNS excitation: it was either depressant or inert in these test systems. The results clearly demonstrate the complexity of the CNS properties of THC and the selectivity of the depressant properties of cannabidiol; moreover, the data illustrate the wide range of neuropharmacologic responses that potentially any cannabinoid can effect.

Animals↗

PubMed1975

Neurochemical changes in the cat's spinal cord due to orthodromic tetanic stimuli. I: phospholipids.

Posttetanic potentiation of monosynaptic reflexes has been used as a paradigm for neuronal plasticity. The explanation for this phenomenon is an increased responsiveness of the synaptic junctions. This would basically require chemical changes of the nervous structures involved. The ventral horn area of the spinal cord was therefore analyzed neurochemically. The determination of the phospholipids revealed an alteration of their composition. Sphingomyelin, phosphatidylcholine and phosphatidylinositide/serine behaved differently, whereas phosphatidylethanolamine and the total phospholipid content remained unchanged.

Animals↗

PubMed2002

Selectivity of the central control of sensory information in the mammalian spinal cord.

Afferent feedback from muscle proprioceptors, as well as movement-induced activation of skin receptors plays an important role in the patterning of motor activity for stepping and postural control. An important component in this control is the presynaptic GABAergic modulation of the synaptic effectiveness of muscle and cutaneous afferents, known to change in phase with the locomotor cycle, during the execution of voluntary movements, or after a peripheral nerve injury. Recent electrophysiological studies, together with ultrastructural observations, indicate that the distribution of GABAa synapses in the intraspinal arborizations of muscle spindle and tendon organ afferents is not homogeneous. Namely, that some collaterals are the targets of one, or more, GABAergic interneurones, while other collaterals of the same fibre receive no GABAergic connections. In addition, both PAD and inhibition of PAD have a local character. This allows, at least in principle, decoupling the information arising from common sensory inputs. A spatially restricted modulation of PAD could play a significant role in the adjustment of the synaptic effectiveness of Ia afferents at the onset of voluntary contractions in humans, during movement-induced stimulation of the skin, or during the compensation of motor activity following partial denervation of muscles. Changes in the synchronization of the PAD-mediating interneurones can also have a profound effect on the information transmitted by a given set of afferent fibres. Data are presented that in the anesthetized cat, variation in the spontaneous activity of a population of dorsal horn neurones in laminae III-VI, that respond to stimulation of low-threshold cutaneous afferents, produce correlated fluctuations of monosynaptic reflexes by means of pre- and postsynaptic mechanisms. It is suggested that correlated changes in the level of PAD can also play a significant role in the presynaptic adjustment of the synaptic effectiveness of the afferent fibres during specific motor tasks.

Animals↗

PubMed1976

Characteristics of the output from the dentate nucleus to spinal neurons via pathways which do not involve the primary sensorimotor cortex.

Experiments were performed to determine the action of the dentate output on neurons in the spinal cord mediated by pathways which do not involve the primary sensorimotor and premotor cortices. The dentate nucleus was electrically stimulated by stereotaxically placed electrodes in Rhesus monkeys whose contralateral sensorimotor and premotor cortices were ablated. The resultant changes in excitability of lumbar alpha motorneurons activated by Ia afferents from nerves innervating femoral, hamstring, gastrocnemius-soleus and peroneal muscles were measured by intracellular recordings and by determining the percent change in the amplitude of the monosynaptic reflex recorded from ventral roots. The effect of stimulation of the dentate nucleus on proprioceptive reflexes was determined by recording the changes in postsynaptic potentials evoked by selective stimulation of Ia and Ib afferent fibers. The results demonstrated that dentate nucleus exerts a significant action on the excitability of spinal neurons via pathways which do not include the sensorimotor and premotor cortices. Whether the dentate stimulus produced an increase or decrease in the excitability of these neurons was dependent upon the site within the dentate nucleus at which the stimulus was applied, demonstrating that, in the decorticate preparation, the output from this nucleus is quite heterogeneous. In addition, stimulation of the dentate nucleus in these monkeys did not affect the Ia reflex pathway but significantly changed the amplitude of the inhibitory postsynaptic potential evoked by Ib afferents in lumbar alpha motorneurons.

Animals↗

PubMed1986

Differential effects of stimulation of the cat's red nucleus on lumbar alpha motoneurones and their Renshaw cells.

The red nucleus region was stereotaxically stimulated with short trains of high-frequency alternating current pulses in anaesthetized cats. The effects were studied, in contralateral lumbar segments, on the responses of microrecorded individual Renshaw cells (RCs) to antidromic or orthodromic test shocks of ventral root or muscle nerve fibres. Monosynaptic reflexes (MRs) of their motoneurone pools were recorded from one of the cut lumbar ventral roots. Averages of 10-20 replicate test responses of the RC (converted into instantaneous frequency curves, IFCs) and of the MR shapes were computed and graphically displayed. 2. Orthodromic (afferent) test shocks induced simultaneously MRs as well as responses of a RC belonging to the same motor pool. From their paired records at systematically varied shock strengths, whole "linkage characteristics" of the relation between the two events could be obtained, representing the functional linkage from the motoraxon collaterals to the RC under study. The overall result of rubral conditioning was a change in the course of the characteristic, which indicated a reduction of this linkage (= relative inhibition of the RC against its recurrent input). 3. Sequential trials with test shocks of constant, submaximal strength were performed with 45 individual RCs. The clearest results were obtained with RC responses to antidromic ventral root shocks: 65% of the RCs were partially inhibited by rubral conditioning. Interposed minor facilitory subcomponents could be seen in the course of inhibited IFCs. Mixed sequences of manifest inhibitory/facilitory effects were observed in 11%; reversed sequences (facilitory/inhibitory) did not occur. A pure but weak facilitation was found in only one case, paralleled by an increase of the MR. RCs belonging to either extensor or flexor motor pools were affected about equally. A little over 20% of the tested RCs remained uninfluenced by rubral stimulation. 4. The MRs, induced by constant, submaximal, orthodromic test shocks, were usually enhanced with only few exceptions, by rubral stimulation. The effects on the orthodromic RC responses were mainly inhibitory, but could be more or less masked by the concurrent increase of the MR, providing a stronger recurrent input to the RC. Such inhibition could be uncovered, however, by observing the above described linkage change. 5. Variation of several parameters of rubral conditioning (train duration, timing of train with respect to test shock, strength of train) modified the inhibitory effects on antidromic RC responses to a certain extent without changing their principal character.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1984

A re-evaluation of the pattern of group I fibre projections in the human lower limb on using randomly alternated stimulations.

Changes in amplitude of soleus, quadriceps and biceps femoris monosynaptic reflexes were studied when preceded by conditioning stimulations applied to group I fibres from different muscles of the human lower limb. Control test reflexes and conditioned reflexes were alternated either regularly or randomly. For the most part, the same qualitative pattern of group I fibre projections was found with both modes of alternation, but the amount of facilitation or inhibition induced by group I fibre stimulation was significantly smaller with the random mode. This may be due to an underestimation of randomly-induced effects and/or an overestimation of regularly-induced effects. Because this overestimation can lead to artefactual results, regular mode of alternation should be avoided.

Electric Stimulation↗

PubMed1981

Neurotoxicology of vincristine in the cat. Electrophysiological studies.

Cats were given vincristine sulfate (50 micrograms/kg i.v. every 4 days) and studied after 7-29 injections when neurological deficits became evident. The conduction velocity spectrum of individual afferent nerves from soleus muscles was shifted toward slower velocities. Relatively few functional muscle spindles or other proprioceptors which responded to muscle stretch were encountered. Those primary endings of soleus muscle spindles which did respond were significantly reduced in dynamic but not length sensitivity. Length sensitivity of secondary endings was unchanged. Thresholds of secondary but not primary endings were elevated. The average conduction velocity of soleus motor axons was reduced 30% but no deficit was detected in motor nerve terminal function. Indirectly-elicited contractile tension of the soleus muscles of the neuropathic cats was not significantly lower than that in untreated animals. Amplitudes of spinal monosynaptic reflexes were unaffected. These data indicate, that in the cat, neurological impairment results partly from dysfunction in muscle spindles and peripheral nerves.

Afferent Pathways↗

PubMed1975

Bilateral effects of vestibular nerve stimulation on activity in the lumbar spinal cord.

These experiments were designed to study the effects of vestibular nerve stimulation on the activity of hindlimb motoneuron pools. Two techniques were used to stimulate the vestibular nerves of precollicularly decerebrated cats. In one set of experiments the individual semicircular canals were stimulated via bipolar electrodes placed near the canal nerves. In the second series of experiments the whole vestibular nerve was stimulated with an electrode placed on the intradural nerve. Activity in the hindlimb motoneuron pools was ascertained by evoking monosynaptic reflexes in the various hindlimb nerves. Stimulation of the individual semicircular canals produced response patterns that varied with both the vestibular branch being stimulated and the hindlimb nerve being conditioned. Intradural stimulation of the vestibular nerve, on the other hand, evoked similar response patterns in the antagonist ankle flexor and extensor nerves. The most common pattern consisted of facilitation followed by a period of inhibition. Lesions of descending fiber tracts produced results which suggest the presence of a diffuse pathway, involving the recitular formation, which mediates the observed responses. It is suggested that the biphasic response pattern is analogous to the startle response and the function of the responses is discussed in that context.

Animals↗

PubMed1980

Electrophysiological evidence for a release of endogenous opiates in stress-induced'analgesia' in man.

The effects of a repetitive stress induced by anticipation of pain were studied on the following somato-vegetative parameters: monosynaptic reflex (H reflex), nociceptive flexion reflex (RIII reflex), heart rate and respiratory frequency, in normal trained volunteers. A progressive increase in heart rate and in respiratory frequency, as well as a facilitation in H reflex parallel to an inhibition of RIII reflex (threshold increased) were observed in all subjects as a function of repetition of stress during 45 min. At this moment, a double-blind injection of a strong dose of naloxone (4 mg) resulted in a rapid exacerbation in vegetative responses (tachycardia, polypnea) as well as in an increase in the facilitation of the H reflex, whereas the RIII reflex was dramatically facilitated (threshold decreased). In contrast, no significant change in these parameters was observed during placebo (saline) injection compared to a control situation (no injection). These data strongly suggest that endogenous opioids are involved in the phenomenon of stress-induced analgesia in man. Moreover, they show that the release of opiates in these conditions possibly modulates non-specific structures which are known to be activated during stress or emotion.

Adult↗

PubMed1988

Involvement of adenosine in synaptic depression induced by a brief period of hypoxia in isolated spinal cord of neonatal rat.

The monosynaptic reflex (MSR), recorded extracellularly from the ventral root isolated, superfused spinal cords of neonatal rats (6-10 days post-partum), was rapidly depressed to 35-45% of control values by either cessation of superfusion (4 min stop-flow period) or by superfusion with anoxic medium (95% N2-5% CO2; 4 min). The depression was reversible, 85-115% recovery occurring after 15 min of restoration of flow or normoxic (95% O2-5% CO2) superfusion. 2-Chloroadenosine, a metabolically stable adenosine analogue, also reversibly inhibited the MSR, an effect which was antagonised by 10(-6) M 8-cyclopentyltheophylline (8-CPT). The depression of the MSR, caused by 4 min of hypoxia (either stop-flow or anoxic superfusion), was prevented by 10(-6) M 8-CPT. These results provide strong evidence for a critical involvement of adenosine in mediating early synaptic depression evoked by a brief period of hypoxia.

2-Chloroadenosine↗

PubMed1989

The actions of two monoamines on spinal motoneurons from stimulation of the locus coeruleus in the cat.

The present study investigates the role of the two putative amine transmitters (norepinephrine and serotonin) in mediating the facilitatory action following locus coeruleus (LC) stimulation on hindlimb flexor and extensor monosynaptic reflexes (MSRs) in unanesthetized, decerebrate cats. When administered sequentially, in either order, methysergide (a serotonergic blocker) and prazosin (an alpha 1-adrenergic blocker) were observed to cause subtotal, decremental changes in the potentiation of gastrocnemius-soleus and common peroneal MSRs by stimuli applied in the LC. These changes were determined to be independent of the blood pressure changes induced by the aminergic blockers. These results support the hypothesis that the facilitation of the group Ia reflex transmission in cat spinal cord by stimulation of LC is mediated in part by alpha 1-noradrenergic and serotonergic mechanisms.

Adrenergic Fibers↗

PubMed1994

Thyrotropin-releasing hormone reverses the supersensitively depressed monosynaptic transmission by serotonin in 5,7-dihydroxytryptamine-treated neonatal rats in vitro.

The interaction of serotonin and thyrotropin-releasing hormone (TRH) on monosynaptic reflex (MSR) in isolated neonatal spinal cords was examined. Superfusion of serotonin (1-30 microM) in untreated cords, depressed the MSR in a dose-dependent manner. The depression was about 25% at 10 microM of serotonin, in either control or vehicle-treated groups. While for the same concentration of serotonin, the depression was 97 +/- 2.1% of the control in cords from 5,7 dihydroxytryptamine (5,7-DHT)-treated animals. The inhibition of the reflex seen in cords obtained from 5,7-DHT-treated animals could not be reversed by washing with normal physiological solution (> 60 min) or in presence of serotonin antagonists. TRH (0.03-1.0 microM) reversed the depression in a concentration-dependent manner and complete reversal could be seen with 1 microM of TRH. These observations indicate that, serotonin and TRH act dissimilarly on the spinal synaptic transmission though they are known to coexist in the descending bulbospinal tracts.

5,7-Dihydroxytryptamine↗

PubMed1985

The effect of local and systemic application of dopaminergic agents on tail flick latency in the rat.

Dopamine (DA) is thought to have a neurotransmitter role in the spinal cord of the rat. Intrathecal administration of the DA receptor agonist apomorphine has previously been shown to reduce nocifensive responses. The present experiments investigated the site of action of apomorphine, and the mechanisms by which DA agonists apparently produce antinociception. Small doses of apomorphine (40-80 micrograms/kg) increased the tail flick latency (TFL) in lightly anaesthetised rats when given intrathecally and intravenously but not intracerebroventricularly. This effect is probably mediated via D2 receptors since the D2 agonist LY171555 had a similar effect whereas the D1 agonist SK&F 38393 was inactive. Furthermore the D2 antagonist sulpiride blocked the effects of apomorphine and LY171555. The spinal monosynaptic reflex was not modified by 150 micrograms/kg apomorphine suggesting that sensory rather than motor processes are being influenced. Pretreatment with the serotonin receptor antagonist methysergide prevented the apomorphine induced increase in TFL. It is concluded that exogenously applied DA agonist can result in antinociception in the spinal cord and that this effect may be dependent upon activity in the spinal 5-hydroxytryptaminergic and noradrenergic systems.

Analgesics↗

PubMed1991

Alpha 2-adrenoceptors inhibit a nociceptive response in neonatal rat spinal cord.

Alpha 2-Adrenoceptors mediate analgesia in vivo. The present study explored the actions of the alpha 2-adrenoceptor agonists dexmedetomidine and clonidine on a nociceptive response in isolated neonatal rat spinal cord. Stimulation of a dorsal root generates a slow ventral root potential (slow VRP) at the corresponding ipsilateral ventral root. The slow VRP meets several criteria for a nociceptive response. Dexmedetomidine (10 nM) and clonidine (200 nM) depressed the slow VRP by approximately 80%. Dexmedetomidine's action was approximately linear over the concentration range 0.5-500 nM, whereas clonidine (20 nM-5 microM) exerted biphasic effects. The profile of agonist and antagonist effectiveness characterized the receptor(s) as alpha 2-adrenoceptors; the subtype could not be identified as either alpha 2A or alpha 2B. Naloxone pretreatment partially blocked dexmedetomidine's effect, suggesting a possible endogenous opiate involvement. Dexmedetomidine (0.5-2.0 nM) also depressed the VRP evoked by application of substance P to the cord, implicating postsynaptic as well as possible presynaptic actions. At high concentrations, dexmedetomidine (50-500 nM) depressed the monosynaptic reflex, probably through non-alpha 2-receptor(s). Results from the neonatal spinal cord correlate well with those from in vivo analgesia studies. They suggest an important direct spinal contribution to alpha 2-adrenoceptor-mediated analgesia.

Adrenergic alpha-Agonists↗