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PubMed2002

[Muscarinic receptors of the neostriatum -- important targets of regulation of instrumental movement and posture].

Chronic experiments with 10 dogs were conducted to study effects of bilateral microinjections of the nonselective agonist of the muscarinic receptors carbachol, nonselective blocker of the muscarinic receptors scopolamine and selective blocker M1 of the muscarinic receptors pyrensepine on the instrumental defensive reflex in the neostriatum to sustain a given flexion amplitude and posture adjustment. Microinjections of carbachol were found to increase tone and stem the phase of the reflex, make posture adjustment more orderly and amplitudinous. Repeated microinjections gave the instrumental movement a ramp-like form. Chronic carbachol microinjections (over several years) resulted in akinesis and rigidity in dogs. However, these led to impairment of the diagonal pattern of posture adjustment as in pathologic so in normal dogs. These developments were partially meliorated by dopamine, scopolamine and pyrensepine which sharply increased the phase component of the instrumental movement. These findings are interpreted in the light of the concept of two neostriatum efferent outputs with opposite effects on respective targets and the muscarinic and dopamine receptors as their triggers and blockers. Results of the experiment bring to the conclusion that activation or blockage of the muscarinic receptors in the neostriatum can modify an existing motor behavior and compensate motor pathology in dogs.

Animals↗
PubMed1995

Cardiac arrest after traffic accident induced through vagal reflex in a case with bilateral stenosis of vertebral arteries.

An 84-year-old driver suffered cardiac arrest after a traffic accident. He was quickly resuscitated and transferred to a hospital where he was treated in a state of unconsciousness and respiratory failure for 20 days until his death. The brain stem was rendered anoxic during cardiac arrest, which caused the respiratory failure. Artificial ventilation and catecholamine infusion were carried out, resulting in myocardial degeneration. Bilateral stenosis of the vertebral arteries was disclosed, but no injuries or hemorrhage of the brain and spinal cord were detected. On days 3 and 4 after admission, immediately after the head of the victim was flexed forward for examinations, cardiac arrest was induced twice, but was controlled either by administering atropine or by restoring the original posture. Positional change is known to induce vagal reflex that results in bradycardia, hypotension or cardiac arrest in sensitive persons. The victim might have undergone the reflex-mediated cardiac arrest after the accident, to which the stenosis of the vertebral arteries may have contributed.

Accidents, Traffic↗
PubMed1996

A dose-response analysis of the behavioral effects of (+)MK-801 in guinea pig: comparison with CPP.

The noncompetitive N-methyl-D-aspartate (NMDA) antagonist, dizocilpine maleate {(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5, 10-imine maleate} [(+)MK-801], has attracted considerable interest because of its potential use as an anticonvulsant and neuroprotectant. However, its cognitive side effects in humans have limited its use in human pharmacotherapy. Although the behavioral effects of (+)MK-801 have been documented in mouse, rat, pigeon, and rhesus monkey, there are no available data on its effects in guinea pig. The objective of this study was to conduct a dose-response analysis of the effects of (+)MK-801 on stereotyped behavior, ataxia, locomotor activity, and righting reflex latency in guinea pig. In the dose range used (0.0625-0.5 mg/kg, IP), we found no significant differences between (+)MK-801 and vehicle in terms of stereotyped behavior and locomotor activity; however, at higher doses, (+)MK-801 caused significant ataxia and impairment of the righting reflex. By comparison, the competitive NMDA receptor antagonist, 3-((+/-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP,5 mg/kg, IP), produced neither stereotyped behavior nor impairment of the righting reflex; at higher doses (10 mg/kg, IP), it produced only ataxia and an increase in locomotor activity.

Animals↗
PubMed2004

Neuromuscular reflexes contribute to knee stiffness during valgus loading.

We have previously shown that abduction angular perturbations applied to the knee consistently elicit reflex responses in knee joint musculature. Although a stabilizing role for such reflexes is widely proposed, there are as of yet no studies quantifying the contribution of these reflex responses to joint stiffness. In this study, we estimate the mechanical contributions of muscle contractions elicited by mechanical excitation of periarticular tissue receptors to medial-lateral knee joint stiffness. We hypothesize that these reflex muscle contractions will significantly increase knee joint stiffness in the adduction/abduction direction and enhance the overall stability of the knee. To assess medial-lateral joint stiffness, we applied an abducting positional deflection to the fully extended knee using a servomotor and recorded the torque response using a six degree-of-freedom load-cell. EMG activity was also recorded in both relaxed and preactivated quadriceps and hamstrings muscles with surface electrodes. A simple, linear, second-order, delayed model was used to describe the knee joint dynamics in the medial/lateral direction. Our data indicate that excitation of reflexes from periarticular tissue afferents results in a significant increase of the joint's adduction-abduction stiffness. Similar to muscle stretch reflex action, which is modulated with background activation, these reflexes also show dependence on muscle activation. The potential significance of this reflex stiffness during functional tasks was also discussed. We conclude that reflex activation of knee muscles is sufficient to enhance joint stabilization in the adduction/abduction direction, where knee medial-lateral loading arises frequently during many activities.

Adult↗
PubMed2004

Bifurcation and stability analysis in musculoskeletal systems: a study in human stance.

Reflexes are important in the control of such daily activities as standing and walking. The goal of this study is to establish how reflexive feedback of muscle length, velocity, and force can lead to stable equilibria (i.e., posture) and limit cycles (e.g., ankle clonus and gait). The influence of stretch reflexes on the behavior and stability of musculoskeletal systems was examined using a model of human stance. We computed branches of fold and Hopf bifurcations by numerical bifurcation analysis of the model. These fold and Hopf branches divide the parameter space, constructed by the reflexive feedback gains, into regions of different behavior: unstable posture, stable posture, and stable limit cycles. These limit cycles correspond to a neural deficiency, termed ankle clonus. We also linked bifurcation analysis to known biomechanical concepts by linearizing the model: the fold branch corresponds to zero ankle stiffness and defines the minimal muscle length feedback necessary for stable posture; the Hopf branch is related to unstable reflex loops. Crossing the Hopf branch can lead to the above-mentioned stable limit cycles. The Hopf branch reduces with increasing time delays, making the subject's posture more susceptible to unstable reflex loops. This might be one of the reasons why elderly people, or those with injuries to the central nervous system, often have trouble with standing and other posture tasks. The influence of cocontraction and force feedback on the behavior of the posture model was also investigated. An increase in cocontraction leads to an increase in ankle stiffness (i.e., intrinsic muscle stiffness) and a decrease in the effective reflex loop gain. On the one hand, positive force feedback increases the ankle stiffness (i.e., intrinsic and reflexive muscle stiffness); on the other hand it makes the posture more susceptible to unstable reflex loops. For negative force feedback, the opposite is true. Finally, we calculated areas of reflex gains for perturbed stance and quiet stance in healthy subjects by fitting the model to data from the literature. The overlap of these areas of reflex gains could indicate that stretch reflexes are the major control mechanisms in both quiet and perturbed stance. In conclusion, this study has successfully combined bifurcation analysis with the more common biomechanical concepts and tools to determine the influence of reflexes on the stability and quality of stance. In the future, we will develop this line of research to look at rhythmic tasks, such as walking.

Ankle↗
PubMed1979

The asymmetrical tonic neck reflex in normal full-term infants.

The purpose of this study was to determine whether the asymmetrical tonic neck reflex was present in normal 1- to 12-week-old infants. Twelve infants were observed seven times within the first 12 weeks: at the first and second week and every other week thereafter. Spontaneous behavior was videotaped while the infant lay supine. Infants maintained a head-turned posture during every visit. The asymmetrical tonic neck reflex was present: 1) in the infants' arms during every visit, at a maximum at the sixth week; 2) in their legs, with the longest duration of the response at the first week's visit; and 3) in both arms and legs, with no change throughout seven visits. There were more movements of the face arm than of the skull arm during the seven visits, and the additional movements were in the extension range. The face leg moved more than the skull leg, but only at the 6th, 8th, and 10th weeks. The study confirms that the asymmetrical tonic neck reflex can be observed in the posture and movement of normal infants and that the pattern of appearance of the reflex differs in arms and legs.

Arm↗
PubMed1990

Distinctions among sedative, disinhibitory, and ataxic properties of ethanol in inbred and selectively bred mice.

Three different domains of behavioral action of ethanol (ETOH) were examined in a battery of seven inbred strains and in the selectively bred Long-Sleep (LS) and Short-Sleep (SS) mice. Sedative effects were examined with the loss of the righting reflex test at 3.8 g/kg. The variation among inbred strains was only half the size of the difference between LS and SS mice which were selectively bred for extremes in this phenotype; such a result is expected for phenotypes controlled polygenically. Blood ETOH levels at waking from the narcosis also showed a range of differences among the inbred strains that was less than the LS/SS difference. Ataxia was measured with the grid test, and the inbred strains fell into two groups, resembling the highly ataxic LS line, and the less ataxic SS line. Biphasic effects of ETOH on locomotor activity were strongly genotype dependent. Variation in degree of activation/disinhibition produced by doses up to 1.5 g/kg (IP) ranged from no activation, in the C57BL/6Abg strain which was larger than that seen for SS mice. The patterns of strain differences for both ataxia and activation were highly different from the duration of loss of righting reflex measure, suggesting multiple independent genetically based "sensitivities" to ETOH.

Animals↗
PubMed1982

Roll tilt reflexes after vestibulospinal tract lesions.

The effects of lesions of the vestibulospinal tracts on vestibular reflexes evoked by roll tilt in forelimb and neck extensors were examined in decerebrate cats. Sectioning the medial longitudinal fasciculus, which contains the medial vestibulospinal tract, had no major effect on the phase of the reflex, although some gain was usually lost at high stimulus frequencies. Spinal lesions at C2-C3, both cord hemisections and more restrictive lesions which cut the lateral vestibulospinal tract, produced two major effects on the forelimb. Background EMG activity was usually abolished in the triceps ipsilateral to the lesion, with partial loss of activity in the opposite limb. The tilt reflex response in the ipsilateral limb appeared normal, although it was usually necessary to raise the background excitability of the preparation by administering L-Dopa in order to observe the reflex. In contrast, the response in the contralateral limb showed a phase reversal of 180 deg at low stimulus frequencies, implying that the reflex in intact cats receives a crossed otolith-spinal input. Responses in the neck extensors splenius and biventer, recorded from compartments caudal to the spinal lesion, were relatively unaffected.

Animals↗
PubMed1981

Diaphragm electrical activity during negative lower torso pressure in quadriplegic men.

We recorded the diaphragm electromyogram (EMG) of quadriplegic men before and during exposure of the lower torso to continuous negative pressure, which caused shortening of the inspiratory muscles by expanding the respiratory system by one tidal volume. The moving-time-averaged diaphragm EMG was larger during expansion of the respiratory system. When we repeated the experiment with subjects who breathed through a mouthpiece, we found qualitatively similar EMG changes and little or no change in tidal volume or end-tidal CO2 partial pressure. When the pressure was applied or removed rapidly, changes in EMG occurred within one or two breaths. Because end-tidal CO2 partial pressure did not increase, and because the response was rapid, we suggest that the response results from proprioceptive, rather than chemoreceptive, reflexes. As most of these men had complete spinal lesions at C6 or C7 the afferent pathways are likely to be vagal or phrenic.

Adult↗
PubMed1992

Posturography in vestibular work-up of the patient. A review.

In order to obtain a complete functional balance in the patient suffering from vestibular disorders it is necessary to examine the spinal reflexes. Computerized posturographic systems allow quantitative and qualitative analysis of body sway. The posturographic test must be preceded by an accurate clinical examination to identify the anomalies of the osteo-arthro-muscular structure that can cause disorders in motor programs and in proprioceptive inputs. A battery of complementary posturographic tests can clarify the influence of the vestibular, proprioceptive and visual inputs. The posturographic tests allow us: to observe particular aspects of postural control which are not usually detected by the common clinical examination; to identify the most correct kind of functional reeducation and to monitor the spontaneous evolution of the disease and the results of the therapy; to show the voluntary simulators or accentuators of unsteadiness in medico-legal reports.

Humans↗
PubMed1989

Cardiovascular reflex responses in patients with unexplained syncope.

1. This study was undertaken to determine whether, in a group of patients complaining of recurrent syncopal attacks but with no apparent cause, there was evidence of abnormal cardiovascular reflex control. 2. The steady-state responses of blood pressure, heart rate and cardiac output to head-up tilting were determined in 67 patients using entirely 'non-invasive' methods. In some patients we also studied the immediate response of pulse interval to carotid baroreceptor stimulation by neck suction. 3. Two of the patients developed vasovagal attacks during the 20 min test period of head-up tilting. Eighteen others showed postural hypotension, defined as a fall in blood pressure to outside the limits of two SDS from the mean values of age-related control subjects. 4. Patients who showed postural hypotension had a mean fall in cardiac output significantly larger than that in age-related control subjects. Responses in the nonhypotensive patients did not differ significantly from controls. 5. Stimulation of carotid baroreceptors resulted in significantly smaller responses of pulse interval in the patients defined as having postural hypotension compared with the non-hypotensive patients and with the age-related control subjects. 6. In some of the patients who did not show postural hypotension during the standard test, the duration of tilt was prolonged for up to 1 h. Five out of 26 patients developed vasovagal attacks. All the vasovagal patients showed an initial tachycardia and the response of pulse interval to neck suction was significantly larger than in the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Pressure↗
PubMed2004

An evaluation of postural stability and the effects of middle-ear drainage on vestibulo-spinal reflexes of children with chronic otitis media with effusion.

OBJECTIVE: Many authors agree that chronic otitis media with effusion (OME) are the main causes of vertigo and balance disturbances in children. The aim of this work was the stabilometric evaluation of postural stability and the influence of middle ear drainage on vestibulo-spinal reflexes in children with OME. METHODS: Fifteen children with OME (5-14 years old, 13 males and two females) were selected for bilateral drainage of the middle ear after conservative treatment proved ineffective. The control group consisted of 15 healthy children of an analogous age range. Static and quasi-dynamic posturography was performed to evaluate balance. The tests were performed three times: 1 day before drainage, 1 day after drainage and 4 weeks after drainage. Parameters including the field of the developed area and the average velocity of body deflection were analysed. RESULTS: There was statistically significant elevation of stabilogram parameters in almost all the tests in children with OME as compared to the control group. The changes in the stabilogram parameters were analysed with reference to the timing of the evaluation. Significant improvement was noted after the fluid was removed from the ear, although recovery was not complete after 4 weeks. CONCLUSIONS: The presence of fluid in the middle ear impairs the functioning of the balance system in children. Postural stability and the quantity of vestibulo-spinal reflexes seem to depend on the functional condition of the middle ear. Prolonged cases of OME could potentially handicap a child's motor development.

Adolescent↗
PubMed2000

The mechanical action of proprioceptive length feedback in a model of cat hindlimb.

Postural regulation is an important part of a variety of motor tasks, including quiet standing and locomotion. Muscle length feedback, both the autogenic length feedback arising from a muscle's own spindles, and heterogenic length feedback, arising from its agonists and antagonists, is a strong modulator of muscle force and well suited to postural maintenance. The effects of this reflex feedback on 3-D force generation and limb mechanics are not known. In this paper, we present a mechanical model for relating 3-D changes in cat hindlimb posture to changes in muscle lengths. These changes in muscle length are used to estimate changes in both intrinsic muscle force generation and muscle activation by length feedback pathways. Few muscles are found to have directly agonist mechanical actions, and most differ by more than 20 degrees. Endpoint force fields are largely uniform across the space investigated. Both autogenic and heterogenic feedback contribute to whole limb resistance to perturbation, autogenic pathways being most dramatic. Length feedback strongly reinforced a restoring force in response to endpoint displacement.

Animals↗
PubMed1985

[Effect of nifedipine on arterial pressure and control of the cardiac reflex].

Nine patients with untreated essential hypertension (random blood pressure 173/109 +/- 14/7 mmHg) were studied before and after 16 weeks' treatment with oral nifedipine 10 mg three times a day. Direct continuous measurement of the systolic and diastolic blood pressures showed that both values were significantly reduced during the 24 hour period. Nifedipine did not change the variability of the blood pressure. There was no significant change in the heart rate after treatment with nifedipine. Long-term nifedipine induced an increase in blood flow in the forearm and decreased the vascular resistances which confirmed the vasodilator effects of the drug. The absolute responses of the blood pressure during postural changes, the hand grip test and cold pressor test were reduced but the treatment did not change the percentage increase in blood pressure during these tests. Long-term nifedipine therapy did not affect the plasma renin activity. The sensitivity and characteristics of the baroreflex response to intravenous phenylephrine were measured. After long-term nifedipine therapy we observed a normalisation of the sino-aortic baroreflex and an increase in its sensitivity. Normalisation of the blood pressure by nifedipine induced a significant reduction in the index of left ventricular mass.

Adult↗
PubMed1982

Sympathetic reflex control of subcutaneous blood flow in tetraplegic man during postural changes.

1. The effect of head-up tilt upon subcutaneous blood flow in the distal arm and leg was studied in 12 patients with complete traumatic spinal cord transection at the cervical level. 2. Blood flow was measured by the local 133Xe washout technique. 3. Leg lowering induced a 47% decrease in blood flow in the distal leg. During head-up tilt (45 degrees) blood flow in the leg decreased by 48%. In the arm remaining at heart level blood flow decreased by 37% during tilt and this vasoconstriction could be prevented by nervous blockade with lignocaine injected subcutaneously 5 cm proximally to the labelled area. Leg blood flow was unaltered by proximal blockade but could be blocked by local infiltration in the labelled area with lignocaine in low doses. 4. Head-up tilt of tetraplegic patients induced vasoconstriction in the subcutaneous tissue of the forearm, which could be prevented by proximal blockade. Thus the vasoconstriction could be due to a spinal sympathetic reflex mechanism. This as well as local mechanisms including the venoarteriolar reflex may play a role in recovery of arterial blood pressure during head-up tilt in the tetraplegic patient.

Adult↗
PubMed2003

Stumbling corrective responses during treadmill-elicited stepping in human infants.

This study examined stumbling corrective (tripping) responses to mechanical disturbances applied to the foot during stepping in healthy human infants, in whom independent walking had not yet developed. During treadmill-elicited stepping, a foam-padded baton instrumented with a force transducer was used to deliver light touches to either the dorsum or the side of the foot at various times of the step cycle. Disturbances to the dorsum of the foot during the swing phase resulted in a general enhancement of flexor activity, including a significant facilitation in the tibialis anterior muscle and an increase in knee flexion during swing. There was also an increase in step cycle duration. Stance phase disturbances resulted in a significant inhibitory effect in the quadriceps muscle and after early stance disturbances, a significant prolongation of the stance phase duration. Disturbances applied to the side of the foot during the swing phase of forward stepping did not result in any effect on the kinematic pattern. If the infant was stepping sideways, however, disturbances to the side of the foot resulted in an increase in flexion during the swing phase. The results show that infants have a phase-dependent reflex response to light touches applied to the foot. Furthermore, the reflex response is location specific and task specific. Thus, much of the sophistication necessary for controlling sensory inputs in walking is present well before the onset of independent walking.

Ankle↗
PubMed1988

Postural adjustments to head movements in the cat.

Head movements induced by motor cortex stimulation in the cat are accompanied by variations in the vertical force exerted by each limb. These postural responses were found to show stereotyped patterns: with head dorsiflexions an increase was observed in the force exerted by the anterior limbs and a decrease at the posterior limb level. From comparison between the latencies of the force variations, the beginning of head acceleration, and EMG activity in the limb extensor muscles, it was concluded that triggering of these postural responses is not reflex, but depends on the same command as the movement itself. This early response might be a means of avoiding the downward movement of the trunk which would otherwise result from the reaction force corresponding to the upward head movement.

Animals↗
PubMed1992

Spatial disorientation and dysfunction of orientation/equilibrium reflexes: aeromedical evaluation and considerations.

Loss of spatial awareness has been implicated as a direct causal factor in 4-10% of serious aircraft mishaps and 10-20% of fatal aircraft mishaps (7). Spatial disorientation in flight usually results from misperception of visual, vestibular, or proprioceptive cues. Pathologic causes have rarely been implicated. A student naval aviator with recurrent loss of spatial awareness due to a defective vestibulo-ocular reflex (VOR), presumably from vestibular neuronitis in adolescence, is reported. His chief complaint, an inability to focus on the instrument panel during turbulent instrument meteorological conditions (IMC), resulted in spatial disorientation and adverse flight attitude. A simple test of visual-vestibular interaction, the dynamic visual acuity test, could identify a defective vestibulo-ocular reflex in aviation personnel. An absent or defective vestibulo-ocular reflex has potential for disorientation in instrument flight. A comprehensive vestibular function test battery is indicated in individuals with recurrent or overwhelming spatial disorientation who fail a screening dynamic visual acuity test. The aeromedical disposition of vertigo and dysequilibrium is discussed.

Adult↗