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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↗
PubMedDate not supplied

Influence of tonic reflex activities on the slow auditory evoked potential.

Possible influences of tonic reflex activities on the slow auditory evoked potential were investigated. For this purpose, the slow auditory evoked potential was picked up in 18 volunteers with normal hearing in relaxed position and in postures corresponding to reflex-induced positions and in 15 patients with cerebral palsy (CP) in tonic reflex patterns. No influence on latency for N120 and P215 due to postures could be observed. Latency within CP patients was age-dependent. The effect of the reflex-inhibiting pattern (RIP) - the pattern inhibiting tonic reflex activity in CP patients as far as possible - on potential amplitude was different in the two groups. The effect of RIP in CP patients was comparable to the relaxed position in volunteers. This difference points toward an influence of tonic reflex activity on the slow auditory evoked potential.

Acoustic Stimulation↗
PubMed2006

Involvement of the transmitter systems of the neostriatum in automation of motor skills in dogs.

Chronic experiments were performed on six dogs to address the influence of automation of a motor skill on the components of an operant defensive reflex, rearrangement of posture, and the characteristics of the projection of the center of mass on a tensometric platform by the forepaws; the effects of activation and blockade of muscarinic and dopamine receptors on the process of automation of the motor skill were also studied. Despite high criteria for execution of the operant reflex, the reproducibility of reflex performance, increases in the tonic component of the response, and the clear diagonal pattern of the postural rearrangement, a local (as opposed to diffuse) projection of the position of the center of mass on the tensometric platform by the forepaws was seen only after prolonged training leading to automation of the skill. The effect of automation of the operant response could be obtained immediately following bilateral microinjection of the muscarinic receptor agonist carbachol into the neostriatum. The same effect, but weaker, was obtained using bilateral microinjections of the dopamine D2 receptor blocker raclopride into the neostriatum. Conversely, bilateral microinjections of the selective muscarinic M1 receptor blocker pirenzepine into the neostriatum gave the opposite result, with increases in the phasic component of the response, impairment of the diagonal pattern of the postural rearrangement, and diffuseness of the projection of the center of mass on the tensometric platform by the forelimbs. It is concluded that the indirect efferent output of the neostriatum has an important role in the process of learning the motor operant reflex involving maintenance of a defined degree of flexion (where the main role is played by the tonic component of the movement) and during the process of automation of the motor skill.

Animals↗
PubMed1991

Postural sway characteristics of the elderly under normal and altered visual and support surface conditions.

One of the most pervasive findings in the literature on the aged is the general slowing of cognitive-motor responses with advancing age. Hence, an increased slowness in the processing of information from vestibular, visual, and somatosensory systems could contribute greatly to a decline in postural stability. To examine this question, in a cross-sectional investigation, postural sway behavior of elderly (n = 18) and young (n = 10) adults was examined under conditions that stressed the slower integrative mechanisms rather than the reflexive mechanisms of postural control. The postural sway behavior of young and elderly subjects was examined for a prolonged duration (80 s), under altered visual and/or support surface (5 cm thick foam surface) conditions, and contrasted with normal stance. Results showed that the exclusion or disruption of one of the sensory inputs, alone, was not consistently sufficient to differentiate between elderly and young adults, because of compensation by the remaining sensory sources. Both alterations together (i.e., visual and surface), however, had a substantially greater effect upon the elderly than the young.

Adult↗
PubMed1997

Differential control of reciprocal inhibition during walking versus postural and voluntary motor tasks in humans.

Experiments were done to determine whether the strength of reciprocal inhibition from ankle flexors to extensors can be controlled independently of the level of ongoing motor activity in a task-dependent manner. In this paper we use the term reciprocal inhibition in the functional sense--inhibition of the antagonist(s) during activity of the agonist(s)--without reference to specific neural pathways that may be involved. The strength of reciprocal inhibition of the soleus alpha-motoneurons was determined by measuring the amplitude of the H reflex during voluntary, postural, and locomotor tasks requiring activity of the ankle flexor tibialis anterior (TA). Differences in the strength of reciprocal inhibition between tasks were determined from plots of the soleus H reflex amplitude versus the mean value of the TA electromyogram (EMG). Additionally, in tasks involving movement, the correlation between the H reflex amplitude and the joint kinematics was calculated. In most subjects (15 of 22) the soleus H reflex decreased approximately linearly with increasing tonic voluntary contractions of the TA. The H reflex also decreased approximately linearly with the TA EMG activity when subjects where asked to lean backward. There were no statistical differences between the regression lines obtained in these tasks. In some subjects (7 of 22), however, the H reflex amplitude was independent of the level of TA EMG activity, except for a sudden drop at high levels of TA activity (approximately 60-80% of maximum voluntary contraction). The type of relation between the soleus H reflex and the TA EMG activity in these tasks was not correlated with the maximum H reflex to maximum M wave (Hmax/Mmax) ratio measured during quiet standing. In marked contrast, during the swing phase of walking--over the same range of TA EMG activity as during the tonic voluntary contraction task--the H reflex was reduced to zero in most subjects (24 of 31). In seven subjects the H reflex during the swing phase was reduced to some 5% of the value during quiet standing. The same result was found when subjects were asked to produce a stepping movement with one leg (OLS) in response to an auditory "go" signal. Additionally, in the OLS task it was possible to examine the behavior of the H reflex during the reaction time and thus to evaluate the relative contribution of central commands versus movement-related afferent activity to the inhibition of the soleus H reflex. In 11 of 12 subjects the H reflex attained its minimum value before either the onset of EMG activity or movement of any of the leg joints. It is significant that the H reflex was most powerfully inhibited during the swing phase of walking and the closely related OLS task. The H reflex was also measured during isolated ankle dorsiflexion movements. The subjects were asked to track a target displayed on a computer screen with dorsiflexion movements of the ankle. The trajectory of the target was the same as that of the ankle during the swing phase of walking. The soleus H reflexes were intermediate in size between the values obtained in the tonic contraction task and the walking or OLS tasks. A negative, but weak, correlation (r2 < 0.68) between the soleus H reflex and the TA EMG was found in 3 of 10 subjects. Furthermore, there was no correlation between the H reflex amplitude and the ankle angular displacement or angular velocity. In this task, as in the OLS task, the H reflex began to decrease during the reaction time before the onset of TA EMG activity. We conclude that the strength of reciprocal inhibition of the soleus alpha-motoneuron pool can thus be controlled independently of the level of motor activity in the ankle flexors. The strength of the inhibition of the antagonist(s) depends on the task, and for each task the strength of the inhibition is not necessarily proportional to the level of motor activity in the agonist(s). (ABSTRACT TRUNCATED)

Adult↗
PubMed1986

Amplitude modulation of the soleus H-reflex in the human during walking and standing.

Experiments were done to determine the amplitude of the monosynaptically mediated H-reflex of the soleus muscle at various phases of the step cycle, using a computer-based analysis procedure. In all subjects tested the amplitude of the H-reflex was strongly modulated in amplitude during the walking cycle and was highest during the stance phase. In many subjects the peak reflex amplitude occurred at about the same time as the peak soleus electromyographic (EMG) activity, but in others it occurred earlier. The form of the reflex variation (i.e., envelope of H-reflex amplitude versus phase in cycle) during the step cycle could also be quite different from that of the EMG produced during stepping. At an equal stimulus strength and EMG level, the H-reflex was always much larger, up to 3.5 X, during steadily maintained contractions while standing than during walking. The large reflexes when subjects were standing are consistent with the control of position required to maintain a stable posture in this task. Similarly, the reflexes during walking are greatest during the stance phase, when they will assist in maintaining the upright position of the body against gravity. The reflexes are smallest during the swing phase when they would oppose ankle flexion. However, since the reflex amplitude is task-dependent (i.e., greater during standing than during walking at the same EMG and stimulus levels) and is not always closely related to the EMG produced during a given task such as walking, the strong modulation of H-reflex during walking is not simply a passive consequence of the alpha-motoneuron excitation level.(ABSTRACT TRUNCATED AT 250 WORDS)

Ankle↗
PubMed1985

Cardiovascular effects of a renin inhibitor in relation to posture in nonhuman primates.

Orthostatic cardiovascular reflexes were evaluated in conscious cynomolgus monkeys during interruption of the renin-angiotensin system with the renin inhibitor: RIP (Pro-His-Pro-Phe-His-Phe-Phe-Val-Tyr-Lys-OH). RIP was synthesized via solid phase techniques and purified to homogeneity. In vitro studies indicated that it exhibited classical competitive inhibition of renin with a KI of 2.3 microM. In vivo, RIP at 2 mg/kg per min inhibited renin and angiotensin I pressor responses indicating that it was not a specific renin inhibitor at this dose. However, in spite of the nonspecificity, RIP did not affect the supine blood pressure of sodium-replete monkeys, but did evoke hypotension in supine sodium depleted monkeys. RIP did not elicit significant orthostatic hypotension in either sodium-replete or sodium depleted monkeys. The cardiovascular effects of RIP described in this study appear to be due to inhibition of the renin-angiotensin system.

Angiotensin I↗
PubMed1995

Modulation of vestibulospinal reflexes through microinjection of GABAergic agents in the dorsal pontine tegmentum of decerebrate cats.

1. The locus coeruleus (LC) neurons control posture as well as the gain of the vestibulospinal (VS) reflexes either through direct coeruleospinal (CS) projections or by inhibiting the dorsal pontine reticular formation (pRF) and the related medullary inhibitory reticulospinal (RS) systems. After the demonstration that the LC neurons are under the inhibitory control of GABAergic afferents, experiments were performed to investigate whether the same system could also suppress the activity of the dorsal pRF, thus intervening in the control of posture and VS reflexes. 2. In precollicular decerebrate cats, unilateral microinjection into the dorsal pRF of the GABA-A antagonist bicuculline or the GABA-B antagonist faclofen (0.13-0.25 microliter at 2.5 micrograms/microliter saline) decreased the tonic contraction of the ipsilateral triceps brachii, but greatly increased the amplitude of the EMG responses of the same muscle to roll tilt of the animal (at 0.15 Hz, +/- 10 degrees). This increase in gain of the VS reflexes was not associated with great changes in phase angle of the responses, which were always characterized by an increased EMG activity during ipsilateral tilt and a decreased activity during contralateral tilt. The same injection also produced in some instances a slight decrease of the extensor tonus of the contralateral forelimb, associated with a moderate increase in the amplitude of modulation and thus in the response gain of contralateral triceps brachii to labyrinth stimulation. However, when the ipsilateral effects were prominent, the response gain of the contralateral triceps muscle was slightly depressed, while the pattern of response reversed. 3. The changes in posture and reflexes described above appeared 5-10 min after unilateral injection of the GABA antagonists in the pRF, reached the highest values in about 30 min and fully recovered to the control levels within 2 h after the injection. These effects were not due to irritative phenomena following injection of the fluid, since neither changes in posture nor in the response gain of the triceps brachii to labyrinth stimulation were observed after injection of an equal volume of vehicle in the pRF of that side. On the other hand, an increase in postural activity associated with a decrease in the response gain of the ipsilateral and contralateral triceps brachii to animal tilt was observed after unilateral microinjection into the dorsal pRF of GABA agonists. 4. Histological controls indicated that the structure responsible for the postural and reflex changes was located in the dorsal pontine reticular formation, ventral to the LC.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2000

Transient focal cerebral ischemia induces sensorimotor deficits in mice.

Rodents have been extensively used for experimental stroke research with rat and gerbil the preferred species. With the advent of transgenesis and gene targeting the number of mutant mouse strains is rapidly increasing. Thus, mouse models of stroke will be of great importance in the analysis of genetic factors affecting stroke. Demonstrating long-term functional recovery is of paramount importance for the pharmacological evaluation of putative stroke therapies. In the present paper we induce mild focal cerebral ischemia by tandem occlusion of the right middle cerebral artery (MCA), via craniotomy, together with the common carotid artery for 45 min in C57BL/6 strain of mice. The effects of ischemia were evaluated acutely by MRI and long-term (> 3 weeks) sensorimotor functional deficits were analyzed using a number of behavioral paradigms including the rotorod, wire hang, horizontal surface approach, eye-closure reflex, and T-maze tests. Although the induced brain damage is mild we show that it leads to clearly detectable and significant sensorimotor defects associated with fine motor coordination, balance, and postural and sensory reflexes. We conclude that the applied behavioral tests will be useful in the analysis of stroke in mutant mice.

Animals↗
PubMed2006

Influence of posture and stimulus parameters on post-activation depression of the soleus H-reflex in individuals with chronic spinal cord injury.

In non-disabled (ND) individuals, reflexes are modulated by influences related to physiologic state (e.g., posture, joint position, load) and activation history. Repeated activation of the H-reflex results in post-activation depression (PAD) of the response amplitude. The modulation associated with physiologic state and activation history is suppressed or abolished in individuals with spinal cord injury (SCI). While posture is known to affect H-reflex amplitude and PAD in non-disabled individuals, the effect of posture on PAD in SCI individuals is not known. Further, while the amount of PAD is also known to be influenced by the stimulus rate and by the amplitude of the evoked reflex, the interaction of posture with stimulus parameters has not been previously investigated in either group. We investigated differences in PAD of the soleus H-reflex between SCI subjects and ND subjects during sitting versus supported standing. Subjects were tested using paired conditioning-test stimulus pulses of 2.5s and 5s interpulse intervals (ISI) and with stimulus intensity adjusted to evoke reflex responses of 20% and 40% of the maximum motor response. We found standing posture to be associated with significantly less PAD in SCI subjects compared to ND subjects. In both groups, shorter ISIs and smaller reflex amplitudes were associated with greater PAD of the H-reflex. These results indicate that postural influences on post-activation modulation, while present, are impaired in individuals with chronic incomplete SCI.

Adolescent↗
PubMed1984

Reflex control of regional circulations in humans.

This study of autonomic control of the peripheral vascular system deals with reflex control of regional circulations, vasoconstriction in the upright posture, disturbances in the normal regulation caused by dysautonomia and spinal cord transection, regional vasomotor responses to thermal stress, and the overall sympathetic nerve activity in humans under stress. Data presented describe local and overall reactions that occur in normal and abnormal states. In varieties of stresses, humans adjust by increasing sympathetic nerve outflow in a highly predictable fashion. However, powerful local or humoral influences, such as those generated by hypoxia, hemorrhage, etc., are pitted against neurogenic vasoconstriction so that prediction of responses is very difficult.

Autonomic Nervous System↗
PubMed1999

Soleus H-reflex tests in causalgia-dystonia compared with dystonia and mimicked dystonic posture.

Dystonia in the causalgia-dystonia syndrome is characterized by a fixed dystonic posture. To identify involvement of central pathophysiologic mechanisms, we analyzed soleus H-reflex tests in five patients with causalgia-dystonia. Soleus H-reflex test results in these patients differed from those in healthy controls but were similar to those in purely dystonic patients and healthy controls mimicking dystonic posture. The results suggest involvement of supraspinal mechanisms in the abnormal posture of causalgia-dystonia.

Adult↗
PubMedDate not supplied

The clinical neurology of scrapie in Irish sheep.

One hundred twenty-nine sheep with scrapie were identified from 20 flocks in which scrapie previously had been confirmed. Physical and neurologic examinations were performed on all animals. Videotape recordings were made and reviewed to assess gait. These procedures were repeated in 46 sheep at 2- to 3-week intervals until recumbency or inappetence necessitated euthanasia. Confirmation of scrapie was made by histopathologic and immunohistochemical examinations of brain tissue. The clinical signs most frequently recorded in the 129 animals on initial presentation were hindlimb ataxia (71%), head tremor (61%), altered mental status (57%), positive nibble reflex (51%), crouching posture (51%), teeth grinding (44%), low head carriage (38%), body condition score (BCS) < 1.5 (38%), and conscious proprioceptive deficits of the hindlimbs (36%). Progression of the disease was characterized by an increase in the frequency and severity of ataxia, weakness and hypermetria of the hindlimbs, a decreasing sway response, a decreasing extensor response to thoracolumbar pressure, and a reduction in the BCS. No effect of farm of origin on the clinical presentation could be shown. The presence of a nibble reflex was strongly associated (P < .0005) with prion protein (PrP) genotypes AA136RR154QH171 and AA136RR154QQ171. Logistic regression modeling of groups with associated clinical signs showed that animals with a crouching posture (odds ratio [OR], 20.036) and an abnormal yield to thoracolumbar pressure (OR, 7.117) were at increased risk of ataxia. Pruritus (OR, 0.168) was negatively associated with ataxia. Pruritus (OR, 4.974) and teeth grinding (OR, 4.279) were associated with a positive nibble reflex.

Animals↗
PubMed1989

Reflex epilepsy and nonketotic hyperglycemia in the elderly: a specific neuroendocrine syndrome.

We present five elderly patients with focal reflex or posture-induced seizures and nonketotic hyperglycemia (NKH). Each patient exhibited interictal focal findings, such as hemiparesis or hemisensory or aphasic deficits. With control of the hyperglycemia, the seizures stopped, and the neurologic deficits resolved. The syndrome of focal reflex epilepsy and neurologic deficits in the elderly is transient and almost invariably related to NKH, thus representing a specific neuroendocrine syndrome.

Aged↗
PubMed1990

Posture in otoneurology. Volume I.

In this study, posture is studied in the context of neuro-otological problems. In the several chapters, postural elements, postural influence upon balance aspects as well as postural components of the balance function in normal and pathological conditions are emphasized. Two main applications are put forward: rehabilitation by postural treatment techniques (REHAB) and examination techniques for the vestibulospinal aspects (posturography--PG). I. Balance function Balance is provided by automatic reflexes for stabilization of the visual field (vestibulo-ocular reflex--VOR) and for a correct posture, erect standing (vestibulo-spinal reflex--VSR) and head position (vestibulo-collic reflex--VCR). The fundamental characteristics of these reflexes are described, especially of those related to posture. The reflexes are elaborated on the basis of sensory inputs that inform about changed relations to space and environment, provided by visual, vestibular and proprioceptive systems. The sensory signals are further processed by the centers to adequate reflexes and to some extent to a conscious awareness. II. Dysfunction and adaptation Dysfunction in the balance mechanisms leads to erroneous reflexes, but most importantly to frightening sensations of vertigo. The peripheral disturbances produce a sensory mismatch which is the primum movens of vertigo. Built-in adaptive mechanisms cope with this disturbance and restore global balance function. The mechanisms involved have been studied as vestibular compensation and habituation, VOR-reflex plasticity and sensory "substitutive" compensation. The mechanisms are set into action by the dysfunctional situation and constitute an error-controlled process. Emphasis is laid upon the items related to rehabilitation treatment and posturography. A survey of clinical entities of vestibular peripheral dysfunction is included. III. Examination techniques The logical approach to the patient with vertigo consists in an analysis of the complaints pattern, correlation of it with the dysfunctional state revealed by clinical observation, and functional tests of balance. Correct interpretation of the test results is a pre-requisite. Postural aspects of these examination techniques, especially posturography, are put into evidence in this review. The strategy used in the department is sketched. IV. Contribution of the examination techniques: functional evaluation results The several data obtained by each examination technique are discussed within the scope of the experiences in the department. Data from the literature and from personal experience, especially interpreted in the context of rehabilitation and posturography, are analysed. V. Reh

Adaptation, Physiological↗
PubMed1995

Microinjections of GABAergic agents in the locus coeruleus modify the gain of vestibulospinal reflexes in decerebrate cats.

1. Precollicular decerebrate cats show a good postural activity in the four limbs and a small-amplitude vestibulospinal (VS) reflex, as revealed by recording the EMG response of the triceps brachii to sinusoidal roll tilt of the animal at 0.15 Hz, +/- 10 degrees. This preparation was used to study whether inactivation of the locus coeruleus (LC) elicited by local administration either of the GABA-A agonist muscimol or of the GABA-B baclofen produced changes in posture as well as in gain of the VS reflexes. 2. Microinjection into the LC of one side of 0.13-0.25 microliter of a muscimol or baclofen solution (at 2.5 or 1 microgram/microliter saline, respectively) stained with 5% pontamine, usually decreased the extensor tonus in the ipsilateral limbs and to a lesser extent also in the contralateral limbs. However, the amplitude of modulation and thus the gain of the first harmonic component of the multiunit EMG responses of the ipsilateral and to a lesser extent also of the contralateral triceps brachii to the same parameters of labyrinth stimulation increased. The phase angle of the responses remained nearly unchanged by this treatment. The effects appeared 5-10 min after the injection of muscimol, fully developed in 30 min and progressively declined within the following 2-2.5 hours. 3. The increased gain of the VS reflexes acting on the triceps brachii did not depend on the decreased postural activity following the injection of the GABA-A or GABA-B agonist, since it was still observed if the reduced EMG activity following the injection was compensated by an increased static stretch of the muscle. Moreover, the postural and reflex changes described above were not due to irritative events following the injection, since they were not observed in control experiments following injection of 0.25 microliter saline within the LC-complex. On the other hand, postural and reflex changes opposite in sign to those elicited by muscimol or baclofen were obtained by local injection into the LC-complex of a GABA-A or GABA-B antagonist (0.25 microliter of bicuculline or faclofen at 8 micrograms/microliters saline). 4. In some experiments, the decrease in postural activity of the forelimbs after injection of muscimol into the LC complex was followed by transient episodes of postural atonia, which affected not only the ipsilateral but also the contralateral triceps muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1997

Comparison of soleus H-reflex gain from prone to standing in dancers and controls.

To examine the differences in soleus H-reflex gain between trained dancers and control subjects, the soleus H-reflex amplitude and background muscle activity of 9 trained dancers (means of 20.3 +/- 2.1 years of age, and 14.3 +/- 3.8 years of training) and 9 control subjects (mean 23.3 +/- 3.2 years of age) were compared at rest and at 10, 20, and 30% of a maximal voluntary soleus contraction during two conditions: prone and standing. The ratio of the maximal H-reflex (H-max) to the maximal motor response (M-max) was also measured during both conditions. Correlation was performed between background EMG and the resultant H-reflex to determine reflex gain. The results demonstrated that the control subjects and the dancers displayed a similar reflex gain during the prone condition (slope = 3.30 vs. 3.64, respectively). However, during the standing condition, dancers demonstrated a significantly lower reflex gain (slope = 1.78) than did control subjects (slop = 3.68). Furthermore, although both groups significantly decreased the H-max/M-max ratio from prone to standing, no differences were found between groups at either condition. This suggests that the differences in standing reflex gain between the dancers and control subjects were a product of differential control of reflex modulation involved in postural control. An initial hypothesis explaining the differences between the standing reflex gain of the groups relates to plasticity of central inhibitory control mechanisms, primarily presynaptic and/or reciprocal inhibition.

Adult↗