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PubMed1986

Behavior of larval and juvenile bullfrogs (Rana catesbeiana) following chronic spinal transection.

The behavior of larval and juvenile bullfrogs (Rana catesbeiana) was examined for 32 days following cervical spinal transection. The threshold for cutaneously elicited hindlimb withdrawal was not changed at either stage of development but righting reflexes were abolished. Forelimb postural support of juveniles was abolished by the transection but recovered within 3 days. Hindlimb posture was normal and hopping could be elicited by stimulation of the rump with a blunt wire probe. Undulatory swimming of larvae was abolished by the transection but began to recover approximately 1 week later. The hindlimbs of larvae were very active following the transection and displayed long sequences of coordinated stepping in response to a variety of stimuli. Gross examination of the spinal cord in situ after 32 days suggested that fibers may have grown across the transection site. Retransection at the site of the original transection on Postoperative Day 33 had no discernable effect on the behavior juveniles or on the stepping of larvae, but it abolished recovered swimming of larvae. Deafferentation of lumbar segments of larvae eliminated stepping but had no effect on swimming. Deafferentation of cervical segments eliminated forelimb support in juveniles. These results suggest that recovery of larval swimming depends at least in part upon the growth of fibers across the transection site. Stepping of spinal larvae appears to be mediated by proprioceptive reflexes rather than by central pattern generators, and in the normal animal is probably under the control of descending inhibition. Recovery of posture and hopping in juveniles was much more rapid than that described for adult frogs and does not depend on growth across the transection site.

Animals↗
PubMed1994

Motor development, infantile reactions and postural responses of preterm, at-risk infants.

Eighty-nine low-birthweight, preterm infants were enrolled in a longitudinal study to describe motor development, infantile reactions and postural responses during the first chronological year of life and to determine the relationship between these behaviors. There was a clear trend from prevalence of primitive patterns, such as the asymmetric tonic neck reflex, towards a prevalence of mature postural reactions such as the Landau, righting and protective extension reflexes. Statistical analysis suggested that a relationship exists between infantile patterns, automatic postural reactions and motor development that is similar to that accepted as normal in term infant development, when allowance is made for preterm birth. Correlations were also obtained between integration of the tonic labyrinthine response and the presence of the asymmetric tonic neck pattern at the time of hospital discharge and later achievement of motor milestones. These relationships warrant further investigation.

Female↗
PubMed2000

Neuronal mechanisms for the control of body orientation in clione II. Modifications in the activity of postural control system.

The marine mollusk Clione limacina, when swimming, can stabilize different body orientations in the gravitational field. The stabilization is based on the reflexes initiated by activation of the statocyst receptor cells and mediated by the cerebro-pedal interneurons that produce excitation of the motoneurons of the effector organs; tail and wings. Here we describe changes in the reflex pathways underlying different modes of postural activity; the maintenance of the head-up orientation at low temperature, the maintenance of the head-down orientation at higher temperature, and a complete inactivation of the postural mechanisms during defense reaction. Experiments were performed on the CNS-statocyst preparation. Spike discharges in the axons of different types of neurons were recorded extracellularly while the preparation was rotated in space through 360 degrees in different planes. We characterized the spatial zones of activity of the tail and wing motoneurons and the CPB3 interneurons mediating the effects of statocyst receptor cells on the tail motoneurons. This was done at different temperatures (10 and 20 degrees C). The "fictive" defense reaction was evoked by electrical stimulation of the head nerve. At 10 degrees C, a tilt of the preparation evoked activation in the tail motoneurons and wing retractor motoneurons contralateral to the tilt and in the wing locomotor motoneurons ipsilateral to the tilt. At 20 degrees C, the responses in the tail motoneurons and in the wing retractor motoneurons occurred reversed; these neurons were now activated with the ipsilateral tilt. In the wing locomotor motoneurons the responses at 20 degrees C were suppressed. During the defense reaction, gravitational responses in all neuron types were suppressed. Changes in the chains of tail reflexes most likely occurred at the level of connections from the statocyst receptor cells to the CPB3 interneurons. The changes in gravitational reflexes revealed in the present study are sufficient to explain the corresponding modifications of the postural behavior in Clione.

Animals↗
PubMedDate not supplied

Foot reflexes and the use of the "inhibitive cast".

The four diametrically opposed tonic reflex movements of the foot that can be elicited in normal children throughout the first year represent the peripheral segments of proximally cascaded reflex balance recovery systems. Clinical persistence of one or more of these obligatory movements in cerebral palsied children may habitually distort foot posture and recruit proximal reflex muscle activity and associated hypertonus. Inhibitive casting has proved to be a significant useful adjunct for management of both foot deformity and associated proximal hypertonicity.

Casts, Surgical↗
PubMed1994

Development of righting when falling from a bipedal standing posture: evidence for the dissociation of dynamic and static righting reflexes in rats.

Righting to prone when placed supine on the ground by rats is present at birth, albeit in incomplete form. In contrast, righting in the air when falling from the supine position does not begin to emerge until the end of the first week and is not complete until the end of the third week postnatally. On the ground, the animals have sensory information from proprioceptive-tactile sources, as well as vestibular; in the air, they have only vestibular. Thus, it is possible that the difference between contact righting and air righting is a reflection of the relative difference in the maturation of tactile vs. vestibular mechanisms. In this study, pups were tested by pushing them backwards from a bipedal standing position. Such a context provided proprioceptive-tactile information during the fall. The results showed that the developmental onset and maturation of righting from the bipedal position resembled that of air righting rather than contact righting. This suggests that the difference between air righting and contact righting is not due to differences in sensory inputs, but to differential maturation of neural mechanisms for acceleratory (i.e., falling) vs. stationary (i.e., lying on the ground) forms of righting. That is, the appropriate neural systems are organized for the type of righting, not for the sensory systems used. Even so, some evidence is provided suggesting a developmental dissociation between righting from falling with vestibular information only, and with proprioceptive-tactile information in addition. Therefore, righting systems appear to need two dimensions of classification--one based on sensory systems involved, and the other in terms of the context of righting (i.e., falling vs. stationary).

Aging↗
PubMed1998

Context-dependent reflex control: some insights into the role of balance.

Recent research suggests that the balance requirements of a task dictate the reflexive response. However, these observations were inferred indirectly from either different tasks or different phases of the same task. This study directly tested the hypothesis of balance-dependent control during recovery from an unexpected trip. The subjects were tripped in two different support conditions: unilimb support (provided by the stance limb) or trilimb support (provided by the stance limb and both arms placed on adjacent parallel bars). The subjects exhibited anticipatory changes: they biased the body center of mass toward the support limb in the mediolateral direction and elevated the swing limb higher when there was a possibility of being tripped. The electromyographic (EMG) latencies were not influenced by the threat to equilibrium. The magnitudes of the EMG reflexive response to the trip were clearly modulated as a function of the threat to stability, not in a simple manner, but rather in a complex manner, which optimized the recovery strategy. It is evident that the overriding concern, equilibrium control during locomotion, has a dominant influence on reflex modulation.

Adaptation, Physiological↗
PubMed2005

Effects of hip joint angle changes on intersegmental spinal coupling in human spinal cord injury.

Pathological expression of movement and muscle tone in human upper motor neuron disorders has been partly associated with impaired modulation of spinal inhibitory mechanisms, such as reciprocal or presynaptic inhibition. In addition, input from specific afferent systems contributes significantly to spinal reflex circuits coupled with posture or locomotion. Accordingly, the objectives of this study were to identify the involved afferents and their relative contribution to soleus H-reflex modulation induced by changes in hip position, and to relate these effects with activity of spinal interneuronal circuits. Specifically, we investigated the actions of group I synergistic and antagonistic muscle afferents (e.g. common peroneal nerve, CPN; medial gastrocnemius, MG) and tactile plantar cutaneous afferents on the soleus H-reflex during controlled hip angle variations in 11 motor incomplete spinal cord injured (SCI) subjects. It has been postulated in healthy subjects that CPN stimulation evokes an inhibition on the soleus H-reflex at a conditioning test (C-T) interval of 2-4 ms. This short latency reflex depression is caused mainly by activation of the reciprocal Ia inhibitory pathway. At longer C-T intervals (beyond 30 ms) the soleus H-reflex is again depressed, and is generally accepted to be caused by presynaptic inhibition of soleus Ia afferents. Similarly, MG nerve stimulation depresses soleus H-reflex excitability at the C-T interval of 6 ms, involving the pathway of non-reciprocal group I inhibition, while excitation of plantar cutaneous afferents affects the activity of spinal reflex pathways in the extensors. In this study, soleus H-reflexes recorded alone or during CPN stimulation at either short (2, 3, 4 ms) or long (80, 100, 120 ms) C-T intervals, and MG nerve stimulation delivered at 6 ms were elicited via conventional methods and similar to those adopted in studies conducted in healthy subjects. Plantar skin conditioning stimulation was delivered through two surface electrodes placed on the metatarsals at different C-T intervals ranging from 3 to 90 ms. CPN stimulation at either short or long C-T intervals and MG nerve stimulation resulted in a significant facilitation of the soleus H-reflex, regardless of the hip angle tested. Plantar skin stimulation delivered with hip extended at 10 degrees induced a bimodal facilitation reflex pattern, while with hip flexed (10 degrees , 30 degrees ) the reflex facilitation increased with increments in the C-T interval. This study provides evidence that in human chronic SCI, classically key inhibitory reflex actions are switched to facilitatory, and that spinal processing of plantar cutaneous sensory input and actions of synergistic/antagonistic muscle afferents interact with hip proprioceptive input to facilitate soleus H-reflex excitability. These actions might be associated with the pathological expression of neural control of movement in individuals with SCI, and potentially could be considered in rehabilitation programs geared to restore sensorimotor function in these patients.

Adolescent↗
PubMed1982

An attempt to explain the mechanism of drop attacks.

We have investigated the possibility that a delay in long-loop (transcortical) reflexes might be responsible for the occurrence of drop attacks which occur in middle-aged women without disturbance of consciousness. We have not been able to confirm this suggestion. However, using simple Newtonian principles, we calculate how far the subject may fall before a long-loop reflex can be generated in the quadriceps muscle. We suggest that in some subjects tension cannot be generated sufficiently quickly to maintain the erect posture. This hypothesis provides a link between subjects who experience drop attacks due to overt muscle weakness and subjects without physical signs.

Adult↗
PubMed1986

Microvibration-related responses to optokinetic stimulation.

The body surface of all warm-blooded animals vibrates constantly. This phenomenon was termed microvibration (MV) by Rohracher. Since 1961 Kawata and students have been studying MV otolaryngologically and they detected slight changes with auditory and vestibular stimuli in the waves of MV. The authors observed changes in the MV responses in the upper extremities, in the presence of optokinetic stimulation. They found a close relationship between the direction of optokinetic stimulation and changes in the MV response. Therefore, these observations suggest that for MV recording, optic stimulation can be used to test the oculospinal reflex.

Adult↗
PubMed2004

Response patterns of vestibulospinal neurons to lumbar rotation in decerebrate rats.

In vestibulospinal neurons projecting to the lumbar enlargement, activities were modulated in response to alternate tilts of the caudal body around the vertebral axis. Three types of neurons were found: Type I (37.8%) showed faster firing during the ipsilateral side-down tilt; type II (51.1%) showed the reverse pattern; type III were unaffected. Types I and II may be important in the tonic lumbar reflex.

Animals↗
PubMed1997

Mechanisms of cutaneous vasoconstriction during upright posture.

The cutaneous circulation is thought to participate in the neurocirculatory adjustments during orthostatic stress, but the underlying mechanisms mediating such reflex cutaneous vasoconstriction are poorly understood. The aim of this study was to assess the relative importance of baroreceptor (cardiopulmonary and arterial) and positional (vestibular, exercise, veno-arteriolar and myogenic) reflexes in triggering cutaneous vasoconstriction during upright posture. First, hypotensive lower body negative pressure (LBNP) was compared with actual postural changes to assess the relative contributions of baroreceptor reflexes and positional reflexes. Then changes in body position were compared with changes in limb position in the absence or presence of proximal (axillary) or distal (local cutaneous) nerve blocks, to assess the relative contributions of vestibular, exercise, veno-arteriolar and myogenic reflexes. Skin sympathetic nerve activity was determined by microneurography, and skin blood flow was determined by laser Doppler velocimetry. LBNP of -50 mm Hg cardiopulmonary + arterial baroreceptors) had no effect on skin sympathetic nerve activity or skin vascular resistance. In contrast, an upright posture with the arms dependent (baroreceptor + vestibular + exercise + veno-arteriolar reflexes) caused a two- to threefold increase in skin vascular resistance. In the supine position passive movement of the arm into a dependent position to activate veno-arteriolar reflexes alone evoked an increase in skin vascular resistance which approximated the response to normal upright posture. Blocking central sympathetic nerve impulses by application of an axillary blockade did not influence the cutaneous vasoconstrictor response to an upright posture or changes in limb position. In contrast, application of a distal nerve block by local cutaneous surface anaesthesia completely blocked vasoconstrictor responses evoked by these manoeuvres. In conclusion, these experiments in human subjects identify a primary role for veno-arteriolar reflexes in triggering vasoconstriction in the cutaneous circulation during upright posture.

Adult↗