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PubMed1993

Spinal ganglioneuroma in a dog.

A 10-year-old mixed-breed dog was examined because of lameness and mutilation of the left hind limb. Neurologic examination revealed ataxia, conscious proprioceptive deficit, muscle atrophy, lack of withdrawal reflex, and hyperreflexia of the patella of the left hind limb. Epidurography revealed right-sided deviation of the dye column at the sixth to seventh lumbar vertebrae. Laminectomy with cytoreduction was performed, and histologic examination revealed ganglioneuroma. Twelve months after surgery, clinical signs recurred and surgery was repeated. The dog's clinical signs were again palliated. The specific type of ganglioneuroma identified in this dog is amenable to surgical resection, unlike many types of spinal cord neoplasia.

Animals↗

PubMed1997

[Cerebrospinal nematodiasis in seven goats].

Clinical findings in seven goats affected with cerebrospinal nematodiasis are described. The animals originated from different parts of Switzerland. The disease occurred mainly in winter. The animals were admitted to the clinic because of progressive pelvic limb ataxia, recumbency, vestibular disease and circling. Clinical findings were complete or incomplete posterior paresis, pelvic limb ataxia, circling, reduced cutaneous sensation and proprioceptive deficits as well as cranial nerve reflexes deficits. The general condition was slightly reduced and the appetite was normal. In three goats predominance of mononuclear and eosinophilic cells in the cerebrospinal fluid was interpreted as typical findings for parasite infestation in the central nervous system. Histopathological changes and the finding of a nematode in cross sections in two affected animals confirmed the diagnosis. Infection with Elaphostrongylus cervi is discussed due to close contact with deer.

Animals↗

PubMed2003

A computer model of rigidity and related motor dysfunction in Parkinson's disease.

This work explores the involvement of spinal circuits in the generation of parkinsonian rigidity and related motor dysfunction. A computer model of spinal proprioceptive input processing, derived from previous work on spasticity modeling, was adapted to the simulation of parkinsonian rigidity. Model parameters were varied to generate simulations reproducing experimental data obtained using the pendulum test of the leg in 10 parkinsonian patients and 3 healthy subjects. Convenient reproductions of experimental traces in rigidity were obtained by the combination of a low reflex gain and a decrease in reflex threshold. These findings are consistent with studies reporting an increase of spinal interneuron excitability and proprioception deficits in Parkinson's disease (PD). Moreover, as the threshold parameter was much lowered, our model generated typical features of parkinsonian resting tremor, endorsing the hypothesis of a participation of a spinal oscillator in this disorder. Finally, tuning the reflex gain during simulations of rigidity resulted in the generation of active movement, opening some hypotheses on pathophysiology of motor dysfunction in PD, and notably, of akinesia. More generally, this work accredits the hypothesis of the involvement of an aperiodic, altered supra-spinal motor drive in PD, resulting in spinal dysfunction, through specific descending motor pathways. This may lead to a search for new (spinal) pharmacological targets in PD. It emphasizes further the value of computer modeling in understanding motor control in health and disease.

Computer Simulation↗

PubMed1997

Changes in dorsal neck muscle activity related to imposed eye movement in the decerebrate pigeon.

Movements of the head and eyes are known to be intimately related. Eye position has also been shown to be closely related to the electromyographic activity of dorsal neck muscles; however, extraocular muscle proprioception has not generally been considered to play a part in the control of such movements. We have previously shown that, in the pigeon, imposed movements of one eye modify the vestibular responses of several dorsal neck muscles in ways that are dependent on stimulus parameters such as the amplitude and velocity of imposed eye movement. The present study examines more closely the interactions between imposed eye movements and different muscle pairs. The three neck muscle pairs studied each responded to afferent signals from the extraocular muscles in discrete and specific ways which appeared to be correlated with their different actions. Complementary effects of imposed eye movements in the horizontal plane were seen for both the complexus and splenius muscle pairs, with imposed eye movements in one direction producing the largest inhibition of the ipsilateral muscle's vestibular response and imposed eye movements in the opposite direction the largest inhibition of the contralateral muscle's vestibular response. During roll tilt oscillation (ear-up/ear-down) in the frontal plane, similar complementary effects of imposed eye movement were seen in the complexus muscle pair, but the splenius muscle pair showed little tuning, with similar inhibition for imposed eye movement directed either upwards or downwards. In contrast to these complementary effects, the biventer cervicis muscle pair showed no vestibular modulation during vestibular stimulation in the horizontal plane and their spontaneous activity was not altered by imposed eye movement. During roll-tilt oscillation (ear-up/ear-down) in the frontal plane imposed eye movement directed vertically upwards increased both muscles' vestibular responses and imposed eye movement directed vertically downwards inhibited both muscles' vestibular responses. Section of the ophthalmic branch of the trigeminal nerve (deafferenting the eye muscles) abolished the effects of imposed eye movement on the neck muscle pairs. In conjunction with further control experiments these results provide compelling evidence that proprioceptive signals from the extraocular muscles reach the neck muscles and provide them with a functionally significant signal. We have previously shown that signals from the extraocular muscles appear to be involved in the control of the vestibulo-ocular reflex. It follows from the experiments reported here that proprioceptive signals from the extraocular muscles are also likely to be involved in the control of gaze.

Animals↗

PubMed1997

Otolithic and extraocular muscle proprioceptive influences on the spatial organization of the vestibulo- and cervico-ocular quick phases.

The cervico-ocular reflex (COR) was studied alone or in combination with the vestibulo-ocular reflex (VOR) in the rabbit. Step stimulations of the body with respect to the fixed head induced small slow compensatory responses followed by large compensatory quick phases (QP). These responses remained aligned with the horizon at different head pitch angles. The QP reorientation in space was due to the gravity influence on the otolithic receptors. The vestibular induced QPs exhibit a similar pattern. Because of this reorientation, the reduction of the amplitude of the vestibular induced QPs, due to the addition of the COR, was maintained even at different static head positions. The electrolytic lesion of the ophthalmic branch of the trigeminal nerve deeply affected the space orientation of the COR. In particular, the cervically induced compensatory QPs of the eye ipsilateral to the lesion showed a remarkable variability of their trajectories and they lost space reorientation. These findings suggest that the coordinate system controlling the QPs is influenced by signals originating from both head position in space and eye position in the orbit.

Animals↗

PubMed2001

Functional recovery after extra-ocular muscle deafferentation in the rabbit.

The present research analysed on chronic animals the functional recovery of eye motility after impairment of the proprioceptive input at the level of the semilunar ganglion. The horizontal vestibulo-ocular reflex (HVOR) was recorded in normal pigmented rabbits before and after a partial electrolytic lesion of the semilunar ganglion. The recordings were repeated daily for 8-10 days to evaluate the recovery. Immediately after the lesion, as previously observed, HVOR slow phases were unaffected, while quick phases (QPs) showed a reduction in peak velocity and a deviation of trajectories from the horizontal plane. QP peak velocity was almost completely restored within 3-5 days, while trajectory deviation was not corrected during the observation period. Furthermore, in some animals, the variability of trajectories showed, starting from days 3-5, a progressive increase that led to a greater spatial disorganization. A process of lesion-induced plasticity takes place. but only the velocity of QPs can be recovered rapidly, while the QP trajectory impairment does not appear to be compensated substantially, which underlines a determinant role in the control of QP spatial orientation exerted by EOM proprioceptive signals.

Afferent Pathways↗

PubMed1993

Octopamine effects mimick state-dependent changes in a proprioceptive feedback system.

The modulatory actions of the biogenic amine octopamine on the femur tibia (FT) control loop in the stick insect Carausius morosus were examined. The response properties of the FT control loop were determined under open loop conditions. Mechanical stimulation of the femoral chordotonal organ (fCO) was the input and tibial movement and motoneuronal activity were measured as the output of the system. Following octopamine injection into the hemolymph of intact, inactive animals, two consecutive phases occurred at the behavioral level. Octopamine caused initially an activation of the animal. During this first phase (3.5-12 min duration) the response properties of the FT control loop were similar to those found in animals that were activated by tactile stimuli under normal conditions. Afterward, animals became inactive. During this second phase (15-20 min duration), the gain of the control loop was zero and no resistance reflex in the FT joint was generated in response to fCO stimulation. However, active movements of the tibia could still be elicited. As we could show in restrained animals, where DL-octopamine was applied topically onto the undesheated mesothoracic ganglion, the complete suppression of the resistance reflex on the motoneuronal level was dose dependent starting at concentrations of 5 x 10(-3) M octopamine. We could show that octopamine specifically suppressed the pathways involved in the resistance reflex, while feedback loop responses to fCO stimuli typical for active animals could still be elicited. Our results indicate that an increase in the octopamine concentration mimicks activation of the animal: Properties being characteristic for the control of the FT joint in the inactive animal are inhibited by octopamine, while properties of the FT control loop typical for the active animal appear to be facilitated following octopamine injection. The results clearly demonstrate that different pathways in the neuronal network underlying the FT control loop are involved in the responses of the control loop to fCO stimuli in the inactive and active behavioral states of the stick insect.

Animals↗

PubMed2001

Rationale for training programs to reduce anterior cruciate ligament injuries in Australian football.

This commentary presents the rationale for training programs to reduce the incidence of knee injuries. Our studies have revealed that the external knee loading patterns during sidestep cutting are what put the anterior cruciate ligament at greatest risk for injury. Compared to running, sidestep cutting involves similar levels of knee flexion loading but increased loading in varus-valgus and internal rotation of the knee, and these external loads need to be stabilized or supported by the internal structures of the knee. People use a generalized hamstrings and quadriceps co-contraction to stabilize these external loads, thereby reducing ligament loading. It is proposed that perturbation of the joint receptors reinforces the use of selective hamstrings and quadriceps co-contraction patterns superimposed on a generalized co-contraction pattern. This is not by immediate ligamento-muscular protective reflex, which is too slow to provide any adequate support, but by enhanced proprioceptive information that may be used in learning. In contrast, the immediate effect of muscle stretch reflexes would be to reduce co-contraction, a possibly negative outcome for joint stabilization. The effects of different types of training on the control of joint stability are examined. It is proposed that resistance training may not be appropriate because it enhances muscle stretch reflexes, which may reduce co-contraction, and produces no reductions in voluntary activation times and time to peak torque. However, stability and balance training is thought to suppress muscle stretch reflexes and, in turn, enhance co-contraction. Also, stability and balance training that stimulates the knee joint ligament and capsular receptors may reinforce co-contraction patterns to facilitate greater improvements in joint stabilization. Stability and balance training and plyometric training produce reductions in voluntary activation times and times to peak torque, which may decrease muscle response times so players are more able to perform rapid and unexpected sports maneuvers. Training programs that emphasize these neuromuscular mechanisms may enhance protection of the anterior cruciate ligament and reduce the incidence of injury.

Anterior Cruciate Ligament↗

PubMed2006

Reflex seizures and reflex epilepsy.

Reflex seizures are evoked by a specific afferent stimulus or by activity of the patient and are divided into those characterized by generalized seizures and those principally manifested by focal seizures. Reflex epilepsies are syndromes in which all epileptic seizures are precipitated by sensory stimuli. Three categories of reflex seizures encountered clinically include pure reflex epilepsies, reflex seizures that occur in generalized or focal epilepsy syndromes that are also associated with spontaneous seizures, and isolated reflex seizures occurring in situations that do not necessarily require a diagnosis of epilepsy. Generalized reflex seizures are precipitated by visual light stimulation, thinking, and decision making. These seizures usually respond to valproate treatment. Numerous triggers can induce focal reflex seizures. The triggers include reading, writing, other language functions, startle, somatosensory stimulation, proprioception, auditory stimuli, immersion in hot water, eating, and vestibular stimulation. The classification and characteristics of reflex seizures and epilepsies are described in this review. Findings on EEG and advanced neuroimaging in the reflex seizures and epilepsies, treatment and preventive options, and animal models and mechanisms are also discussed.

Animals↗

PubMed2004

Coupling sensory inputs to the appropriate motor responses: new aspects of cerebellar function.

It is known that proprioceptive signals modify the spatial organization of the postural reflexes, thus leading to body stability. The neurophysiological basis of this phenomenon are at present unknown. The present report documents that, in decerebrate cat, body-to-head rotation in the horizontal plane modified the preferred response direction to labyrinthine stimulation of the forelimb extensor triceps brachii. Such direction resulted always perpendicular to the longitudinal body axis of the animal, whatever its relative position with respect to the head could be. The rotation of the preferred response direction of the triceps was greatly reduced by functional inactivation of the ipsilateral cerebellar vermis. On the other hand, following body-to-head displacement, the preferred response directions of the corresponding P-cells tended, on the average, to rotate in the same direction and by the same angle as the body. We propose that the neck input finely tunes parallel vestibular channels, endowed with different spatial and temporal properties, impinging upon P-cells, thus modifying their responses to animal tilt and, as a consequence, the spatial properties of VS reflexes. It is possible that, by a similar mechanism, the cerebellum may contribute to the changes in reference frame occurring in sensorimotor transformations of reflex and voluntary nature.

Afferent Pathways↗

PubMed1987

Proprioceptive input resets central locomotor rhythm in the spinal cat.

The reflex regulation of stepping is an important factor in adapting the step cycle to changes in the environment. The present experiments have examined the influence of muscle proprioceptors on centrally generated rhythmic locomotor activity in decerebrate unanesthetized cats with a spinal transection at Th12. Fictive locomotion, recorded as alternating activity in hindlimb flexor and extensor nerves, was induced by administration of nialamide (a monoamine oxidase inhibitor) and L-DOPA. Brief electrical stimulation of group I afferents from knee and ankle extensors were effective in resetting fictive locomotion in a coordinated fashion. An extensor group I volley delivered during a flexor burst would abruptly terminate the flexor activity and initiate an extensor burst. The same stimulus given during an extensor burst prolonged the extensor activity while delaying the appearance of the following flexor burst. Intracellular recordings from motoneurones revealed that these actions were mediated at premotoneuronal levels resulting from a distribution of inhibition to centres generating flexor bursts and excitation of centres generating extensor bursts. These results indicate that extensor group I afferents have access to central rhythm generators and suggest that this may be of importance in the reflex regulation of stepping. Experiments utilizing natural stimulation of muscle receptors demonstrate that the group I input to the rhythm generators arises mainly from Golgi tendon organ Ib afferents. Thus an increased load of limb extensors during the stance phase would enhance and prolong extensor activity while simultaneously delaying the transition to the swing phase of the step cycle.

Afferent Pathways↗

PubMed2007

A stretch reflex in extraocular muscles of species purportedly lacking muscle spindles.

It is generally assumed that proprioceptive feedback plays a crucial role in limb posture and movement. However, the role of afferent signals from extraocular muscles (EOM) in the control of eye movement has been a matter of continuous debate. These muscles have atypical sensory receptors in several species and it has been proposed that they are not supported by stretch reflexes. We recorded electromyographic activity of EOM during passive rotations of the eye in sedated rats and squirrel monkeys and observed typical stretch reflexes in these muscles. Results suggest that there is a similarity in the reflexive control of limb and eye movement, despite substantial differences in their biomechanics and sensory receptors. Like in some limb skeletal muscles, the stretch reflex in EOM in the investigated species might be mediated by other length-sensitive receptors, rather than muscle spindles.

Animals↗

PubMed1982

Is morphine-induced akinesia related to inhibition of reflex activation of flexor alpha-motoneurones? Role of the nucleus accumbens.

Unilateral injections of morphine (5-15 micrograms) into the nucleus accumbens of non-anesthetized rats produces a decrease of locomotor activity and a catalepsy. In a similar dose-response relationship, injections of morphine into this area inhibited the reflex activation of alpha-motoneurones by mild tetanic stimulation of the ipsilateral peroneal nerve (flexor alpha-motoneurones) in halothane-anesthetized rats. All these effects were antagonized by systemic administration of naloxone. Our results suggest that a reduction in reflex activation of flexor alpha-motoneurones by proprioceptive stimuli seems to be relevant for the development and/or mediation of akinesia and catalepsy, and that the nucleus accumbens plays a key role in these effects produced by morphine.

Animals↗

PubMed2004

A new form of congenital proprioceptive sensory neuropathy associated with arthrogryposis multiplex.

We report two siblings who presented with non-progressive marked sensory ataxia associated with arthrogryposis multiplex congenita (AMC). Deep tendon reflexes and H reflex were completely absent, but F waves were preserved. The sensory nerve conduction studies indicated the presence of relatively mild sensory polyneuropathy. The conventional somatosensory evoked potentials (SEPs) showed mildly prolonged latency for both the peripheral and cortical responses, suggesting a slowed conduction through the peripheral as well as central pathway. However, the 'proprioceptive SEPs' were absent, in conformity with complete loss of joint sense. Sural nerve biopsy revealed only mild thinning of myelin in the younger sister but was entirely normal in her brother. Taken together with the characteristic electrophysiological findings, the symptoms were considered to be due to predominant involvement of a selective population of somatosensory ganglions. The present cases showed no progression of the neurological deficit what-so-ever since birth, which strongly suggests a developmental anomaly or aplasia of a limited population of peripheral sensory neurons.

Action Potentials↗

PubMed1999

Peroneal motoneuron excitability increases immediately following application of a semirigid ankle brace.

STUDY DESIGN: Within-session, within-subject comparison of 2 conditions. OBJECTIVES: To determine the influence of application of a semirigid ankle brace on the excitability of the peroneus longus muscle motoneuron pool as measured by the H-reflex. BACKGROUND: The literature suggests that cutaneous mechanoreceptors can contribute to proprioception, especially during conditions in which skin experiences displacement. Further, skin displacement and stimulation of cutaneous mechanoreptors have been shown to increase motoneuron excitability. METHODS AND MEASURES: H-reflexes and M-waves of the peroneus longus muscle were acquired by stimulating the common peroneal nerve of 11 uninjured subjects during 2 randomly ordered conditions, with and without application of an Aircast Air-Stirrup. Five reflexes were collected at each of 12 stimulation voltages. The peak-to-peak amplitudes of the M-wave and H-reflex from each subject's ensemble-averaged data at each stimulation voltage was used to generate H-reflex and M-wave recruitment curves. The H-reflex amplitude was subsequently expressed as a percentage of the maximum M-wave amplitude. RESULTS: The normalized H-reflex amplitude increased by approximately 10% during the braced condition compared to the nonbraced condition. The peroneus longus H-reflex latency and M-wave amplitude were not affected by the bracing condition. CONCLUSIONS: Application of the ankle brace excited afferents possibly arising from a number of candidate mechanoreceptors, 1 of which is likely cutaneous. The findings raise questions as to whether the increased motorneuron excitability can be used for the purposes of rehabilitation from ankle injury.

Adult↗

PubMed2006

Hemicerebellectomy impairs the modulation of cutaneomuscular reflexes by the motor cortex following repetitive somatosensory stimulation.

We examined the cutaneomuscular reflex of the plantaris muscle of rats in response to cutaneous stimulation in isolation and in conjunction with subthreshold high-frequency trains of stimuli applied on the motor cortex, prior to and following repetitive peripheral stimulation. The cutaneomuscular reflex was also investigated under the same paradigm following hemicerebellectomy. The enhancement of cutaneomuscular responses associated with subthreshold high-frequency trains of stimulation following repetitive peripheral stimulation was prevented by hemicerebellectomy. Our results suggest that the pathways passing through the cerebellum are involved in the calibration of cutaneomuscular responses.

Afferent Pathways↗

PubMed1998

Long-term deficits in otolith, canal and optokinetic ocular reflexes of pigmented rats after unilateral vestibular nerve section.

Static and dynamic otolith, horizontal vestibular and optokinetic ocular reflexes were investigated in pigmented rats 1-6 and more months after unilateral vestibular nerve (UVN) section. Evoked responses were compared with published data from control rats studied under identical conditions. Static lateral tilt of UVN rats in the light evoked a vertical deviation in static eye position that was as large as in controls. In darkness, the evoked responses in UVN rats 6 months after the lesion were consistently smaller than in controls. Linear horizontal acceleration in darkness evoked vertical and torsional response components in UVN rats that were parallel-shifted towards lower gains and larger phase lags. Off-vertical axis rotation on a platform provoked responses that differed markedly from those recorded in intact rats with respect to the bias velocity component. These results suggest a permanent deficiency in the static and dynamic otolith-ocular reflex performance of UVN rats. Ocular responses to horizontal table velocity steps in darkness exhibited a direction-specific asymmetry in UVN rats. Step responses evoked by acceleration towards the intact side were larger in gain and longer in duration than responses evoked by acceleration towards the operated side. When compared with control data, responses to either side were reduced in UVN rats and the velocity store mechanism was barely activated by velocity steps towards the operated side. Responses evoked by horizontal optokinetic stimulation with constant pattern velocities were below control values in either direction. Slow-phase eye velocity saturated at much lower values than in intact rats, particularly during pattern motion towards the intact side. The duration of the optokinetic afternystagmus was asymmetrically reduced with respect to control data. Practically identical reductions in duration were found for vestibulo-ocular responses in the opposite directions. Behaving animals exhibited no obvious impairment in their spontaneous locomotory or exploratory activities. However, each UVN rat was impaired, even 2 years after the lesion, in its postural reaction to being lifted by the tail in the air. This observation suggests the presence of a permanent deficit in static and dynamic otolith-spinal reflexes that may be substituted on the ground by proprioceptive inputs.

Animals↗

PubMed1994

Reflex hamstring contraction latency in anterior cruciate ligament deficiency.

Decreased dynamic stability of the knee joint associated with functional disability is a feature of anterior cruciate ligament deficiency (ACLD). The purposes of this study were to examine the between-limbs difference in reflex contraction latency of the hamstring muscles in patients with unilateral ACLD and to investigate its relationship with instability and function. Fifty patients with arthroscopically diagnosed unilateral ACLD were measured bilaterally for reflex hamstring contraction latency (RHCL), and 20 normal volunteers were similarly tested. The subjects were measured in a position of single-limb full weight-bearing with the knee flexed 30 degrees. An anteriorly directed shear force was applied to the tibia, and surface electromyographs (EMGs) recorded the activity of the hamstrings in response to the applied force. The latency of contraction was defined as the time from initial tibial movement, identified by accelerometry, to the onset of increased hamstring EMG activity. Both legs were tested and a between-limbs difference was computed. A significant difference in RHCL was found between the limb with ACLD and the control limb. The mean RHCL of the limb with ACLD was nearly double that of the unaffected limb, for a significant mean between-limbs difference (p < 0.05). The mean between-limbs difference for the control subjects was not statistically significant. The conclusion is that patients with ACLD have an increased RHCL of the injured leg. As the RHCL is dependent on proprioceptive activity around the joint, it can be used as a measure of proprioceptive ability. The loss of the neurophysiological protective reflex involving the anterior cruciate ligament and hamstrings in patients with ACLD is likely to be a contributory factor in the decreased joint stability experienced by these patients.

Adult↗