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Biomedical subjects

M Lacour

Publications and source records attributed to M Lacour.

At least 91 records · Page 5Linked to original sources
PubMed1980

Compensation of postural reactions to free-fall in the vestibular neurectomized monkey. Role of the visual motions cues.

In previous studies a contribution of vision to vestibular-dependent muscle responses during free-fall was found in the intact monkey, and the role of remaining labyrinthine afferents in compensation of these postural reactions was studied in vestibular neurectomized monkeys. In the present investigation we have compared the role of visual motion cues in the recovery of muscle responses to fall in unilateral (U.N.) and bilateral vestibular neurectomized (B.N.) baboons. During free-fall, electromyographic (EMG) responses were recorded from splenius capitis, soleus and tibialis anterior muscles. EMG activities were recorded in two randomly presented conditions: with normal motion of the visual world (NV) and with the visual world stabilized with respect to the baboon's head (SV) until 6 weeks after surgery. In B.N. baboons, results showed that condition SV was accompanied by a very strong motor depression during the entire test period. A greater decrease was observed in the splenius and soleus muscles. In U.N. baboons, significantly depressed EMG responses were recorded in the SV condition during the first two stages of compensation only (0--2 weeks), in all tested muscles except the tibialis anterior muscle. On the other hand, these motor depressions appeared to depend upon the level of neuronal resting activity in the vestibular nuclei. It is inferred that the partial recovery of muscle responses to fall observed in B.N. baboons in the NV condition is mainly due to visual information concerning motion, which replaces to the labyrinthine afferents. In U.N. baboons, the visual motion cues would fulfil only a transitory substitution function by supplying the decrease of neuronal activity in the vestibular nuclei. Later on, full compensation would be carried out by means of the remaining labyrinth.

Animals↗
PubMed1979

Compensation of postural reactions to fall in the vestibular neurectomized monkey. Role of the reamining labyrinthine afferences.

The electromyographic (EMG) responses from soleus and tibialis anterior muscles and the monosynaptic H- and T-reflex responses from soleus muscles were recorded bilaterally from conscious baboon while unexpectedly dropping it with unrestricted vision. These responses were recorded either after unilateral vestibular neurectomy (U.N. Baboons) or after bilateral neurectomy performed in one stage (B.N. 1 baboons) and in two stages (B.N. 2 baboons). A positive correlation was found between modifications and development of EMG responses and reflex data. In the U.N. baboons, some differences were observed when comparing data from the H- and T-reflex methods, suggesting that recovery of normal responses to fall is achieved both by means of direct influences on alpha-motoneurons and via the gamma-loop. In the U.N. baboons postural reactions to fall developed in three distinct periods. The first or critical stage showed asymmetrical EMG and reflex responses with increased responses from contralateral soleus muscle and decreased responses from ipsilateral soleus. Opposite effects were recorded from tibialis anterior flexor muscles. The second or acute stage which began around 4 to 7 days after surgery exhibited symmetrical, but very reduced, responses when compared to the control in soleus muscles, and symmetrical, but increased, responses from tibialis anterior muscles. This stage lasted until about the end of the second postoperative week and was followed by the third or compensatory stage during which EMG as well as reflex responses developed towards the control pattern in all tested muscles. Almost normal responses were recorded on both sides 3 weeks after surgery. Only a partial recovery was found in the B.N. 1 baboons, indicating that the contralateral remaining labyrinthine afferences constitute a necessary condition for the full compensation of postural reactions to fall in the case of unilateral vestibular neurectomy. The Bechterew's compensation was obtained in the B.N. 2 baboons. These results are discussed in relation with the general organization of the vestibulospinal pathways and with those concerning development of the postoperative activity at the vestibular nuclei level. A model of vestibular compensation achieved by means of a multisensory substitution process is suggested.

Afferent Pathways↗
PubMed1979

Contribution of vision to muscle responses in monkey during free-fall: visual stabilization decreases vestibular dependent responses.

In a previous study the muscle responses from the lower limbs were studied in the Baboon (Papio-Papio) during sudden falls. On the other hand, recent findings concerning the role of vision in the control of posture during rapid perturbations in man have stimulated the present investigation. EMG activities were recorded from the fully conscious animal using chronic electrodes implanted in various muscles (splenius, quadriceps femoris, soleus, and tibialis anterior). For testing, the monkey was seated in a special chair suspended from an electromagnet and unexpectedly dropped 90 cm. EMG responses were recorded in three randomly presented conditions: with normal motion of visual world (N), with visual world stabilized with respect to the head (S) using a box covered inside by a black and white checkboard pattern surrounding the animal's head, and in total darkness (D). Results showed that condition S is accompanied in all tested muscles by a significant decrease in the EMG response; this effect is particularly evident in the interval 60--120 ms but may occur earlier. Condition D is in most of the cases accompanied by a less important decrease which is situated between condition N and condition S. These results are in contrast to previous concludions of other authors which negated the role of vision in similar situations.

Animals↗
PubMed1978

Muscle responses and monosynaptic reflexes in falling monkey. Role of the vestibular system.

The free fall has been used in our laboratory as a way to test vestibular function in baboons in order to quantify vestibular compensation in the hemilabyrinthectomized animal. This study presents only those results that concern the contribution of the vestibular system to muscle responses due to sudden fall. EMG activity was recorded from the fully conscious animal using chronic electrodes implanted in various muscles. Spinal monosynaptic reflexes (Hoffmann's and tendon reflexes) were studied in the soleus muscle. Baboons were seated in a special chair suspended from an electromagnet and unexpectedly dropped 90 cm. Experiments were performed in normal, unilateral and bilateral vestibular neurectomized baboons. 1. In normal baboons, results showed a first short-latency response in all tested muscles, followed by a second peak of EMG activity in these muscles. Comparison with data from bilateral vestibular neurectomized baboons demonstrates that normal vestibular function is essential for the appearance of the first peak; the second peak rapidly disappears in our experimental situation where the animal's fall is mechanically braked and interrupted, so the animal does not have to make the postural adjustments necessary for landing, It is suggested that the first peak is concerned with the automatic and reflex control of landing, the second with the voluntary breaking of landing. 2. The modulation of monosynaptic spinal reflexes is closely related to the EMG response in soleus muscle. Facilitation of the H-reflex begins just prior to the onset of the EMG activity and continues as long as the baboon is falling. The T-reflex modulation presents a similar time course except in its early phase where it is depressed. Decrease in T and increase in H-reflexes suggest that the EMG response is most likely due to direct activation of alpha-motoneurons and not by means of the gamma-loop. 3. In unilateral vestibular neurectomized baboons, EMG and reflexological data show the classical asymmetry characterized by a strong decrease of the responses on the side of the lesion, and by a pronounced increase on the contralateral side. It is concluded that this represents the imbalance between the resting discharge of the vestibular neurons, and discloses the influence of labyrinthine afferences at the spinal level. We suggest consequently the use of EMG responses and modulation of spinal reflexes to fall in order to quantify vestibular compensation.

Animals↗
PubMed1976

Modifications and development of spinal reflexes in the alert baboon (Papio papio) following an unilateral vestibular neurotomy.

Unilateral vestibular neurotomy performed on 6 baboons was followed by the classical postural and locomotor postoperative disorders. Postoperative spinal reflex excitability was studied in these awake baboons by measuring monosynaptic recruitment ratios in soleus motoneuronal pool and the recovery cycle of the monosynaptic response. Vestibular neurotomy induces: (1) asymmetrical spinal reflexes with a decrease of the recruitment on the side of the section and an increase on the opposite side. (2) a modification of phases IV and V of the ipsilateral recovery cycle. The recovery during postoperative days of normal recruitment curves and recovery cycles is described. This recovery is relatively fast and relates closely to the compensation of postural and locomotor disorders. We note the importance of an early active motor exploration on the time-course of recovery: postoperative disorders in posture and locomotion are reduced much later when baboons are submitted to a motor restriction. These findings suggest a combined alpha and gamma-hypoexcitability of the ipsilateral hindlimb. The study of the recovery process suggests that the cerebellum is involved in the compensatory mechanisms. The regression of postural disorders, observed both in restrained and unrestrained baboons, demonstrates the importance of central regulations using proprioceptive afferents for recovery.

Animals↗
PubMed1976

[Experimental study of vestibular neurectomy].

The authors describe an experimental study carried out on baboons. After unilateral vestibular neurectomy, the behaviour disorders on the one hand, and on the other, modifications and temporal development of reflex muotatic excitability of the spine using Hoffmann's reflex method are analyzed. As far as behaviour is concerned, a four-day period of motor restriction following the operation causes more marked residual disorders in comparison with controls. From the neurophysiological point of view, neurectomy results in seriously disordered spinal reflexes characterized by ipsilateral hypo-excitability developing in there stages: a tw-day initial critical phase during which the disorders are at their worst, a four-day recuperative stage with partial regression of the disorders, finally a chronic compensation stage in which spinal excitability returns to normal after several months.

Animals↗