Postural development in rats.

Mammals adopt a limited number of postures during their day-to-day activities. These stereotyped skeletal configurations are functionally adequate and limit the number of degrees of freedom to be controlled by the central nervous system. The temporal pattern of emergence of these configurations in altricial mammals is unknown. We therefore carried out an X-ray study in unrestrained rats from birth (P0) until postnatal day 23 (P23). The X-rays showed that many of the skeletal configurations described in adult rodents were already present at birth. By contrast, limb placement changed abruptly at around P10. These skeletal configurations, observed in anesthetized pups, required the maintenance of precise motor control. On the other hand, motor control continued to mature, as shown by progressive changes in resting posture and head movements from P0 to P23. We suggest that a few innate skeletal configurations provide the necessary frames of reference for the gradual construction of an adult motor repertoire in altricial mammals, such as the rat. The apparent absence of a requirement for external sensorial cues in the maturation of this repertoire may account for the maturation of postural and motor control in utero in precocial mammals (Muir et al., 2000 for a review on the locomotor behavior of altricial and precocial animals).

Postural and locomotor control in normal and vestibularly deficient mice.

We investigated how vestibular information is used to maintain posture and control movement by studying vestibularly deficient mice (IsK-/- mutant). In these mutants, microscopy showed degeneration of the cristae of the semicircular canals and of the maculae of the utriculi and sacculi, while behavioural and vestibulo-ocular reflex testing showed that vestibular function was completely absent. However, the histology of Scarpa's ganglia and the vestibular nerves was normal in mutant mice, indicating the presence of intact central pathways. Using X-ray and high-speed cineradiography, we compared resting postures and locomotion patterns between these vestibularly deficient mice and vestibularly normal mice (wild-type and IsK+/-). The absence of vestibular function did not affect resting posture but had profound effects on locomotion. At rest, the S-shaped, sagittal posture of the vertebral column was the same for wild-type and mutant mice. Both held the head with the atlanto-occipital joint fully flexed, the cervico-thoracic junction fully flexed, and the cervical column upright. Wild-type mice extended the head and vertebral column and could walk in a straight line. In marked contrast, locomotion in vestibularly deficient mice was characterized by circling episodes, during which the vertebral column maintained an S-shaped posture. Thus, vestibular information is not required to control resting posture but is mandatory for normal locomotion. We propose that vestibular inputs are required to signal the completion of a planned trajectory because mutant mice continued rotating after changing heading direction. Our findings support the hypothesis that vertebrates limit the number of degrees of freedom to be controlled by adopting just a few of the possible skeletal configurations.

Immunocytochemical characteristics of elbow, knee and ankle muscles of the five-toed jerboa (Allactaga elater).

Biochemical adaptations of limb myofibres to intensive bipedal hopping were investigated using the five-toed jerboa Allactaga elater as a model in comparison with the rat. Immunofluorescence methods included immunoreactivity to anti-fast and anti-slow MHC and troponin I. There is no specialization of triceps caput mediale for postural function in the minute non-locomotor forelimbs, unlike quadruped mammals. The various elbow extensor heads and the flexor muscles are alike with regard to fibre type population and cross-sectional areas of each type of fibre. The extensor muscle in the elongated hindlimbs of the five-toed jerboa, at both the knee and the ankle joints, differ from each other extensively. One head, made up of an extremely high percentage of type I, fatigue-resistant fibres, is suited to postural function. Two extensor heads at each joint contain a very high percentage of type IIB fibres (having the greatest maximal velocity of contraction) and are able to produce the powerful acceleration needed to trigger the leap. The relative cross-sectional areas of the myofibres are characteristic of hopping locomotion: predominance in number of one type of myofibre in a muscle accompanies greater cross-sectional area, which increases muscle efficiency in either postural or accelerative function of the muscle.

Comparative aspects of gait, scaling and mechanics in mammals.

In phylogenetically based systematics, Mammalia is the nomenclatural term which designates the clade stemming from the most recent common ancestry of monotremes and theria [, Sys. Biol. 43 (1994) 497]. Considering that locomotor performance is a prevalent function to provide the necessary conditions to survive and transmit genes, it may be questioned if the diverse types of locomotion exhibited by extant mammals could have played a role in their evolution, or have only followed it. We may look after the structural and behavioural features which are involved in mammal locomotion compared to other tetrapods and test if they fit with the proposed phylogeny. Several factors may be checked: scaling effect in relation to gravitational constraints; geometrical distribution of masses in the body, and relative mechanical role of the limbs in the production of the external forces necessary to forward motion. Classically, it was thought that the fastest gaits used by terrestrial mammals were based upon a unique kind of limb motion co-ordination, called asymmetrical gaits, which in turn may be thought to be related to a peculiar neuronal wiring. Kinematic analysis brings an insight to this topic. Is the search for an ancestral mammalian locomotor pattern judicious? Notice the small size of many of the first mammals and their probable locomotor plasticity. (relation between grain size of the elements within the substrate and the organism scale). At a small size, the gravitational constraint is less important, and the distinction between terrestrial and arboreal has probably no sense when the limbs are the principal motor elements. There remains the importance of the geometrical distribution of body elements, the proportions of the limbs and of the head-neck complex, the tail merely as an appendix, a set of factors which may have generated the frame of constraints within which diverse locomotor modes have evolved.

Modelisation of an unspecialized quadruped walking mammal.

Kinematics and structural analyses were used as basic data to elaborate a dynamic quadruped model that may represent an unspecialized mammal. Hedgehogs were filmed on a treadmill with a cinefluorographic system providing trajectories of skeletal elements during locomotion. Body parameters such as limb segments mass and length, and segments centre of mass were checked from cadavers. These biological parameters were compiled in order to build a virtual quadruped robot. The robot locomotor behaviour was compared with the actual hedgehog to improve the model and to disclose the necessary changes. Apart from use in robotics, the resulting model may be useful to simulate the locomotion of extinct mammals.

[Distinctive morphofunctional features of the bill and hyoid apparatus of turacos (Aves, Musophagidae): relations with frugivory]. / Les particularités morphofonctionnelles des appareils du bec et hyoïdien chez les touracos (Aves, Musophagidae): relations avec la frugivorie.

The present study points to morpho-anatomical features that allow vegetarian but mainly frugivorous turacos to fill at best their specific feeding requirements. Mechanisms are analysed which the bird can use to detach a fruit and avoid it rolls out of the bill. It is also examined how vegetable items can be processed particularly when they have to be cut, and what can facilitate their ingestion particularly when they are fruits that have to be swallowed entirely and are large and/or have dry or fibrous skin or flesh. The skeletal and muscular anatomy of the bill and hyoid apparatus is described in details and illustrated. The particularly short and stout bill coupled with a relatively simple system of aponevroses of the adductors reflects a trade-off between two important jaw functional requirements: huge efforts for clamping, and a wide opening for plucking, processing and swallowing relatively large fruit. The clearly oblique orientation of the modified outer adductor seems an adaptation to the detachment of fruits. The os uncinatum, particularly developed in this bird family, is interpreted as maintaining transversal stability, particularly when jaws act as a pair of scissors. Most food items being processed near the base of the bill, mechanisms have been developed which contribute to overcome the risk of breakage at the level of the prokinetic hinge because of a vertically oriented force there.

[Skeletal configurations of cervical column during rest to motion transition: generalization that underlie the motor repertoire in rodents]. / Géométrie du squelette cervical durant la transition repos-locomotion: généralisation aux caractéristiques du répertoire moteur des rongeurs.

During forward locomotion, guinea pigs adopted a posture which, although different, was as stereotyped as at rest. The whole extent of the vertebral column was extended, parallel to the earth-horizontal plane. This result supports the hypothesis that, in mammals, gaze and postural control by the central nervous system would be simplified by the adoption of a limited number of skeletal configurations. They would be optimized for energy saving, biomechanical efficacy and limitation of the number of degrees of freedom of the skeletal apparatus. Transition between rest and forward locomotion displayed two prominent characteristics: the head was stabilized versus space throughout the whole transition and the modifications of the skeletal geometry were confined to the median plane and to two major articular regions. Such an organization revealed a fourth characteristic of the guinea pig postural control: the skeletal configurations retained by evolution would ensure that smooth transitions take place between rest and the various activities of its motor repertoire. Finally, our purely descriptive data shed new light on the architecture of the neuronal network which underlies the vestibular control of gaze and posture.

Abnormal vestibular control of gaze and posture in a strain of a waltzing rat.

The waltzing behavior is usually attributed to vestibular dysfunction. However, the vestibular control of gaze and posture has not yet been measured quantitatively in any waltzing mutant. Therefore, this study was aimed at investigating the relationship between inner-ear morphology, the circling behavior, and the vestibular control of gaze and posture in a new strain of waltzing rats. Light- and electron-microscopy studies of these mutants did not reveal any structural abnormalities of the vestibular neural epithelia. In addition, the expression of Calretinin and 200-kD phosphorylated and non-phosphorylated neurofilaments was also found to be normal in the vestibular neural epithelia and ganglion cells. In contrast, the mutants showed severe dysfunctions of the vestibular control of gaze and posture. The skeletal geometry of the alert unrestrained animals was studied using cineradiography. At rest, waltzing rats held their heads tilted down: the horizontal semicircular-canal's plane was near the earth-horizontal's plane, instead of being tilted up as in Long Evans control rats. In addition, their cervical column was pitched more forward (33.6 degrees) than in the control group (6.9 degrees). The circling behavior was observed frequently, and the rats had episodes of circling in both directions. The episodes of circling amounted to an average of 17 turns, and the average angular velocity of the circling was 645 degrees/s. Unilateral labyrinthectomy induced the same postural and oculomotor syndromes in the waltzing and control groups. This indicates that the mutant vestibular nerve had a significant resting discharge before the lesion. Eye movements were recorded using acutely implanted search coils. Although waltzing rats were able to perform normal spontaneous eye movements, they showed a complete deficit of the horizontal vestibulo-ocular reflex (HVOR) and an impairment of the maculo-ocular reflex (MOR) during constant velocity, off-vertical axis rotation (OVAR). These results show, for the first time, that deficient transduction and/or processing of the horizontal-canal- and macular-related information can be causally related to the circling behavior and abnormal posture, respectively.

[Morphofunctional analysis and trophic adaptations: the case of bill apparatus of Old World flycatchers]. / Analyse morphofonctionnelle et adaptations trophiques: le cas de l'appareil du bec des gobe-mouches de l'Ancien Monde.

A morphofunctional analysis of the bill apparatus was conducted on some African forest flycatchers (Muscicapidae, Platysteiridae, Monarchidae) in relation to detailed eco-ethological data available on these species. The aim was to evaluate relationships between anatomical structures and habitat constraints and also identify the most pertinent trophic adaptations. If forest Muscicapidae have essentially conserved the generalized passerine structures and occupy open-habitat niches in the forest, Platysteiridae and Monarchidae have adapted to forest conditions and show a key-adaptation based on specific changes in the structure of the bill apparatus in response to particular light patterns and habitat clogginess, constraints that require speed and precision for the capture of prey and protection of the skull against collisions.

Plastic changes underlying vestibular compensation in the guinea-pig persist in isolated, in vitro whole brain preparations.

Vestibular compensation for the postural and oculomotor deficits induced by unilateral labyrinthectomy is a model of post-lesional plasticity in the central nervous system. Just after the removal of one labyrinth, the deafferented, ipsilateral vestibular nucleus neurons are almost silent, and the discharge of the contralateral vestibular nucleus neurons is increased. The associated static disorders disappear in a few days, as normal activity is restored in both vestibular nuclei. In this study, we searched for traces of vestibular compensation in isolated whole brains taken from adult guinea-pigs. The electrophysiological responses evoked in control brains were compared to those evoked in brains taken from animals that had previously been labyrinthectomized. Guinea-pigs compensated for an initial labyrinthectomy within three days. In vivo, subsequent deafferentation of vestibular nucleus neurons on the intact side triggered "Bechterew's phenomenon": a new postural and oculomotor syndrome appeared, similar to the one induced by the first lesion, but directed to the newly deafferented side. These disturbances would be caused by the new imbalance between the discharges of neurons in the two vestibular nuclei triggered by the second deafferentation. Experiments were designed to search for a similar imbalance in vitro in brains taken from labyrinthectomized animals, where the intact vestibular nerve is cut during the dissection. Isolated whole brains were obtained from young guinea-pigs at various times (one to seven days) following an initial labyrinthectomy. An imbalance between the resting activities of medial vestibular nucleus neurons on both sides of the brainstem was revealed in brains taken more than three days after the lesion: their discharge was higher on the compensated, initially lesioned side than on the newly deafferented side. In some cases, an oscillatory pattern of discharge, reminiscent of the spontaneous nystagmus associated in vivo with Bechterew's syndrome, appeared in both abducens nerves. These data demonstrate that most of the changes underlying vestibular compensation persist, and can thus be investigated in the isolated whole brain preparation. Brains removed only one day after the lesion displayed normal commissural responses and symmetric spinal inputs to vestibular nucleus neurons. However, an unusually large proportion of the neurons recorded on both sides of the preparation had very irregular spontaneous discharge rates. These data suggest that the first stages of vestibular compensation might be associated with transient changes in the membrane properties of vestibular nucleus neurons. Brains taken from compensated animals displayed a significant, bilateral decrease of the inhibitory commissural responses evoked in the medial vestibular nucleus by single-shock stimulation of the contralateral vestibular nerve. The sensitivity of abducens motoneurons on the initially lesioned, compensated side to synaptic activation from the contralesional vestibular nucleus neurons was also decreased. Both changes may explain the long-term, bilateral decrease of vestibular-related reflexes observed following unilateral labyrinthectomy. Spinal inputs to vestibular nucleus neurons became progressively asymmetric: their efficacy was increased on the lesioned side and decreased on the intact one. This last modification may support a functional substitution of the deficient, vestibular-related synergies involved in gaze and posture stabilization by neck-related reflexes.

Respective role of the axial and appendicular systems in relation to the transition to limblessness.

In lower quadrupedal vertebrates locomotor efficiency seems to result from the associate movements of the axial and appendicular systems, which are totally independent in structure and embryological origin. The curvature of the trunk, produced by a standing wave, magnifies the propulsive action of the limbs. In intermediate forms, the association of an elongate trunk with limbs reduced in size brings about functional consequences which may be noticeably diverse according to the degree of trunk elongation and limb reduction. According to environmental constraints, animals search for better locomotor efficiency, which implies the maintenance or breakage of this association of both locomotor systems. In some cases, limb action on the ground is added to the axial wave action through a perfect mutual adjustment of rhythmic activity, until mechanical inefficiency of the limbs is reached by possible loss of contact with the ground. In other cases, the limbs dragged on the ground during the stance phase act against the axial action or, on the contrary, are inhibited by the axial system. A review of available data tries to contribute to an understanding of the respective roles of both systems in the transition to limblessness.

[The mechanism of digging in Arvicola terrestris and Spalax ehrenbergi: functional and evolutional studies]. / Les mécanismes du fouissage chez Arvicola terrestris et Spalax ehrenbergi: étude fonctionelle et évolutive.

The cineradiographic study of the digging modalities in Arvicola terrestris and Spalax erenbergi showed important convergences in the mechanisms used by both species. Head and incisors are the burrowing tools, acting as a "scraping-shovel" in Spalax and as a "scratching-shovel" in Arvicola. They are moved forward by a force originated by the pressure of the hind limbs against the ground, and transmitted through the vertebral axis. The myological study of these species revealed the increase of the insertional areas for the cephalic muscles. However, the adaptative answer of the cervical vertebrae to the mechanical constraints of digging are different in Arvicola and Spalax; the former developed high resistance moments and the latter increased vertebral stiffness. The characters of the post-cranial skeleton in the digging rodents tend to constitute a morphocline in which Spalax is the final stage and Arvicola an intermediate stage. Then, the adaptative divergences noted above between these animals might reflect their phyletic distance.

Propulsive action of a snake pushing against a single site: Its combined analysis.

The simultaneous use of electromyography (EMG), strain gauges, and cinematography show that the capacity of continuous displacement from a single peg is based on the following: sequential activity of the tested muscles from front to rear; activity restricted to the short portion of the body in contact with the peg; alternate action of the muscle longissimus dorsi on the two sides, the transition between one side to the other occurring at the site of contact with the peg; unilateral activity of the muscle supracostalis ventralis responsible for a bulging against the peg; a great stability in the direction of the resultant force, which makes only a small angle with the directio of the motion.

Patterns of correspondence between skin rings and vertebrae in gymnophiona (Amphibia).

The skin annulation seems to have a direct relation with the vertebral column segmentation. The type of rings, primary, secondary, tertiary, or quaternary set by binary division, probably results in an induction process during morphogenesis. The diverse stages of this division appear and are rubbed out from front to rear. The topographical correspondence is different for 3 distinct parts of the body: the collar, the trunk, and the posterior part. In this last region, we can find a more or less reduced true tail or a terminal appendage without vertebral element. All these new morphological data support elements of functional indications.

Preliminary note on biometric data relating to the human coraco-acromial arch.

A biometric study based on 20 human scapulae made it possible to specify the variations in the gap of the coraco-acromial arch in relation to its depth and height. A graphic representation in rectangular coordinates, then in spatial representation in relation to the three planes of reference, leads to the following findings: the bony variations in the arch occur essentially: at the coracoid apophysis, and two types of arch can be distinguished depending on the predominance of bony or of ligamentous components.

[Biomechanics of the skull and the beak in Ramphastos (Ramphastidae, Aves) I. Description of anatomical elements]. / Biomécanique du crâne et du bec chez Ramphastos (Ramphastidae, Aves). I. Description des éléments anatomiques.

The different cranial kinetic systems described in Birds are limited in Ramphastos by the dorsal and backward position of the nostrils, the shape of the fronto-nasal suture, the lateral fit-in between nasal, lacrymal and frontal bones, and the divergent directions of the 2 otic processes of the quadrate, 5 ligaments joint the posterior skull elements to the quadrate and the mandible. Small sesamoid bones strengthen the external jugo-mandibular ligament in its retro-articular portion. The nomenclature of the aponeuroses is not useful by itself to compare the organizations and homology of the diverses muscular layers in the different birds groups. The differences observed in the relative position of the muscular bundles have to be related to the shape and particular relationships between skeletal structures. We have to consider the osteo-muscular systems as a whole and analyse them from a functional viewpoint.

[Biomechanics of the skull and the bill in Ramphastos (Ramphastidae, Aves). II. Analysis of the conditions of movement of the bill]. / Biomécanique du crâne et du bec chez Ramphastos (Ramphastidae, Aves). II. Analyse des conditions du mouvement du bec.

As all the anatomical conditions are not present to permit any movement between the cranial segments, the bill aperture and closure by the rotation on the quadrato mandibular joint is, in Ramphastos , the only action studied in relation to muscles organization and bone architecture by torques analysis. From a mechanical advantage viewpoint, the beginning of the closure seems to be performed by velocity muscles, while the action is ended by power muscles. The stresses issued by the muscles actions are balanced by bone trabeculae and other muscles, and may be considered as responsible of the mechanical stiffness of the whole bill system.