Marc Herbin

The vesicular glutamate transporter VGLUT3 synergizes striatal acetylcholine tone

Three subtypes of vesicular transporters accumulate glutamate into synaptic vesicles to promote its vesicular release. One of the subtypes, VGLUT3, is expressed in neurons, including cholinergic striatal interneurons, that are known to release other classical transmitters. Here we showed that disruption of the Slc17a8 gene (also known as Vglut3) caused an unexpected hypocholinergic striatal phenotype. Vglut3−/− mice were more responsive to cocaine and less prone to haloperidol-induced catalepsy than wild-type littermates, and acetylcholine release was decreased in striatum slices lacking VGLUT3. These phenotypes were associated with a colocalization of VGLUT3 and the vesicular acetylcholine transporter (VAChT) in striatal synaptic vesicles and the loss of a synergistic effect of glutamate on vesicular acetylcholine uptake. We propose that this vesicular synergy between two transmitters is the result of the unbalanced bioenergetics of VAChT, which requires anion co-entry for continuing vesicular filling. Our study reveals a previously unknown effect of glutamate on cholinergic synapses with potential functional and pharmacological implications.

Steady locomotion in dogs: temporal and associated spatial coordination patterns and the effect of speed

SUMMARY Only a few studies on quadrupedal locomotion have investigated symmetrical and asymmetrical gaits in the same framework because the mechanisms underlying these two types of gait seem to be different and it took a long time to identify a common set of parameters for their simultaneous study. Moreover, despite the clear importance of the spatial dimension in animal locomotion, the relationship between temporal and spatial limb coordination has never been quantified before. We used anteroposterior sequence (APS) analysis to analyse 486 sequences from five malinois (Belgian shepherd) dogs moving at a large range of speeds (from 0.4 to 10.0 m s–1) to compare symmetrical and asymmetrical gaits through kinematic and limb coordination parameters. Considerable continuity was observed in cycle characteristics, from walk to rotary gallop, but at very high speeds an increase in swing duration reflected the use of sagittal flexibility of the vertebral axis to increase speed. This change occurred after the contribution of the increase in stride length had become the main element driving the increase in speed– i.e. when the dogs had adopted asymmetrical gaits. As the left and right limbs of a pair are linked to the same rigid structure, spatial coordination within pairs of limbs reflected the temporal coordination within pairs of limbs whatever the speed. By contrast, the relationship between the temporal and spatial coordination between pairs of limb was found to depend on speed and trunk length. For trot and rotary gallop, this relationship was thought also to depend on the additional action of trunk flexion and leg angle at footfall.

Gait parameters of treadmill versus overground locomotion in mouse

Many studies of interest in motor behaviour and motor impairment in mice use equally treadmill or track as a routine test. However, the literature in mammals shows a wide difference of results between the kinematics of treadmill and overground locomotion. To study these discrepancies, we analyzed the locomotion of adult SWISS-OF1 mice over a large range of velocities using treadmill and overground track. The use of a high-speed video camera combined with cinefluoroscopic equipment allowed us to quantify in detail the various space and time parameters of limb kinematics. The results show that mice maintain the same gait pattern in both conditions. However, they also demonstrate that during treadmill exercise mice always exhibit higher stride frequency and consequently lower stride length. The relationship of the stance time and the swing time against the stride frequency are still the same in both conditions. We conclude that the conflict related to the discrepancy between the proprioceptive, vestibular, and visual inputs contribute to an increase in the stride frequency during the treadmill locomotion.

Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz–Jampel syndrome neuromyotonia

Schwartz-Jampel syndrome (SJS) is a recessive neuromyotonia with chondrodysplasia. It results from hypomorphic mutations of the gene encoding perlecan, leading to a decrease in the levels of this heparan sulphate proteoglycan in basement membranes (BMs). It has been suggested that SJS neuromyotonia may result from endplate acetylcholinesterase (AChE) deficiency, but this hypothesis has never been investigated in vivo due to the lack of an animal model for neuromyotonia. We used homologous recombination to generate a knock-in mouse strain with one missense substitution, corresponding to a human familial SJS mutation (p.C1532Y), in the perlecan gene. We derived two lines, one with the p.C1532Y substitution alone and one with p.C1532Y and the selectable marker Neo, to down-regulate perlecan gene activity and to test for a dosage effect of perlecan in mammals. These two lines mimicked SJS neuromyotonia with spontaneous activity on electromyogramm (EMG). An inverse correlation between disease severity and perlecan secretion in the BMs was observed at the macroscopic and microscopic levels, consistent with a dosage effect. Endplate AChE levels were low in both lines, due to synaptic perlecan deficiency rather than major myofibre or neuromuscular junction disorganization. Studies of muscle contractile properties showed muscle fatigability at low frequencies of nerve stimulation and suggested that partial endplate AChE deficiency might contribute to SJS muscle stiffness by potentiating muscle force. However, physiological endplate AChE deficiency was not associated with spontaneous activity at rest on EMG in the diaphragm, suggesting that additional changes are required to generate such activity characteristic of SJS.

Bird terrestrial locomotion as revealed by 3D kinematics.

Most birds use at least two modes of locomotion: flying and walking (terrestrial locomotion). Whereas the wings and tail are used for flying, the legs are mainly used for walking. The role of other body segments remains, however, poorly understood. In this study, we examine the kinematics of the head, the trunk, and the legs during terrestrial locomotion in the quail (Coturnix coturnix). Despite the trunk representing about 70% of the total body mass, its function in locomotion has received little scientific interest to date. This prompted us to focus on its role in terrestrial locomotion. We used high-speed video fluoroscopic recordings of quails walking at voluntary speeds on a trackway. Dorso-ventral and lateral views of the motion of the skeletal elements were recorded successively and reconstructed in three dimensions using a novel method based on the temporal synchronisation of both views. An analysis of the trajectories of the body parts and their coordination showed that the trunk plays an important role during walking. Moreover, two sub-systems participate in the gait kinematics: (i) the integrated 3D motion of the trunk and thighs allows for the adjustment of the path of the centre of mass; (ii) the motion of distal limbs transforms the alternating forward motion of the feet into a continuous forward motion at the knee and thus assures propulsion. Finally, head bobbing appears qualitatively synchronised to the movements of the trunk. An important role for the thigh muscles in generating the 3D motion of the trunk is suggested by an analysis of the pelvic anatomy.

Experimental study of coordination patterns during unsteady locomotion in mammals

SUMMARY A framework to study interlimb coordination, which allowed the analysis of all the symmetrical and asymmetrical gaits, was recently proposed. It suggests that gait depends on a common basic pattern controlling the coordination of the forelimbs (fore lag, FL), the coordination of the hindlimbs (hind lag, HL) and the relationship between these two pairs of limbs (pair lag, PL) in an anteroposterior sequence of movement (APS). These three time parameters are sufficient for identifying all steady gaits. We assumed in this work that this same framework could also be used to study non-steady locomotion, particularly the transitions between symmetrical and asymmetrical gaits. Moreover, as the limbs are coordinated in time and also in space during locomotion, we associated three analogous space parameters (fore gap, FG; hind gap, HG and pair gap, PG) to the three time parameters. We studied the interlimb coordination of dogs and cats moving on a runway with a symmetrical gait. In the middle of the runway, the gait was disturbed by an obstacle, and the animal had to change to an asymmetrical coordination to get over it. The time (FL, HL, PL) and space (FG, HG, PG) parameters of each sequence of the trials were calculated. The results demonstrated that the APS method allows quantification of the interlimb coordination during the symmetrical and asymmetrical phases and during the transition between them, in both dogs and cats. The space and time parameters make it possible to link the timing and the spacing of the footfalls, and to quantify the spatiotemporal dimension of gaits in different mammals. The slight differences observed between dogs and cats could reflect their morphological differences. The APS method could thus be used to understand the implication of morphology in interlimb coordination. All these results are consistent with current knowledge in biomechanics and neurobiology, therefore the APS reflects the actual biological functioning of quadrupedal interlimb coordination.

The Giant Cretaceous Coelacanth (Actinistia, Sarcopterygii) Megalocoelacanthus dobiei Schwimmer, Stewart & Williams, 1994, and Its Bearing on Latimerioidei Interrelationships

We present a redescription of Megalocoelacanthus dobiei, a giant fossil coelacanth from Upper Cretaceous strata of North America. Megalocoelacanthus has been previously described on the basis of composite material that consisted of isolated elements. Consequently, many aspects of its anatomy have remained unknown as well as its phylogenetic relationships with other coelacanths. Previous studies have suggested that Megalocoelacanthus is closer to Latimeria and Macropoma than to Mawsonia. However, this assumption was based only on the overall similarity of few anatomical features, rather than on a phylogenetic character analysis. A new, and outstandingly preserved specimen from the Niobrara Formation in Kansas allows the detailed description of the skull of Megalocoelacanthus and elucidation of its phylogenetic relationships with other coelacanths. Although strongly flattened, the skull and jaws are well preserved and show many derived features that are shared with Latimeriidae such as Latimeria, Macropoma and Libys. Notably, the parietonasal shield is narrow and flanked by very large, continuous vacuities forming the supraorbital sensory line canal. Such an unusual morphology is also known in Libys. Some other features of Megalocoelacanthus, such as its large size and the absence of teeth are shared with the mawsoniid genera Mawsonia and Axelrodichthys. Our cladistic analysis supports the sister-group relationship of Megalocoelacanthus and Libys within Latimeriidae. This topology suggests that toothless, large-sized coelacanths evolved independently in both Latimeriidae and Mawsoniidae during the Mesozoic. Based on previous topologies and on ours, we then review the high-level taxonomy of Latimerioidei and propose new systematic phylogenetic definitions.

Kinematics of treadmill locomotion in mice raised in hypergravity.

The study compared the motor performance of adult C57Bl/6J mice previously exposed to a 2G gravity environment during different periods of their development. 12 mice were housed in a large diameter centrifuge from the conception to Postnatal day 10 (P10). Another group of 10 mice was centrifuged form P10 to P30, and a third group of 9 mice was centrifuged from conception to P30. Their gait parameters, and kinematics of joint excursions were compared with 11 control mice, at the age of 2 months using a video-radiographic apparatus connected to a motorized treadmill. The mice that returned to Earth gravity level at the age of P10 showed a motor pattern similar to control mice. At variance the two groups that were centrifuged from P10 to P30 showed a different motor pattern with smaller and faster strides to walk at the same velocity as controls. On the other hand all the centrifuged mice showed significant postural changes, particularly with a more extended ankle joint, but the mice centrifuged during the whole experimental period differed even more. Our results showed that the exposure to hypergravity before P10 sufficed to modify the posture, suggesting that postural control starts before the onset of locomotion, whereas the gravity constraint perceived between P10 and P30 conditioned the tuning of quadruped locomotion with long term consequences. These results support the existence of a critical period in the acquisition of locomotion in mice.

Limb preference in the gallop of dogs and the half-bound of pikas on flat ground

During fast locomotion—gallop, half-bound, bound—of quadruped mammals, the ground contact of the limbs in each pair does not alternate symmetrically. Animals using such asymmetrical gait thus choose whether the left or the right limb will contact the ground first, and this gives rise to limb preference. Here, we report that dogs (Mammalia, Carnivora) and pikas (Mammalia, Lagomorpha) prefer one forelimb as trailing limb and use it as such almost twice as often as the other. We also show that this choice depends on the individual and is not a characteristic of the species, and that the strength of the preference was not dependent on the animals running speed.

Variability and asymmetry of the sulcal contours defining Broca's area homologue in the chimpanzee brain.

There has been recent motivation to search for neuroanatomical asymmetries in nonhuman primates in order to provide comparative information on how the human brain is structurally organized to support specific cognitive capabilities, such as language functions. We took the opportunity to study Brocas area homologue in a novel sample of 80 preserved postmortem chimpanzee (Pan troglodytes) cerebral hemispheres. Consistent with the only prior study documenting the morphology of Brocas area homologue in the chimpanzee (Sherwood et al. [2003] Anat Rec 271:276–285), we report great interindividual variation in the structure and connections of the sulci investigated, most notably a left‐sided bias in the bifurcation of the inferior precentral sulcus, an anatomical feature that occurs much more frequently in chimpanzees relative to humans. Consistent with our recent neuroimaging report (Keller et al. [2009b] J Neurosci 29:14607–14616), no population‐based interhemispheric asymmetries of sulcal length existed that could be considered markers of the size of Brocas area homologue. With strict anatomical guidelines, we report that the diagonal sulcus was present in 25% left and 20% right chimpanzee hemispheres studied, which is substantially less that the general prevalence in humans. Through the presentation of schematic drawings, photographs, morphological recordings and sulcal length metrics, our data illustrate the interindividual variability of Brocas area homologue in the chimpanzee and support the notion of no macroscopic asymmetry of this important homologous language brain region in one of the closest evolutionary ancestor to modern humans J. Comp. Neurol. 520:1165–1180, 2012.