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Vascularization in the core of crocodylian osteoderms, and in their superficial pits has been hypothesized to be a key feature involved in physiological thermoregulation and/or acidosis buffering during anoxia (apnea). However, up to now, there have been no quantitative data showing that the inner, or superficial, blood supply of the osteoderms is greater than that occurring in neighboring dermal tissues. We provide such data: our results clearly indicate that the vascular networks in both the osteoderms and the pits forming their superficial ornamentation are denser than in the overlying dermis. These results support previous physiological assumptions and indicate that vascularization in pseudosuchian (crocodylians and close relatives) ornamented osteoderms could be part of a broad eco-physiological adaptation towards ectothermy and aquatic ambush predation acquired by the crocodylomorphs during their post-Triassic evolution. Moreover, regressions demonstrate that the number of enclosed vessels is correlated with the sectional area of the cavities housing them (superficial pits and inner cavities). These regressions can be used to infer the degree of vascularization on dry and fossilized osteoderms and thus document the evolution of the putative function of the osteoderms in the Pseudosuchia. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 301:175-183, 2018. © 2017 Wiley Periodicals, Inc.

International audience; We present a short historical review of the major figures, their administrative functions and their works that contributed to make Paris a renowned centre of physiology and neurology during the XIXth and the first half of the XXth century. We purposely chose to focus on the period 1800-1950, as 1800 corresponds to the actual beginning of neurosciences, and 1950 marks their exponential rise. Our presentation is divided into four chapters, matching the main disciplines which have progressed and contributed the most to the knowledge we have of the brain sciences: anatomy, physiology, neurology, and psychiatry-psychology. The present article is the third of four parts of this review, and deals with neurology. A special credit should be given to Jean-Martin Charcot who founded the Salpêtriè re School of neurology and became one of the world's most important neurologists of the XIXth century. We provide below the biographical sketches of Armand Trousseau,; Nous présentons une revue générale historique brève sur les principales personnalités, leurs activités administratives et leurs travaux qui ont contribué à faire de Paris un centre renommé de physiologie et de neurologie au cours du XIX e siècle et de la première partie du XXe siècle. La raison du choix de cette période allant de 1800 à 1950 s’explique par le fait que 1800 marque les débuts des neurosciences et 1950 leur développement exponentiel. Notre présentation est divisée en quatre chapitres, correspondant aux principales disci- plines ayant progressé et contribué le plus aux connaissances que nous avons sur les sciences du cerveau : anatomie, physiologie, neurologie, et psychiatrie-psychologie. Le présent article est la troisième des quatre parties de cette revue générale, qui porte sur le chapitre de la neurologie. Une mention particulière doit eˆtre faite à Jean-Martin Charcot qui fut le fondateur de l’école de neurologie de la Salpeˆtrière et fut l’un des plus célèbres neurologues au monde du XIXe siècle. Nous présentons ci-après les biographies résumées de Armand Trousseau, Guillaume Benjamin Amand Duchenne, Jean-Martin Charcot, Alfred Vulpian, Désiré-Magloire Bourneville, Paul Richer, Henri Parinaud, Albert Pitres, Jules Joseph Dejerine, Mrs. Augusta Dejerine-Klumpke, Édouard Brissaud, Pierre Marie, Georges Édouard Brutus Gilles de la Tourette, Joseph Babinski, André Thomas, Georges Marinesco, Achille Alexandre Souques, Georges Guillain, et Charles Foix.

We present a short historical review of the major figures and institutions that contributed to make Paris a renowned centre of physiology and neurology during the xixth and the first half of the xxth century. We purposely chose to focus on the period 1800-1950, as 1800 corresponds to the actual beginning of experimental physiology of the nervous system - what is here referred to as "neuroscience"-and 1950 marks its exponential rise. Our presentation is divided into four chapters, matching the main disciplines which have progressed and contributed the most to the knowledge we have of the brain sciences: anatomy, physiology, neurology, and psychiatry-psychology. The present article is the second of four parts of this review which includes the chapter on neurophysiology with selected biographical sketches of François Magendie, Marie Jean-Pierre Flourens, Claude Bernard, Charles-Édouard Brown-Séquard, Étienne-Jules Marey, Alfred Fessard and Denise Albe-Fessard.

We present a short historical review on the major institutions and figures that contributed to make Paris a renowned centre of physiology and neurology during the xixth and the first half of the xxth centuries. We purposely chose to focus on the period 1800-1950, as 1800 corresponds to the development of brain science and 1950 marks the true beginning of neuroscience. Our presentation is divided into four chapters, matching the main disciplines which have progressed and contributed the most to the knowledge we have of the brain sciences: anatomy, physiology, neurology, and psychiatry-psychology. The present article is the first of four parts of this review, which includes an introduction followed by the chapter on neuroanatomy and on anatomo-pathology, which includes biographical sketches of Félix Vicq d'Azyr, François-Xavier Bichat, Franz Joseph Gall, Jean Cruveilhier, Jules Bernard Luys, Paul Broca, Louis Ranvier, André-Victor Cornil, Albert Gombault, Jean Nageotte and René Couteaux.

Bone ornamentation, that is, hollow (pits and grooves) or protruding (ridges) repetitive reliefs on the surface of dermal bones, is a frequent, though poorly studied and understood, feature in vertebrates. One of the most typical examples of this characteristic is given by the Crurotarsi, a taxon formed by the crocodilians and their closest allies, which generally display deep ornamentation on skull roof and osteoderms. However, the ontogenetic process responsible for the differentiation and development of this character remains controversial. This study was conducted to settle the question on histological and microanatomical evidence in several crurotarsan taxa. Observational and experimental data in extant and extinct crocodyliforms show that bone ornamentation is initially created, and later maintained during somatic growth (that is indefinite in crocodilians), by a complex process of bone remodeling comprising local resorption of superficial bone cortices, followed by partial reconstruction. The superficial reliefs of crocodilian dermal bones are thus permanently modified through pit enlargement, drift, stretching, shrinking, or complete filling. Ridges are also remodeled in corresponding ways. These processes allow accommodation of unitary ornamental motifs to the overall dimensions of the bones during growth. A parsimony optimization based on the results of this study, but integrating also published data on bone histology in non-crocodyliform crurotarsans and some non-crurotarsan taxa, suggests that the peculiar mechanism described above for creating and maintaining bone ornamentation is a general feature of the Crurotarsi and is quite distinct from that attributed by previous authors to other vertebrates.

The first postnatal week is a critical period for the development of posture in the rat. The use of ankle extensor muscles in postural reactions increases during this period. Changes in excitability of motoneurons are probably an important factor underlying this maturation. The aim of this study was to identify whether variations in the maturation exist between motor pools innervating antagonistic muscles. Intracellular recordings in the in vitro brain stem-spinal cord preparation of neonatal rats (from postnatal day 0-5) were used to examine the developmental changes in excitability of motoneurons innervating the ankle flexors (F-MNs) and the antigravity ankle extensors (E-MNs). No significant difference in resting potential, action potential threshold, input resistance or rheobase was observed at birth. The age-related increase in rheobase was more pronounced for F-MNs than for E-MNs. The development of discharge properties of E-MNs lagged behind that of F-MNs. More F-MNs than E-MNs were able to fire repetitively in response to current injection at birth. F-MNs discharged at a higher frequency than E-MNs at all ages. Differences in the duration of action potential afterhyperpolarization accounted, at least partly, for the differences in discharge frequency between E-MNs and F-MNs at birth, and for the age-related increase in firing rate. These results suggest that E-MNs are more immature at birth than F-MNs and that there is a differential development of motoneurons innervating antagonistic muscles. This may be a critical factor in the development of posture and locomotion.

How is load sensed by receptors, and how is this sensory information used to guide locomotion? Many insights in this domain have evolved from comparative studies since it has been realized that basic principles concerning load sensing and regulation can be found in a wide variety of animals, both vertebrate and invertebrate. Feedback about load is not only derived from specific load receptors but also from other types of receptors that previously were thought to have other functions. In the central nervous system of many species, a convergence is found between specific and nonspecific load receptors. Furthermore, feedback from load receptors onto central circuits involved in the generation of rhythmic locomotor output is commonly found. During the stance phase, afferent activity from various load detectors can activate the extensor part in such circuits, thereby providing reinforcing force feedback. At the same time, the flexion is suppressed. The functional role of this arrangement is that activity in antigravity muscles is promoted while the onset of the next flexion is delayed as long as the limb is loaded. This type of reinforcing force feedback is present during gait but absent in the immoble resting animal.

The development of the early stage of locomotion (between Postnatal Days 3 and 10) was studied in newborn rats. At this age, rats are known to perform limited locomotor activities, consisting of an inefficient nonpostural gait termed crawling. By providing appropriate olfactory stimulation, it was possible to override the pups' reluctance to walk and to discover their actual locomotor abilities. The step period decreased from 1,200 ms to 900 ms from Postnatal Days 4 to 9, showing both a regular decrease in the swing and a discontinuous decrease in the stance phase. The fore- and hindlimb periods stabilized early on an alternate pattern of coupling. The ipsilateral coupling shifted progressively from 220 degrees to 260 degrees in relation with the change in the gait pattern. In parallel with the change in timing, the newborn rats showed gradual changes in the foot position and in the interlimb spatial coordination. These results show that quadruped locomotion develops before postural control is acquired, in a continuous process as the nervous system develops.

Motor neurones of the crayfish walking system display inhibitory responses evoked either by γ-amino butyric acid (GABA) or glutamate, possibly involving the same receptor (Pearlstein et al. 1994). In order to test if this sensibility to both GABA and glutamate was a specific property of crayfish GABA receptors, pharmacological characteristics of GABA-evoked responses in both sensory terminals from CB chordotonal organ and motor neurones of the walking system have been compared. Both receptors are GABA-gated Cl− channels activated by specific GABAA (muscimol, isoguvacine), GABAB (3-aminopropyl phosphinic acid), and GABAC (cis-4-amino crotonic acid) agonists, and blocked by competitive (β-guanidino propionic acid) and non-competitive (picrotoxin) antagonists. They were insensitive to specific GABAA (bicuculline, SR-95531) and GABAB (phaclofen) antagonists. Furthermore, in both cases, nipecotic acid and the modulatory drug diazepam had no effect. However, our results demonstrate that GABA receptors of sensory terminals are different from those of motor neurones. GABA-induced desensitisation only occurred in sensory terminals. Moreover, glutamate was shown to activate GABA-gated Cl− channels in motor neurones, but not in sensory terminals. Therefore, GABA is likely to be the endogenous neurotransmitter of presynaptic inhibition in sensory terminals, whereas inhibition between antagonistic motor neurones would be achieved by glutamate.

We present a short historical review on the major institutions and figures who contributed to make Paris a renowned centre of physiology and neurology during the XIXth and the first half of the XXth century. We purposely chose to focus on the period 1800-1950, as 1800 corresponds to the actual beginning of neurosciences, and as 1950 marks their exponential rise. Our presentation is divided into four chapters, matching the main disciplines that have progressed and contributed most to the knowledge we have of the brain sciences: anatomy, physiology, neurology, and psychiatry-psychology. The present article is the fourth of the four parts of this review, which deals with the chapter on psychiatry and psychology. When the French Revolution occurred, only a few institutions were taking care of the mentally ill. In the Paris area, these included Maison Royale de Charenton, Les Petites Maisons, and one of the departments of larger hospitals such as Hotel-Dieu, the Salpetriere Hospital and Bicetre Hospital. One of the founders of psychiatry in Paris at that time and thereafter was Philippe Pinel (1745-1826) who was the first to distinguish insane/alienated patients from misfits, beggars, and other vagabonds. During the first half of the XIXth century, his student Jean-Etienne Esquirol (1772-1840) also played a major role with his treatise on mental diseases and the 1838 law and the creation of asylums in all parts of France. Alienists were in general caregivers and learned by themselves. In contrast, at the academic level, the emerging disciplines psychiatry and neurology were very close to each other in the second half of the XIXth century, the best example being Jules Baillarger (1809-1890). The actual development of psychiatry and psychology and the foundation of psychoanalysis later in the XIXth century and in the first half of the XXth century owed much to several European doctors and scientists, particularly those from British institutions and from German-speaking universities in Central Europe. In France, important advances were once again initiated in Paris by Jean-Martin Charcot (1825-1893) and some of his pupils who renewed the concept of hysteria and the use of hypnosis. Sainte-Anne Hospital was created in 1867. This new institution located in the southern part of Paris became (and is still) one of the most important places in France for the treatment, research and teaching of mental diseases. Thereafter started new disciplines such as clinical psychology and neuropsychology; the scientific basis of psychology and notably the psychopathology hypothesis were established. A major revolutionary step occurred in Paris in the early 1950s with the discovery of neuroleptics and the birth of psychopharmacology. Here we present the biographical sketches of the most important Parisian scientists of these disciplines from that era, Philippe Pinel, Jean-Etienne Esquirol, Theodule Armand Ribot, Pierre Janet, Henri Louis Charles Pieron, Henry Ey, Jean Delay, Henri Laborit and Henri Hecaen.

The Middle Ages saw the development of numerous universities in the different provinces that later became the kingdom of France. In 1794, Napoleon I established 3 medical schools in Paris, Montpellier and Strasbourg, which were transformed into medical faculties in 1808. France had always been a highly centralized country, but during the 19th century, this trend started to change with the creation of medical faculties in Nancy (1872), Lille (1877), Lyon (1878), Bordeaux (1879), Toulouse (1891), Algiers (1910) and Marseille (1930). Following the creation of the 12 foundation courses, specialized chairs were progressively established in Paris, but for a long time this remained restricted to the French capital. However, with the emergence of medicine as an academic discipline in several towns outside Paris, came the development of neurology. This was greatly influenced by former students of Jean-Martin Charcot, local personalities, and the interactions between the two. Leading figures included Albert Pitres in Bordeaux, Leon Ingelrans in Lille, Eugene Devic and Jules Froment in Lyon, Lucien Cornil in Marseille, Joseph Grasset in Montpellier, and Marcel Riser in Toulouse. The interaction between French and Germanic medical communities also developed at this turbulent time under the influence of several great physicians such as Wilhelm Waldeyer, Adolf Kussmaul, and later Jean Alexandre Barre in Strasbourg, and Hippolyte Bernheim in Nancy. There are a number of other university towns outside Paris in which the development of neurology was probably influenced by the same interactions with psychiatry. It would be worth carrying out a thorough analysis of these towns in order to present an exhaustive overview of the development of neurology in France.

Charcot-Marie-Tooth (CMT) disease is the most frequent hereditary peripheral neuropathy in humans. Its prevalence is about one in 2500. A subform, CMT1A, is transmitted as an autosomal dominant trait. An estimated 75% of patients are affected. This disorder has been shown to be associated with the duplication of a 1.5 Mb region of the short arm of chromosome 17, in which the PMP22 gene has been mapped. We have constructed a murine model of CMT1A by inserting into the murine genome a human YAC containing peripheral myelin protein 22 (PMP22) and its flanking controlling elements. We describe the behaviour of the C22 line (seven copies of YAC, 2.1 times PMP22 overexpression) during the myelination process. Electron microscopy, morphometry, electrophysiology, nerve conduction and expression of specific markers (e.g. Krox20) in normal and pathological Schwann cells demonstrated that PMP22 overexpression leads to a defect in the myelination of axons. The largest axons are the most affected. Only a few demyelination/remyelination processes were observed. Moreover, PMP22 overexpression probably enhances collagen synthesis by fibroblasts, before myelination, demonstrating that structures other than Schwann cells are affected by PMP22 overexpression. Classically, CMT1A was thought to be induced by a demyelination process following a phase of normal myelination, yet our data suggest that dysmyelination should be considered as a major factor for the disease.

Different features of motor behaviour were studied on a transgenic mouse model of Charcot-Marie-Tooth's disease (CMT). Mutants with 4 or 7 copies of the human PMP22 gene leading to a phenotype significantly close to CMT's disease type 1A were compared with control animals. The aim of the study was to validate this transgenic model and to characterise the impairments occurring in the various lines. Three main types of analysis were performed in 2-month-old mice without any peculiar visible deficit: (i) a study of standardised clinical tests (SHIRPA protocol) demonstrated that only a few motor deficits were expressed; (ii) a measurement of general spontaneous activity by means of a commercial video-tracking system was performed and revealed that the main spontaneous activities were identical in the three lines with, however, some slight localised modifications; and, (iii) by contrast, the three lines respond very differently to the footprints, grip strength, splay test and rotarod test. Even in lines with a significantly limited copy number of the transgene, we observed and quantified impairments. In conclusion, mutants of CMT1A seem to be a very pertinent model of this human pathology and will certainly be useful for therapeutic procedures and for theoretical studies on this disease.

The first postnatal week is a critical period for the development of posture in the rat. The use of ankle extensor muscles in postural reactions increases during this period. Changes in excitability of motoneurons are probably an important factor underlying this maturation. The aim of this study was to identify whether variations in the maturation exist between motor pools innervating antagonistic muscles. Intracellular recordings in the in vitro brain stem-spinal cord preparation of neonatal rats (from postnatal day 0-5) were used to examine the developmental changes in excitability of motoneurons innervating the ankle flexors (F-MNs) and the antigravity ankle extensors (E-MNs). No significant difference in resting potential, action potential threshold, input resistance or rheobase was observed at birth. The age-related increase in rheobase was more pronounced for F-MNs than for E-MNs. The development of discharge properties of E-MNs lagged behind that of F-MNs. More F-MNs than E-MNs were able to fire repetitively in response to current injection at birth. F-MNs discharged at a higher frequency than E-MNs at all ages. Differences in the duration of action potential afterhyperpolarization accounted, at least partly, for the differences in discharge frequency between E-MNs and F-MNs at birth, and for the age-related increase in firing rate. These results suggest that E-MNs are more immature at birth than F-MNs and that there is a differential development of motoneurons innervating antagonistic muscles. This may be a critical factor in the development of posture and locomotion.

The in vitro brain stem-spinal cord preparation of neonatal rats (0-5 days old) was used to examine the contribution of GABAA (gamma-aminobutyric acid) receptors to the spontaneous and locomotor-related antidromic firing in the dorsal roots of neonatal rats. Spontaneous bursts of antidromic discharges were generated by the underlying afferent terminal depolarizations reaching spiking threshold. The number of antidromic action potentials increased significantly in saline solution with Cl- concentration reduced to 50% of control. Bath application of the GABAA receptor antagonist bicuculline, at low concentrations (1-2 microM), or picrotoxin blocked the antidromic discharges in the dorsal roots almost completely. The increase in Cl- conductance was therefore mediated by an activation of GABAA receptors. Increasing the concentration of bicuculline to 10-20 microM never blocked these discharges further. On the contrary, in half of the preparations, the number of antidromic action potentials was higher in the presence of high concentrations of bicuculline (10-20 microM) than in the presence of picrotoxin or low concentrations of bicuculline. This suggests that bicuculline, at high concentrations, may have other effects, in addition to blocking GABAA receptors. Dorsal root firing was observed during fictive locomotion induced by bath application of excitatory amino acids and serotonin. A rhythmical pattern was often demonstrated. Bicuculline at low concentrations caused a decrease of the antidromic discharge whereas, at high concentrations, bursts of discharges appeared. A double-bath with a barrier built at the L3 level was then used to separate the mechanisms which generate locomotion from those mediating primary afferent depolarizations. Excitatory amino acids and serotonin were perfused in the rostral pool only. Decreasing the concentration of chloride in the caudal bath caused a sharp increase in the number of antidromic action potentials recorded from the L5 dorsal root. These discharges, which were modulated in phase with the locomotor rhythm, were blocked by bicuculline. These data demonstrate the existence of a locomotor-related GABAergic input onto primary afferent terminals in the neonatal rat.

The curve walking of freely moving crayfish trained to walk along a curved path during homing behaviour was investigated using a video-analysis system. The leg kinematics and leg phase relationships, as well as the relationship between stepping patterns and body axis rotation measured relative to external references, were studied. The anterior and posterior extreme positions of the power stroke (AEP and PEP, respectively) and step amplitudes were analysed. As in a previous study on crayfish curve walking on a treadmill, PEPs were more posterior in outer legs (the legs on the outside of the turn) than in the inner legs. As a result, outer legs showed larger step amplitudes than inner legs. Leg kinematics varied within each walking sequence. AEP leg angles (the angles between the body and leg axes at the AEP) tended to decrease over time for inner legs and increase for outer legs. This leg angle drift was present mainly in the anterior legs and it suggests that these legs did not completely compensate for the body rotation after each step. In addition, leg angle asymmetries in a direction opposite to that of leg angle drift were observed at the start of each curve-walking sequence, suggesting that the extensive training (3 weeks) may have allowed crayfish to anticipate the leg angle drift. The rotational component of curve walking showed a discontinuous pattern, with the animal’s body axis turning towards the inside of the curve only periodically. Analysis of cross-correlation functions showed that the angular acceleration of the body axis in the direction of the turn occurred during the power strokes of inner legs 2 and 5 and outer leg 4. While the tripod formed by these three legs showed in-phase relationships, the legs of the corresponding contralateral tripod (outer legs 2 and 5 and inner leg 4) were not in phase. We hypothesize that inner legs 2 and 5 and outer leg 4 act synergically causing the inward body rotation observed in curve-walking crayfish and that some of the asymmetries found in step geometry may be a passive phenomenon due to the body rotation.

Freely walking crayfish, Procambarus clarkii, were studied using a video analysis procedure adapted especially for use with crayfish. The animals were placed in a tank and their homing behaviour was filmed as they returned in a straight line to their shelter. Various sequences were studied at the two following levels. First, the trajectory of each pair of legs (from leg 2 to leg 5) during the step cycle (power stroke and return stroke) was studied to measure stride length and to analyse in detail changes in acceleration. Each leg was found to contribute in a specific manner to locomotion. Second, ipsi-and contralateral leg coordination was investigated. Ipsilateral coordination was found to involve a metachronal organization from front to back in all the walking sequences recorded, whereas contralateral coordination involved, in addition to the weak alternate coupling commonly observed in treadmill walking, another coordination pattern where the legs on each side (legs 3 and 4) are in phase. The results obtained in these free-walking sequences are discussed and compared with those obtained previously, in particular in treadmill situations.

Bath application of muscarinic agonists induced rhythmic motor activity in an in vitro preparation of the thoracic nervous system of the crayfish, Procambarus clarkii. In 70% of the cases, the rhythm was organized into 1 of the 2 normal patterns: “backward” walking or “forward” walking. In the rest (30%), the ganglion produced either a series of bursts of impulses or no rhythm at all, just an increase in the tonic activity. When it was isolated from all ascending and descending afferents, the fourth thoracic ganglion was still able to generate rhythmic motor output during bath application of muscarinic agonists. In certain motor neurons, muscarinic agonists induced plateau potentials. Under these conditions, some of these motor neurons were able to change the period of the motor pattern, which might suggest that these motor neurons were part of the central pattern generator (CPG) for locomotion. In the presence of 5 x 10(-6)M TTX, the membrane potential of these motor neurons continued to oscillate with organized rhythmic membrane potential oscillations into 1 of the 2 patterns. Under these conditions, current injection into certain motor neurons demonstrated that they continued to affect the CPG. Two classes of walking leg interneurons have been found. First, there are those with a sustained membrane potential: injection of a steady depolarizing current into some of these interneurons induced rhythmic activity in all thoracic motor nerves, even in the absence of any pharmacological activation. Second, there are those with an oscillating membrane potential: these seemed to enable silent motor neurons to be involved in an ongoing rhythm.

Decapod Crustacea display a slow metachronal rhythm of the third maxillipeds and pereiopod pairs one to four when undisturbed in the natural habitat. The dactyl tips are lifted off the substrate, and the unweighted limbs promote and remote at a slow frequency (range for all species 9–30min− 1). Movement is limited to the T-C joint. This behaviour, called waving, has been observed in many macrurans and an analogous activity, limited to the third maxillipeds, has been seen in several brachyurans. Analysis of EMGs shows: (a) the promotor activity increases in strength during a burst due to facilitation and motoneurone recruitment; (b) the rhythm period is stable throughout long waving sessions; (c) the promotor and remotor strokes are of equal duration and co-vary with period. Ipsilateral coupling is strong, with equal phases between adjacent limbs of 0· 05. The metachronal wave can pass anteriorly or posteriorly along an ipsilateral row. Bilateral coupling is weak. The two sides maintain equal frequency, and antiphasic coordination between the two ipsilateral sets of limbs is favoured. Possible functions for waving include gill grooming and supplementary gill ventilation. Comparisons between waving and other rhythmical motor programmes are discussed. Waving is an alternative programme for the walking legs, and is expressed when proprioceptive feedback is reduced.

Neuromuscular activity underlying lateral walking was studied in the shore crab Carcinus maenas. Electromyograms (EMGs) were recorded from legs on both the trailing and leading sides during free walking on land and under water in a pool (Figs 1, 2, 6, 7). In a trailing leg, the levator, flexor and closer muscles were active during the return stroke (RS) in alternation with the depressor, extensor and opener muscles which were responsible for the power stroke (PS). In a leading leg a different pattern of activity was observed. The flexor and closer muscles were active during the PS, and the extensor and opener muscles during the RS. Trailing steps were shorter and less variable in duration than leading steps (Figs 2, 3 for walking under water, Fig. 6 for walking on land, see also Fig. 7). A comparison of the activity patterns of the single common motor neurone innervating the opener and the stretcher muscle during trailing and leading showed a difference in burst length and instantaneous frequency (Fig. 2C,D). The discharge of this motor neurone usually lasted longer in leading steps. The discharge frequency started at a high level and then decreased during a trailing step, whereas in a leading step it was irregular (Fig. 8). In all walking situations the stretcher and opener muscles, which share a common excitatory motor neurone, received identical excitatory input (Fig. 4). The discharge frequencies of motor neurones innervating the extensor, the stretcher/opener and the closer muscles were investigated (Fig. 5). For motor neurones active during the PS, the frequency was high at the onset of the burst and then declined gradually. With the exception of the closer muscle, the discharge of motor neurones during the RS was more or less constant during the burst. A comparison between walking under water and on land showed that the overall EMG patterns were essentially similar (Fig. 7). However, on land the PS lasted longer and involved the activation of additional motor neurones in muscles which are innervated by several motor neurones, e.g. the extensor (Fig. 6). During walking on land maximal discharge frequencies up to 350 Hz were recorded. Homologous muscles in the three different walking legs operated similarly during trailing or leading movements without major differences in their EMG patterns. This indicates a similar load distribution on the different legs (Fig. 9).

In rock lobsters,Panilurus vulgaris, Jasus lalandii, the coxo-basipodite (C-B) and the mero-carpopodite (M-C) joints are mainly involved in body posture and in locomotion. In order to determine the functional relationships between these two joints the reflex effects induced by the C-B and M-C proprioceptors onto the muscles of their own joint (intrasegmental reflexes) or of the other joint (intersegmental reflexes) have been studied.

1. Ipsilateral interlimb coordination is studied in the rear legs of the rock lobster during driven backward walking. It shows examples of both relative and absolute coordination (Fig. 1). 2. The absolute coordination is defined by a stable step period which decreases or increases in relation to the belt speed. The value of phase ratio is stable. This value is depending upon the walking speed. In the 2 phases of the step, the return stroke duration is almost constant while the power stroke changes with speed (Figs. 2, 4, 6). 3. In relative coordination these parameters alter: the frequency of stepping is only loosely correlated with the belt speed. The phase relationship varies continuously, nevertheless the mean value is around 0.5 whatever the belt speed. The return stroke duration is as variable as the step duration (Figs. 2, 4, 6). 4. Relative coordination occurs when two legs are walking at different step frequencies but disappears as soon as the step period of the legs becomes identical (Figs. 2, 3). Two strategies are used by the animal to improve the coordination: it can make a double step or can increase the duration of the return stroke when the phase ratio is below 0.3 (Figs. 5, 6). The ‘magnet effect’ defined by von Holst as the mechanism underlying relative coordination is discussed as a mutual influence between the oscillators (Figs. 3, 5). 5. These data are discussed in relation to the previous results in order to: i) show the interest and limitations of a driven walking study; ii) explain the role of the return stroke in regulating each step duration; iii) point out the importance of metachronal factors as described by the model of Wilson (1966) and of connectivity pathways mainly controlled by peripheral receptors.

1. In intactHomarus gammarus, the swimmeret motor patterns present during the startle response and in gravid females, are very different. Kinetics and electromyograms (EMGs) reveal that the major difference is that the curler muscles of the rami (endopodite and exopodite) are active in the first response and silent in the second (Figs. 2, 3, 4). 2. An in vitro preparation has been used (Fig. 1) to analyze the activity of the curler motor neurons (MNs). In this preparation, all peripheral structures have been kept intact. This allowed us to show that the curler MNs axons run through root Ia (Fig. 5). 3. The in vitro preparation is sometimes spontaneously rhythmic. An individual curler MN is active either during the powerstroke (PS) or the returnstroke (RS) of the swimmeret rhythm (Fig. 6). There are more ‘PS’ curler MNs than ‘RS’ curler MNs. 4. Curler MNs active in the same stroke are often electrically coupled regardless of the ramus that they innervate (Fig. 8). 5. Sensory activity from a swimmeret ramus strongly modifies the activities of the curler MNs of the two rami as well as those of other swimmeret MNs (Fig. 9). In rhythmic preparations, periodic electrical stimulation can entrain the MN rhythm within a certain range of stimulus frequencies (Figs. 10, 11). 5. Thus, the curler MNs from both rami are linked centrally (electrical coupling) and peripherally (sensory afferents activated by movement). These two mechanisms synchronize the activities of the two rami.

International audience; Influence of walking on swimmeret beating in intact lobsters, Homarus gammarus, has been analyzed using a treadmill experimental device. Belt movement activates both leg stepping and swimmeret beating. The simultaneity of the onset of the two motor systems in this situation is demonstrated to be the result of a startle response initiated when the belt begins to move. This reaction consists of a non-specific motor activity involving several antagonist postural and dynamic muscles. Abdominal extension and vigorous swimmeret beating are the main features of this reaction. The main characteristics of the swimmeret beating as defined by Davis (1969) has been observed here in sequences without walking. However during long walking sequences a very different swimmeret beating pattern occurs. It is suggested that this slow swimmeret beating is completely subordinate to the walking rhythm during sequences of absolute coordination. In more rapid swimmeret beating a relative coordination with leg stepping is very common. The functional meaning of this linkage between legs and swimmerets is discussed.

The study compares the relative validity of the data obtained from two experimental situations, i.e. free walking and driven walking, in relation to leg coordination in Jasus lalandii (Milne-Edwards). The relationship between ipsilateral and contralateral legs during the forward as well as the backward walking sequences has been analysed in the two situations. They operate roughly in opposition. Although little dif ference in the mean phase values has been observed in the two experimental situations, the strength of coupling is greater in the driven walking animals. The power stroke (PS) duration correlates well with the period, but the return stroke (RS) is more variable and varies according to the leg considered. The phase does not appear to be correlated with the step period during free walking, but is correlated in the treadmill situation. Initially, several of the properties of the single motor unit discharges correlated with movement have identical mean values in both free and driven walking. However, several significant differences have been observed in the intra-burst organization. These differences indicate that the constraint of the treadmill decreases the variability of all parameters and produces a stable and more stereotyped walking pattern.

One of the most common reflexes observed in invertebrates is the resistance reflex, in which a proprioceptor at a given joint excites the motor neurones innervating the muscles controlling the joint so as to resist imposed movement (Bush, 1962, 1963, 1965; Barnes, Spirito & Evoy, 1972). As well as these intrasegmental reflexes, proprioceptive reflexes in which sensory information is used to control muscles at joints other than the one spanned by a given proprioceptor have been reported (Ayers & Davis, 1977; Clarac, Vedel & Bush, 1978). These intersegmental reflexes may also control the state of excitation of other receptors (Moody, 1970; Clarac et al. 1978). Resistance reflexes and intersegmental reflexes are presumed to have a role in postural maintenance and load compensation (op. cit.; for review see Mill, 1976). However, resistance reflexes can be suppressed during locomotion (Barnes et al. 1972) and intersegmental reflexes may be modified during walking (Ayers & Davis, 1977). In addition, we have recently shown that a resistance reflex elicited by the thoracic-coxal muscle receptor organ (TCMRO) in the crab can be reversed to become a positive feedback assistance reflex (DiCaprio & Clarac, 1981). In this report we demonstrate that an intersegmental reflex activation of the basipodite levator and depressor motor neurones mediated by the TCMRO can also be reversed with respect to movement of the thoracic-coxal (TC) joint.

In the decapod Crustacea, Palinurus vulgaris and Fasus lalandii, the reflex influences of one particular proprioceptor organ, the coxo-basal chordotonal organ (CB), on all the muscles operating the proximal and distal joints of the same leg, have been analysed. The distal end of CB was clamped in fine forceps mounted on a servo-controlled stretcher, and CB length changes of 2 mm were applied. Motor unit activity of the different muscles was recorded as electromyograms (EMGs). 1. Two types of proprioceptive reflex evoked by CB length changes have been investigated: (a) resistance reflexes of the two levator and two depressor muscles of the same leg segment, the coxopodite, i.e. ‘intrasegmental reflexes’, (b) ‘intersegmental reflexes’ induced in the muscles operating the proximal (T-C) joint of the same leg, and in all eight muscles of the limb segments distat to CB. 2. Both levator muscles respond reflexly to imposed CB stretch (which normally occurs with limb ‘depression’), while both depressors respond during CB shortening (or passive “elevation” of the leg). 3. Intersegmentally CB stretch reflexly activates the M-C extensor muscle, and sometimes facilitates the T-C remotor and C-P bender muscles. Shortening of the single CB organ of a leg excites one or two tonic motor units of the T-C promotor and M-C flexor muscles, and also facilitates the remotor, I-M reductor, and the single stretcher-opener excitatory motoneurone. 4. Some of the muscles, particularly the M-C flexor and extensor muscles, are also influenced intersegmentally by the resting length of CB, usually but not invariably in the same direction as for the corresponding dynamic reflexes. The role of the CB chordotonal organ is discussed, with particular consideration of its intersegmental reflex influence on the posture of the entire leg, and on the more complex motor behaviour of locomotion, where it may be specially significant in coordination of the limb in lateral walking. A complex picture of both tonic and dynamic, inra- and intersegmental reflex regulation of the positions and movements of the limb segments, thus emerges.

The present work concerns previously undescribed external sense organs observed on the rock lobster Palinurus vulgaris L. Each sensilla is composed of a feather‐like extension inserted in a cuticular depression in the rim of which there is a knob, the significance of which is discussed. Two or three bipolar cells innervate each organ. These organs are present in great numbers broadly distributed on the dorsal and lateral parts of the exoskeleton and have been named, considering their physiological properties, “hydrodynamic receptors”; (HR). Various stimulations (micromanipulation, water current and vibration) have been applied to determine the different responses. Electrophysiological findings demonstrate their bidirectional sensitivity. The role of the different HR in behavioural activities of rock lobster is discussed. It is suggested that during escape they can contribute information to the animal of its o4wn displacement.

Spatial and temporal stepping parameters have been studied in a rock-lobster walking on a treadmill moving at a wide range of speeds. The stride and the return stroke (RS) duration remain more or less stable and independent of the belt speed. Nevertheless, these ‘invariant’ parameters can act as spatial and temporal buffers resulting in a very precise adjustment of individual steps. A careful study of the power stroke (PS) duration demonstrates that the rock-lobster, although constrained to walk at an imposed belt speed, continues to correct its leg speed over a narrow range when the speed is considerably different from its natural one. Ipsilateral phases are always speed dependent, with an interleg ascending delay that is almost constant. The contralateral phase between legs of the same pair is approximately constant. Some of the parameters described are greatly influenced by gradual or abrupt variations in the belt speed. For a given speed, there is no absolute significance in the step period and ipsilateral phase. At very slow speeds, the interleg relations are significantly changed and have been studied separately. The metachrony observed at other speeds is discussed in relation to data from other arthropods.

In the walking legs of decapod crustaceans, intersegmental reflex actions originate from various joint proprioceptors. The activity of the ‘accessory flexor’ (AF) muscle, which with the myochordotonal organ (MCO) constitutes a muscle proprioceptor for the mero-carpopodite (M-C) joint, is modulated by the sensory discharge of a joint receptor (CB chordotonal organ) for the more proximal, coxo-basal (C-B) joint. Selective mechanical stimulation of the CB organ also reflexly modifies the motor activities of the main M-C flexor and extensor muscles (recorded as EMGs). 1. Dynamic CB stretch (as would occur during a dorso-ventral C-B movement - i.e. ‘depression’ of the limb) stimulates motor discharge to the M-C extensor muscle, while dynamic release of CB (as during a ventrodorsal C-B movement - or leg ‘elevation’) excites the accessory flexor as well as the main flexor muscle. 2. Successive M-C muscle responses to repetitive sinusoidal changes of CB length differ quantitatively according to the direction (stretch or release) of the first CB movement, in some cases increasing but more commonly ‘adapting’ with repetition. 3. Reflex discharge frequencies of the extensor, flexor and accessory flexor motoneurones increase with velocity of CB movement. 4. Eye illumination, and spontaneous or other sources of increased central excitability, generally increase the CB reflex drive to the flexor and accessory flexor muscles and, in parallel, decrease the reflex action on the extensor muscle. The results are discussed in terms of the role of proprioceptive reflexes in intersegmental co-ordination of the leg joints. In particular the significance of the reflex regulation of the myochordotonal receptors, and thereby the gain of the M-C resistance reflexes, is considered in the light of the observed ‘co-activation’ of main flexor and receptor muscle motoneurones.

In the rock lobster Palinurus vulgaris the activity of two mechanoreceptors is compared; one is a chordotonal structure, MC1, the other is myochordotonal, MCO1; they are functionally associated with the same joint (M‐C: merus‐carpopodite) of walking legs. We have compared the afferent activity of MC1 and MCO1 during joint movements and during isometric contractions of the flexor muscles induced by the stimulation of their motor nerve in order to determine their respective sensitivities to different kinds of mechanical stimuli. MC1 records both movement and position of the M‐C joint; the possibility that it records muscular tension is discussed but this appears very restricted. In contrast MCO1 activity is increased by movement of the joint and by the contraction of the proximal part of the AF muscle. The findings confirm that the term mychordotonal is appropriate and is conferred by its very original properties.

1. The flagellum ofPalinurus vulgaris is moved by three joints. The neuro-muscular organization of the two distal joints is presented (Figs. 1–3); the main study concerns only the last distal joint, J3, which is moved by a flexor FF and by an extensor muscle FB. 2. Passive sinusoidal movement of the flagellum induces a response of the different motoneurones. Nevertheless they are not stimulated identically. The tonic motoneurones are primarily concerned whereas the phasic and the inhibitory seem secondarily affected (Figs. 4, 5 and 7). 3. There is a significant response of the tonic motoneurones during the first passive movement of the flagellum whatever its direction (Fig. 6). Thus, the FF tonic motoneurone responds to the first flexion and the FE tonic one to the first extension. This is a positive feedback that is defined as a “synergistic reflex”. Its main characteristics are discussed. 4. The prolongation of the imposed sinusoidal movement reveal clearly some characteristics of the resistance reflex response of the two tonic FE and FF motoneurones. FE tonic excitability decreases very rapidly in all cases meanwhile FF tonic one increases during the first 5–10 cycles (Fig. 8). Quantitative but not qualitative modification occurs in FE or FF discharge when the speed of the movement, the temperature of the animal or the angular joint movement arc, are modified (Figs. 9–13).

The musculature and associated skeleton, peripheral nervous system, and central projections of motor and sensory neurones of the two basal (thoracic and coxal) segments of the shore crab leg (fifth pereiopod, P5) were examined in vivo and with methylene blue or cobalt staining. Each of the four main basal muscles, promotor/remotor, levator/depressor, controlling the thoracico-coxal (T-C) and coxo-basal (C-B) limb joints, respectively, comprises several more or less discrete fibre bundles (total 14), with little morphological segregation of different functional groups. The innervation to the basal leg region is carried in two nerve roots arising from the thoracic ganglion. The anterior Th-Cx root carries both sensory and motor axons, while the posterior Th-Cx root is purely motor. Three previously undescribed sensory branches (two "epidermal" nerves and an "accessory" branch), in addition to that innervating the coxobasal chordotonal receptor, have been found in the distal part of the anterior Th-Cx root. Two clusters of 10 to 15 multipolar somata (diam. 30-125 micron) are located proximally at the bifurcation of the accessory nerve and distally where the latter enters the basipodite. The cell bodies (diameter 20-80 micron) of basal leg motoneurones (total ca. 30) lie in the dorsal cortex of the ganglion, with somata of functionally related motoneurones tending to form discrete structural groups. The morphology of individual motoneurones conforms to the general arthropod pattern. All are confined to the ipsilateral hemiganglion and their main neuropilar processes run parallel and in close apposition to each other with overlapping dendritic structures. Sensory projections arising from the CB chordotonal organ also ramify in the region of the neuropile invaded by motoneurones. The possible physiological significance of such structural associations within the CNS is discussed, as are the functional implications of basal limb anatomy in general.

This paper gives a full account of the number and structure of the chordotonal organs present at all joints between the coxopodite and dactylopodite of the pereiopods and 3rd maxilliped of the macruran Homarus gammarus L. (H. vulgaris M. Ed.). Some comparative data is supplied for other macruran decapods. As the form of the receptors depends to some degree upon the structure of the joint we have included details of musculature, planes of movement and degrees of freedom at each of the joints. The third maxilliped has a smaller number of chordotonal organs than the pereiopod, in particular at the mero-carpopodite and carpopodite-propodite joints where only one organ is present. In some species the propodite-dactylopodite organ is absent from this limb. The electrical activity recordable from the receptors in the 3rd maxilliped shows considerable differences from the corresponding receptors in the pereiopod. The structure of the carpopodite-propodite joint of both limbs is discussed in detail as this joint differs greatly from that of the Brachyura. In the 3rd maxilliped and 2nd pereiopod three muscles are present. In the latter the joint is capable of rotation about the longitudinal axis but the third muscle does not appear to produce this rotation. A small number of units in the CP2 receptor respond to rotation. A receptor is described in the basipodite of the pereiopod and 3rd maxilliped situated just proximal to the plane through which the limb breaks at autotomy or autospasy. This receptor does not monitor joint movement and may detect cuticular strain, thus preventing accidental autotomy of limbs. A similar receptor has been observed in Carcinus. Cuticular receptor structures (CAP organs) are described as present at the M-C and C-P joints in both limbs, and at the I-M joint of the pereiopod.

1. L'activite comparee de l'organe myochordotonal MCO1 et du recepteur chordotonal MC1 de la langouste Palinurus vulgaris a ete etudiee au cours de stimulations diverses. 2. Des etirements bien definis, appliques directement aux muscles flechisseurs, ont permis de souligner la variete et la richesse de la decharge proprioceptive de MCO1 (fig. 4–6). 3. La contraction du muscle flechisseur principal et de l'extenseur mettent en jeu des cellules sensorielles differentes de MCO1 et MC1 (fig. 7). 4. La contraction du MFA peut provoquer l'apparition d'informations de nature opposee de MCO1 et MC1, cette particularite semble s'expliquer par l'orientation des forces exercees sur les propriocepteurs (fig. 9 et 10). a)La stimulation selective du faisceau musculaire distal du MFA provoque une legere flexion de l'articulation M-C; l'organe chordotonal MC1, associe a lui, est beaucoup plus sensible a ces mouvements articulaires qu'a des variations de tension musculaire (fig. 12). b)Le faisceau musculaire proximal du MFA module l'activite proprioceptive de MCO1 sans provoquer de mouvement de M-C. 5. Les differences fonctionnelles observees sur la langouste sont discutees en les comparant aux travaux des precedent auteurs. Une nouvelle denomination des deux parties du MFA est suggeree.

Situated in the basi-ischiopodite of the brachyuran Carcinus maenas are two receptors which resemble the chordotonal receptors of the limb articulations but are obviously not part of the series associated with the joints. The receptors have large numbers of bipolar neurons with their dendrites embedded in distinct connective tissue strands which insert onto discrete areas of thin or soft cuticle. The receptor strands do not span a limb joint nor do they attach to a muscle or its tendon. The receptors are referred to as cuticular stress detectors (CSD). CSD.1 lies proximal to the preformed breakage plane and the area of cuticle onto which the strand inserts, lies close to the attachment of the anterior levator muscle tendon (autotomiser muscle). CSD.2 which lies distal to the breakage plane is located in the ventral ischiopodite.

1. Suivant le sens du deplacement lateral, les appendices locomoteurs du crabe se trouvent situes du cote de la direction de la marche (membre epidromique ou ≪Leading Leg≫) ou de l'autre cote de cephalothorax (membre apodromique ou ≪trailing leg≫). Les angles des trois articulations qui assurent des mouvements dorsoventraux, C-B, M-C et P-D, ont ete mesures sur film a 50 images sec au cours de deplacements parfaitement lateraux. L'activite electromyographique du couple flechisseur-extenseur (meropodite) et de l'elevateur a ete enregistre. 2. La locomotion peut se resumer a une action simultanee de l'elevation basale, de la flexion et de la fermeture pour un appendice apodromique, de l'elevation, de l'extension et de la fermeture pour un membre epidromique; chacune de ces series de mouvement est separee par la contraction des muscles antagonistes. Les secteurs angulaires parcourus au niveau de chaque articulation semblent caracteristiques d'un cote a l'autre. 3. Par des blocages articulaires (C-B ou M-C) et des sections musculaires nous avons pu mettre en evidence des boucles proprioceptives intersegmentaires dues a la persistance de la perturbation. 4. L'elevation de chaque appendice semble resulter de l'action conjuguee d'un programme central et d'une information proprioceptive qui l'ajuste.

1. L'activite des principaux propriocepteurs de la region appendiculaire basi-ischio-meropodite de l'ecrevisse Astacus leptodactylus a ete etudie electrophysiologiquement. a) L'organe myochordotonal MCO possede, principalement, des fibres sensibles a l'extension du carpopodite (Fig. 1). Des rameaux separes de l'afference ont permis de distinguer differents types unitaires (Fig. 2). Le role des deux groupes musculaires du flechisseur accessoire et des cellules annexes est discute. b) La decharge des deux recepteurs de l'ischiopodite differe: IM1 se comporte comme uniquement sensible a la projection vers l'avant du meropodite, un retour en arriere le reduit au silence (Figs. 3 et 4); IM2 presente des resultats moins significatifs mais semble preferentiellement indiquer la ≪reduction≫ du meropodite (Fig. 5). c) BI, propriocepteur associe au muscle du basipodite, s'apparente fonctionellement a IM1 (Fig. 6). 2. L'enregistrement des nerfs moteurs du mero et de l'ischiopodite confirme le role de ces recepteurs en tant qu'initiateur de ≪reflexes de resistance≫ (Figs. 7–9). 3. A l'aide des travaux anterieurs, une tentative de classification des differents types de propriocepteurs appendiculaires, suivant les mouvements qui les mettent en jeu, est presentee. Le fonctionnement de l'armature sensorielle de l'articulation M-C de l'ecrevisse et du crabe est discutee.

By definition, locomotion is a succession of steps with alternating swing and stance phases. In Crustacea, the stance phase is a slow ramp propulsive movement for which sensory control is particularly important. Spatio-temporal as well as free components can define the stance phase as opposed to the swing phase. Contact and force mechanoreceptors situated at the tip of the legs in several Decapods seemed to provide important cues to stance phase parameters. Their selective stimulation elicits a reflex which seems to be able to reset the stepping cycle. This reflex was also studied in Crayfish isolated ganglion preparations, where its role is discussed.