The evolution of dermal shield vascularization in Testudinata and Pseudosuchia: phylogenetic constraints versus ecophysiological adaptations.

Studies on living turtles have demonstrated that shells are involved in the resistance to hypoxia during apnea via bone acidosis buffering; a process which is complemented with cutaneous respiration, transpharyngeal and cloacal gas exchanges in the soft-shell turtles. Bone acidosis buffering during apnea has also been identified in crocodylian osteoderms, which are also known to employ heat transfer when basking. Although diverse, many of these functions rely on one common trait: the vascularization of the dermal shield.

Static osteogenesis does not precede dynamic osteogenesis in periosteal ossification of Pleurodeles (Caudata, Amphibia) and Pogona (Squamata, Lepidosauria).

Two successive mechanisms have been described in perichondral ossification: (1) in static osteogenesis, mesenchymal cells differentiate into stationary osteoblasts oriented randomly, which differentiate into osteocytes in the same site; (2) in dynamic osteogenesis, mesenchymal cells differentiate into osteoblasts that are all oriented in the same direction and move back as they secrete collagen fibers. This study is aimed at testing the hypothesis that the ontogenetic sequence static then dynamic osteogenesis observed in the chicken and in the rabbit is homologous and was acquired by the last common ancestor of amniotes or at a more inclusive node. For this we analyze the developmental patterns of Pleurodeles (Caudata, Amphibia) and those of the lizard Pogona (Squamata, Lepidosauria).

A quantitative assessment of bone area increase due to ornamentation in the Crocodylia.

Bone ornamentation, in the form of highly repetitive motives created by pits and ridges, is a frequent feature on vertebrate skull roofs and osteoderms. The functional significance of this character remains a matter of controversy and speculation. The many diverging hypotheses proposed to explain it all share a common logical prerequisite: bone ornamentation should increase significantly the surface area of the bones that bear it.

Historical concepts on the relations between nerves and muscles.

This review addresses the history since antiquity of studies on the anatomical and functional relations between nerves and muscles, and the progressive use of newer approaches to this topic. By the Hippocratic era (almost 2500 years ago) the digestive, circulatory and nervous systems were thought to participate in the production of animal spirits. This concept had strong support for nervous conduction, even after the dawn of electrophysiology in the late 18th C.

The emergence of the "motoneuron concept": from the early 19th C to the beginning of the 20th C.

This article addresses the emergence of the "motoneuron concept," i.e., the idea that this cell had properties of particular advantage for its control of muscle activation.

Neurology outside Paris following Charcot.

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).

Chapter 40: history of neurology in France.

The history of neurology in France is characterized by the very high degree of centralization in that country where "everything seems to happen in Paris," and yet the considerable degree of autonomous diversity in the evolution of some other medical schools such as Montpellier and Strasbourg. It could be argued that France saw the birth of clinical neurology as a separate discipline since Jean Martin Charcot at the Salpêtrière Hospital obtained a chair of diseases of the nervous system in 1892, a first in the history of the academic world. The chapter shows, however, that the work of Charcot was preceded by a long evolution in medical thinking, which culminated with the introduction of experimental medicine developed by Claude Bernard and François Magendie, and by the study of aphasia by Paul Broca and its localization of language in a specific area of the brain.

Duchenne, Charcot and Babinski, three neurologists of La Salpetrière Hospital, and their contribution to concepts of the central organization of motor synergy.

Many currently accepted notions of motor control originate from a few seminal concepts developed in the latter half of the 19th century (see Bennett and Hacker, 2002). The goal of this review is to retrace some current ideas about motor control back to the thought of three French neurologists of Hospital of the Salpetrière hospital in Paris during the latter half of the 19th century and early 20th century (Fig. 1): Guillaume Duchenne de Boulogne (1806-1875), Jean-Martin Charcot (1825-1893), and Joseph Babinski (1857-1932).

Reflections on Jacques Paillard (1920-2006)--a pioneer in the field of motor cognition.

This article reviews the scientific contributions of Jacques Paillard (1920-2006), who strengthened substantially the role of physiological psychology in the field of movement neuroscience. His research began in 1947 under the direction of the French neurophysiologist, Alfred Fessard (1900-1982), with whom he then collaborated for 9 years while an undergraduate and then graduate student and junior faculty member in psychology at the University of Paris (the Sorbonne). Paillard moved to the University of Marseille in 1957 as a Professor of Psychophysiology.

Some historical reflections on the neural control of locomotion.

Thought on the neural control of locomotion dates back to antiquity. In this article, however, the focus is more recent by starting with some major 17th century concepts, which were developed by René Descartes, a French philosopher; Thomas Willis, an English anatomist; and Giovanni Borelli, an Italian physiologist and physicist. Each relied on his personal expertise to theorize on the organization and control of movements.

Invertebrate preparations and their contribution to neurobiology in the second half of the 20th century.

This review summarized the contribution to neurobiology achieved through the use of invertebrate preparations in the second half of the 20th century. This fascinating period was preceded by pioneers who explored a wide variety of invertebrate phyla and developed various preparations appropriate for electrophysiological studies. Their work advanced general knowledge about neuronal properties (dendritic, somatic, and axonal excitability; pre- and postsynaptic mechanisms).

Perinatal development of the motor systems involved in postural control.

Motor behaviors of some species, such as the rat and the human baby, are quite immature at birth. Here we review recent data on some of the mechanisms underlying the postnatal maturation of posture in the rat, in particular the development of pathways descending from the brain stem and projecting onto the lumbar enlargement of the spinal cord. A short-lasting depletion in serotonin affects both posture and the excitability of motoneurons.

The maturation of locomotor networks.

In both vertebrates and invertebrates, the elaboration of locomotion, and its neural control by the central nervous system, are extremely flexible. This is due not only to the network properties of relevant sets of central neurons, but also to the active participation of mutually co-operative central and peripheral loops of neural projections and activity. In this chapter, we describe experiments in which the above concepts have been advanced by comparing locomotor properties in the adult vs.

Reversible disorganization of the locomotor pattern after neonatal spinal cord transection in the rat.

The central pattern generators (CPGs) for locomotion, located in the lumbar spinal cord, are functional at birth in the rat. Their maturation occurs during the last few days preceding birth, a period during which the first projections from the brainstem start to reach the lumbar enlargement of the spinal cord. The goal of the present study was to investigate the effect of suppressing inputs from supraspinal structures on the CPGs, shortly after their formation.

Development of posture and locomotion: an interplay of endogenously generated activities and neurotrophic actions by descending pathways.

The adult pattern of locomotion is observed at the end of the second postnatal week in the rat. The in vitro spinal cord isolated from immature rats has served as a valuable preparation to study the mechanisms underlying the development of locomotion. Although the rat is unable to walk at birth, because of an immature posture, its spinal cord networks can generate at least two kinds of motor patterns in vitro.

Postural modifications and neuronal excitability changes induced by a short-term serotonin depletion during neonatal development in the rat.

Serotonin (5-HT) plays an important role both in the development and in the recovery of locomotion after spinalization in vertebrates. We investigated the contribution of the serotonergic system to the maturation of the lumbar motoneurons and networks in the neonatal rat. A 5-HT synthesis inhibitor, p-chlorophenylalanine (PCPA), was administered daily from the first postnatal day (P0) onward.

Picrotoxin and bicuculline have different effects on lumbar spinal networks and motoneurons in the neonatal rat.

Bicuculline is the most commonly used GABA(A) receptor antagonist to investigate the contribution of these receptors in motor control. However, this compound has been shown recently to potentiate the burst firing of neurons in various brain regions by blocking a calcium-activated potassium current underlying the spike after-hyperpolarization (AHP). This effect may distort our understanding of the role of GABA(A) receptors at the network level.