Pioneers in CNS inhibition: 2. Charles Sherrington and John Eccles on inhibition in spinal and supraspinal structures.

This article reviews the contributions of the English neurophysiologist, Charles Scott Sherrington [1857-1952], and his Australian PhD trainee and collaborator, John Carew Eccles [1903-1997], to the concept of central inhibition in the spinal cord and brain. Both were awarded Nobel Prizes; Sherrington in 1932 for "discoveries regarding the function of neurons," and Eccles in 1963 for "discoveries concerning the ionic mechanisms involved in excitation and inhibition in central portions of the nerve cell membrane." Both spoke about central inhibition at their Nobel Prize Award Ceremonies.

Discharge characteristics of motor units during long-duration contractions.

The purpose of the study was to determine how long humans could sustain the discharge of single motor units during a voluntary contraction. The discharge of motor units in first dorsal interosseus of subjects (27.8 ± 8.

Pioneers in CNS inhibition: 1. Ivan M. Sechenov, the first to clearly demonstrate inhibition arising in the brain.

This article reviews the contributions of Ivan Michailovich Sechenov [1829-1905] to the neurophysiological concept of central inhibition. He first studied this concept in the frog and on himself. Later his trainees extended the study of central inhibition to other mammalian species.

The beginning of intracellular recording in spinal neurons: facts, reflections, and speculations.

Intracellular (IC) recording of action potentials in neurons of the vertebrate central nervous system (CNS) was first reported by John Eccles and two colleagues, Walter Brock and John Coombs, in Dunedin, NZL in 1951/1952 and by Walter Woodbury and Harry Patton in Seattle, WA, USA in 1952. Both groups studied spinal cord neurons of the adult cat. In this review, we discuss the precedents to their notable achievement and reflect and speculate on some of the scientific and personal nuances of their work and its immediate and later impact.

Whither motoneurons?

In the preceding series of articles, the history of vertebrate motoneuron and motor unit neurobiological studies has been discussed. In this article, we select a few examples of recent advances in neuroscience and discuss their application or potential application to the study of motoneurons and the control of movement. We conclude, like Sherrington, that in order to understand normal, traumatized, and diseased human behavior, it is critical to continue to study motoneuron biology using all available and emerging tools.

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.

Thomas Graham Brown (1882--1965), Anders Lundberg (1920-), and the neural control of stepping.

Thomas Graham Brown (1882--1965) undertook experiments on the neural control of stepping in the University of Liverpool laboratory of Charles Sherrington (1857--1952) in 1910--13 and his own laboratory in 1913--15 at the University of Manchester. His results revealed the intrinsic capability of the spinal cord in the guinea pig and cat to generate a stepping output pattern whose timing did not depend upon descending or sensory inputs. This idea was then revolutionary because the prevailing viewpoint was that the stepping rhythm was generated by spinal reflexes.

Reflections on integrative and comparative movement neuroscience.

Integrative movement neuroscience involves blending "inside-out" and "outside-in" approaches in the study of posture and movement. The former is characterized by determining the properties of single cells within the central nervous system (CNS) and then ascertaining how these properties influence the operation of CNS microcircuits, single reflexes, groups of reflexes, and generators of central pattern. This information is then used to theorize about CNS control of overt motor behavior.

Does motoneuron adaptation contribute to muscle fatigue?

To help reduce the gap between the cellular physiology of motoneurons (MNs) as studied "bottom-up" in animal preparations and the "top-down" study of the firing patterns of human motor units (MUs), this article addresses the question of whether motoneuron adaptation contributes to muscle fatigue. Findings are reviewed on the intracellularly recorded electrophysiology of spinal MNs as studied in vivo and in vitro using animal preparations, and the extracellularly recorded discharge of MUs as studied in conscious humans. The latter "top-down" approach, combined with kinetic measurements, has provided most of what is currently known about the neurobiology of muscle fatigue, including its task and context dependencies.

The academic lineage of Sir John Carew Eccles (1903-1997).

This report reviews the academic lineage of Sir John Eccles; who trained him, whom he then trained and with whom he collaborated, and the subsequent impact of his trainees and collaborators on neuroscience and other areas. In a post-training career at five institutions in four countries (Great Britain, Australia, New Zealand, back to Australia, USA) and during retirement in Switzerland, Eccles trained and collaborated with over 180 people (mostly neuroscientists) from 21 countries. Most of them have had stellar research and training records that span the cellular-behavioral-philosophical spectrum of neuroscience, with a focus from peripheral neuromuscular issues to the forebrain.

Integration of posture and movement: contributions of Sherrington, Hess, and Bernstein.

Neural mechanisms that integrate posture with movement are widespread throughout the central nervous system (CNS), and they are recruited in patterns that are both task- and context-dependent. Scientists from several countries who were born in the 19th century provided essential groundwork for these modern-day concepts. Here, the focus is on three of this group with each selected for a somewhat different reason.

Slow-tonic muscle fibers and their potential innervation in the turtle, Pseudemys (Trachemys) scripta elegans.

A description is provided of the ratio of slow-tonic vs. slow- and fast-twitch fibers for five muscles in the adult turtle, Pseudemys (Trachemys) scripta elegans. The cross-sectional area of each fiber type and an estimation of the relative (weighted) cross-sectional area occupied by the different fiber types are also provided.

Fatigue of rat hindlimb motor units: biochemical-physiological associations.

Associations between fatigability and biochemical properties within motor unit (MU) types were explored in two hindlimb muscles of the adult rat. Type FF MUs in extensor digitorum longus and type S units in soleus were subjected either to a moderate (type FF) or severe (type S) 6-min, fatigue-inducing stimulation protocol. For both MU types, the range of values for their fatigability was considerably greater than the ranges in the activity levels of three enzymes in the units' constituent muscle fibers (MFs).

Associations between the morphology and physiology of ventral-horn neurons in the adult turtle.

This study compared some morphologic and physiological properties of adult turtle spinal motoneurons (MNs) vs. interneurons (INs). Reconstructions were made of 20 biocytin-stained cells, which had been previously studied physiologically in 2-mm-thick slices of lumbosacral spinal cord.

Reflections on spinal reflexes.

Over the past four decades, the understanding of proprioceptive spinal reflexes has advanced far more rapidly than generally considered. This problem could be largely obviated in undergraduate and graduate training programs if the topic of reflexes was introduced subsequent to the concept and mechanisms of pattern generation within the central nervous system. The key advantage would then be that the neuroscience community as a whole would gain appreciation of the fact that proprioceptive reflexes are not hard-wired but rather are context- and phase-dependent, with the central nervous system selecting input-output pathways appropriate for the task at hand.

Effects of excitatory modulation on intrinsic properties of turtle motoneurons.

The purpose of this study was to quantify the effects of excitatory modulation on the intrinsic properties of motoneurons (MNs) in slices of spinal cord taken from the adult turtle. Responses were noted following application of an excitatory modulator: serotonin (5-HT), muscarine, trans-1-amino-1,3-cyclopentane dicarboxylic acid (tACPD), or all three combined. A sample of 44 MNs was divided into 2 groups, on the basis of whether MNs did (28/44) or did not (16/44) demonstrate a nifedipine-sensitive acceleration of discharge during a 2-s, intracellularly injected stimulus pulse.

Motoneurons: A preferred firing range across vertebrate species?

The term "preferred firing range" describes a pattern of human motor unit (MU) unitary discharge during a voluntary contraction in which the profile of the spike-frequency of the MU's compound action potential is dissociated from the profile of the presumed depolarizing pressure exerted on the unit's spinal motoneuron (MN). Such a dissociation has recently been attributed by inference to the presence of a plateau potential (PP) in the active MN. This inference is supported by the qualitative similarities between the firing pattern of human MUs during selected types of relatively brief muscle contraction and that of intracellularly stimulated, PP-generating cat MNs in a decerebrate preparation, and turtle MNs in an in vitro slice of spinal cord.