Spinal Interneurons

The spinal cord is comprised of four types of neurons: motor neurons, pre-ganglionic neurons, ascending projection neurons, and spinal interneurons. Interneurons are neurons that process information within local circuits, and have an incredible ability for neuroplasticity, whether due to persistent activity, neural injury, or in response to disease. Although, by definition, their axons are restricted to the same structure as the soma (in this case the spinal cord), spinal interneurons are capable of sprouting and rewiring entire neural circuits, and contribute to some restoration of disrupted neural communication after injury to the spinal cord (i.e., “bypassing the lesion site). Spinal Interneurons provides a focused overview of how scientists classify interneurons in general, the techniques used to identify subsets of interneurons, their roles in specific neural circuits, and the scientific evidence for their neuroplasticity. Understanding the capacity for neuroplasticity and identity of specific spinal interneurons that are optimal for recovery, may help determine cellular candidates for developing therapies. Spinal Interneurons provides neuroscientists, clinicians, and trainees a reference book exclusively concentrating on spinal interneurons, the techniques and experiments employed to identify and study these cells as part of normal and compromised neural circuits, and highlights the therapeutic potential of these cells by presenting the relevant pre-clinical and clinical work to date. People in industry will also benefit from this book, which compiles the latest in therapeutic strategies for targeting spinal interneurons, what considerations there are for the development and use of treatments, and how such treatments can not only be translated to the clinic, but how existing treatments should be appropriately reverse-translated to the bench. Comprehensive overview of techniques used to identify, characterize, and classify spinal interneurons and their role in neural circuits Description of the role that spinal interneurons play in mediating plasticity after compromise to spinal neural networks In-depth discussion of therapeutic potential of spinal interneurons for spinal cord injury and/or disease

Even though spinal cord research has expanded enormously during the past decades, we still lack a precise understanding of how spinal interneuron networks perfectly integrate sensory feedback with motor control, and how these neuron circuits give rise to specific functions. The present study thus has three basic aims: (1) to investigate propriospinal interneurons connecting rostral and caudal lumbar spinal cord in the rat; (2) to investigate input properties of identified spinal interneurons interposed in different pathways; (3) to investigate cholinergic terminals in the ventral horn of adult rat and cat. There was no evidence to support the presence of vesicular glutamate transporters in motoneuron axon terminals of either species. In addition, there was no obvious relationship between motoneuron terminals and R2 subunit of the AMPA receptor (GluR2). However, a population of cholinergic terminals in lamina VII, which did not originate from motoneurons, was found to be immunoreactive for VGLUT2 and formed appositions with GluR2 subunits. These terminals were smaller than motoneuron terminals and, unlike them, formed no relationship with Renshaw cells. The evidence suggests that glutamate does not act as a cotransmitter with acetylcholine at central synapses of motoneurons in the adult cat and rat. However, glutamate is present in a population of cholinergic terminals which probably originate from interneurons where its action is via an AMPA receptor. In conclusion, the present studies add to the understanding of the organization of neuronal networks involved in sensorimotor integration. Propriospinal interneurons located within the lumbar segments have extensive intra-segmental projections to motor nuclei. First order interneurons interposed in reflex pathways and descending pathways receive a significantly different pattern of inputs. A similar proportion of monosynaptic excitatory input from primary afferents has been found in both excitatory and inhibitory interneurons and these two types of cells are subject to presynaptic inhibitory control of this input.

In the last decade, we have witnessed a striking maturation of our understanding of how neurons in the spinal cord control muscular activity and movement. Paradoxically, a host of new findings have revealed an unexpected versatility in the behavior of these well-studied neural elements and circuits. In this volume, the world's leading experts review the current state of our knowledge of motor control, outline their latest results and developments, and delineate the seminal unresolved questions in this vibrant field of research. The volume begins with a commentary and overview of our current understanding of the peripheral and spinal basis of motor control. The remainder of the volume is divided into seven sections, each focused on a different problem. The first chapter in each section provides some historical review and presages the experimental findings and hypotheses that are discussed in subsequent chapters.Topics include the biomechanics of neuromuscular systems, the properties of motoneurons and the muscle units they control, spinal interneurons, pattern generating circuits, locomotion, descending control of spinal circuits, comparative physiology of motor systems, and motor systems neurophysiology studied in man. The book serves as a unique reference volume and should be essential reading for anyone interested in motor systems. Moreover, the volume's comprehensive coverage of a wide range of topics make it an effective textbook for graduate level courses in motor control neurobiology, kinesiology, physical therapy, and rehabilitation medicine.

Motor Neurobiology of the Spinal Cord provides a comprehensive description of the experimental tools available for investigating the neuronal properties that allow populations of spinal cord neurons to control muscles responsible for limb movements and posture control. By integrating data from many new approaches, this text demonstrates how spinal cord circuits operate under a variety conditions and explores the new and exciting developments that are being made in motor neurobiology of the spinal cord. It also elucidates concepts and principles relevant to function and structure throughout the nervous system and presents information about changes induced by injury and disease.

Movement is a fundamental behavior that is generated and patterned by premotor neural networks that reside in the ventral spinal cord of vertebrates. Despite ongoing investigations in multiple animal models, including humans, non-human primates, cats and rodents, identifying the functional neuron cell types that shape various motor tasks has proved difficult. One of the key issues in the field is the criteria by which neuronal cell types are characterized and defined. This dissertation describes my work tackling this problem using a comprehensive anatomical approach aimed at identifying neuronal subsets within major classes of ipsilateral premotor spinal interneurons. The first chapter provides a historical background of spinal motor system research developed from the beginning of the 20th century that summarizes our current knowledge of motor circuits in the spinal cord and the contribution that this dissertation makes to bridging the gaps that exist in our understanding of premotor interneuron cell types. The second chapter describes the anatomical approach I pursued, which is based on spatial distribution, connectivity and morphology to identify potential groups of functional premotor interneuron cell types. In the third chapter I discuss the relevance of these findings, by highlighting how the strategy used in this work can be applied to other spinal cord populations and used to lay the groundwork to build an anatomical reference for motor functional studies, including electrophysiology and behavioral assays. This work provides an important and necessary framework to understand the complicated logic governing the organization of motor networks in the vertebrate spinal cord.

Movement is arguably the most fundamental and important function of the nervous system. Purposive movement requires the coordination of actions within many areas of the cerebral cortex, cerebellum, basal ganglia, spinal cord, and peripheral nerves and sensory receptors, which together must control a highly complex biomechanical apparatus made up of the skeleton and muscles. Beginning at the level of biomechanics and spinal reflexes and proceeding upward to brain structures in the cerebellum, brainstem and cerebral cortex, the chapters in this book highlight the important issues in movement control. Commentaries provide a balanced treatment of the articles that have been written by experts in a variety of areas concerned with movement, including behaviour, physiology, robotics, and mathematics.

Providing clear, well-illustrated descriptions of brain structures in light of their functions, this cohesive and well-established textbook fosters understanding of the intimate relationship between the structure and function of the nervous system. Its focus on the integration of basic sciences with their clinical applications makes the book particularly well-suited for medical students needing knowledge of neuroscience as a basis for clinical thinking. For the third edition, two new chapters have been added on the vestibular system and control of eye movements, and all other chapters have been thoroughly revised.