0006-Ch00.pdf

Introduction

The ﬁeld of spinal motor neurobiology has grown dramatically over the last decade.

One can argue that our understanding of spinal motoneurons and functionally related

interneurons at both the cellular and systems levels advanced during the past 10

years as much as at any time since neurobiologists, including Sir Charles Sher-

rington, David Lloyd, and John Eccles established the foundations of the ﬁeld. It

was a relatively simple task, therefore, to identify topics to ﬁll this book. By contrast,

it was not easy to restrict the number of topics and contributors. The chief guiding

principle used to select contributions to the book was one of providing a broad

description of recent conceptual and technical advances in the ﬁeld. This principle

is met by chapters which collectively cover topics ranging from genetics to kine-

matics, examining cells, tissues, or whole animals, in species ranging from ﬁsh to

humans that are normal, injured, or diseased, using techniques including immuno-

cytochemisty, optical imaging, and electrical and mechanical analyses. Despite the

breadth of coverage, our book is not comprehensive. Fortunately, the reader can

compensate for some of our omissions by looking at recent books, including, Neu-

ronal Mechanisms for Generating Locomotor Activity, O. Kiehn, R.M. Harris-War-

rick, L.M. Jordan, H. Hultborn, and N. Kudo, Eds., 1998, and Presynaptic Inhibition

and Neural Control, P. Rudomin, R. Romo, and L. Mendell, Eds., 1998.

The reader will ﬁnd that each chapter is a rich source of information relevant

to a variety of issues. Indeed, these features made it difﬁcult to sequence the chapters,

which might have been arranged in several ways other than the one chosen. The

versatility expressed by each chapter also deﬁes adequate description. Nonetheless,

the following few comments describing each chapter are offered to give the reader

a rough notion of content.

The book begins with a chapter from Joe Fetcho that focuses on the neural

circuits involved in swimming movements in ﬁsh. Discussion of the information

using conventional electrophysiological and anatomical techniques is followed by

introduction to new optical and genetic methods. The next group of three chapters

focuses attention on the integrative properties of motoneuron dendrites and/or the

synaptic inputs they receive. Speciﬁc details about the distribution and density of

various synapses, receptors, and ion channels are examined morphologically by

Robert Fyffe, pharmacologically by Shawn Hochman and co-authors, and electro-

physiogically by Bob Lee and C.J. Heckman. The two chapters that follow address

analyses of motoneuron ﬁring: Randy Powers and Kemal Türker describe advances

in measuring and interpreting synaptic effects on human motoneuron discharge,

while Tom Hamm and co-authors evaluate correlation in the frequency domain and

its value in discovering the organization of neural circuits involved in rhythmic motor

patterns in the cat spinal cord. Subsequently, Steve Perlmutter and Yifat Prut describe

their studies of spinal interneuron responses recorded in association with hand

movements made by awake, behaving monkeys. Two other chapters examine the

role of sensory feedback in modulating motor output: Andrew Sharp and Anne

Beckoff describe how speciﬁc sensory modalities contribute to the development of

motility in chick embryos, while Thomas Sinkjær and co-workers report on the

effects of proprioception on human gait. The book ends with four chapters examining

the responses of motoneurons and segmental motor circuits to injury and disease.

Marty Pinter and co-authors promote the notion that dysfunction at the neuromus-

cular junction results in muscular weakness far in advance of neural degeneration

in a mutant dog. In the next chapter, Ken Rose and co-authors present evidence that

cutting the axons of motoneurons supplying neck muscles in cats causes the moto-

neuron’s dendrites to acquire axon-like characteristics, thereby raising questions

about the molecular polarity of motoneurons and the pleural potentiality of their

neuritic projections. Tim Cope and co-authors explore the potential role of afferent

activity, neurotrophins, and glutamate receptors in enhancing central synaptic

strength following peripheral nerve injury. Finally, Richard Nichols and Tim Cope

present ﬁndings that challenge traditional notions about speciﬁc spinal reﬂexes that

are released by spinal cord injury.

I am sincerely grateful to all contributing authors for their efforts, responsive-

ness, and success in generating high quality chapters. Thanks also to Miguel

Nicolelis for his invitation to produce a book in this series, and to Barbara Norwitz,

Tiffany Lane, and Pat Roberson at CRC Press for their assistance. High praise

and gratitude go to Anne Shirley and her assistants, Katie Bannister and Amy

Gandhi, for their conscientious efforts in communicating with authors and orga-

nizing incoming materials.

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