New principles for the topographical organisation of sensory input to the spinal cord

New principles for the topographical organisation of sensory input to the spinal cord

Field: Sensory systems

Authors: Levinsson, Anders
Holmberg, H
Zhang, M
Broman, J
Schouenborg, J

Address of presenting
author: Sölvegatan 19
223 62 Lund

E-mail: Anders.Levinsson@mphy.lu.se

Phone: 046-2224651

Fax: 046-2224546

Text of abstract: The spinal cord contains a number of distinct motor systems, subserving for example withdrawal or locomotion, which performs finely tuned sensorimotor transformations. The projection of peripheral receptors onto the spinal cord interneurons constitutes the first step in such transformations. Despite extensive mapping studies on this projection, considerable uncertainties still remain, particularly concerning the degree of representational overlap and multimodal congruency. To clarify these issues, we have reexamined this projection using both anatomical and physiological techniques and related this input organization to that of the withdrawal reflex interneurons. Primary afferent terminations of thin and coarse skin afferents were characterized histochemically. The corresponding functional weights of these projections were studied by mapping tactile and nociceptive monosynaptic extracellular synaptic currents.

The results suggest that the body representation is best described as a 'mosaic', with a high degree of representational overlap. Furthermore, both anatomical and physiological data indicate that the termination of thin and coarse skin afferents in lamina II and laminae III-IV, respectively are spatially congruent in the horizontal plane. The weight distribution of the cutaneous input to the superficial laminae were similar to that of the input to putative reflex interneurons in the deep laminae indicating that the cutaneous convergence, is related to the interneuronal organization in the deep dorsal horn. The assembly of the dorsal horn topography may thus be largely dependent on the spatial relations to reflex interneurons or motorneurons. Furthermore, the previously shown postnatal tuning of the receptive fields of withdrawal reflex modules may, in part, reflect tuning of the first order synapses of the dorsal horn.

Keywords: tactile, nociceptive, primary-afferent, somatotopy, reflex

	New principles for the topographical organisation of sensory input to the spinal cord
Field:	Sensory systems
Authors:	Levinsson, Anders Holmberg, H Zhang, M Broman, J Schouenborg, J
Address of presenting author:	Sölvegatan 19 223 62 Lund
E-mail:	Anders.Levinsson@mphy.lu.se
Phone:	046-2224651
Fax:	046-2224546
Text of abstract:	The spinal cord contains a number of distinct motor systems, subserving for example withdrawal or locomotion, which performs finely tuned sensorimotor transformations. The projection of peripheral receptors onto the spinal cord interneurons constitutes the first step in such transformations. Despite extensive mapping studies on this projection, considerable uncertainties still remain, particularly concerning the degree of representational overlap and multimodal congruency. To clarify these issues, we have reexamined this projection using both anatomical and physiological techniques and related this input organization to that of the withdrawal reflex interneurons. Primary afferent terminations of thin and coarse skin afferents were characterized histochemically. The corresponding functional weights of these projections were studied by mapping tactile and nociceptive monosynaptic extracellular synaptic currents. The results suggest that the body representation is best described as a 'mosaic', with a high degree of representational overlap. Furthermore, both anatomical and physiological data indicate that the termination of thin and coarse skin afferents in lamina II and laminae III-IV, respectively are spatially congruent in the horizontal plane. The weight distribution of the cutaneous input to the superficial laminae were similar to that of the input to putative reflex interneurons in the deep laminae indicating that the cutaneous convergence, is related to the interneuronal organization in the deep dorsal horn. The assembly of the dorsal horn topography may thus be largely dependent on the spatial relations to reflex interneurons or motorneurons. Furthermore, the previously shown postnatal tuning of the receptive fields of withdrawal reflex modules may, in part, reflect tuning of the first order synapses of the dorsal horn.

Keywords:	tactile, nociceptive, primary-afferent, somatotopy, reflex

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Created 2000-03-31

Department of Physiological Sciences, Lund University

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