Journal of Neurophysiology, Vol 74, Issue 6 2336-2348, Copyright © 1995 by APS

ARTICLES

Morphology of functional long-ranging primary afferent projections in the cat spinal cord

H. R. Koerber and K. Mirnics
Department of Neurobiology, University of Pittsburgh, School of Medicine, Pennsylvania 15261, USA.

1. A beta-cutaneous primary afferent fibers were impaled in the dorsal columns of alpha-chloralose-anesthetized cats. Penetrations were made with the use of electrodes filled with 2 or 5% N-(2-aminoethyl) biotinamide hydrochloride (Neurobiotin, NB) in 0.1 or 1 M KCl. After determining its adequate stimulus, each fiber was activated by current pulses (18 Hz) injected via the microelectrode. The resulting cord dorsum potential (CDP) was recorded at four locations. NB was then injected into the fiber with the use of positive current pulses (11-22 nA) and a 75% duty cycle. 2. After allowing 2-8 h for diffusion, animals were perfused with saline (37 degrees C) followed by 4% paraformaldehyde (4 degrees C). Frozen 50-microns sections were cut in either the transverse or sagittal plane, processed on slides with the use of standard avidin-biotin protocols, and visualized by the nickel-enhanced diaminobenzidine (DAB) reaction. 3. A total of 15 A beta-cutaneous afferents innervating both rapidly (RA) and slowly adapting (SA) receptors were adequately stained and their central projections recovered. For selected fibers the rostrocaudal and laminar bouton distributions were determined and compared with the distribution of monosynaptic CDP amplitudes recorded at the four surface locations. 4. The rostrocaudal extent of a single A beta-afferent fiber bouton distribution visualized with NB ranged from 8 to 17.5 mm (14.4 +/- 2.4 mm, mean +/- SD), or two to three times greater than that previously shown with the use of horseradish peroxidase (HRP). 5. The strong correlation between the rostrocaudal distribution of boutons and monosynaptic CDP amplitudes, and the improved agreement between modeled and observed CDP amplitudes over that seen previously with the use of HRP (mean percent error, HRP = 23 +/- 2.9%; NB = 9 +/- 2.3%), suggest that boutons along the entire length of the visualized distribution contribute to the recorded potentials. 6. Taken together, these findings suggest that inputs from a given point on the skin can directly influence sensory information processing over a much greater rostrocaudal extent than predicted by dorsal horn somatotopic maps. These findings are discussed in terms of their implications for spinal cord plasticity.

This article has been cited by other articles:

				M. D. Boada and C. J. Woodbury Myelinated Skin Sensory Neurons Project Extensively throughout Adult Mouse Substantia Gelatinosa J. Neurosci., February 27, 2008; 28(9): 2006 - 2014. [Abstract] [Full Text] [PDF]

				G. Kato, Y. Kawasaki, R.-R. Ji, and A. M. Strassman Differential wiring of local excitatory and inhibitory synaptic inputs to islet cells in rat spinal lamina II demonstrated by laser scanning photostimulation J. Physiol., May 1, 2007; 580(3): 815 - 833. [Abstract] [Full Text] [PDF]

				A. Levinsson, H. Holmberg, J. Broman, M. Zhang, and J. Schouenborg Spinal Sensorimotor Transformation: Relation between Cutaneous Somatotopy and a Reflex Network J. Neurosci., September 15, 2002; 22(18): 8170 - 8182. [Abstract] [Full Text] [PDF]

				K. Mirnics and H. R. Koerber Properties of Individual Embryonic Primary Afferents and Their Spinal Projections in the Rat J Neurophysiol, September 1, 1997; 78(3): 1590 - 1600. [Abstract] [Full Text] [PDF]