Similar Electrophysiological Changes in Axotomized and Neighboring Intact Dorsal Root Ganglion Neurons

• Published in: Journal of neurophysiology Vol. 89; no. 3; pp. 1588 - 1602
• Main Authors: Ma, Chao, Shu, Yousheng, Zheng, Zheng, Chen, Yong, Yao, Hang, Greenquist, Kenneth W, White, Fletcher A, LaMotte, Robert H
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01-03-2003
• Subjects: Acute Disease; Animals; Axotomy; Electrophysiology; Female; Ganglia, Spinal - cytology; Ganglia, Spinal - physiology; Hindlimb - innervation; Hyperalgesia - physiopathology; Nerve Fibers, Myelinated - physiology; Neural Conduction - physiology; Neuralgia - physiopathology; Neurons, Afferent - physiology; Neurons, Afferent - ultrastructure; Physical Stimulation; Rats; Rats, Sprague-Dawley
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00855.2002

Department of Anesthesiology, Yale University School of Medicine,
New Haven, Connecticut 06510
Ma, Chao,
Yousheng Shu,
Zheng Zheng,
Yong Chen,
Hang Yao,
Kenneth W. Greenquist,
Fletcher A. White, and
Robert H. LaMotte.
Similar Electrophysiological Changes in Axotomized and
Neighboring Intact Dorsal Root Ganglion Neurons. J. Neurophysiol. 89: 1588-1602, 2003. We investigated
electrophysiological changes in chronically axotomized and neighboring
intact dorsal root ganglion (DRG) neurons in rats after either a
peripheral axotomy consisting of an L5 spinal nerve ligation (SNL) or a
central axotomy produced by an L5 partial rhizotomy (PR). SNL produced
lasting hyperalgesia to punctate indentation and tactile allodynia to
innocuous stroking of the foot ipsilateral to the injury. PR produced
ipsilateral hyperalgesia without allodynia with recovery by day 10. Intracellular recordings were obtained in vivo from the cell bodies
(somata) of axotomized and intact DRG neurons, some with functionally
identified peripheral receptive fields. PR produced only minor
electrophysiological changes in both axotomized and intact somata in L5
DRG. In contrast, extensive changes were observed after SNL in large-
and medium-sized, but not small-sized, somata of intact (L4) as well as
axotomized (L5) DRG neurons. These changes included (in relation to
sham values) higher input resistance, lower current and voltage
thresholds, and action potentials with longer durations and slower
rising and falling rates. The incidence of spontaneous activity,
recorded extracellularly from dorsal root fibers in vitro, was
significantly higher (in relation to sham) after SNL but not after PR,
and occurred in myelinated but not unmyelinated fibers from both L4
(9.1%) and L5 (16.7%) DRGs. We hypothesize that the changes in the
electrophysiological properties of axotomized and intact DRG neurons
after SNL are produced by a mechanism associated with Wallerian
degeneration and that the hyperexcitability of intact neurons may
contribute to SNL-induced hyperalgesia and allodynia.