J Korean Pain Soc.  1996 Jun;9(1):26-38.

Sympathetic Excitation of Afferent Neurons within Dorsal Root Ganglia in a Rat Model of Sympathetically Medicated Pain

• Leem JW
• Kang MJ
• Paik KS
• Nam YT

Abstract

In a normal state, sympathetic efferent activity does not elicit discharges of sensory neurons, whereas it becomes associated with and excites sensory neurons in a pathophysiological state such as injury to a peripheral nerve. Although this sympathetic-sensory interaction is reportedly adrenergic, involved subtypes of adrenoreceptors are not yet clearly revealed. The purpose of this study was to determine which adrenoreceptor subtypes were involved in sympathetic-sensory interaction that was developed in rats with an experimental peripheral neuropathy. Using rats that received a tight ligation of one or two of L4-L6 spinal nerves 10-15 days previously, a recording was made from afferent fibers in microfilaments teased from the dorsal root that was in continuity with the ligated spinal nerve. Electrical stimulation of sympathetic preganglionic fibers in T13 or Ll ventral root (50 Hz, 2-5 mA, 0.5 ms pulse duration, l0sec) was made to see if the activity of recorded afferents was modulated. About half of afferents showing spontaneous discharges responded to sympathetic stimulation, and had the conduction velocities in the A-fiber range. Most of the sympathetically induced afferent responses were excitation. This sympathetically induced exciitation occurred in the dorsal root ganglion (DRG), and was blocked by yohimbine (a2 blocker), neither by propranolol B blocker) nor by prazosine (a1 blocker). The results suggest that after spinal nerve ligation, sympathetic efferents interact with sensory neurons having A-fiber axons in DRG where adrenaline released from sympathetic nerve endings excites the activity of sensory neurons by acting on 2-adrenoreceptors. This 2-adrenoreceptor mediated excitation of sensory neurons may account for sympathetic involvement in neuropathic pain.

Keyword

Neuropathic pain; Sympathetically mediated pain; Alpha-2 adrenoreceptor; Dorsal root ganglion

MeSH Terms

Actin Cytoskeleton
Animals
Axons
Diagnosis-Related Groups
Electric Stimulation
Epinephrine
Ganglia, Spinal*
Ligation
Models, Animal*
Nerve Endings
Neuralgia
Neurons, Afferent*
Peripheral Nerves
Peripheral Nervous System Diseases
Prazosin
Propranolol
Rats*
Sensory Receptor Cells
Spinal Nerve Roots*
Spinal Nerves
Yohimbine
Epinephrine
Prazosin
Propranolol
Yohimbine