• S I Nakamura and R R Myers.
• Departments of Anesthesiology and Pathology (Neuropathology), Veterans Affairs Medical Center, San Diego, USA.
• Spine. 2000 Mar 1;25(5):537-42.

Study DesignA study of the relation between the development of mechanical allodynia and the reorganization of primary afferent terminals in the sensory lamina of the rat spinal cord dorsal horn after partial dorsal root ganglion injury in rats.ObjectivesTo investigate the pathologic mechanisms of mechanical allodynia after partial dorsal root ganglion injury.Summary Of Background DataAfter experimental peripheral nerve injury causing neuropathic pain, myelinated afferent fibers sprout into lamina II of the dorsal horn. This lamina is associated with nociceptive-specific neurons that generally are not stimulated by myelinated fiber input from mechanical receptors. These morphologic changes are suggested to have significance in the pathogenesis of chronic mechanical allodynia, although it is not known whether this kind of morphologic change occurs after dorsal root ganglion injury.MethodsAfter partial dorsal root ganglion crush injury, the mechanical force causing footpad withdrawal was measured with von Frey hairs, and myelinated primary afferents were labeled with cholera toxin B subunit horseradish peroxidase, a selective myelinated fiber tracer that identifies transganglionic synapses.ResultsAfter partial dorsal root ganglion injury, mechanical allodynia developed in the corresponding footpad within 3 days and persisted throughout the experimental period. At 2 and 4 weeks after the injury, B subunit horseradish peroxidase-positive fibers, presumably myelinated afferents, were observed to be sprouting into lamina II of the dorsal horn on the injured side, but not on the contralateral control side.ConclusionsMorphologic change in spinal cord dorsal horn lamina II occurs after partial dorsal root ganglion injury. This change may have significance in the pathogenesis of chronic mechanical allodynia after partial dorsal root ganglion injury.

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