Pain
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Tight ligation and transection of the L5 spinal nerve (SNL) gives rise to pain which is dependent upon activity in the sympathetic nervous system. It also results in novel adrenergic sympathetic innervation of the dorsal root ganglion (DRG) with the formation of pericellular axonal basket structures around some DRG neurons. Since the sympathetic sprouting and basket formation may represent an anatomical basis for pain-generating interactions between the sympathetic efferent neurons and sensory afferent neurons, it is of great interest to determine possible chemical mediators of this phenomenon. ⋯ On the other hand, in the IL-6 mice, mechanoallodynia (as assessed with von Frey filaments) was markedly delayed. Sympathetic invasion of the fiber tract and cell layer of the DRG, and the formation of pericellular axonal baskets were all significantly reduced in the IL-6 knockout mice compared to the control strain. These results imply a facilitatory role for IL-6 in pain and sympathetic sprouting induced by nerve injury, and add to the growing list of roles for IL-6 in neuropathological events.