SPROUTING SYMPATHETIC FIBERS FORM SYNAPTIC VARICOSITIES IN THE DORSAL-ROOT GANGLION OF THE RAT WITH NEUROPATHIC INJURY

Peripheral nerve injury in a rat model (spinal nerve ligation) of neur opathic pain triggers sprouting of sympathetic fibers in the dorsal ro ot ganglion (DRG). This sympathetic sprouting has been suggested as an important underlying mechanism for pain behaviors, To investigate the possibility of functional interaction between sprouted sympathetic fi bers and sensory neurons, the present study examined the fine morpholo gy and structural relationship between sympathetic fibers and the DRG neurons by electron microscopy. Sympathetic postganglionic fibers, as identified by electron microscopic immunostaining for tyrosine hydroxy lase (TH), were all unmyelinated fibers and some of them ended as grow th cones. In addition, many vesicle-containing axonal enlargements (we will refer these as synaptic varicosities) were found in the intersti tial space around DRG neurons, and some were enclosed within the satel lite cell capsule which surrounded the DRG soma. The presence of sympa thetic synaptic varicosities near or in apposition with either the DRG somata or their processes provides a structural basis for possible in teractions between sensory neurons and sympathetic fibers in the DRG o f neuropathic rats. (C) 1997 Elsevier Science B.V.