Structural basis of sympathetic-sensory coupling in rat and human dorsal root ganglia following peripheral nerve injury

Tyrosine hydroxylase immunocytochemistry was used to reveal the sympathetic postganglionic axons that sprout to form basket-like skeins around the som ata of some primary sensory neurons in dorsal root ganglia (DRGs) following sciatic nerve injury. Ultrastructural observations in rats revealed that t hese sprouts grow on the surface of glial lamellae that form on the neurons . Sciatic nerve injury triggers glial cell proliferation in the DRG, and th e formation of multilamellar pericellular onion bulb sheaths, primarily aro und large diameter DRG neurons. We infer that these glia participate in the sprouting process by releasing neurotrophins and expressing growth support ive cell surface molecules. Many DRG cell somata, and their axons in intact nerves and nerve end neuromas, express alpha 2A adrenoreceptors intracytop lasmically and on their membrane surface. However, sympathetic axons never make direct contacts with the soma membrane. The functional coupling known to occur between sympathetic efferents and DRG neurons must therefore be me diated by the diffusion of neurotransmitter molecules in the extracellular space. Sympathetic basket-skeins were observed in DRGs removed from human n europathic pain patients, but the possibility of a functional relation betw een these structures and sensory symptoms remains speculative.