Axonal sprouts containing calcitonin gene-related peptide and substance P form pericellular baskets around large diameter neurons after sciatic nerve transection in the rat.

Trauma to a peripheral nerve is followed by anatomical remodelling proximal to the lesion, including sprouting of perivascular axons to form baskets of noradrenergic terminals ("rings") around large diameter primary afferent somata in the dorsal root ganglia containing lesioned neurons and sprouting of Abeta axons terminating deep in the dorsal horn into Lamina II. These abnormal structural associations may contribute to the changes in sensory processing that lead to neuropathic pain. The trigger for sprouting of sympathetic axons is probably a neurotrophin (such as nerve growth factor) concentrated locally. Nerve growth factor messenger RNA is known to be increased in dorsal root ganglia after sciatic nerve transection and increased local nerve growth factor elicits collateral sprouting of intact sympathetic terminals into adjacent denervated skin. Nociceptive terminals containing calcitonin gene-related peptide, with or without substance P, also sprout in response to raised concentrations of nerve growth factor. We have found that axons of small sensory neurons immunoreactive for these peptides also form rings around large diameter dorsal root ganglion cells of adult rats after sciatic nerve transection, concurrently with the development of rings of noradrenergic terminals.