A role for nerve growth factor in sympathetic sprouting in rat dorsal rootganglia

The role of nerve growth factor (NGF) and glial-derived neurotrophic factor (GDNF) in sympathetic sprouting within the dorsal root ganglion was invest igated. In nerve-intact rats, intrathecal NGF (1 mg/ml, 14 days) but not GD NF (1 mg/ml, 14 days) induced extensive sprouting of tyrosine hydroxylase i mmunoreactive (TH-IR) fibres and formation of pericellular TH-IR baskets wi thin lumbar DRGs. TH-LR baskets were distributed equally to trkA-expressing and trkA-negative neuronal profiles. Sciatic nerve transection (14-21 days ) induced TH-IR baskets within lumbar DRG's around neuronal profiles with b oth intact and lesioned axons. The percentage of neuronal profiles surround ed by TH-IR baskets following sciatic transection was unaffected following peripheral application of the NGF sequestering antibody, trkA-IgG (1 mg/ml, 14 days), Intracellular responses were recorded from sensory neurons in an in vitro DRG/peripheral nerve preparation following bath application of no radrenaline. In preparations from animals treated 14 days previously with i ntrathecal NGF, 69% of neurons responded with depolarizing responses whilst 18% of neurons responded to bath applied noradrenaline in tissue prepared from naive animals. Our data indicate that sympathetic neurons sprout into the DRG in response to sciatic nerve injury and intrathecal NGF but not GDN F. Distribution of sympathetic sprouts within the DRG is independent of whe ther target neurons are injured or express trkA. Sequestration of NGF at th e peripheral injury site does not influence basket formation within the DRG . It is likely that functional noradrenergic connections exist between symp athetic sprouts and sensory neuron cell bodies following exogenous NGF. (C) 1999 International Association for the Study of Pain. Published by Elsevie r Science B.V.