European Journal of Neuroscience, Vol. 11, pp.1711–1722, 1999 © European Neuroscience Association Satellite-cell-derived nerve growth factor and neurotrophin-3 are involved in noradrenergic sprouting in the dorsal root ganglia following peripheral nerve injury in the rat Xin-Fu Zhou, Yan-Shen Deng, Edward Chie, Qing Xue, Jin-Hua Zhong, Elspeth M. McLachlan, 1 Robert A. Rush and Cory J. Xian 2 Department of Human Physiology and Centre for Neuroscience, Flinders University of South Australia, GPO Box 2100, Adelaide 5001, Australia 1 Prince of Wales Medical Research Institute, Randwick, NSW 2031, Australia 2 Children Health Research Institute, Women and Children’s Hospital, Adelaide, South Australia 5001, Australia Keywords: in situ hybridization, NGF, NT3, RT-PCR, sensory neurons Abstract Injury to a peripheral nerve induces in the dorsal root ganglia (DRG) sprouting of sympathetic and peptidergic terminals around large-diameter sensory neurons that project in the damaged nerve. This pathological change may be implicated in the chronic pain syndromes seen in some patients with peripheral nerve injury. The mechanisms underlying the sprouting are not known. Using in situ hybridization and immunohistochemical techniques, we have now found that nerve growth factor (NGF) and neurotrophin-3 (NT3) synthesis is upregulated in satellite cells surrounding neurons in lesioned DRG as early as 48 h after nerve injury. This response lasts for at least 2 months. Quantitative analysis showed that the levels of mRNAs for NT3 and NGF increased in ipsilateral but not contralateral DRG after nerve injury. Noradrenergic sprouting around the axotomized neurons was associated with p75-immunoreactive satellite cells. Further, antibodies specific to NGF or NT3, delivered by an osmotic mini-pump to the DRG via the lesioned L5 spinal nerve, significantly reduced noradrenergic sprouting. These results implicate satellite cell-derived neurotrophins in the induction of sympathetic sprouting following peripheral nerve injury. Introduction There is clinical evidence suggesting that sympathetic nerves are involved in neuropathic pain after nerve injury, as alpha adrenergic antagonists have been reported to alleviate the pain (Bonica, 1990; Janig & Schmidt, 1992). After sciatic transection in rats, sympathetic stimulation can excite sensory neurons (McLachlan et al., 1993; Devor et al., 1994), and axotomized sensory neuron somata have been shown to possess an abnormal sensitivity to noradrenaline (Petersen et al., 1996; Abdulla & Smith, 1997). Following other experimental nerve lesions that involve loss of only some of the innervation of peripheral tissue, rats exhibit hyperalgesia which can be blocked by sympathectomy (Kim et al., 1993; Kinnman & Levine, 1995). Recently, it has been reported that in response to several forms of peripheral nerve injury or overexpression of nerve growth factor (NGF), sympathetic nerves innervating blood vessels within dorsal root ganglia (DRG) and trigeminal ganglia sprout between the cell bodies and form varicose perineuronal baskets around some large sensory neurons (McLachlan et al., 1993; Chung et al., 1996; Zhou et al., 1996; Walsh & Kawaja, 1998). It is possible that release of noradrenaline from sympathetic sprouts in sensory ganglia is involved in the genesis of signals that lead to neuropathic pain. The mechanisms underlying the sympathetic and peptidergic sprout- Correspondence: X.-F. Zhou, as above. E-mail: pzxfz@cc.flinders.edu.au Received 21 August 1998, revised 22 December 1998, accepted 7 January 1998 ing within the DRG are not known. NGF is a survival factor for developing sympathetic neurons (Levi-Montalcini & Angeletti, 1963), and is a potent neurotrophic factor for neurite outgrowth in culture (Levi-Montalcini & Booker, 1960) and in vivo (Isaacson et al., 1992). Sprouting of undamaged nociceptive and sympathetic terminals occurs in partially denervated skin due to excessive amounts of NGF (Diamond et al., 1987, 1992). In response to septal lesions, intact sympathetic terminals sprout in the hippocampus where NGF is also synthesized (Yu & Crutcher, 1995). Therefore, NGF may similarly be responsible for the sprouting of sympathetic and peptidergic axons in the DRG after nerve lesions (Chung et al., 1996; Zhou et al., 1996; McLachlan & Hu, 1998). Recent studies have shown that the level of NGF in DRGs is increased following sciatic nerve injury, as measured both by mRNA analysis (Sebert & Shooter, 1993) and ELISA assay (Herzberg et al., 1997). In addition, sprouting occurs more rapidly and extensively when the nerve lesion is close to the ganglion (Hong & Kang, 1996), suggesting that factors within the damaged ganglia play a role. However, it is not known whether NGF is present in damaged sensory neurons or in glial cells, or whether it is locally synthesized; these changes might trigger local axon sprouting. The NGF homologue, neurotrophin-3 (NT3), is also a neurotrophic factor essential for the development of sympathetic neurons (DiCicco- Bloom et al., 1993; Verdi & Anderson, 1994; Verdi et al., 1996; Zhou & Rush, 1996). Mature sympathetic neuron somata derive NT3, like NGF, from their effector tissues after retrograde transport (Zhou