Neurotrophin-3 antisense oligonucleotide attenuates nerve injury-induced Abeta-fibre sprouting

It is proposed that following peripheral nerve injury abnormal sprouting of A beta -fibre primary afferent neurons in the spinal cord contributes to t he allodynia that often occurs with such injury. Allodynia is characterized as pain due to a stimulus which is normally non-noxious. Our recent in viv o experiments show that intrathecal administration of neurotrophin-3 (NT-3) , in normal animals, induces allodynia and sprouting of AP-fibres. In this study, we examine whether intrathecal administration of NT-3 antisense olig onucleotides (50 muM), via an osmotic pump for 14 days, attenuates nerve in jury-induced sprouting and allodynia. The oligonucleotides used in this stu dy were phosphorothioate modified and control experiments, using an ELISA, confirm that intrathecal administration of the antisense induces a signific ant decrease in NT-3 levels in the spinal cord. All surgery was conducted o n anaesthetized Wistar rats (sodium pentobarbitone, i.p. 50 mg/kg). Consist ent with previous studies, transganglionic labelling of AP-fibres with chol eragenoid-horseradish peroxidase (C-HRP) shows that complete transection of the sciatic nerve induces an expansion of C-HRP label into lamina II of th e spinal dorsal hem. Using image analysis, we find that intrathecal adminis tration of NT-3 antisense attenuates the density of C-HRP labelling in lami na II in nerve injured animals. A NT-3 sense oligonucleotide (50 muM) has n o effect. To test the effect of NT-3 antisense on allodynia, the nociceptiv e flexion reflex is examined, using an Ugo Basile Analgesymeter, in animals with partial sciatic nerve ligation. Intrathecal administration of 50 muM NT-3 antisense significantly attenuates nerve injury-induced allodynia, whe reas the sense oligonucleotide has no effect. These results provide further evidence that endogenous NT-3 contributes to both nerve injury-induced AP- fibre sprouting and allodynia and demonstrates the potential of neurotrophi n-3 antisense oligonucleotides as therapeutic agents for neuropathic pain. (C) 2000 Elsevier Science B.V. All rights reserved.