Blocking CTGF/CCN2 reverses neural fibrosis and sensorimotor declines in a rat model of overuse-induced median mononeuropathy.

Encapsulation of median nerves is a hallmark of overuse-induced median mononeuropathy and contributes to functional declines. We tested if an antibody against CTGF/CCN2 (termed FG-3019 or Pamrevlumab) reduces established neural fibrosis and sensorimotor declines in a clinically relevant rodent model of overuse in which median mononeuropathy develops. Young adult female rats performed a high repetition high force (HRHF) lever-pulling task for 18 weeks. Rats were then euthanised at 18 weeks (HRHF untreated), or rested and systemically treated for 6 weeks with either an anti-CCN2 monoclonal antibody (HRHF-Rest/FG-3019) or IgG (HRHF-Rest/IgG), with results compared with nontask control rats. Neuropathology was evident in HRHF-untreated and HRHF-Rest/IgG rats as increased perineural collagen deposition and degraded myelin basic protein (dMBP) in median nerves, and increased substance P in lower cervical dorsal root ganglia (DRG), compared with controls. Both groups showed functional declines, specifically, decreased sensory conduction velocity in median nerves, noxious cold temperature hypersensitivity, and grip strength declines, compared with controls. There were also increases of ATF3-immunopositive nuclei in ventral horn neurons in HRHF-untreated rats, compared with controls (which showed none). FG-3019-treated rats showed no increase above control levels of perineural collagen or dMBP in median nerves, Substance P in lower cervical DRGs, or ATF3-immunopositive nuclei in ventral horns, and similar median nerve conduction velocities and thermal sensitivity, compared with controls. We hypothesize that neural fibrotic processes underpin the sensorimotor declines by compressing or impeding median nerves during movement, and that inhibiting fibrosis using an anti-CCN2 treatment reverses these effects.

Effects of local lidocaine treatment before and after median nerve injury on mechanical hypersensitivity and microglia activation in rat cuneate nucleus.

This study examined the relationship between microglia activation in the cuneate nucleus (CN) and behavioral hypersensitivity after chronic constriction injury (CCI) of the median nerve. We also investigated effects of local lidocaine pre- and post-treatment on microglia activation and development of hypersensitivity in this model. By immunohistochemistry and immunoblotting, little immunoreactivity of OX-42, a microglia activation marker, was detected in the CN of normal rats. As early as 1 day after CCI, there was a significant increase in OX-42 immunoreactivity in the lesion side of CN, which reached a maximum at 14 days. Microinjection of minocycline, a microglia activation inhibitor, into the CN 1 day after CCI attenuated injury-induced behavioral hypersensitivity in a dose-dependent manner. Furthermore, the animals received 1%, 2% or 5% lidocaine 15 min prior to median nerve CCI (pre-treatment), 5h (early post-treatment) or 1 day (late post-treatment) after median nerve CCI. Pre-treatment and early post-treatment with 2% and 5% lidocaine, but not 1% lidocaine, attenuated OX-42 immunoreactivity and behavioral hypersensitivity following median nerve injury. Late post-treatment with 1%, 2%, or 5% lidocaine failed to decrease OX-42 immunoreactivity and mechanical hypersensitivity in CCI rats. In conclusion, median nerve injury-induced microglia activation in the CN modulated development of behavioral hypersensitivity. High-concentration lidocaine was effective in decreasing microglia activation in the CN and in attenuating neuropathic pain sensations at the early stage following nerve injury, when microglia had not yet been activated.

Effects of pre-emptive drug treatment on astrocyte activation in the cuneate nucleus following rat median nerve injury.

In this study, we examined the relationship between astrocyte activation in the cuneate nucleus (CN) and behavioral hypersensitivity after chronic constriction injury (CCI) of the median nerve. In addition, we also examined the effects of pre-emptive treatment with a number of drugs on astrocyte activation and hypersensitivity development in this model. Using immunohistochemistry and immunoblotting, little glial fibrillary acidic protein (GFAP; an astrocyte marker) immunoreactivity was detected in the CN of the normal rats. As early as 3 days after CCI, there was a significant increase in GFAP immunoreactivity in the lesion side of CN, and this reached a maximum at 7 days, and was followed by a decline. Counting of GFAP-immunoreactive astrocytes revealed that astrocytic hypertrophy, but not proliferation, contributes to increased GFAP immunoreactivity. Furthermore, microinjection of the glial activation inhibitor, fluorocitrate, into the CN at 3 days after CCI attenuated injury-induced behavioral hypersensitivity in a dose-dependent manner. These results suggest that median nerve injury-induced astrocytic activation in the CN modulated the development of behavioral hypersensitivity. Animals received MK-801 (glutamate N-methyl-d-aspartate (NMDA) receptor antagonist), clonidine (alpha(2)-adrenoreceptor agonist), tetrodotoxin (TTX, sodium channel blocker) or lidocaine (local anesthetic) 30 min prior to median nerve CCI. Pre-treatment with MK-801, TTX, and 2% lidocaine, but not clonidine, attenuated GFAP immunoreactivity and behavioral hypersensitivity following median nerve injury. In conclusion, suppressing reactions to injury, such as the generation of ectopic discharges and activation of NMDA receptors, can decrease astrocyte activation in the CN and attenuate neuropathic pain sensations.

Local administration of DFO-loaded lipid particles improves recovery after end-to-end reconstruction of rat median nerve.

PURPOSE: The improvement of regeneration and functional recovery after peripheral nerve injury is a major challenge in neurosurgery. Although microsurgical techniques for nerve reconstruction have seen great advancements over the last years, the clinical outcome with patients is often unsatisfactory. The aim of the present study was to investigate if administration of the iron chelator Deferroxamine (DFO), can improve postoperative outcome in the rat median nerve reconstruction model. METHODS: After complete transection, the right median nerve was repaired by end-to-end neurorrhaphy. The suture site was wrapped by a 1-cm-long external jugular vein segment, either empty or filled with DFO-loaded lipid particles (Perineurin or with a vehicle (unloaded lipid particles) alone. Functional testing was carried out weekly by means of the grasping test. At the time of withdrawal, 12 weeks post-operatively, muscle tropism recovery was assessed by weighing flexor digitorum sublimis muscle that is innervated by the median nerve only. Before harvesting of the nerve specimens electrophysiological analyses were performed with measuring the latency, the threshold and the conduction velocity. Finally, the repaired nerves were withdrawn for immunocytochemistry with a neurofilament antibody and axon quantitative morphology. RESULTS: The comparison between the groups showed that intraoperative application of the DFO-loaded lipid particles at the neurorrhaphy site led to a significant increase in the density of regenerating axons as well as to an accelerated recovery of both muscle tropism and motor function. The electrophysiological results demonstrated a decrease of the threshold, a lower latency, and a higher conduction velocity in the Perineurin-treated animals. CONCLUSIONS: The results of the present study suggest that local administration of Perineurin might have a therapeutic potential for improving the postoperative outcome after microsurgical nerve reconstruction in patients.

Recovery of nerve injury-induced alexia for Braille using forearm anaesthesia.

Nerve injuries in the upper extremity may severely affect hand function. Cutaneous forearm anaesthesia has been shown to improve hand sensation in nerve-injured patients. A blind man who lost his Braille reading capability after an axillary plexus injury was treated with temporary cutaneous forearm anaesthesia. After treatment sensory functions of the hand improved and the patient regained his Braille reading capability. The mechanism behind the improvement is likely unmasking of inhibited or silent neurons, but after repeated treatment sessions at increasing intervals the improvement has remained at 1-year follow-up, implying a structural change in the somatosensory cortex.