Nuovi trattamenti per il dolore infiammatorio e neuropatico

New treatments for neuropathic pain Stefano Cobianchi, Institute of Neuroscience, CNR, Rome (Italy). Experiment 1: Botulinum neurotoxins. Aim. Botulinum neurotoxins have been successfully used in clinical practice for the treatment of dystonias and a number of syndromes associated to hyperfunctioning of cholinergic terminals. Recent data support the use of Botulinum neurotoxins (BoNTs) as new therapeutic agents in pain relief. It has been demonstrated that the Botulinum neurotoxin serotype-A is able to induce analgesia in inflammatory pain conditions (1). In this study we investigated the effects of two different serotypes, A and B (BoNT/A and BoNT/B), in the development and recovering from neuropathic pain in mice subjected to the sciatic nerve ligation (Chronic Constriction Injury, Bennett and Xie model) (2, 3). Methods. Mice were subcutaneously injected into the plantar surface of both hindpaws either with BoNT/A (two doses: 7.5 or 15 pg/paw), BoNT/B (3.75 pg/paw) or saline, on different days before and after CCI. The temporal trend of neuropathy over a long time interval (80 days) was analyzed measuring the mechanical allodynic response to the Dynamic Aesthesiometer Test. Functional recovery of the injured paw was followed examining the mice walking pattern, measured by the Sciatic Static Index (SSI) (4), as well as by the weight bearing (Incapacitance test). Results. Remarkably, a single administration of BoNT/A, but not BoNT/B, was sufficient to induce antiallodynic effects starting from the day after the injection. The effect was dose-dependent and lasted for at least 3 weeks. The administration of BoNT/A before the CCI was ineffective. Furthermore, BoNT/A injection accelerated the functional recovery, enhancing the SSI scores and restoring the normal weight bearing. Conclusion. This result is particularly relevant since neuropathic pain is poorly treated by current drug therapies. The different modulatory action of the two botulinum serotypes is an important and useful result to take into account for both the study and the comprehension of the mechanisms involved in their action and for the use of the BoNTs in the clinical practice. Experiment 2: Treadmill locomotion. Aim. Treadmill locomotion is widely used for physical rehabilitative therapy. Although several studies demonstrate the positive effects of treadmill running on the functional recovery after a peripheral nerve injury (5, 6, 7), the effects on pain symptoms have not been investigated. In this study we analyzed which treadmill protocol could be effective both on functional recovery and on alleviation of neuropathic pain symptoms. Methods. The CCI model was used to induce neuropathy in mice. We measured the onset of mechanical allodynia in mice undergoing short- (1 week) or long-lasting (8 weeks) daily sessions of treadmill exercise. Functional recovery of the injured paw was examined by analyzing weight bearing of hind limb, walking track analysis and SSI. Behavioural data were correlated with data deriving from immunofluorescence staining for markers of cellular proliferation (Cdc2, GAP-43) in injured nerves and of activated glial cells (Cd11b, GFAP) in lumbar spinal cord. Results. An early mild and short-lasting treadmill exercise was effective in counteracting the development of mechanical allodynia induced by CCI and to speed up the functional recovery of injured paw, as demonstrated by the normalization of the weight bearing and of walking pattern of mice. On the contrary, long-lasting treadmill exercise did not show substantial beneficial effects compared to animals that were not subjected to treadmill. Behavioural data strongly correlated with nerve regeneration immunofluorescence markers. Only the short-lasting treadmill exercise was coupled, with an increased expression in injured sciatic nerves of Cdc2 and GAP-43. In the same mice, a reduced expression of Cd11b and GFAP-labeled glial cells was also observed in the lumbar spinal cord. Conclusion. Results show that only an immediate short-lasting exercise induces pain relief, stimulates nerve regeneration, and speeds up the complete functional recovery. When prolonged for more than a week, treadmill exercise can have deleterious effects after peripheral nerve injury. Supported by research grants FISR-CNR Neurobiotecnologia 2003 and FILAS Regione Lazio (Italy). References (1) Luvisetto S, Marinelli S, Lucchetti F, Marchi F, Cobianchi S, Rossetto O, Montecucco C, Pavone F, 2006. Botulinum neurotoxins and formalin-induced pain: central vs. peripheral effects in mice. Brain Res 1082:124. (2) Bennet GJ, Xie YK,1988. A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man. Pain 33:87-107. (3) Luvisetto S, Marinelli S, Cobianchi S and Pavone F, 2007. Anti-allodynic efficacy of Botulinum neurotoxin A in a model of neuropathic pain. Neurosci 145:1-4. (4) Baptista AF, de Souza Gomes JR, Oliveira JT, Santos SMG, Vannier-Santos MA, Martinez AMB, 2007. A new approach to assess function after sciatic nerve lesion in the mouse – Adaptation of the sciatic static index. J Neurosci Meth 161:259-264. (5) Marqueste T, Alliez JR, Alluin O, Jammes Y, Decherchi P, 2004. Neuromuscular rehabilitation by treadmill running or electrical stimulation after peripheral nerve injury and repair. J Appl Physiol 96:1988-1995. (6) Sabatier MJ, Redmon N, Schwartz G, English AW, 2008. Treadmill training promotes axon regeneration in injured peripheral nerves. Exp Neurol 211:489-493. (7) Seo TB, Han IS, Yoon JH, Hong KE, Yoon SJ, Namgung U, 2006. Involvement of Cdc2 in axonal regeneration enhanced by exercise training in rats. Med Sci Sports Exerc 38:1267-1276.