Tubulization with chitosan guides for the repair of long gap peripheral nerve injury in the rat

Biosynthetic guides can be an alternative to nerve grafts for reconstructing severely injured peripheral nerves. The aim of this study was to evaluate the regenerative capability of chitosan tubes to bridge critical nerve gaps (15 mm long) in the rat sciatic nerve compared with silicone (SIL) tubes and nerve autografts (AGs). A total of 28 Wistar Hannover rats were randomly distributed into four groups (n = 7 each), in which the nerve was repaired by SIL tube, chitosan guides of low (∼2%, DAI) and medium (∼5%, DAII) degree of acetylation, and AG. Electrophysiological and algesimetry tests were performed serially along 4 months follow-up, and histomorphometric analysis was performed at the end of the study. Both groups with chitosan tubes showed similar degree of functional recovery, and similar number of myelinated nerve fibers at mid tube after 4 months of implantation. The results with chitosan tubes were significantly better compared to SIL tubes (P < 0.01), but lower than with AG (P < 0.01). In contrast to AG, in which all the rats had effective regeneration and target reinnervation, chitosan tubes from DAI and DAII achieved 43 and 57% success, respectively, whereas regeneration failed in all the animals repaired with SIL tubes. This study suggests that chitosan guides are promising conduits to construct artificial nerve grafts.

Experimental diabetes in neonatal mice induces early peripheral sensorimotor neuropathy

Animal models of diabetes do not reach the severity of human diabetic neuropathy but relatively mild neurophysiological deficits and minor morphometric changes. The lack of degenerative neuropathy in diabetic rodent models seems to be a consequence of the shorter length of the axons or the shorter animal life span. Diabetes-induced demyelination needs many weeks or even months before it can be evident by morphometrical analysis. In mice myelination of the peripheral nervous system starts at the prenatal period and it is complete several days after birth. Here we induced experimental diabetes to neonatal mice and we evaluated its effect on the peripheral nerve 4 and 8 weeks after diabetes induction. Neurophysiological values showed a decline in sensory nerve conduction velocity at both time-points. Morphometrical analysis of the tibial nerve demonstrated a decrease in the number of myelinated fibers, fiber size and myelin thickness at both time-points studied. Moreover, aldose reductase and poly(ADP-ribose) polymerase activities were increased even if the amount of the enzyme was not affected. Thus, type 1 diabetes in newborn mice induces early peripheral neuropathy and may be a good model to assay pharmacological or gene therapy strategies to treat diabetic neuropathy.

Anti-allodynic efficacy of botulinum neurotoxin A in a model of neuropathic pain

Neuropathic pain is typified by injuries to the peripheral and central nervous system and derives from such causes as cancer, diabetes, multiple sclerosis, post-herpetic neuralgia, physical trauma or surgery, and many others. Patients suffering neuropathic pain do not respond to conventional treatment with non-steroidal anti-inflammatory drugs and show a reduced sensitivity to opiates often associated with serious side effects. Recently, it has been demonstrated that botulinum neurotoxin serotype-A (BoNT/A) is able to induce analgesia in inflammatory pain conditions. The goal of this research was to test if BoNT/A was able to relieve also neuropathic pain symptoms. By using chronic constriction injury of the sciatic nerve, a mouse model of neuropathic pain, we observed that peripheral administration of BoNT/A strongly reduced the mechanical allodynia associated with this neuropathy. Remarkably, a single non-toxic dose of BoNT/A was sufficient to induce anti-allodynic effects, which lasted for at least 3 weeks. This result is particularly relevant since neuropathic pain is poorly treated by current drug therapies. This communication enlarges our knowledge on potentially new medical uses of BoNT/A in efforts to ameliorate human health conditions, with very important implications in the development of new pharmacotherapeutic approaches against neuropathic pain.