NEUROTROPHIN-3 DELIVERED LOCALLY VIA FIBRONECTIN MATS ENHANCES PERIPHERAL-NERVE REGENERATION

A better understanding of the mechanisms of nerve regeneration could i mprove the outcome of surgical nerve repair. We have previously shown that axonal regeneration is increased by nerve growth factor. Neurotro phin-3 (NT-3) belongs to the same family as nerve growth factor but ac ts on a distinct neuron subpopulation. As little is known about its ro le following nerve injury, we have investigated the effect of NT-3 del ivered via fibronectin mats, previously shown to support nerve regener ation comparable to nerve grafts. NT-3 stimulation (0.1-1000 ng/ml) of neurite extension from embryonic chick dorsal root ganglia in vitro h as shown that fibronectin can bind and release bioactive NT-3. Fibrone ctin mats impregnated with NT-3 (500 ng/ml) were grafted into 1 cm sci atic nerve defects in adult Lewis rats. Plain mats were used as contro ls. Computerized quantification of penetration distance, volume of axo nal regeneration and myelinated fibre counts was undertaken using immu nostaining for axonal markers (growth-associated protein 43, calcitoni n gene-related peptide, substance P, vasoactive intestinal peptide and neuropeptide tyrosine), or S100 or thionine blue staining up to 8 mon ths postoperatively. The maximal effect of NT-3 occurred at day 15, wh en for GAP43-immunostained axons both penetration distance (NT-3, 6.10 +/- 0.42 mm; control, 4.11 +/- 0.41 mm; P< 0.01) and staining area (N T-3, 0.137 +/- 0.012 mm(2); control, 0.077 +/- 0.018 mm(2); P < 0.05) were significantly increased. Similar results were found for each neur onal subpopulation investigated. By 8 months after repair, the NT-3 gr oup supported a significantly greater number of myelinated axons (NT-3 , 7003 +/- 402; control, 4932 +/- 725; P < 0.05) of similar diameter a nd g-ratio to controls. These results demonstrate the contribution of NT-3 to the increase of nerve regeneration promoted by growth factors.