THE EFFECT OF EXOGENOUS MELATONIN ON THE EXTRAFASCICULAR CONNECTIVE TISSUE IN TRANSECTED RAT SCIATIC NERVE

Previous studies linking the effect of certain pharmacological agents with the status of connective tissue and nerve fiber regeneration after traumatic transection were focused mainly on the proximal nerve stump. In our study, qualitative and quantitative histological analysis of the proximal and the distal nerve stump were done. Male Wistar rats underwent transection and excision of an 8-mm nerve segment of the left sciatic nerve. The vehiculum group of animals (n=7) was administered with 5% ethanol in Ringer solution (vehiculum), while the melatonin group (n=10) received 30mg/kg of melatonin dissolved in vehiculum, daily, intraperitoneally (i.p.) for 14 consecutive days. Then, intravital excision of the marginal zone of the proximal and distal nerve stump was performed and the samples were further processed for qualitative photomicroscopic and stereological analysis. Macroscopic and microscopic examinations of both nerve stumps showed absent or slight stump thickening in the melatonin group compared to the vehiculum group of animals, which is the result of reduced connective tissue proliferation. The mean epineurial volume density of the proximal nerve stump was statistically significantly lower (p=0,003) in the melatonin (0,36) than in the vehiculum group of animals (0,51). The difference in mean epineurial volume density of the distal stump was also statistically significant (p=0,039) with 0,33 in melatonin and 0,46 in the vehiculum group. Our study revealed that the administration of exogenous melatonin was effective in suppression of trauma-caused extrafascicular connective tissue proliferation in neuroma of the proximal nerve stump as well as fibroma formation in the distal nerve stump.