Spontaneous regeneration after resection of various lengths of hypoglossal nerve in rats.

The objective of this study was to investigate spontaneous neural regeneration and functional recovery after resection of various lengths of the hypoglossal (XII) nerve in adult rats. Twelve weeks after XII nerve resection at lengths ranging from 0.0 to 15.8 mm, the tongue deviation angle of rats was measured to evaluate the severity of paralysis; thereafter, the XII neurons in the XII nucleus were labeled with Fluoro-Gold (FG), which was injected into the tongue to visualize regenerated XII neurons re-innervating the tongue muscles. In the XII nerve-resected rats, the regenerative rates, that is, the percentage of the total number of FG-positive neurons on the injured side relative to that on the uninjured side, were divided into two groups; the regenerative rates were more than 77% and less than 6%, respectively. Upon comparing the two groups, the boundary resection length was approximately 10.0 mm. Moreover, the former and latter groups demonstrated tongue deviation angles less than or greater than 15°, respectively. The critical nerve gap length for spontaneous neural regeneration was approximately 10.0 mm in XII nerve-resected adult rats, and nerve regeneration occurred in both morphological and functional aspects after resection at less than the critical length. • Spontaneous regeneration occurred in rat relatively long-gap nerve resection models. • Morphological and functional regeneration occurred in the nerve-resected rats. • A critical nerve gap length exists for spontaneous nerve regeneration. [ABSTRACT FROM AUTHOR]