Quantitative image analysis of the chromatolysis in rat facial and hypoglossal motoneurons following axotomy with and without reinnervation

Image analysis was used to quantify the time course of chromatolysis in regenerating and degenerating motoneurons. Following facial-facial, hypoglossal-hypoglossal nerve suture, or resection of facial and hypoglossal nerves with postoperative survival times of 4 h to 112 days, the texture of the Nissl substance of facial and hypoglossal motoneurons was analyzed on both sides of the brainstem in paraffin serial sections with a VIDASplus image analyzer. In this quantitative study of 149 Wistar rats, alterations of the Nissl substance were measured that were statistically significant but not yet visible to the human eye. Chromatolysis started significantly as early as 8 h and was not fully reversed 112 days after any of the types of axotomy, The reaction was more intense and longer lasting following axotomy without reinnervation than with reinnervation. Thus, chromatolysis starts much faster and lasts far longer than was previously known. The quantified chromatolysis is much stronger after permanent target deprivation than during complete regeneration of motoneurons but is reversible in both cases.