FATE OF REACTIVE AXONAL SWELLINGS INDUCED BY HEAD-INJURY

  • 1 January 1985
    • journal article
    • research article
    • Vol. 52  (5) , 540-552
Abstract
The fate of those reactive axonal swellings seen following head injury was assessed in cats subjected to mild to moderate fluid-percussion head injury. To allow for the ready visualization of any traumatically induced reactive axonal change at the light and electron microscopic level, the anterograde axonal transport of wheat germ agglutinin conjugated to horesradish peroxidase was employed over a 21 day posttraumatic period in selected cerebral and cerebellar efferents coursing through the brain stem. At the designated posttraumatic survival time, the animals were perfused with aldehydes, processed for the light and electron microscopic visualization of the peroxidase reaction product, and examined for any evidence of ractive axonal change. At the 3rd and 4th posttraumatic days, peroxidase-laden swellings could be identified. Some reactive swellings were packed with organelles and were encompassed by a distended myelin sheath or lacked myelin investment. Other reactive swellings demonstrated lobulation or increased electron density with macrophage accumulation, all of which indicated degeneration. Wallerian change occurred distal to the reactive swellings; however, with the exception of these changes the related brain parenchyma and vasculature demonstrated no significant abnormality. With continued survival, reactive swellings comparable to those just described were consistently observed; however, now regenerative responses were also seen. At the 5th and 7th days, reactive sprouts were observed originating from reactive swellings which displayed a reduction in size and in organelle content. By the 9th and 14th posttraumatic days, some sprout-containing swellings demonstrated several robust extensions. These regenerative changes were seen in myelin and nonmyelin-invested swellings and persisted through the 21st day, occurring in concert with lobulated, electron dense and unchanged, swollen reactive axons. Head injury apparently elicits axonal swelling that may persist unchanged, degenerate or undergo a regenerative response. The sustained regenerative responses are considered intriguing and may have relevance for head-injured humans and for future studies of CNS regeneration.