Freeze-fracture and cytochemical evidence for structural and functional alteration in the axolemma and myelin sheath of adult guinea pig optic nerve fibers after stretch injury

Recent work in animal models of human diffuse axonal injury has generated t he hypothesis that, rather than there being physical disruption of the axol emma at the time of injury, a pertubation of the membrane occurs, which lea ds, over time, to a dysfunction of the physiology of the axolemmal, This dy sfunction is posited to lead to a disruption of ionic homeostasis within th e injured axon, leading to secondary axotomy some hours after the initial i nsult, We decided to test the hypothesis that membrane pump/ion channel act ivity or function is compromised and this would be reflected in structural changes within the axolemma and myelin sheath. We used freeze fracture and cytochemical techniques to provide evidence for change in membrane structur e and the activity of membrane pumps after nondisruptive axonal injury in t he adult guinea pig optic nerve. Within 10 min of injury, structural change s occurred in the distribution and number of intramembranous particles (IMP s) in the internodal axolemma, By 4 h, there was novel labeling for Ca-ATPa se membrane pump activity at the same site, There was loss of IMPs from the nodal axolemma extending over several hours after injury, There was loss o f both membrane pump Ca-ATPase and p-nitrophenylphosphatase (p-NPPase) acti vity of the node. There was loss of ecto-Ca-ATPase activity but increased l abeling for p-NPPase activity at sites of dissociation of compacted myelin, Quantitative freeze-fracture demonstrated statistically significant change s in membrane structure, We provide support for the hypothesis that structu ral and functional changes occur in the axolemma and myelin sheath at nondi sruptive axonal injury.