Ultrastructural Studies of Diffuse Axonal Injury in Humans

Abstract

Diffuse axonal injury (DAI) is observed commonly in traumatically brain injured humans. However, traditional histologic methods have proven of limited use in identifying reactive axonal change early (< 12 h) in the posttraumatic course. Recently, we have reported, in both humans and animals, that antibodies targeting neurofilament subunits are useful in the light microscopic recognition of early reactive change. In the present study, we extend our previous efforts in humans by analyzing the progression of traumatic brain injury (TBI)-induced axonal change at the ultrastructural level. This effort was initiated to follow the subcellular progression of reactive axonal change in humans and to determine whether this progression parallels that described in animals. Two commercially prepared antibodies were used to recognize reactive axonal change in patients surviving from 6 to 88 h. The NR4 antibody was used to target the light neurofilament subunit (NF-L), and the SMI32 antibody was used to target the heavy neurofilament subunit (NF-H). Plastic-embedded tissue sections were screened for evidence of reactive axonal change, and once identified, this reactive change was analyzed at the ultrastructural level. At 6 h survival, focally enlarged, immunoreactive axons with axolemmal infolding or disordered neurofilaments were seen within fields of axons exhibiting no apparent abnormality. By 12 h, some axons exhibited continued neurofilamentous misalignment, pronounced immunoreactivity, vacuolization, and, occasionally, disconnection. At later stages, specifically 30 and 60 h survival, further accumulation of neurofilaments and organelles had led to the further expansion of the axis cylinder, and clearly disconnected reactive swellings were recognized. These contained a dense core of disordered immunoreactive neurofilaments partially encompassed by a cap of less densely aggregated organelles. At 88 h, the reactive axons were larger and elongated, consistent with the continued delivery of organelles by axoplasmic transport. At the later time points, considerable heterogeneity was observed, with focally enlarged disconnected axons being observed in relation to axons showing less advanced reactive change. Our findings suggest that neurofilamentous disruption is a pivotal event in axonal injury.

Therapy Development for Diffuse Axonal Injury

“…3,6,11 More modern approaches using antibodies to transported proteins, Research, NICHD, NIH such as amyloid precursor protein (APP), however, have become the gold standard in evaluating the occurrence of DAI in both the routine neuropathologic and forensic settings as well as animal investigations. 10,[12][13][14][15][16][17][18] Specifically, as APP moves down the axonal cylinder via anterograde axonal transport, any focal disruption/ perturbation of the axon and its transport kinetics can lead to local swelling that then can be easily identified by the pooling of APP. 19,20 Through the use of these antibodies in both neuropathologic and forensic settings, the overall occurrence and distribution of traumatically induced axonal change has become even more apparent and has extended many of those observations initially made via the use of more traditional histological approaches (Fig.…”

“…3,11,24,31 Typically in humans, reactive axonal swellings can be recognized within the first hours post-injury as large focal axonal swellings 10-20 lm in diameter that expand in size over 24-48 h reaching up to approximately 50 lm. 1,3,8,15,18,25,32 During this time, both axonal bulbs and varicosities are often observed together in various ratios, presumably reflecting the different rates of swelling and progression toward disconnection in individual injured axons. It is thought that axons sustaining more severe injury manifest local calcium dysregulation that causes progressive focal dissolution of the subaxolemmal spectrin and ankyrin network.…”

Pathophysiology of Cerebral Ischemia and Brain Trauma: Similarities and Differences

“…Diffuse axonal injury (DAI) is a common consequence of TBI (Adams et al, 1982b;Christman et al, 1994;Gentleman et al, 1995;Povlishock, 1992). In terms of neurological deficits, DAI has been reported to significantly contribute to poor outcome.…”

Relationship between Flow-Metabolism Uncoupling and Evolving Axonal Injury after Experimental Traumatic Brain Injury

“…Axonal injury is a common finding in TBI and is associated with both morbidity and mortality (Adams et al, 1989;Christman et al, 1994;Maxwell et al, 1997). The original assumption that TBI results in immediate axotomy because of mechanical shearing of the axon describes only a small percentage of the most severely injured fibers (Maxwell et al, 1993(Maxwell et al, , 1997.…”