Ac. Bain et al., Dynamic stretch correlates to both morphological abnormalities and electrophysiological impairment in a model of traumatic axonal injury, J NEUROTRAU, 18(5), 2001, pp. 499-511
In this investigation, the relationships between stretch and both morpholog
ical and electrophysiological signs of axonal injury were examined in the g
uinea pig optic nerve stretch model. Additionally, the relationship between
axonal morphology and electrophysiological impairment was assessed. Axonal
injury was produced in vivo by elongating the guinea pig optic nerve betwe
en 0 and 8 mm (N-total = 70). Morphological damage was detected using neuro
filament immunohistochemistry (SMI 32). Electrophysiological impairment was
determined using changes in visual evoked potentials (VEPs) measured prior
to injury, every 5 min for 40 min following injury, and at sacrifice (72 h
). All nerves subjected to ocular displacements greater than 6 mm demonstra
ted axonal swellings and retraction bulbs, while nerves subjected to displa
cements below 4 mm did not show any signs of morphological injury. Planned
comparisons of latency shifts of the N-35 peak in the VEPs showed that ocul
ar displacements greater than 5 mm produced electrophysiological impairment
that was significantly different from sham animals. Logit analysis demonst
rated that less stretch was required to elicit electrophysiological changes
(5.5 mm) than morphological signs of damage (6.8 mm). Moreover, Student t
tests indicated that the mean latency shift measured in animals exhibiting
morphological injury was significantly greater than that calculated from an
imals lacking morphological injury (p < 0.01). These data show that distinc
t mechanical thresholds exist for both morphological and electrophysiologic
al damage to the white matter. In a larger context, the distinct injury thr
esholds presented in the report will aid in the biomechanical assessment of
animate models of head injury, as well as assist in extending these findin
gs to predict the conditions that cause white matter injury in humans.