Wallerian degeneration in the optic nerve stretch-injury model of traumatic brain injury: a stereological analysis.

Patients with chronic traumatic encephalopathy (CTE) show loss of central white matter, central gray matter, and cortical gray matter with increasing post-traumatic survival. The majority of experimental studies using animals have, however, discussed only the ultrastructural pathophysiology of injured central white matter leading to secondary axotomy and the formation of axonal terminal bulbs. Using the stretch-injured optic nerve model in adult guinea pigs, the present study provides novel quantitative data concerning Wallerian degeneration of disconnected axonal fragments following secondary axotomy out to 12 weeks after injury to an optic nerve. The time course of Wallerian degeneration at the level of an individual nerve fiber is comparable to that reported in earlier studies over 48 h to two weeks after secondary axotomy. But only a relatively small proportion of nerve fibers within the optic tract degenerate via Wallerian degeneration during the first two weeks. Rather, examples of each of the three stages of Wallerian degeneration-acute axonal degeneration, latency of the distal axonal segment, and granular fragmentation-occur within the optic tract across the entire experimental survival of 12 weeks used in the present study. This data suggests that some nerve fibers initiate Wallerian degeneration days and weeks after the initial time of mechanical injury to an optic nerve. The number of intact nerve fibers continues to fall over at least three months after injury in the stretch-injury model of traumatic axonal injury. It is suggested that these novel findings relate to the mechanism(s) whereby central white matter volume decreases over months and years in CTE patients.

Damage to myelin and oligodendrocytes: a role in chronic outcomes following traumatic brain injury?

There is increasing evidence in the experimental and clinical traumatic brain injury (TBI) literature that loss of central myelinated nerve fibers continues over the chronic post-traumatic phase after injury. However, the biomechanism(s) of continued loss of axons is obscure. Stretch-injury to optic nerve fibers in adult guinea-pigs was used to test the hypothesis that damage to the myelin sheath and oligodendrocytes of the optic nerve fibers may contribute to, or facilitate, the continuance of axonal loss. Myelin dislocations occur within internodal myelin of larger axons within 1-2 h of TBI. The myelin dislocations contain elevated levels of free calcium. The volume of myelin dislocations increase with greater survival and are associated with disruption of the axonal cytoskeleton leading to secondary axotomy. Waves of Ca2+ depolarization or spreading depression extend from the initial locus injury for perhaps hundreds of microns after TBI. As astrocytes and oligodendrocytes are connected via gap junctions, it is hypothesized that spreading depression results in depolarization of central glia, disrupt axonal ionic homeostasis, injure axonal mitochondria and allow the onset of axonal degeneration throughout an increasing volume of brain tissue; and contribute toward post-traumatic continued loss of white matter.

Neuropathology of mild traumatic brain injury: relationship to neuroimaging findings.

Neuroimaging identified abnormalities associated with traumatic brain injury (TBI) are but gross indicators that reflect underlying trauma-induced neuropathology at the cellular level. This review examines how cellular pathology relates to neuroimaging findings with the objective of more closely relating how neuroimaging findings reveal underlying neuropathology. Throughout this review an attempt will be made to relate what is directly known from post-mortem microscopic and gross anatomical studies of TBI of all severity levels to the types of lesions and abnormalities observed in contemporary neuroimaging of TBI, with an emphasis on mild traumatic brain injury (mTBI). However, it is impossible to discuss the neuropathology of mTBI without discussing what occurs with more severe injury and viewing pathological changes on some continuum from the mildest to the most severe. Historical milestones in understanding the neuropathology of mTBI are reviewed along with implications for future directions in the examination of neuroimaging and neuropathological correlates of TBI.

Traumatic brain injury in the neonate, child and adolescent human: an overview of pathology.

In the middle of the last century it had been thought that a good recovery of function and behavior would occur after traumatic brain injury (TBI) in very young human beings. A recent major change in thinking states that early childhood TBI may result in a severe compromise of normal brain growth and development such that TBI, rather, may compromise later normal development resulting in a need for very long term patient care and management. The mechanisms of injury and pathology within the injured brain are reviewed and compared between when injury occurs at or close to the time of birth, in an infant, in a young child, in a child between ages 5 and 10, in young and older adolescents and in young adulthood. Our understanding of pathophysiological responses by cells of the human central nervous system has recently greatly increased but has really only served to illustrate the great complexity of interactions between different types of cell within the growing and developing CNS. The hypothesis is developed that the outcome for a very young patient differs with the relative state of development of injured cells at the locus of injury. And that the potential for either repair, re-instatement of normal cellular and organ function or for continued normal development is much reduced after an early brain insult (EBI) compared with TBI in a slightly older child or young adult patient. The advent of increasingly sophisticated non-invasive imaging technology has allowed assessment of the influence and time course of brain pathology both early and late after TBI. This has generated greater confidence on the part of clinicians in forecasting outcomes for an injured patient. But our increased understanding has still not allowed development of therapeutic strategies that might ameliorate the effect of an injury. It is suggested that an improved integration of major clinical and scientific effort needs to be made to appreciate the import of multiple interactions between cells forming the neurovascular unit in order to improve any potential for post-traumatic recovery after TBI in neonates and young children.

Neuroimaging and neuropathology of TBI.

Neuroimaging at all stages of a traumatic brain injury (TBI) provides information about gross brain pathology. In this review, post-mortem TBI cases are matched to neuroimaging findings from TBI survivors to demonstrate the close correlation between observable pathology with in vivo neuroimaging to the underlying neuropathology. An emphasis of this review focuses on neuroimaging identification of trauma induced cortical and white matter degeneration along with hydrocephalus ex vacuo expansion of the ventricular system as the injured brain exhibits atrophic changes. The role of hippocampal atrophy and thalamic injury along with the vulnerability of the corpus callosum in TBI are also reviewed. The aim of this review is to provide pathological confirmation of observable neuroimaging abnormalities that relate directly to trauma-induced effects of the injury.

Stereology and ultrastructure of chronic phase axonal and cell soma pathology in stretch-injured central nerve fibers.

Magnetic resonance imaging (MRI) suggests that with survival after human traumatic brain injury (TBI), there is ongoing loss of white and grey matter from the injured brain during the chronic phase. However; direct quantitative experimental evidence in support of this observation is lacking. Using the guinea pig stretch-injury optic nerve model, quantitative evidence by stereology of damage to the optic nerve and retina was sought. Stretch injury was applied to the right optic nerve of 15 adult male guinea pigs. Three animals each at 1, 2, 3, 8, or 12 weeks' survival were killed and prepared for transmission electron microscopy (TEM). The estimated number of intact and injured axons within bins of transverse diameters 0-0.5, 0.51-1.0, 1.01-1.5, 1.51-2.0, 2.01-2.5, and 2.51-3.0 µm in the middle segment of each injured optic nerve and from 5 control animals were compared across all survival time points. The estimated numbers of intact and pyknotic retinal ganglion cells from the same animals were also compared. Loss of myelinated fibers continued throughout the experimental period. The most rapid loss was of the largest fibers; loss of intermediate-sized fibers continued, but the numbers of the smallest fibers increased from 3 weeks onward. There was hypertrophy and proliferation of glial cells within the surrounding neuropil. A relatively low-grade loss of retinal ganglion cells occurred throughout the experiment, with about 60% remaining at 12 weeks' survival. We provide quantitative evidence that after traumatic axonal injury (TAI) there is a continuing loss of nerve fibers and their cell bodies from a CNS tract over a 3-month post-traumatic interval.

Stereology of cerebral cortex after traumatic brain injury matched to the Glasgow outcome score.

Magnetic resonance imaging provides evidence for loss of both white and grey matter, in terms of tissue volume, from the cerebral hemispheres after traumatic brain injury. However, quantitative histopathological data are lacking. From the archive of the Department of Neuropathology at Glasgow, the cerebral cortex of 48 patients was investigated using stereology. Patients had survived 3 months after traumatic brain injury and were classified using the Glasgow Outcome Scale as follows: moderately disabled (n = 13), severely disabled (n = 12) and vegetative state (n = 12); and controls. Some patients from the archive were diagnosed with diffuse axonal injury post-mortem. Comparisons of changes in cortical neuron population across Glasgow Outcome Scale groups between diffuse axonal injury and non-diffuse axonal injury patients were undertaken using effect size analyses. The hypotheses tested were that (i) thinning of the cerebral cortex occurred after traumatic brain injury; (ii) changes in thickness of cortical layers in Brodmann areas 11, 10, 24a and 4 differed; and (iii) different changes occurred for neuronal number, their size and nearest neighbour index across Glasgow Outcome Scale groups. There was a greater loss of large pyramidal and large non-pyramidal neurons with a more severe score on the Glasgow Outcome Scale from all four cortical regions, with the greatest loss of neurons from the prefrontal cortex of patients with diffuse axonal injury. There were differences in the changes of number of medium and small pyramidal and non-pyramidal neurons between different cortical regions, and between patients with and without diffuse axonal injury. Generally, a decrease in the somatic diameter of pyramidal and non-pyramidal neurons was associated with a more severe clinical outcome. However, in the motor cortex a more severe Glasgow Outcome Scale was associated with an increased diameter of medium pyramidal neurons and small non-pyramidal cells. Pyramidal and non-pyramidal neurons did not follow a Poisson distribution within the neuropil of control patients. Pyramidal neurons were usually scattered while medium and small non-pyramidal neurons were clustered. An increased spacing between remaining neurons usually occurred across Glasgow Outcome Scale groups. It is concluded that loss of neurons resulted in reduced executive and integrative capability in patients after traumatic head injury.

Minor traumatic brain injury in sports: a review in order to prevent neurological sequelae.

Minor traumatic brain injury (mTBI) is caused by inertial effects, which induce sudden rotation and acceleration forces to and within the brain. At less severe levels of injury, for example in mTBI, there is probably only transient disturbance of ionic homeostasis with short-term, temporary disturbance of brain function. With increased levels of severity, however, studies in animal models of TBI and in humans have demonstrated focal intra-axonal alterations within the subaxolemmal, neurofilament and microtubular cytoskeletal network together with impairment of axoplasmic transport. These changes have, until very recently, been thought to lead to progressive axonal swelling, axonal detachment or even cell death over a period of hours or days, the so-called process of "secondary axotomy". However, recent evidence has suggested that there may be two discrete pathologies that may develop in injured nerve fibers. In the TBI scenario, disturbances of ionic homeostasis, acute metabolic changes and alterations in cerebral blood flow compromise the ability of neurons to function and render cells of the brain increasingly vulnerable to the development of pathology. In ice hockey, current return-to-play guidelines do not take into account these new findings appropriately, for example allow returning to play in the same game. It has recently been hypothesized that the processes summarized above may predispose brain cells to assume a vulnerable state for an unknown period after mild injury (mTBI). Therefore, we recommend that any confused player with or without amnesia should be taken off the ice and not be permitted to play again for at least 72h.

Thalamic nuclei after human blunt head injury.

Paraffin-embedded blocks from the thalamus of 9 control patients, 9 moderately disabled, 12 severely disabled, and 10 vegetative head-injured patients assessed using the Glasgow Outcome Scale and identified from the Department of Neuropathology archive. Neurons, astrocytes, macrophages, and activated microglia were differentiated by Luxol fast blue/cresyl violet, GFAP, CD68, and CR3/43 staining and stereological techniques used to estimate cell number in a 28-microm-thick coronal section. Counts were made in subnuclei of the mediodorsal, lateral posterior, and ventral posterior nuclei, the intralaminar nuclei, and the related internal lamina. Neuronal loss occurred from mediodorsal parvocellularis, rostral center medial, central lateral and paracentral nuclei in moderately disabled patients; and from mediodorsal magnocellularis, caudal center medial, rhomboid, and parafascicular nuclei in severely disabled patients; and all of the above and the centre median nucleus in vegetative patients. Neuronal loss occurred primarily from cognitive and executive function nuclei, a lesser loss from somatosensory nuclei and the least loss from limbic motor nuclei. There was an increase in the number of reactive astrocytes, activated microglia, and macrophages with increasing severity of injury. The study provides novel quantitative evidence for differential neuronal loss, with survival after human head injury, from thalamic nuclei associated with different aspects of cortical activation.

Slow, medium, or fast re-warming following post-traumatic hypothermia therapy? An ultrastructural perspective.

It was hypothesized that rapid rather than slow re-warming following traumatic brain injury (TBI) and short-term hypothermia results in secondary, ultrastructural pathology. After stretch injury to the right optic nerve, adult guinea pigs were randomly allocated to one of six experimental groups. Either (1) sham (all procedures but not stretch-injured; n = 4); injured and (2) maintained at normal temporalis core temperature (38.5 degrees C) for 8 hours (n = 6); (3) cooled rapidly to 32.5 degrees C (temporalis temperature), maintained for 4 h and re-warmed to 38.5 degrees C at 1 degrees C rise every 10 min (fast; n = 6); (4) cooled and re-warmed at 1 degrees C rise every 20 min (medium; n = 6); (5) cooled and rewarmed at 1 degrees C rise every 40 min (slow; n = 6) before being killed 8 h after injury; and (6) uninjured animals (n = 6) cooled to 32.5 degrees C for 4 h and then re-warmed at 1 degrees C every 10 min before killing 4 h later. Tissue was processed for light immunocytochemistry (beta-APP and RMO-14) and ultrastructural stereology. In both uninjured and injured fast re-warmed animals, there was almost total loss of axonal microtubules (MT) and an increased number of neurofilaments (NF) within the axoplasm. In the former, there was also compaction of NF. The number of MT was reduced to 40% of control values, NFs were increased but were not compacted after medium rate re-warming. Following slow re-warming the axonal cytoskeleton did not differ from that in control animals. It is concluded that re-warming faster than 1 degrees C every 40 min following mild post-traumatic hypothermia induces secondary axonal pathology.

Differential responses in three thalamic nuclei in moderately disabled, severely disabled and vegetative patients after blunt head injury.

In vivo imaging techniques have indicated for many years that there is loss of white matter after human traumatic brain injury (TBI) and that the loss is inversely related to cognitive outcome. However, correlated, quantitative evidence for loss of neurons from either the cerebral cortex or the diencephalon is largely lacking. There is some evidence in models of TBI that neuronal loss occurs within the thalamus, but no systematic studies of such loss have been undertaken in the thalamus of humans after blunt head injury. We have undertaken a stereological analysis of changes in numbers of neurons within the dorsomedial, ventral posterior and lateral posterior thalamic nuclei in patients assessed by the Glasgow Outcome Scale as moderately disabled (n = 9), severely disabled (n = 12) and vegetative (n = 10) head-injured patients who survived between 6 h and 3 years, and controls (n = 9). In histological sections at the level of the lateral geniculate body, the cross-sectional area of each nucleus and the number and the mean size of neurons within each nucleus was quantified. A statistically significant loss of cross-sectional area and number of neurons occurred in the dorsomedial nucleus in moderately disabled, and both the dorsomedial and ventral posterior thalamic nuclei in severely disabled and vegetative head-injured patients. However, there was no change in neuronal cell size. In the lateral posterior nucleus, despite a reduction in mean cell size, there was not a significant change in either nuclear area or number of neurons in cases of moderately disabled, severely disabled or vegetative patients. We posit, although detailed neuropsychological outcome for the patients included within this study was not available, that neuronal loss in the dorsomedial thalamus in moderately and severely disabled and vegetative patients may be the structural basis for the clinical assessment in the Glasgow Outcome Scale. In severely disabled and vegetative patients, loss of neurons from the ventral posterior thalamic nucleus may also reflect loss of response to afferent stimuli.

Post-acute alterations in the axonal cytoskeleton after traumatic axonal injury.

All previous analyses of axonal responses to traumatic axonal injury (TAI) have described the ultrastructure of changes in the cytoskeleton and axolemma within 6 h of injury. In the present study we tested the hypothesis that there are, in addition, ultrastructural pathological changes up to 1 week after injury. TAI was induced in the adult guinea pig optic nerve of nine animals. Three animals were killed at either 4 h, 24 h, or 7 days (d) after injury. Quantitative analysis of the number or proportion of axons within 0.5-micro m-wide bins showed an increase in the number of axons with a diameter of less than 0.5 micro m at 4 h, 24 h, and 7 d, the presence of lucent axons at 24 h and 7 d and that the highest number of injured axons occurred about half way along the length of the nerve. A spectrum of pathological changes occurred in injured fibers-pathology of mitochondria; dissociation of myelin lamellae but little damage to the axon; loss of linear register of the axonal cytoskeleton; differential responses between microtubules (MT) and neurofilaments (NF) in different sizes of axon; two different sites of compaction of NF; loss of both NF (with an increase in their spacing) and MT (with a reduction in their spacing); replacement of the axoplasm by a flocculent precipitate; and an increased length of the nodal gap. These provide the first ultrastructural evidence for Wallerian degeneration of nerve fibers in an animal model of TAI.