Light and electron microscopic assessment of progressive atrophy following moderate traumatic brain injury in the rat

Reduced fractional anisotropy does not change the shape of the hemodynamic response in survivors of severe traumatic brain injury

The hemodynamic response (HDR) function is the basis for standard functional magnetic resonance imaging (fMRI) analysis. HDR is influenced by white matter inflammation. Traumatic brain injury (TBI) is frequently accompanied by diffuse white matter injury, but the effect of this on the HDR has not been investigated. The aims of the present study were to describe the HDR in visual cortex and examine its relationship with the microstructure of the optic radiation in severe TBI survivors and controls. Ten severe TBI survivors without visual impairments, but with known diffuse axonal injury, and 9 matched controls underwent diffusion tensor imaging (DTI) and fMRI. From the fMRI time series obtained during brief randomized visual stimuli, blood oxygenation level-dependent (BOLD) signal changes for each subject were estimated in V1, and group HDR curves were produced. Standard between-group analysis of BOLD activation in V1 + V2 was performed. For each individual the optic radiations were identified and fractional anisotropy (FA) plus mean apparent diffusion coefficient (ADC(mean)) values for these tracts were calculated. Group HDR curves from the visual cortex were fully transposable between TBI survivors and controls, despite a significant reduction in FA in the optic radiation in TBI survivors. A significant correlation between BOLD signal in the visual cortex and FA values in the optical tract was present in controls, but not in TBI survivors. Between-group comparisons showed that TBI survivors had increased areas of activation in V1 and V2. The HDR appears to be intact in traumatic white matter damage, supporting the validity of using standard fMRI methodology to study neuroplasticity in TBI.

Association of chronic vascular changes with functional outcome after traumatic brain injury in rats

We tested the hypothesis that vascular remodeling in the cortex, hippocampus, and thalamus is associated with long-term functional recovery after traumatic brain injury (TBI). We induced TBI with lateral fluid-percussion (LFP) injury in adult rats. Animals were followed-up for 9 months, during which we tested motor performance using a neuroscore test, spatial learning and memory with a Morris water maze, and seizure susceptibility with a pentylenetetrazol (PTZ) test. At 8 months, they underwent structural MRI, and cerebral blood flow (CBF) was assessed by arterial spin labeling (ASL) MRI. Then, rats were perfused for histology to assess the density of blood vessels. In the perilesional cortex, the CBF decreased by 56% (p < 0.01 compared to controls), and vessel density increased by 28% (p < 0.01). There was a negative correlation between CBF in the perilesional cortex and vessel density (r = -0.75, p < 0.01). However, in the hippocampus, we found a 13% decrease in CBF ipsilaterally (p < 0.05) and 20% contralaterally (p < 0.01), and no change in vessel number. In the ipsilateral thalamus, the increase in CBF (34%, p < 0.01) was associated with a remarkable increase in vessel density (78%, p < 0.01). Animals showed motor impairment that was not associated with vascular changes. Instead, poor performance in the Morris water maze correlated with enhanced thalamic vessel density (r = -0.81, p < 0.01). Finally, enhanced seizure susceptibility was associated with reduced CBF in the ipsilateral hippocampus (r = 0.78, p < 0.05) and increased vascular density in the thalamus (r = 0.69, p < 0.05). There was little interaction between the behavioral measures. The present study demonstrates that each of the investigated brain areas has a unique pattern of vascular abnormalities. Chronic alterations in CBF could not be attributed to changes in vascular density. Association of thalamic hypervascularity to epileptogenesis warrants further studies. Finally, hippocampal hypoperfusion may predict later seizure susceptibility in the LFP injury model of TBI, which could be of value for pre-clinical antiepileptogenesis trials.

Traumatic brain injury causes long-term reduction in serum growth hormone and persistent astrocytosis in the cortico-hypothalamo-pituitary axis of adult male rats

In humans, traumatic brain injury (TBI) causes pathological changes in the hypothalamus (HT) and the pituitary. One consequence of TBI is hypopituitarism, with deficiency of single or multiple hormones of the anterior pituitary (AP), including growth hormone (GH). At present no animal model of TBI with ensuing hypopituitarism has been demonstrated. The main objective of this study was to investigate whether cortical contusion injury (CCI) could induce long-term reduction of serum GH in rats. We also tested the hypothesis that TBI to the medial frontal cortex (MFC) would induce inflammatory changes in the HT and AP.

METHODS

Nine young adult male rats were given sham surgery (n = 4) or controlled impact contusions (n = 5) of the MFC. Two months post-injury they were killed, trunk blood collected and their brains and AP harvested. GH was measured in serum and AP using ELISA and Western blot respectively. Interleukin-1beta (IL-1beta) and glial fibrillary acidic protein (GFAP) were measured in the cortex (Cx), HT, and AP by Western blot.

RESULTS

Lesion rats had significantly (p < 0.05) lower levels of GH in the AP and serum, unaltered serum IGF-1, and significantly (p < 0.05) higher levels of IL-1beta in the Cx and HT and GFAP in the Cx, HT, and AP compared to that of shams.

CONCLUSION

CCI leads to a long-term depletion of serum GH in male rats. This chronic change in GH post-TBI is probably the result of systemic and persistent inflammatory changes observed at the level of HT and AP, the mechanism of which is not yet known.

Traumatic brain injury causes long-term reduction in serum growth hormone and persistent astrocytosis in the cortico-hypothalamo-pituitary axis of adult male rats

In humans, traumatic brain injury (TBI) causes pathological changes in the hypothalamus (HT) and the pituitary. One consequence of TBI is hypopituitarism, with deficiency of single or multiple hormones of the anterior pituitary (AP), including growth hormone (GH). At present no animal model of TBI with ensuing hypopituitarism has been demonstrated. The main objective of this study was to investigate whether cortical contusion injury (CCI) could induce long-term reduction of serum GH in rats. We also tested the hypothesis that TBI to the medial frontal cortex (MFC) would induce inflammatory changes in the HT and AP.

METHODS

Nine young adult male rats were given sham surgery (n = 4) or controlled impact contusions (n = 5) of the MFC. Two months post-injury they were killed, trunk blood collected and their brains and AP harvested. GH was measured in serum and AP using ELISA and Western blot respectively. Interleukin-1beta (IL-1beta) and glial fibrillary acidic protein (GFAP) were measured in the cortex (Cx), HT, and AP by Western blot.

RESULTS

Lesion rats had significantly (p < 0.05) lower levels of GH in the AP and serum, unaltered serum IGF-1, and significantly (p < 0.05) higher levels of IL-1beta in the Cx and HT and GFAP in the Cx, HT, and AP compared to that of shams.

CONCLUSION

CCI leads to a long-term depletion of serum GH in male rats. This chronic change in GH post-TBI is probably the result of systemic and persistent inflammatory changes observed at the level of HT and AP, the mechanism of which is not yet known.

A highly toxic cellular prion protein induces a novel, nonapoptotic form of neuronal death

Several different deletions within the N-terminal tail of the prion protein (PrP) induce massive neuronal death when expressed in transgenic mice. This toxicity is dose-dependently suppressed by coexpression of full-length PrP, suggesting that it results from subversion of a normal physiological activity of cellular PrP. We performed a combined biochemical and morphological analysis of Tg(DeltaCR) mice, which express PrP carrying a 21-aa deletion (residues 105-125) within a highly conserved region of the protein. Death of cerebellar granule neurons in Tg(DeltaCR) mice is not accompanied by activation of either caspase-3 or caspase-8 or by increased levels of the autophagy marker, LC3-II. In electron micrographs, degenerating granule neurons displayed a unique morphology characterized by heterogeneous condensation of the nuclear matrix without formation of discrete chromatin masses typical of neuronal apoptosis. Our data demonstrate that perturbations in PrP functional activity induce a novel, nonapoptotic, nonautophagic form of neuronal death whose morphological features are reminiscent of those associated with excitotoxic stress.

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.

Neural correlates of motor dysfunction in children with traumatic brain injury: exploration of compensatory recruitment patterns

Traumatic brain injury (TBI) is a common form of disability in children. Persistent deficits in motor control have been documented following TBI but there has been less emphasis on changes in functional cerebral activity. In the present study, children with moderate to severe TBI (n = 9) and controls (n = 17) were scanned while performing cyclical movements with their dominant and non-dominant hand and foot according to the easy isodirectional (same direction) and more difficult non-isodirectional (opposite direction) mode. Even though the children with TBI were shown to be less successful on various items of a clinical motor test battery than the control group, performance on the coordination task during scanning was similar between groups, allowing a meaningful interpretation of their brain activation differences. fMRI analysis revealed that the TBI children showed enhanced activity in medial and anterior parietal areas as well as posterior cerebellum as compared with the control group. Brain activation generally increased during the non-isodirectional as compared with the isodirectional mode and additional regions were involved, consistent with their differential degree of difficulty. However, this effect did not interact with group. Overall, the findings indicate that motor impairment in TBI children is associated with changes in functional cerebral activity, i.e. they exhibit compensatory activation reflecting increased recruitment of neural resources for attentional deployment and somatosensory processing.

Magnetic resonance imaging evidence of progression of subacute brain atrophy in moderate to severe traumatic brain injury

OBJECTIVE

To demonstrate subacute progression of brain atrophy (from 4.5-29mo postinjury) in moderate to severe traumatic brain injury (TBI) using structural magnetic resonance imaging (MRI).

DESIGN

Within-subjects, repeated-measures design.

SETTING

Inpatient neurorehabilitation program and teaching hospital (MRI department).

PARTICIPANTS

Adults (N=14) with moderate to severe TBI.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Neuroradiologist readings and volumetric measurements (total brain cerebrospinal fluid and hippocampus) at 4.5 months and 2.5 years postinjury.

RESULTS

Ten of 14 patients showed visible atrophy progression. Significant increase in cerebrospinal fluid (CSF) volume (t(13)=-4.073, P<.001) and decrease in right and left hippocampal volumes (t(13)=4.221, P<.001 and t(13)=3.078, P<.005, respectively) were observed from 4.5 months to 2.5 years. Compared with published normative data, patients with TBI showed significantly more pathologic percent annual volume change for the hippocampi (t(26)=-3.864, P<.001, right; and t(26)=-2.737, P<.01, left), and a trend for CSF (t(26)=1.655, P=.059).

CONCLUSIONS

This study provides strong MRI evidence for subacute progression of atrophy, as distinct from early, acute neurologic changes observed.

Transient blockage of the CD11d/CD18 integrin reduces contusion volume and macrophage infiltration after traumatic brain injury in rats

The early inflammatory response to traumatic brain injury (TBI) may result in secondary damage. The purpose of this study was to evaluate the effects of a transient treatment employing a blocking monoclonal antibody (mAb) to the CD11d/CD18 integrin on histopathological outcome and macrophage infiltration following TBI. A parasagittal fluid percussion (FP) brain injury (1.8-2.1 atm) was induced in male Sprague-Dawley rats. Rats were randomized into two trauma groups, treated (N=7) and nontreated (N=8) animals. In the treated group, a mAb to the CD11d subunit of the CD11d/CD18 integrin was administered 30 min, 24 and 48 h after brain injury. Control animals received an isotype-matched irrelevant mAb using the same dose and treatment regimen. At 3 days after TBI, animals were perfusion-fixed for histopathological and immunocytochemical analysis. The anti-CD11d mAb treatment reduced contusion areas as well as overall contusion volume compared to vehicle treated animals. For example, overall contusion volume was reduced from 2.7+/-0.5 mm(3) (mean+/-SEM) to 1.4+/-0.4 with treatment (p<0.05). Immunocytochemical studies identifying CD68 immunoreactive macrophages showed that treatment caused significant attenuation of leukocyte infiltration into the contused cortical areas. These data emphasize the beneficial effects of blocking inflammatory cell recruitment into the injured brain on histopathological outcome following traumatic brain injury.

Neuroinflammatory responses after experimental diffuse traumatic brain injury

Little is known about microglial activation and macrophage localization after diffuse brain injury (DBI). DBI-mediated perisomatic traumatic axonal injury (TAI) was recently identified within the neocortex, hippocampus, and thalamus, providing an opportunity to characterize immune cell responses within diffusely injured brain loci uncomplicated by contusion. By using moderate midline/central fluid percussion injury, microglial/macrophage responses were examined with antibodies targeting immune cell phenotypes and amyloid precursor protein, a marker of TAI. Parallel assessments of blood-brain barrier alterations were also performed. Within 6 to 48 hours postinjury, microglial activation within injured loci was observed, whereas microglia within non-TAI-containing regions maintained a resting phenotype. Microglial activation shared a spatiotemporal relationship with TAI though no clear interactions were observed. By 7 to 28 days postinjury, activated microglia contained myelin debris, yet revealed limited aggregation. Immunophenotypic macrophages were also localized to injured loci. Select macrophages approximated somatic membranes of perisomatically axotomized neurons with evidence of bouton disruption. No causality was established between blood-brain barrier alterations and these inflammatory responses. These findings indicate rapid, yet initially nonspecific, and persistent microglial/macrophage responses to DBI. DBI-mediated inflammatory responses suggest further expansion of traumatic brain injury histopathologic evaluations to identify neuroinflammation indicative of diffuse pathology.

Multi-modal magnetic resonance imaging alterations in two rat models of mild neurotrauma

Magnetic resonance imaging (MRI) is increasingly used in the assessment of the severity and progression of neurotrauma. We evaluated temporal and regional changes after mild fluid percussion (FPI) and controlled cortical impact (CCI) injury using T2-weighted-imaging (T2WI) and diffusion-weighted imaging (DWI) MRI over 7 days. Region of interest analysis of brain areas distant to the injury site (such as the hippocampus, retrosplenial and piriform cortices, and the thalamus) was undertaken. In the hippocampus of CCI animals, we found a slow increase (51%) in apparent diffusion coefficients (ADC) over 72 h, which returned to control values. The hippocampal T2 values in the CCI animals were elevated by 18% over the 7-day time course compared to control, indicative of edema formation. Histological analysis supported the lack of overt cellular loss in most brain regions after mild CCI injury. FPI animals showed a generalized decrease in hippocampal ADC values over the first 72 h, which then returned to sham levels, with decreased T2 values over the same period, which remained depressed at 7 days. Histological assessment of FPI animals revealed numerous shrunken cells in the hippocampus and thalamus, but other regions showed little damage. Increased immunohistochemical staining for microglia and astroglia at 7 days post-injury was greater in FPI animals within the affected brain regions. In summary, traumatic brain injury is less severe in mild CCI than FPI, based on the temporal events assessed with MRI.

Perisomatic Thalamic Axotomy After Diffuse Traumatic Brain Injury Is Associated With Atrophy Rather Than Cell Death

Morbidity and mortality associated with traumatic brain injury (TBI) stem from diffuse axonal injury (DAI) throughout subcortical and brainstem white matter and subcortical nuclei. After midline fluid percussion brain injury, DAI in the thalamus includes perisomatic axotomy and resembles human post-traumatic pathology where the degree of morbidity correlates with thalamic damage. After axotomy, acute somatic perturbations resolve and appear compatible with cell survival; however, the long-term fate of neurons in an area with perisomatic axotomy is unknown. From brain-injured and uninjured rats at 1, 7 and 28 days after injury (injury, n = 5/group; sham, n = 4), alternate sections were immunostained for amyloid precursor protein (APP) to detect perisomatic axotomy or Giemsa stained for quantification of neuronal number, neuronal density, regional volume, and neuronal nuclear volume using design-based stereology. One day postinjury, APP-immunoreactive axons were identified consistently within the perisomatic domains of thalamic neurons of the ventral basal complex. Bilateral systematic-random quantification of the ventral basal complex indicated a significant reduction in neuronal density (number per mm, but not number alone) at 1 week after injury, compared with sham and 1 day postinjury. Furthermore, by 1 day and persisting through 1 week after injury, the mean neuronal nuclear volume was atrophied significantly compared with sham. Therefore, diffuse TBI results in early perisomatic axonal injury followed by neuronal atrophy in the ventral basal complex, without gross degeneration. Enduring atrophy in thalamic relays could underlie circuit disruption responsible for post-traumatic morbidity.

Progressive damage after brain and spinal cord injury: pathomechanisms and treatment strategies

The pathophysiology of brain and spinal cord injury (SCI) is complex and involves multiple injury mechanisms that are spatially and temporally specific. It is now appreciated that many of these injury mechanisms remain active days to weeks after a primary insult. Long-term survival studies in clinically relevant experimental studies have documented the structural changes that continue at the level of the insult as well as in remote brain structures. After traumatic brain injury (TBI), progressive atrophy of both gray and white matter structures continues up to 1 year post-trauma. Progressive changes may therefore underlie some of the long-term functional deficits observed in this patient population. After SCI, similar features of progressive injury are observed including delayed cell death of neurons and oligodendrocytes, axonal demyelination of intact fiber tracts and retrograde tract degeneration. SCI also leads to supraspinal changes in cell survival and remote brain circuitry. The progressive changes in multiple structures after brain and SCI are important because of their potential consequences on chronic or developing neurological deficits associated with these insults. In addition, the better understanding of these injury cascades may one day allow new treatments to be developed that can inhibit these responses to injury and hopefully promote recovery. This chapter summarizes some of the recent data regarding progressive damage after CNS trauma and mechanisms underlying these changes.