Histopathologic consequences of moderate concussion in an animal model: correlations with duration of unconsciousness

Loss of Consciousness and Righting Reflex Following Traumatic Brain Injury: Predictors of Post-Injury Symptom Development (A Narrative Review)

Identifying predictors for individuals vulnerable to the adverse effects of traumatic brain injury (TBI) remains an ongoing research pursuit. This is especially important for patients with mild TBI (mTBI), whose condition is often overlooked. TBI severity in humans is determined by several criteria, including the duration of loss of consciousness (LOC): LOC < 30 min for mTBI and LOC > 30 min for moderate-to-severe TBI. However, in experimental TBI models, there is no standard guideline for assessing the severity of TBI. One commonly used metric is the loss of righting reflex (LRR), a rodent analogue of LOC. However, LRR is highly variable across studies and rodents, making strict numeric cutoffs difficult to define. Instead, LRR may best be used as predictor of symptom development and severity. This review summarizes the current knowledge on the associations between LOC and outcomes after mTBI in humans and between LRR and outcomes after experimental TBI in rodents. In clinical literature, LOC following mTBI is associated with various adverse outcome measures, such as cognitive and memory deficits; psychiatric disorders; physical symptoms; and brain abnormalities associated with the aforementioned impairments. In preclinical studies, longer LRR following TBI is associated with greater motor and sensorimotor impairments; cognitive and memory impairments; peripheral and neuropathology; and physiologic abnormalities. Because of the similarities in associations, LRR in experimental TBI models may serve as a useful proxy for LOC to contribute to the ongoing development of evidence-based personalized treatment strategies for patients sustaining head trauma. Analysis of highly symptomatic rodents may shed light on the biological underpinnings of symptom development after rodent TBI, which may translate to therapeutic targets for mTBI in humans.

Acute axon damage and demyelination are mitigated by 4-aminopyridine (4-AP) therapy after experimental traumatic brain injury

Damage to long axons in white matter tracts is a major pathology in closed head traumatic brain injury (TBI). Acute TBI treatments are needed that protect against axon damage and promote recovery of axon function to prevent long term symptoms and neurodegeneration. Our prior characterization of axon damage and demyelination after TBI led us to examine repurposing of 4-aminopyridine (4-AP), an FDA-approved inhibitor of voltage-gated potassium (Kv) channels. 4-AP is currently indicated to provide symptomatic relief for patients with chronic stage multiple sclerosis, which involves axon damage and demyelination. We tested clinically relevant dosage of 4-AP as an acute treatment for experimental TBI and found multiple benefits in corpus callosum axons. This randomized, controlled pre-clinical study focused on the first week after TBI, when axons are particularly vulnerable. 4-AP treatment initiated one day post-injury dramatically reduced axon damage detected by intra-axonal fluorescence accumulations in Thy1-YFP mice of both sexes. Detailed electron microscopy in C57BL/6 mice showed that 4-AP reduced pathological features of mitochondrial swelling, cytoskeletal disruption, and demyelination at 7 days post-injury. Furthermore, 4-AP improved the molecular organization of axon nodal regions by restoring disrupted paranode domains and reducing Kv1.2 channel dispersion. 4-AP treatment did not resolve deficits in action potential conduction across the corpus callosum, based on ex vivo electrophysiological recordings at 7 days post-TBI. Thus, this first study of 4-AP effects on axon damage in the acute period demonstrates a significant decrease in multiple pathological hallmarks of axon damage after experimental TBI.

Spatial Distribution of Neuropathology and Neuroinflammation Elucidate the Biomechanics of Fluid Percussion Injury

Diffuse brain injury is better described as multi-focal, where pathology can be found adjacent to seemingly uninjured neural tissue. In experimental diffuse brain injury, pathology and pathophysiology have been reported far more lateral than predicted by the impact site. We hypothesized that local thickening of the rodent skull at the temporal ridges serves to focus the intracranial mechanical forces experienced during brain injury and generate predictable pathology. We demonstrated local thickening of the skull at the temporal ridges using contour analysis on magnetic resonance imaging. After diffuse brain injury induced by midline fluid percussion injury (mFPI), pathological foci along the anterior-posterior length of cortex under the temporal ridges were evident acutely (1, 2, and 7 days) and chronically (28 days) post-injury by deposition of argyophilic reaction product. Area CA3 of the hippocampus and lateral nuclei of the thalamus showed pathological change, suggesting that mechanical forces to or from the temporal ridges shear subcortical regions. A proposed model of mFPI biomechanics suggests that injury force vectors reflect off the skull base and radiate toward the temporal ridge, thereby injuring ventral thalamus, dorsolateral hippocampus, and sensorimotor cortex. Surgically thinning the temporal ridge before injury reduced injury-induced inflammation in the sensorimotor cortex. These data build evidence for temporal ridges of the rodent skull to contribute to the observed pathology, whether by focusing extracranial forces to enter the cranium or intracranial forces to escape the cranium. Pre-clinical investigations can take advantage of the predicted pathology to explore injury mechanisms and treatment efficacy.

Behavioral responses following repeated bilateral frontal region closed head impacts and fear conditioning in male and female mice

The frontal lobes are among the most vulnerable sites in traumatic brain injuries. In the current study, a balanced 2 × 2 × 2 design (n = 18 mice/group), female and male C57Bl/6J mice received repeated bilateral frontal concussive brain injury (frCBI) and underwent fear conditioning (FC) to assess how injured mice respond to adverse conditions. Shocks received during FC impacted behavior on all subsequent tests except the tail suspension test. FC resulted in more freezing behavior in all mice that received foot shocks when evaluated in subsequent context and cue tests and induced hypoactivity in the open field (OF) and elevated zero maze (EZM). Mice that sustained frCBI learned the FC association between tone and shock. Injured mice froze less than sham controls during context and cue tests, which could indicate memory impairment, but could also suggest that frCBI resulted in hyperactivity that overrode the rodent's natural freezing response to threat, as injured mice were also more active in the OF and EZM. There were notable sex differences, where female mice exhibited more freezing behavior than male mice during FC context and cue tests. The findings suggest frCBI impaired, but did not eliminate, FC retention and resulted in an overall increase in general activity. The injury was characterized pathologically by increased inflammation (CD11b staining) in cortical regions underlying the injury site and in the optic tracts. The performance of male and female mice after injury suggested the complexity of possible sex differences for neuropsychiatric symptoms.

Traumatic Brain Injury Temporal Proteome Guides KCC2-Targeted Therapy

Advancing therapeutics for traumatic brain injury (TBI) remains a challenge, necessitating testable targets with interventions appropriately timed to intercede on evolving secondary insults. Neuroproteomics provides a global molecular approach to deduce the complex post-translational processes that underlie secondary events after TBI. Yet method advancement has outpaced approaches to interrogate neuroproteomic complexity, in particular when addressing the well-recognized temporal evolution of TBI pathobiology. Presented is a detailed account of the temporal neuroproteomic response to mild-moderate rat controlled cortical impact within perilesioned somatosensory neocortex across the first two weeks after injury. Further, this investigation assessed use of artificial neural network and functional enrichment analyses to discretize the temporal response across some 2047 significantly impacted proteins. Results were efficiently narrowed onto ion transporters with phenotypic relevance to abnormal GABAergic transmission and a delayed decline amenable to intervention under managed care conditions. The prototypical target potassium/chloride co-transporter 2 (KCC2 or SLC12A5) was investigated further with the KCC2-selective modulator CLP290. Guided by post-translational processing revealed one-day after insult to precede KCC2 protein loss a day after, CLP290 was highly effective at restoring up to 70% of lost KCC2 localization, which was significantly correlated with recovery of sham-level function in assessed somatosensory behavioral tasks. The timing of administration was important, with no significant improvement observed if given earlier, one-hour after insult, or later when KCC2 protein decline begins. Results portend importance for a detailed post-translational characterization when devising TBI treatments, and support the therapeutic promise of KCC2-targeted CLP290 intervention for positive functional recovery after brain injury.

A Systematic Review of Closed Head Injury Models of Mild Traumatic Brain Injury in Mice and Rats

Mild TBI (mTBI) is a significant health concern. Animal models of mTBI are essential for understanding mechanisms, and pathological outcomes, as well as to test therapeutic interventions. A variety of closed head models of mTBI that incorporate different aspects (i.e., biomechanics) of the mTBI have been reported. The aim of the current review was to compile a comprehensive list of the closed head mTBI rodent models, along with the common data elements, and outcomes, with the goal to summarize the current state of the field. Publications were identified from a search of PubMed and Web of Science and screened for eligibility following PRISMA guidelines. Articles were included that were closed head injuries in which the authors classified the injury as mild in rats or mice. Injury model and animal-specific common data elements, as well as behavioral and histological outcomes, were collected and compiled from a total of 402 articles. Our results outline the wide variety of methods used to model mTBI. We also discovered that female rodents and both young and aged animals are under-represented in experimental mTBI studies. Our findings will aid in providing context comparing the injury models and provide a starting point for the selection of the most appropriate model of mTBI to address a specific hypothesis. We believe this review will be a useful starting place for determining what has been done and what knowledge is missing in the field to reduce the burden of mTBI.

Repetitive Diffuse Mild Traumatic Brain Injury Causes an Atypical Astrocyte Response and Spontaneous Recurrent Seizures

Focal traumatic brain injury (TBI) induces astrogliosis, a process essential to protecting uninjured brain areas from secondary damage. However, astrogliosis can cause loss of astrocyte homeostatic functions and possibly contributes to comorbidities such as posttraumatic epilepsy (PTE). Scar-forming astrocytes seal focal injuries off from healthy brain tissue. It is these glial scars that are associated with epilepsy originating in the cerebral cortex and hippocampus. However, the vast majority of human TBIs also present with diffuse brain injury caused by acceleration-deceleration forces leading to tissue shearing. The resulting diffuse tissue damage may be intrinsically different from focal lesions that would trigger glial scar formation. Here, we used mice of both sexes in a model of repetitive mild/concussive closed-head TBI, which only induced diffuse injury, to test the hypothesis that astrocytes respond uniquely to diffuse TBI and that diffuse TBI is sufficient to cause PTE. Astrocytes did not form scars and classic astrogliosis characterized by upregulation of glial fibrillary acidic protein was limited. Surprisingly, an unrelated population of atypical reactive astrocytes was characterized by the lack of glial fibrillary acidic protein expression, rapid and sustained downregulation of homeostatic proteins and impaired astrocyte coupling. After a latency period, a subset of mice developed spontaneous recurrent seizures reminiscent of PTE in human TBI patients. Seizing mice had larger areas of atypical astrocytes compared with nonseizing mice, suggesting that these atypical astrocytes might contribute to epileptogenesis after diffuse TBI.SIGNIFICANCE STATEMENT Traumatic brain injury (TBI) is a leading cause of acquired epilepsies. Reactive astrocytes have long been associated with seizures and epilepsy in patients, particularly after focal/lesional brain injury. However, most TBIs also include nonfocal, diffuse injuries. Here, we showed that repetitive diffuse TBI is sufficient for the development of spontaneous recurrent seizures in a subset of mice. We identified an atypical response of astrocytes induced by diffuse TBI characterized by the rapid loss of homeostatic proteins and lack of astrocyte coupling while reactive astrocyte markers or glial scar formation was absent. Areas with atypical astrocytes were larger in animals that later developed seizures suggesting that this response may be one root cause of epileptogenesis after diffuse TBI.

Cerebral Concussion Primes the Lungs for Subsequent Neutrophil-Mediated Injury

OBJECTIVES

Mild traumatic brain injury in the form of concussion is extremely common, and the potential effects on pulmonary priming have been underestimated. The aim of this study was to characterize the pulmonary response following mild traumatic brain injury and assess the pulmonary susceptibility to lung injury after a subsequent innocuous pulmonary insult.

DESIGN

Experimental in vivo study.

SETTING

University research laboratory.

SUBJECTS

Male CD1 mice.

INTERVENTIONS

We developed a model of concussive traumatic brain injury in mice followed by pulmonary acid microaspiration. To assess the dependent role of neutrophils in mediating pulmonary injury, we specifically depleted neutrophils.

MEASUREMENTS AND MAIN RESULTS

Lateral fluid percussion to the brain resulted in neuronal damage and neutrophil infiltration as well as extensive pulmonary interstitial neutrophil accumulation but no alveolar injury. Following subsequent innocuous acid microaspiration, augmented alveolar neutrophil influx led to the development of pulmonary hemorrhage that was reduced following neutrophil depletion.

CONCLUSIONS

This model shows for the first time that innocuous acid microaspiration is sufficient to induce neutrophil-mediated lung injury following mild concussion and that the extracranial effects of mild traumatic brain injury have been underestimated.

Mild Traumatic Brain Injury Induces Structural and Functional Disconnection of Local Neocortical Inhibitory Networks via Parvalbumin Interneuron Diffuse Axonal Injury

Diffuse axonal injury (DAI) plays a major role in cortical network dysfunction posited to cause excitatory/inhibitory imbalance after mild traumatic brain injury (mTBI). Current thought holds that white matter (WM) is uniquely vulnerable to DAI. However, clinically diagnosed mTBI is not always associated with WM DAI. This suggests an undetected neocortical pathophysiology, implicating GABAergic interneurons. To evaluate this possibility, we used mild central fluid percussion injury to generate DAI in mice with Cre-driven tdTomato labeling of parvalbumin (PV) interneurons. We followed tdTomato+ profiles using confocal and electron microscopy, together with patch-clamp analysis to probe for DAI-mediated neocortical GABAergic interneuron disruption. Within 3 h post-mTBI tdTomato+ perisomatic axonal injury (PSAI) was found across somatosensory layers 2-6. The DAI marker amyloid precursor protein colocalized with GAD67 immunoreactivity within tdTomato+ PSAI, representing the majority of GABAergic interneuron DAI. At 24 h post-mTBI, we used phospho-c-Jun, a surrogate DAI marker, for retrograde assessments of sustaining somas. Via this approach, we estimated DAI occurs in ~9% of total tdTomato+ interneurons, representing ~14% of pan-neuronal DAI. Patch-clamp recordings of tdTomato+ interneurons revealed decreased inhibitory transmission. Overall, these data show that PV interneuron DAI is a consistent and significant feature of experimental mTBI with important implications for cortical network dysfunction.

Dietary therapy restores glutamatergic input to orexin/hypocretin neurons after traumatic brain injury in mice

Study Objectives

In previous work, dietary branched-chain amino acid (BCAA) supplementation, precursors to de novo glutamate and γ-aminobutyric acid (GABA) synthesis, restored impaired sleep-wake regulation and orexin neuronal activity following traumatic brain injury (TBI) in mice. TBI was speculated to reduce orexin neuronal activity through decreased regional excitatory (glutamate) and/or increased inhibitory (GABA) input. Therefore, we hypothesized that TBI would decrease synaptic glutamate and/or increase synaptic GABA in nerve terminals contacting orexin neurons, and BCAA supplementation would restore TBI-induced changes in synaptic glutamate and/or GABA.

Methods

Brain tissue was processed for orexin pre-embed diaminobenzidine labeling and glutamate or GABA postembed immunogold labeling. The density of glutamate and GABA immunogold within presynaptic nerve terminals contacting orexin-positive lateral hypothalamic neurons was quantified using electron microscopy in three groups of mice (n = 8 per group): Sham/noninjured controls, TBI without BCAA supplementation, and TBI with BCAA supplementation (given for 5 days, 48 hr post-TBI). Glutamate and GABA were also quantified within the cortical penumbral region (layer VIb) adjacent to the TBI lesion.

Results

In the hypothalamus and cortex, TBI decreased relative glutamate density in presynaptic terminals making axodendritic contacts. However, BCAA supplementation only restored relative glutamate density within presynaptic terminals contacting orexin-positive hypothalamic neurons. BCAA supplementation did not change relative glutamate density in presynaptic terminals making axosomatic contacts, or relative GABA density in presynaptic terminals making axosomatic or axodendritic contacts, within either the hypothalamus or cortex.

Conclusions

These results suggest TBI compromises orexin neuron function via decreased glutamate density and highlight BCAA supplementation as a potential therapy to restore glutamate density to orexin neurons.

Concussion

Concussion has been recognized as a clinical entity for more than 1000 years. Throughout the 20th century it was studied extensively in boxers, but it did not pique the interest of the general population because it is the accepted goal of the boxer to inflict such an injury on their opponent. In 2002, however, the possibility that repetitive concussions could result in chronic brain damage and a progressive neurologic disorder was raised by a postmortem evaluation of a retired player in the most popular sports institution in the United States, the National Football League. Since that time concussion has been a frequent topic of conversation in homes, schools, and on television and has become a major focus of sports programs in communities and schools at all levels. Now all 50 states, the District of Columbia, and the National Collegiate Athletic Association have enacted laws and rules to protect the athlete.

Mild Traumatic Brain Injury Evokes Pyramidal Neuron Axon Initial Segment Plasticity and Diffuse Presynaptic Inhibitory Terminal Loss

The axon initial segment (AIS) is the site of action potential (AP) initiation, thus a crucial regulator of neuronal activity. In excitatory pyramidal neurons, the high density of voltage-gated sodium channels (NaV1.6) at the distal AIS regulates AP initiation. A surrogate AIS marker, ankyrin-G (ankG) is a structural protein regulating neuronal functional via clustering voltage-gated ion channels. In neuronal circuits, changes in presynaptic input can alter postsynaptic output via AIS structural-functional plasticity. Recently, we showed experimental mild traumatic brain injury (mTBI) evokes neocortical circuit disruption via diffuse axonal injury (DAI) of excitatory and inhibitory neuronal systems. A key finding was that mTBI-induced neocortical electrophysiological changes involved non-DAI/ intact excitatory pyramidal neurons consistent with AIS-specific alterations. In the current study we employed Thy1-yellow fluorescent protein (YFP)-H mice to test if mTBI induces AIS structural and/or functional plasticity within intact pyramidal neurons 2 days after mTBI. We used confocal microscopy to assess intact YFP+ pyramidal neurons in layer 5 of primary somatosensory barrel field (S1BF), whose axons were continuous from the soma of origin to the subcortical white matter (SCWM). YFP+ axonal traces were superimposed on ankG and NaV1.6 immunofluorescent profiles to determine AIS position and length. We found that while mTBI had no effect on ankG start position, the length significantly decreased from the distal end, consistent with the site of AP initiation at the AIS. However, NaV1.6 structure did not change after mTBI, suggesting uncoupling from ankG. Parallel quantitative analysis of presynaptic inhibitory terminals along the postsynaptic perisomatic domain of these same intact YFP+ excitatory pyramidal neurons revealed a significant decrease in GABAergic bouton density. Also within this non-DAI population, patch-clamp recordings of intact YFP+ pyramidal neurons showed AP acceleration decreased 2 days post-mTBI, consistent with AIS functional plasticity. Simulations of realistic pyramidal neuron computational models using experimentally determined AIS lengths showed a subtle decrease is NaV1.6 density is sufficient to attenuate AP acceleration. Collectively, these findings highlight the complexity of mTBI-induced neocortical circuit disruption, involving changes in extrinsic/presynaptic inhibitory perisomatic input interfaced with intrinsic/postsynaptic intact excitatory neuron AIS output.

Validation of Acoustic Wave Induced Traumatic Brain Injury in Rats

BACKGROUND

This study looked to validate the acoustic wave technology of the Storz-D-Actor that inflicted a consistent closed-head, traumatic brain injury (TBI) in rats. We studied a range of single pulse pressures administered to the rats and observed the resulting decline in motor skills and memory. Histology was observed to measure and confirm the injury insult.

METHODS

Four different acoustic wave pressures were studied using a single pulse: 0, 3.4, 4.2 and 5.0 bar (n = 10 rats per treatment group). The pulse was administered to the left frontal cortex. Rotarod tests were used to monitor the rats' motor skills while the water maze test was used to monitor memory deficits. The rats were then sacrificed ten days post-treatment for histological analysis of TBI infarct size.

RESULTS

The behavioral tests showed that acoustic wave technology administered an effective insult causing significant decreases in motor abilities and memory. Histology showed dose-dependent damage to the cortex infarct areas only.

CONCLUSIONS

This study illustrates that the Storz D-Actor effectively induces a repeatable TBI infarct, avoiding the invasive procedure of a craniotomy often used in TBI research.

Sleep-Wake Disturbances After Traumatic Brain Injury: Synthesis of Human and Animal Studies

Sleep-wake disturbances following traumatic brain injury (TBI) are increasingly recognized as a serious consequence following injury and as a barrier to recovery. Injury-induced sleep-wake disturbances can persist for years, often impairing quality of life. Recently, there has been a nearly exponential increase in the number of primary research articles published on the pathophysiology and mechanisms underlying sleep-wake disturbances after TBI, both in animal models and in humans, including in the pediatric population. In this review, we summarize over 200 articles on the topic, most of which were identified objectively using reproducible online search terms in PubMed. Although these studies differ in terms of methodology and detailed outcomes; overall, recent research describes a common phenotype of excessive daytime sleepiness, nighttime sleep fragmentation, insomnia, and electroencephalography spectral changes after TBI. Given the heterogeneity of the human disease phenotype, rigorous translation of animal models to the human condition is critical to our understanding of the mechanisms and of the temporal course of sleep-wake disturbances after injury. Arguably, this is most effectively accomplished when animal and human studies are performed by the same or collaborating research programs. Given the number of symptoms associated with TBI that are intimately related to, or directly stem from sleep dysfunction, sleep-wake disorders represent an important area in which mechanistic-based therapies may substantially impact recovery after TBI.

Brain Injury Alters Volatile Metabolome

Chemical signals arising from body secretions and excretions communicate information about health status as have been reported in a range of animal models of disease. A potential common pathway for diseases to alter chemical signals is via activation of immune function-which is known to be intimately involved in modulation of chemical signals in several species. Based on our prior findings that both immunization and inflammation alter volatile body odors, we hypothesized that injury accompanied by inflammation might correspondingly modify the volatile metabolome to create a signature endophenotype. In particular, we investigated alteration of the volatile metabolome as a result of traumatic brain injury. Here, we demonstrate that mice could be trained in a behavioral assay to discriminate mouse models subjected to lateral fluid percussion injury from appropriate surgical sham controls on the basis of volatile urinary metabolites. Chemical analyses of the urine samples similarly demonstrated that brain injury altered urine volatile profiles. Behavioral and chemical analyses further indicated that alteration of the volatile metabolome induced by brain injury and alteration resulting from lipopolysaccharide-associated inflammation were not synonymous. Monitoring of alterations in the volatile metabolome may be a useful tool for rapid brain trauma diagnosis and for monitoring recovery.

Brain Injury Impairs Working Memory and Prefrontal Circuit Function

More than 2.5 million Americans suffer a traumatic brain injury (TBI) each year. Even mild to moderate TBI causes long-lasting neurological effects. Despite its prevalence, no therapy currently exists to treat the underlying cause of cognitive impairment suffered by TBI patients. Following lateral fluid percussion injury (LFPI), the most widely used experimental model of TBI, we investigated alterations in working memory and excitatory/inhibitory synaptic balance in the prefrontal cortex. LFPI impaired working memory as assessed with a T-maze behavioral task. Field excitatory postsynaptic potentials recorded in the prefrontal cortex were reduced in slices derived from brain-injured mice. Spontaneous and miniature excitatory postsynaptic currents onto layer 2/3 neurons were more frequent in slices derived from LFPI mice, while inhibitory currents onto layer 2/3 neurons were smaller after LFPI. Additionally, an increase in action potential threshold and concomitant decrease in firing rate was observed in layer 2/3 neurons in slices from injured animals. Conversely, no differences in excitatory or inhibitory synaptic transmission onto layer 5 neurons were observed; however, layer 5 neurons demonstrated a decrease in input resistance and action potential duration after LFPI. These results demonstrate synaptic and intrinsic alterations in prefrontal circuitry that may underlie working memory impairment caused by TBI.

Greater neurobehavioral deficits occur in adult mice after repeated, as compared to single, mild traumatic brain injury (mTBI)

Mild traumatic brain injury (mTBI) accounts for the majority of all brain injuries and affected individuals typically experience some extent of cognitive and/or neuropsychiatric deficits. Given that repeated mTBIs often result in worsened prognosis, the cumulative effect of repeated mTBIs is an area of clinical concern and on-going pre-clinical research. Animal models are critical in elucidating the underlying mechanisms of single and repeated mTBI-associated deficits, but the neurobehavioral sequelae produced by these models have not been well characterized. Thus, we sought to evaluate the behavioral changes incurred after single and repeated mTBIs in mice utilizing a modified impact-acceleration model. Mice in the mTBI group received 1 impact while the repeated mTBI group received 3 impacts with an inter-injury interval of 24h. Classic behavior evaluations included the Morris water maze (MWM) to assess learning and memory, elevated plus maze (EPM) for anxiety, and forced swim test (FST) for depression/helplessness. Additionally, species-typical behaviors were evaluated with the marble-burying and nestlet shredding tests to determine motivation and apathy. Non-invasive vibration platforms were used to examine sleep patterns post-mTBI. We found that the repeated mTBI mice demonstrated deficits in MWM testing and poorer performance on species-typical behaviors. While neither single nor repeated mTBI affected behavior in the EPM or FST, sleep disturbances were observed after both single and repeated mTBI. Here, we conclude that behavioral alterations shown after repeated mTBI resemble several of the deficits or disturbances reported by patients, thus demonstrating the relevance of this murine model to study repeated mTBIs.

Inhibition of injury-induced cell proliferation in the dentate gyrus of the hippocampus impairs spontaneous cognitive recovery after traumatic brain injury

Neurogenesis persists throughout life in the neurogenic regions of the mature mammalian brain, and this response is enhanced after traumatic brain injury (TBI). In the hippocampus, adult neurogenesis plays an important role in hippocampal-dependent learning and memory functions and is thought to contribute to the spontaneous cognitive recovery observed after TBI. Utilizing an antimitotic agent, arabinofuranosyl cytidine (Ara-C), the current study investigated the direct association of injury-induced hippocampal neurogenesis with cognitive recovery. In this study, adult rats received a moderate lateral fluid percussion injury followed by a 7-day intraventricular infusion of 2% Ara-C or vehicle. To examine the effect of Ara-C on cell proliferation, animals received intraperitoneal injections of 5-bromo-2-deoxyuridine (BrdU), to label dividing cells, and were sacrificed at 7 days after injury. Brain sections were immunostained for BrdU or doublecortin (DCX), and the total number of BrdU(+) or DCX(+) cells in the hippocampus was quantified. To examine the outcome of inhibiting the injury-induced cell proliferative response on cognitive recovery, animals were assessed on Morris water maze (MWM) tasks at 21-25 or 56-60 days postinjury. We found that a 7-day infusion of Ara-C significantly reduced the total number of BrdU(+) and DCX(+) cells in the dentate gyrus (DG) in both hemispheres. Moreover, inhibition of the injury-induced cell proliferative response in the DG completely abolished the innate cognitive recovery on MWM performance at 56-60 days postinjury. These results support the causal relationship of injury-induced hippocampal neurogenesis on cognitive functional recovery and suggest the importance of this endogenous repair mechanism on restoration of hippocampal function.

Augmented Inhibition from Cannabinoid-Sensitive Interneurons Diminishes CA1 Output after Traumatic Brain Injury

The neurological impairments associated with traumatic brain injury include learning and memory deficits and increased risk of seizures. The hippocampus is critically involved in both of these phenomena and highly susceptible to damage by traumatic brain injury. To examine network activity in the hippocampal CA1 region after lateral fluid percussion injury, we used a combination of voltage-sensitive dye, field potential, and patch clamp recording in mouse hippocampal brain slices. When the stratum radiatum (SR) was stimulated in slices from injured mice, we found decreased depolarization in SR and increased hyperpolarization in stratum oriens (SO), together with a decrease in the percentage of pyramidal neurons firing stimulus-evoked action potentials. Increased hyperpolarization in SO persisted when glutamatergic transmission was blocked. However, we found no changes in SO responses when the alveus was stimulated to directly activate SO. These results suggest that the increased SO hyperpolarization evoked by SR stimulation was mediated by interneurons that have cell bodies and/or axons in SR, and form synapses in stratum pyramidale and SO. A low concentration (100 nM) of the synthetic cannabinoid WIN55,212-2, restored CA1 output in slices from injured animals. These findings support the hypothesis that increased GABAergic signaling by cannabinoid-sensitive interneurons contributes to the reduced CA1 output following traumatic brain injury.

The effect of NADPH-oxidase inhibitor apocynin on cognitive impairment induced by moderate lateral fluid percussion injury: role of inflammatory and oxidative brain damage

Traumatic brain injury (TBI) is a devastating disease that commonly causes persistent mental disturbances and cognitive deficits. Although studies have indicated that overproduction of free radicals, especially superoxide (O2(-)) derived from nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is a common underlying mechanism of pathophysiology of TBI, little information is available regarding the role of apocynin, an NADPH oxidase inhibitor, in neurological consequences of TBI. Therefore, the present study evaluated the therapeutic potential of apocynin for treatment of inflammatory and oxidative damage, in addition to determining its action on neuromotor and memory impairments caused by moderate fluid percussion injury in mice (mLFPI). Statistical analysis revealed that apocynin (5mg/kg), when injected subcutaneously (s.c.) 30min and 24h after injury, had no effect on neuromotor deficit and brain edema, however it provided protection against mLFPI-induced object recognition memory impairment 7days after neuronal injury. The same treatment protected against mLFPI-induced IL-1β, TNF-α, nitric oxide metabolite content (NOx) 3 and 24h after neuronal injury. Moreover, apocynin treatment reduced oxidative damage (protein carbonyl, lipoperoxidation) and was effective against mLFPI-induced Na(+), K(+)-ATPase activity inhibition. The present results were accompanied by effective reduction in lesion volume when analyzed 7days after neuronal injury. These data suggest that superoxide (O2(-)) derived from NADPH oxidase can contribute significantly to cognitive impairment, and that the post injury treatment with specific NADPH oxidase inhibitors, such as apocynin, may provide a new therapeutic approach to the control of neurological disabilities induced by TBI.

17β-estradiol confers protection after traumatic brain injury in the rat and involves activation of G protein-coupled estrogen receptor 1

Abstract Traumatic brain injury (TBI) is a significant public health problem in the United States. Despite preclinical success of various drugs, to date all clinical trials investigating potential therapeutics have failed. Recently, sex steroid hormones have sparked interest as possible neuroprotective agents after traumatic injury. One of these is 17β-estradiol (E2), the most abundant and potent endogenous vertebrate estrogen. The goal of our study was to investigate the acute potential protective effects of E2 or the specific G protein-coupled estrogen receptor 1 (GPER) agonist G-1 when administered in an intravenous bolus dose 1 hour post-injury in the lateral fluid percussion (LFP) rodent model of TBI. The results of this study show that, when assessed at 24 hours post-injury, E2 or G-1 confers protection in adult male rats subjected to LFP brain injury. Specifically, we found that an acute bolus dose of E2 or G-1 administered intravenously 1 hour post-TBI significantly increases neuronal survival in the ipsilateral CA 2/3 region of the hippocampus and decreases neuronal degeneration and apoptotic cell death in both the ipsilateral cortex and CA 2/3 region of the hippocampus. We also report a significant reduction in astrogliosis in the ipsilateral cortex, hilus, and CA 2/3 region of the hippocampus. Finally, these effects were observed to be chiefly dose-dependent for E2, with the 5 mg/kg dose generating a more robust level of protection. Our findings further elucidate estrogenic compounds as a clinically relevant pharmacotherapeutic strategy for treatment of secondary injury following TBI, and intriguingly, reveal a novel potential therapeutic target in GPER.

Analysis of functional pathways altered after mild traumatic brain injury

Concussive injury (or mild traumatic brain injury; mTBI) can exhibit features of focal or diffuse injury patterns. We compared and contrasted the cellular and molecular responses after mild controlled cortical impact (mCCI; a focal injury) or fluid percussion injury (FPI; a diffuse injury) in rats. The rationale for this comparative analysis was to investigate the brain's response to mild diffuse versus mild focal injury to identify common molecular changes triggered by these injury modalities and to determine the functional pathways altered after injury that may provide novel targets for therapeutic intervention. Microarrays containing probes against 21,792 unique messenger RNAs (mRNAs) were used to investigate the changes in cortical mRNA expression levels at 3 and 24 h postinjury. Of the 354 mRNAs with significantly altered expression levels after mCCI, over 89% (316 mRNAs) were also contained within the mild FPI (mFPI) data set. However, mFPI initiated a more widespread molecular response, with over 2300 mRNAs differentially expressed. Bioinformatic analysis of annotated gene ontology molecular function and biological pathway terms showed a significant overrepresentation of genes belonging to inflammation, stress, and signaling categories in both data sets. We therefore examined changes in the protein levels of a panel of 23 cytokines and chemokines in cortical extracts using a Luminex-based bead immunoassay and detected significant increases in macrophage inflammatory protein (MIP)-1α (CCL3), GRO-KC (CXCL1), interleukin (IL)-1α, IL-1β, and IL-6. Immunohistochemical localization of MIP-1α and IL-1β showed marked increases at 3 h postinjury in the cortical vasculature and microglia, respectively, that were largely resolved by 24 h postinjury. Our findings demonstrate that both focal and diffuse mTBI trigger many shared pathobiological processes (e.g., inflammatory responses) that could be targeted for mechanism-based therapeutic interventions.

Histopathological and behavioral effects of immediate and delayed hemorrhagic shock after mild traumatic brain injury in rats

The purpose of this study was to investigate the increased susceptibility of the brain, after a controlled mild cortical impact injury, to a secondary ischemic insult. The effects of the duration and the timing of the secondary insult after the initial cortical injury were studied. Rats anesthetized with isoflurane underwent a 3 m/sec, 2.5-mm deformation cortical impact injury followed by hypotension to 40 mm Hg induced by withdrawing blood from a femoral vein. The duration of hypotension was varied from 40 to 60 min. The timing of 60 min of hypotension was varied from immediately post-injury to 7 days after the injury. Outcome was assessed by behavioral tasks and histological examination at 2 weeks post-injury. A separate group of animals underwent measurement of the acute physiology including mean blood pressure (MAP), intracranial pressure (ICP), and cerebral blood flow (CBF) using a laser Doppler technique. Increasing durations of hypotension resulted in marked expansion of the contusion, from 6.5±1.8 mm³ with sham hypotension to 27.1±3.9 mm³ with 60 min of hypotension. This worsening of the contusion was found only when then hypotension occurred immediately after injury or at 1 h after injury. CA3 neuron loss followed a similar pattern, but the injury group differences were not significant. Motor tasks, including beam balance and beam walking, were significantly worse following 50 and 60 min of hypotension. Performance on the Morris water maze task was also significantly related to the injury group. Studies of the acute cerebral hemodynamics demonstrated that CBF was significantly more impaired during hypotension in the animals that underwent the mild TBI compared to those that underwent sham TBI. The perfusion deficit was worst at the impact site, but also significant in the pericontusional brain. With 50 and 60 min of hypotension, CBF did not recover following resuscitation at the impact site, and recovered only transiently in the pericontusional brain. These results demonstrate that mild TBI, like more severe levels of TBI, can impair the brain's ability to maintain CBF during a period of hypotension, and result in a worse outcome.

The effect of epidermal growth factor in the injured brain after trauma in rats

Epidermal growth factor (EGF) is a known mitogen for neural stem and progenitor cells (NS/NPCs) in the central nervous system (CNS). In vitro, EGF maintains NS/NPCs in the proliferative state, whereas in the normal rodent brain it promotes their proliferation and migration in the subventricular zone (SVZ). Additionally, EGF administration can augment neuronal replacement in the ischemic-injured adult striatum. Recently we found that the SVZ and the hippocampus display an injury-induced proliferative response following traumatic brain injury (TBI) that is linked to increased EGF expression. As adult neurogenesis is associated with cognitive function, we hypothesized that post-TBI administration of EGF could affect neurogenesis and cognitive recovery. Adult rats were intraventricularly infused with EGF or vehicle for 7 days following TBI. 5-Bromo-2-deoxyuridine (BrdU) was administered to label proliferating cells and the animals were sacrificed at 1 or 4 weeks post-injury. Using immunohistochemistry and stereology, we found that at 1 week post-injury, compared to vehicle-infused animals EGF-infused animals had significantly more BrdU-positive cells in the SVZ and hippocampus concomitant with enhanced EGF receptor expression. At 4 weeks post-injury, the number of BrdU-positive cells in the hippocampus was similar in both groups, suggesting that EGF does not support long-term survival of newly generated cells. Furthermore, we found that the EGF-induced proliferative population differentiated preferentially toward astroglial phenotype. Nevertheless, animals treated with EGF showed significant improvement in cognitive function, which was accompanied by reduced hippocampal neuronal cell loss. Collectively, the data from this study demonstrate that EGF exerts a neuroprotective rather than neurogenic effect in protecting the brain from injury.

Basic fibroblast growth factor-enhanced neurogenesis contributes to cognitive recovery in rats following traumatic brain injury

Stem/progenitor cells reside throughout the adult CNS and are actively dividing in the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus. This neurogenic capacity of the SVZ and DG is enhanced following traumatic brain injury (TBI) suggesting that the adult brain has the inherent potential to restore populations lost to injury. This raises the possibility of developing strategies aimed at harnessing the neurogenic capacity of these regions to repair the damaged brain. One strategy is to enhance neurogenesis with mitogenic factors. As basic fibroblast growth factor (bFGF) is a potent stem cell mitogen, we set out to determine if an intraventricular administration of bFGF following TBI could affect the levels of injury-induced neurogenesis in the SVZ and DG, and the degree to which this is associated with cognitive recovery. Specifically, adult rats received a bFGF intraventricular infusion for 7 days immediately following TBI. BrdU was administered to animals daily at 2-7 days post-injury to label cell proliferation. At 1 or 4 weeks post-injury, brain sections were immunostained for BrdU and neuronal or astrocytic markers. We found that injured animals infused with bFGF exhibited significantly enhanced cell proliferation in the SVZ and the DG at 1 week post-TBI as compared to vehicle-infused animals. Moreover, following bFGF infusion, a greater number of the newly generated cells survived to 4 weeks post-injury, with the majority being neurons. Additionally, animals infused with bFGF showed significant cognitive improvement. Collectively, the current findings suggest that bFGF-enhanced neurogenesis contributes to cognitive recovery following TBI.

Time window for voluntary exercise-induced increases in hippocampal neuroplasticity molecules after traumatic brain injury is severity dependent

We recently found that an exercise-induced increase in hippocampal brain-derived neurotrophic factor (BDNF) is dependent when exercise is initiated after traumatic brain injury (TBI). When voluntary exercise was delayed by 2 weeks after a mild fluid-percussion injury (FPI) in rats, an increase in BDNF and an improvement in behavioral outcome were observed. This suggests that following FPI there is a therapeutic window for the implementation of voluntary exercise. To determine if more severely injured animals require more time after TBI before voluntary exercise can increase neuroplasticity, adult male rats with a moderate lateral FPI or sham injury were housed with or without access to a running wheel from post-injury-day (PID) 0-6, 14-20 or 30-36. Rats with a mild injury only had access to the running wheel from PID 0-6 or 14-20. Rats were sacrificed at PID 7, 21, or 37. BDNF, synapsin I, and cyclic AMP response element binding protein (CREB) were analyzed within the ipsilateral hippocampus. Whereas BDNF levels significantly increased with exercise in the mild FPI rats that were exercised from PID 14 to 20, the moderate FPI rats only showed significant increases in BDNF when exercised from PID 30 to 36. In addition, moderate FPI rats that were allowed to exercise from PID 30 to 36 also exhibited significant increases in synapsin I and CREB. These results indicate that the time window for exercise-induced increases in BDNF, synapsin I, and CREB is dependent on injury severity.

New Rat Model for Diffuse Brain Injury Using Coronal Plane Angular Acceleration

A new experimental model was developed to induce diffuse brain injury (DBI) in rats through pure coronal plane angular acceleration. An impactor was propelled down a guide tube toward the lateral extension of the helmet fixture. Upon impactor-helmet contact, helmet and head were constrained to rotate in the coronal plane. In the present experimental series, the model was optimized to generate rotational kinematics necessary for concussion. Twenty-six rats were subjected to peak angular accelerations of 368 +/- 30 krad/sec2 (mean +/- standard deviation) with 2.1 +/- 0.5-msec durations. Following rotational loading, unconsciousness was defined as time between reversal agent administration and return of corneal reflex. All experimental rats demonstrated transient unconsciousness lasting 8.8 +/- 3.7 min that was significantly longer than control rats. Macroscopic damage was noted in 51% of experimental animals: 38% subarachnoid hemorrhage, and 15% intraparenchymal lesion. Microscopic analysis indicated no evidence of axonal swellings at sacrifice times of 24, 48, 72, and 96 h. All rats survived rotational loading without skull fracture. Injuries were classified as concussion based on transient unconsciousness, scaled biomechanics, limited macroscopic damage, and minimal histological abnormalities. The experimental methodology remains adjustable, permitting investigation of increasing DBI severities through modulation of model parameters, and inclusion of further functional and histological outcome measures.

Inbred mouse strains as a tool to analyze hippocampal neuronal loss after brain injury: a stereological study

Traumatic brain injury (TBI) damages the hippocampus both in experimental animal models and in humans. In particular, the mechanical injury in combination with the genetic susceptibility to injury may result in neuronal loss from the hippocampus. This report explores the time-course of neuronal loss in the four primary subregions of the mouse hippocampus after a lateral fluid percussion injury (FPI) to the brain, and how subtle genetic differences between C57BL/6J and C57BL/10J mouse strains influence the extent and time course of neuronal loss. Using design-based stereological procedures, our results indicate negligible neuronal loss ipsilateral to the injury at 2 days postinjury in C57BL/6J mice, whereas a significant number (30-40%) of neurons are lost across all subregions of the hippocampus (dentate, hilus, area CA3, and area CA1) by 1 week, which does not appear to progress at 1 month, compared to sham. Additionally, neuronal counts after lateral FPI in a genetically similar, yet kainic acid-sensitive, mouse strain (C57BL/10J) showed no statistically significant differences in neuron number compared to the C57BL/6J strain in response to brain injury. Hippocampal neuronal loss after lateral FPI and its consequent circuit disruption may depend more on factors related to the mechanics and secondary consequences of the injury, as opposed to subtle genetic variations between inbred mouse strains. The loss of neurons appears to be restricted to the first week post-injury, and the remaining neurons may serve as a substrate for recovery.

Response of the contralateral hippocampus to lateral fluid percussion brain injury

Traumatic brain injury is a leading cause of death and disability in the United States. Pathological examinations of humans and animal models after brain injury demonstrate hippocampal neuronal damage, which may contribute to cognitive impairments. Data from our laboratories have shown that, at 1 week after brain injury, mice possess significantly fewer neurons in all ipsilateral hippocampal subregions and a cognitive impairment. Since cognitive function is distributed across both cerebral hemispheres, the present paper explores the morphological and physiological response of the contralateral hippocampus to lateral brain injury. We analyzed the contralateral hippocampus using design-based stereology, Fluoro-Jade (FJ) histochemistry, and extracellular field recordings in mice at 7 and 30 days after lateral fluid percussion injury (FPI). At 7 days, all contralateral hippocampal subregions possess significantly fewer healthy neurons compared to sham-injured animals and demonstrate FJ-positive neuronal damage, but not at 30 days. Both the ipsilateral and contralateral dentate gyri demonstrate significantly increased excitability at 7 days post-injury, but only ipsilateral dentate gyrus hyperexcitability persists at 30 days compared to sham. In the contralateral hippocampus, the transient decrease in the number of healthy neurons, concomitant with FJ damage, and electrophysiological alterations establish a stunned period of cellular and circuit dysfunction. The return of healthy neuron number, absence of FJ damage, and sham level of excitability in the contralateral hippocampus suggest recovery of structure and function by 30 days after injury. The cognitive recovery observed after human traumatic brain injury may stem from a differential injury exposure and time course of recovery between homologous regions of the two hemispheres.

Regional hippocampal alteration associated with cognitive deficit following experimental brain injury: a systems, network and cellular evaluation

Cognitive deficits persist in patients who survive traumatic brain injury (TBI). Lateral fluid percussion brain injury in the mouse, a model of human TBI, results in hippocampal-dependent cognitive impairment, similar to retrograde amnesia often associated with TBI. To identify potential substrates of the cognitive impairment, we evaluated regional neuronal loss, regional hippocampal excitability and inhibitory synaptic transmission. Design-based stereology demonstrated an approximate 40% loss of neurons through all subregions of the hippocampus following injury compared with sham. Input/output curves recorded in slices of injured brain demonstrated increased net synaptic efficacy in the dentate gyrus in concert with decreased net synaptic efficacy and excitatory postsynaptic potential-spike relationship in area CA1 compared with sham slices. Pharmacological agents modulating inhibitory transmission partially restored regional injury-induced alterations in net synaptic efficacy. Both evoked and spontaneous miniature inhibitory postsynaptic currents (mIPSCs) recorded in surviving dentate granule neurons were smaller and less frequent in injured brains than in uninjured brains. Conversely, both evoked and spontaneous mIPSCs recorded in surviving area CA1 pyramidal neurons were larger in injured brains than in uninjured brains. Together, these alterations suggest that regional hippocampal function is altered in the injured brain. This study demonstrates for the first time that brain injury selectively disrupts hippocampal function by causing uniform neuronal loss, inhibitory synaptic dysfunction, and regional, but opposing, shifts in circuit excitability. These changes may contribute to the cognitive impairments that result from brain injury.

Animal models of head trauma

Animal models of traumatic brain injury (TBI) are used to elucidate primary and secondary sequelae underlying human head injury in an effort to identify potential neuroprotective therapies for developing and adult brains. The choice of experimental model depends upon both the research goal and underlying objectives. The intrinsic ability to study injury-induced changes in behavior, physiology, metabolism, the blood/tissue interface, the blood brain barrier, and/or inflammatory- and immune-mediated responses, makes in vivo TBI models essential for neurotrauma research. Whereas human TBI is a highly complex multifactorial disorder, animal trauma models tend to replicate only single factors involved in the pathobiology of head injury using genetically well-defined inbred animals of a single sex. Although such an experimental approach is helpful to delineate key injury mechanisms, the simplicity and hence inability of animal models to reflect the complexity of clinical head injury may underlie the discrepancy between preclinical and clinical trials of neuroprotective therapeutics. Thus, a search continues for new animal models, which would more closely mimic the highly heterogeneous nature of human TBI, and address key factors in treatment optimization.

Lateral fluid percussion brain injury: a 15-year review and evaluation

This article comprehensively reviews the lateral fluid percussion (LFP) model of traumatic brain injury (TBI) in small animal species with particular emphasis on its validity, clinical relevance and reliability. The LFP model, initially described in 1989, has become the most extensively utilized animal model of TBI (to date, 232 PubMed citations), producing both focal and diffuse (mixed) brain injury. Despite subtle variations in injury parameters between laboratories, universal findings are evident across studies, including histological, physiological, metabolic, and behavioral changes that serve to increase the reliability of the model. Moreover, demonstrable histological damage and severity-dependent behavioral deficits, which partially recover over time, validate LFP as a clinically-relevant model of human TBI. The LFP model, also has been used extensively to evaluate potential therapeutic interventions, including resuscitation, pharmacologic therapies, transplantation, and other neuroprotective and neuroregenerative strategies. Although a number of positive studies have identified promising therapies for moderate TBI, the predictive validity of the model may be compromised when findings are translated to severely injured patients. Recently, the clinical relevance of LFP has been enhanced by combining the injury with secondary insults, as well as broadening studies to incorporate issues of gender and age to better approximate the range of human TBI within study design. We conclude that the LFP brain injury model is an appropriate tool to study the cellular and mechanistic aspects of human TBI that cannot be addressed in the clinical setting, as well as for the development and characterization of novel therapeutic interventions. Continued translation of pre-clinical findings to human TBI will enhance the predictive validity of the LFP model, and allow novel neuroprotective and neuroregenerative treatment strategies developed in the laboratory to reach the appropriate TBI patients.

Comparison of behavioral deficits and acute neuronal degeneration in rat lateral fluid percussion and weight-drop brain injury models

The behavioral and histological effects of the lateral fluid percussion (LFP) brain injury model were compared with the weight drop impact-acceleration model with 10 min of secondary hypoxia (WDIA + H). LFP injury resulted in significant motor deficits on the beam walk and inclined plane, and memory deficits on the radial arm maze and Morris water maze. Motor deficits following LFP remained throughout 6 weeks of behavioral testing. WDIA + H injury produced significant motor deficits on the beam walk and inclined plane immediately following injury, but these effects were transient and recovered by 14 days post-injury. In contrast to the LFP injury, the WDIA + H injured animals showed no memory deficits on the radial arm maze and Morris water maze. In order to determine if the differences in behavioral outcome between models were due to differences in injury mechanism or injury severity, 10 LFP-injured animals were matched with 10 WDIA-injured animals based on injury severity (i.e., time to regain righting reflex after brain injury). The LFP-matched injury group showed greater impairment than the WDIA + H matched injury group on the radial arm maze and Morris water maze. Histological examination of LFP-injured brains with Fluoro-Jade staining 24 h, 48 h, and 7 days post-injury revealed degenerating neurons in the cortex, thalamus, hippocampus, caudate-putamen, brainstem, and cerebellum, with degenerating fibers tracts in the corpus callosum and other major tracts throughout the brain. Fluoro-Jade staining following WDIA+H injury revealed damage to fibers in the optic tract, lateral olfactory tract, corpus callosum, anterior commissure, caudate-putamen, brain stem, and cerebellum. While both models produce reliable and characteristic behavioral and neuronal pathologies, their differences are important to consider when choosing a brain injury model.

Experimental models of head trauma

Traumatic brain injury is one of the most common causes for chronic disability in young people. Despite this there are currently no widely available modes of therapy that would limit the extent of brain damage secondary to trauma. Therefore, new insights into the pathological mechanisms involved in head trauma possibly leading to the identification of new therapeutic targets are urgently needed. In order to attain these goals adequate animal models for traumatic brain injury are needed. In the following paper the authors will review the various animal models for head trauma and emphasize their potential strengths and weaknesses.

Evidence-based review of sport-related concussion: basic science

The evidence base for sport-related concussive brain injury is reviewed in this paper. In the past, pathophysiological understanding of this common condition has been extrapolated from studies of severe brain trauma. More recent scientific study demonstrates that this approach is unsatisfactory, and the clinical features of concussion represent a predominantly functional brain injury rather than manifest by structural or neuropathological damage. Such understanding of this condition remains incomplete at this stage.

Evidence disputing the importance of excitotoxicity in hippocampal neuron death after experimental traumatic brain injury

The hippocampus is selectively vulnerable to experimental traumatic brain injury (TBI). Beneficial effects of glutamate receptor antagonists and increased extracellular levels of glutamate have suggested that glutamate-mediated excitotoxicity may be responsible for this selective damage. In order to clarify this important issue, we applied a severe parasagittal fluid percussion injury (FPI) to strains of mice shown to be susceptible and resistant to kainic acid (KA)-induced excitotoxic hippocampal damage. Dystrophic neurons were present by 10 min after FPI in the hippocampi of both strains. Damaged hippocampal neurons were absent at 4 days and 7 days. Additionally, there was no significant difference (p = 1.00) in CA3 neuron survival between KA-susceptible and -resistant mice at 4 days. In conclusion, excitotoxicity does not significantly contribute to hippocampal neuron loss after FPI and, in contrast to classic studies of excitotoxicity in vivo, the pattern of hippocampal cell death after TBI is extremely acute.

P-selectin blockade following fluid-percussion injury: behavioral and immunochemical sequelae

Traumatic brain injury (TBI) can cause polymorphonuclear leukocyte (PMN) migration into brain parenchyma, mediating various cytodestructive mechanisms. We examined the effect of blocking leukocyte/endothelial cell adhesion molecules (CAMs) on the anatomic and behavioral sequelae in lateral fluid-percussion injury in rats. Monoclonal antibodies (MAb) directed against a functional (PB1.3) or nonfunctional (PNB1.6) epitope on endothelial P-selectin were used as treatments. Subjects were tested in the Morris water maze (MWM) at 7 and 14 days postinjury then immunohistochemistry was performed using antibodies that recognize ChAT, GFAP and OX-42. A second set of animals underwent myeloperoxidase (MPO) assay in the brain parenchyma and a third set was used to examine neutrophil migration using the MAb RP-3. Time in quadrant, but not escape latency or proximity improved with PB1.3 (p < 0.05). Similarly, PB1.3 reduced MPO levels after injury (p < 0.05), in the ipsilateral cortex. No significant difference occurred in neutrophil counts in cortex, corpus callosum, hippocampus, and thalamus between injured only rats and injured rats treated with PB1.3. Quantitative analysis of cholinergic cells in the medial septum showed a protective effect by PB1.3. Densitometry readings of GFAP and OX-42 immunolabeling revealed no discernible differences between the treated and untreated injured rats. Qualitatively, there was no difference in microglia or astrocyte response to treatment. Treatment with P-selectin blockade in brain-injured rats may reduce PMN migration into brain, help preserve cholinergic immunolabeling of medial septal nucleus neurons, and may alleviate mnemonic deficits.

Adaptation of the fluid percussion injury model to the mouse

Fluid percussion injury (FPI) is a well-characterized experimental model of traumatic brain injury (TBI) in the rat. Many pathophysiologic consequences and mechanisms of recovery after TBI rely on neurochemical pathways that can be examined in genetically altered mice. Therefore, FPI applied to mice may be a useful experimental tool to investigate TBI at the molecular level. In the present study, we establish FPI as a viable model of TBI in the mouse by characterizing acute neurological, histopathological, and behavioral changes. Right-sided parasagittal FPI or sham treatment was administered in male C57BL/6 mice. Acute neurological evaluation revealed righting reflexes in the injured animals (p < 0.001). Deficits in spatial learning and memory were observed in the Morris water maze (MWM) 5 and 6 days after injury. A novel MWM data analysis protocol is described. The injured group (n = 18) demonstrated impaired performance in the MWM during acquisition (p < 0.05) and probe trials (p < 0.025) compared to sham animals (n = 16). At 7 days postinjury, glial fibrillary acidic protein immunohistochemistry revealed intense cortical, callosal, and hippocampal gliosis. The modified Gallyas silver degeneration stain consistently labeled cell bodies and terminals throughout the ipsilateral cortex, axons in the gray matter-white matter interface above the corpus callosum and within the corpus callosum bilaterally, and terminals and fibers in the thalamus bilaterally. Additionally, the mouse FPI model described is immediately employable in labs already using the FPI rat model with no modifications to a pre-existing FPI apparatus.

Fluid percussion injury causes disruption of the septohippocampal pathway in the rat

Fluid percussion injury (FPI) causes memory deficits, loss of hippocampal neurons, and basal forebrain cholinergic immunoreactivity in rats. Basal forebrain septohippocampal projections terminate in specific hippocampal regions. The purpose of this study was to examine the effects of FPI on the septohippocampal pathway (SHP). Halothane-anesthetized rats received either a sham injury or a parasagittal FPI. To characterize the anatomical effects of FPI on the SHP, silver stains were performed on brains of animals at 1, 5, and 10 days following FPI and were compared to sham-injured preparations. To characterize the effects of FPI on retrograde transport in the SHP, a separate group of FPI and sham-injured animals with survival times of 2, 5, and 10 days received bilateral WGA-HRP injections into the hippocampal formation 24 h prior to sacrifice. Argyrophilic CA3 neurons were present 1 day following FPI. Five days following FPI, terminal degeneration was present in the inner third of the molecular layer of the dentate gyrus bilaterally that was not present 1 day after injury. Fiber and terminal degeneration was not observed in the basal forebrain until 10 days after FPI. WGA-HRP-labeled septal neurons decreased significantly (P < 0.05) ipsilateral to injury in animals sacrificed 5 and 10 days following FPI but not 2 days after injury. This investigation demonstrated that FPI produces focal injury in the hippocampal formation. In addition, the appearance of terminal degeneration in the dentate molecular layer correlated with the significant reduction in axonal transport 5 days following injury. This correlation illustrates the secondary processes that structurally damage the SHP up to 10 days after injury.