Evaluation of learning and memory dysfunction and histological findings in rats with chronic stage contusion and diffuse axonal injury

Neurodegeneration and Sensorimotor Deficits in the Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) can result in persistent sensorimotor and cognitive deficits, which occur through a cascade of deleterious pathophysiological events over time. In this study, we investigated the hypothesis that neurodegeneration caused by TBI leads to impairments in sensorimotor function. TBI induces the activation of the caspase-3 enzyme, which triggers cell apoptosis in an in vivo model of fluid percussion injury (FPI). We analyzed caspase-3 mediated apoptosis by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining and poly (ADP-ribose) polymerase (PARP) and annexin V western blotting. We correlated the neurodegeneration with sensorimotor deficits by conducting the animal behavioral tests including grid walk, balance beam, the inverted screen test, and the climb test. Our study demonstrated that the excess cell death or neurodegeneration correlated with the neuronal dysfunction and sensorimotor impairments associated with TBI.

Epileptogenesis following experimentally induced traumatic brain injury - a systematic review

Traumatic brain injury (TBI) is a complex neurotrauma in civilian life and the battlefield with a broad spectrum of symptoms, long-term neuropsychological disability, as well as mortality worldwide. Posttraumatic epilepsy (PTE) is a common outcome of TBI with unknown mechanisms, followed by posttraumatic epileptogenesis. There are numerous rodent models of TBI available with varying pathomechanisms of head injury similar to human TBI, but there is no evidence for an adequate TBI model that can properly mimic all aspects of clinical TBI and the first successive spontaneous focal seizures follow a single episode of neurotrauma with respect to epileptogenesis. This review aims to provide current information regarding the various experimental animal models of TBI relevant to clinical TBI. Mossy fiber sprouting, loss of dentate hilar neurons along with recurrent seizures, and epileptic discharge similar to human PTE have been studied in fluid percussion injury, weight-drop injury, and cortical impact models, but further refinement of animal models and functional test is warranted to better understand the underlying pathophysiology of posttraumatic epileptogenesis. A multifaceted research approach in TBI model may lead to exploration of the potential treatment measures, which are a major challenge to the research community and drug developers. With respect to clinical setting, proper patient data collection, improved clinical trials with advancement in drug delivery strategies, blood-brain barrier permeability, and proper monitoring of level and effects of target drug are also important.

Intranasal Administration of the Antisecretory Peptide AF-16 Reduces Edema and Improves Cognitive Function Following Diffuse Traumatic Brain Injury in the Rat

A synthetic peptide with antisecretory activity, antisecretory factor (AF)-16, improves injury-related deficits in water and ion transport and decreases intracranial pressure after experimental cold lesion injury and encephalitis although its role in traumatic brain injury (TBI) is unknown. AF-16 or an inactive reference peptide was administrated intranasally 30 min following midline fluid percussion injury (mFPI; n = 52), a model of diffuse mild-moderate TBI in rats. Sham-injured (n = 14) or naïve (n = 24) animals were used as controls. The rats survived for either 48 h or 15 days post-injury. At 48 h, the animals were tested in the Morris water maze (MWM) for memory function and their brains analyzed for cerebral edema. Here, mFPI-induced brain edema compared to sham or naïve controls that was significantly reduced by AF-16 treatment (p < 0.05) although MWM performance was not altered. In the 15-day survival groups, the MWM learning and memory abilities as well as histological changes were analyzed. AF-16-treated brain-injured animals shortened both MWM latency and swim path in the learning trials (p < 0.05) and improved probe trial performance compared to brain-injured controls treated with the inactive reference peptide. A modest decrease by AF-16 on TBI-induced changes in hippocampal glial acidic fibrillary protein (GFAP) staining (p = 0.11) was observed. AF-16 treatment did not alter any other immunohistochemical analyses (degenerating neurons, beta-amyloid precursor protein (β-APP), and Olig2). In conclusion, intranasal AF-16-attenuated brain edema and enhanced visuospatial learning and memory following diffuse TBI in the rat. Intranasal administration early post-injury of a promising neuroprotective substance offers a novel treatment approach for TBI.

Chronic Histopathological and Behavioral Outcomes of Experimental Traumatic Brain Injury in Adult Male Animals

The purpose of this review is to survey the use of experimental animal models for studying the chronic histopathological and behavioral consequences of traumatic brain injury (TBI). The strategies employed to study the long-term consequences of TBI are described, along with a summary of the evidence available to date from common experimental TBI models: fluid percussion injury; controlled cortical impact; blast TBI; and closed-head injury. For each model, evidence is organized according to outcome. Histopathological outcomes included are gross changes in morphology/histology, ventricular enlargement, gray/white matter shrinkage, axonal injury, cerebrovascular histopathology, inflammation, and neurogenesis. Behavioral outcomes included are overall neurological function, motor function, cognitive function, frontal lobe function, and stress-related outcomes. A brief discussion is provided comparing the most common experimental models of TBI and highlighting the utility of each model in understanding specific aspects of TBI pathology. The majority of experimental TBI studies collect data in the acute postinjury period, but few continue into the chronic period. Available evidence from long-term studies suggests that many of the experimental TBI models can lead to progressive changes in histopathology and behavior. The studies described in this review contribute to our understanding of chronic TBI pathology.

A novel traumatic brain injury model for induction of mild brain injury in rats

BACKGROUND

Due to the marked heterogeneity of human traumatic brain injury (TBI), none of the available animal model can reproduce the entire spectrum of TBI, especially mild focal TBI. This study was designed to develop a modified TBI weight drop model for induction of focal mild cerebral injury.

NEW METHOD

A stereotaxic coupled weight drop device was designed. Principle arm of device carries up to 500g weights which their force was conveyed to animal skull through a thin nail like metal tip. To determine the optimal configuration of the device to induce mild TBI, six different trials were designed. The optimal configuration of the instrument was used for evaluation of behavioral, histopathological and molecular changes of mild TBI.

RESULTS

Neurologic and motor coordination deficits observed sharply within 24h post injury period. Histological studies revealed a remarkable increase in the number of dark neurons in trauma site. TBI increased the expression of apoptotic proteins, Bax, BCl2 and cleaved caspase-3 in the hippocampus.

COMPARISON WITH EXISTING METHODS

Our designed TBI device is capable to produce variable severity of TBI from mild to severe. The main advantage of the new TBI model is induction of mild local unilateral brain injury instead of traumatization of the whole brain. This model does not require craniotomy for induction of brain injury.

CONCLUSION

This novel animal TBI model mimics human mild focal brain injury. This model is suitable for evaluation of pathophysiology as well as screening of new therapies for mild TBI.

Functional assessment of long-term deficits in rodent models of traumatic brain injury

Traumatic brain injury (TBI) ranks as the leading cause of mortality and disability in the young population worldwide. The annual US incidence of TBI in the general population is estimated at 1.7 million per year, with an estimated financial burden in excess of US$75 billion a year in the USA alone. Despite the prevalence and cost of TBI to individuals and society, no treatments have passed clinical trial to clinical implementation. The rapid expansion of stem cell research and technology offers an alternative to traditional pharmacological approaches targeting acute neuroprotection. However, preclinical testing of these approaches depends on the selection and characterization of appropriate animal models. In this article we consider the underlying pathophysiology for the focal and diffuse TBI subtypes, discuss the existing preclinical TBI models and functional outcome tasks used for assessment of injury and recovery, identify criteria particular to preclinical animal models of TBI in which stem cell therapies can be tested for safety and efficacy, and review these criteria in the context of the existing TBI literature. We suggest that 2 months post-TBI is the minimum period needed to evaluate human cell transplant efficacy and safety. Comprehensive review of the published TBI literature revealed that only 32% of rodent TBI papers evaluated functional outcome ≥1 month post-TBI, and only 10% evaluated functional outcomes ≥2 months post-TBI. Not all published papers that evaluated functional deficits at a minimum of 2 months post-TBI reported deficits; hence, only 8.6% of overall TBI papers captured in this review demonstrated functional deficits at 2 months or more postinjury. A 2-month survival and assessment period would allow sufficient time for differentiation and integration of human neural stem cells with the host. Critically, while trophic effects might be observed at earlier time points, it will also be important to demonstrate the sustainability of such an effect, supporting the importance of an extended period of in vivo observation. Furthermore, regulatory bodies will likely require at least 6 months survival post-transplantation for assessment of toxicology/safety, particularly in the context of assessing cell abnormalities.

Concussive brain trauma in the mouse results in acute cognitive deficits and sustained impairment of axonal function

Concussive brain injury (CBI) accounts for approximately 75% of all brain-injured people in the United States each year and is particularly prevalent in contact sports. Concussion is the mildest form of diffuse traumatic brain injury (TBI) and results in transient cognitive dysfunction, the neuropathologic basis for which is traumatic axonal injury (TAI). To evaluate the structural and functional changes associated with concussion-induced cognitive deficits, adult mice were subjected to an impact on the intact skull over the midline suture that resulted in a brief apneic period and loss of the righting reflex. Closed head injury also resulted in an increase in the wet weight:dry weight ratio in the cortex suggestive of edema in the first 24 h, and the appearance of Fluoro-Jade-B-labeled degenerating neurons in the cortex and dentate gyrus of the hippocampus within the first 3 days post-injury. Compared to sham-injured mice, brain-injured mice exhibited significant deficits in spatial acquisition and working memory as measured using the Morris water maze over the first 3 days (p<0.001), but not after the fourth day post-injury. At 1 and 3 days post-injury, intra-axonal accumulation of amyloid precursor protein in the corpus callosum and cingulum was accompanied by neurofilament dephosphorylation, impaired transport of Fluoro-Gold and synaptophysin, and deficits in axonal conductance. Importantly, deficits in retrograde transport and in action potential of myelinated axons continued to be observed until 14 days post-injury, at which time axonal degeneration was apparent. These data suggest that despite recovery from acute cognitive deficits, concussive brain trauma leads to axonal degeneration and a sustained perturbation of axonal function.

Experimental traumatic brain injury

Traumatic brain injury, a leading cause of death and disability, is a result of an outside force causing mechanical disruption of brain tissue and delayed pathogenic events which collectively exacerbate the injury. These pathogenic injury processes are poorly understood and accordingly no effective neuroprotective treatment is available so far. Experimental models are essential for further clarification of the highly complex pathology of traumatic brain injury towards the development of novel treatments. Among the rodent models of traumatic brain injury the most commonly used are the weight-drop, the fluid percussion, and the cortical contusion injury models. As the entire spectrum of events that might occur in traumatic brain injury cannot be covered by one single rodent model, the design and choice of a specific model represents a major challenge for neuroscientists. This review summarizes and evaluates the strengths and weaknesses of the currently available rodent models for traumatic brain injury.

Neuronal and glial cell number in the hippocampus after experimental traumatic brain injury: analysis by stereological estimation

Fluid percussion (FP) brain injury causes spatial memory dysfunction in rats regardless of injury location (midline vs. lateral). Standard histological analysis of the injured brains shows hippocampal neuronal loss after lateral, but not midline FP injury. We have used the optical volume fractionator (OVF) stereological procedure to quantify neuronal loss and glial proliferation within specific subregions of the hippocampus after midline or lateral FP injury. The OVF method is a design-based cell counting procedure, which combines cellular numerical density estimates (from the optical disector) with volume estimates (generated by point counting and the fractionator stereology method) to produce an estimate of the absolute cell number. Fifteen adult male Sprague-Dawley rats were randomly divided into 3 groups (n = 5/group): midline injury, lateral injury and naive. A single fluid percussion pulse was delivered to anesthetized rats in the injured groups. At 14 days post-injury, strict morphological criteria enabled the estimation of neurons, astrocytes, oligodendrocytes, and microglia in defined hippocampal subregions. The results confirm that hippocampal neurons are selectively vulnerable to brain injury, particularly observed as a significant loss in the hilus following both types of injury and in area CA3 after lateral injury. In contrast, the number of astrocytes and oligodendrocytes remains unaffected by brain injury, regardless of subregion. However, the significant increase in microglia number (bilaterally after midline and ipsilateral following lateral injury) suggests that underlying cellular processes continue weeks following injury. The implications of the observed cell population changes are discussed in relation to the reported cognitive deficits associated with both lateral and midline FP brain injury.

Multiple head injuries in rats: effects on behavior

BACKGROUND

Evidence suggests that mild head injuries in humans can result in cumulative damage. No investigation to date has considered the effects of multiple subacute mild head injuries in an animal model.

METHODS

Forty-one male Long-Evans hooded rats were trained in a Morris water maze. All animals were fitted with a hollow intracranial screw. Concussions were generated using a fluid percussion device. Animals were then evaluated in the water maze until performance returned to baseline. Control animals received no concussions. The remaining animals were randomized to receive one, two, or three concussions. Animals were allowed to return to baseline after each concussion and were then killed. Motor performance was evaluated on a balance beam both before and after concussions.

RESULTS

After one concussion, 85% of animals showed performance deviation from baseline as measured by time to reach the platform, returning to baseline within a mean of 14.0 trials. After two concussions, 48% of animals showed deviation, with a mean return to baseline of 6.8 trials. After three concussions, 25% of animals showed deviation, with a mean return to baseline of 2.3 trials. Of postconcussive animals, 42% developed new inconsistent baseline levels of performance. Balance beam performance was unaffected.

CONCLUSION

Multiple concussions cause immediate transient impairment in spatial recognition and have extended effects on baseline performance in rats. Motor performance is not affected.

Regional vulnerability after traumatic brain injury: gender differences in mice that overexpress human copper, zinc superoxide dismutase

Neuronal loss was quantified in both cortical and subcortical brain regions after traumatic brain injury in male and female nontransgenic (nTg) and transgenic (Tg) mice that overexpress human copper, zinc superoxide dismutase. Mice were euthanized at 7 days after a controlled cortical impact injury. Sections of brain were processed for immunolocalization of NeuN, a neuronal nuclear antigen, and the complement type 3 receptor, a marker of microglia/macrophages, and stained for iron. Cortical lesion volume and neuronal loss in the medial and/or lateral ventroposterior thalamic nuclei were significantly less in the nTg female compared to the nTg male (P = 0.0373 and P = 0.0023, respectively). In contrast, in CA3 of the hippocampus and laterodorsal thalamic nucleus (LD), there were no gender differences in neuronal loss between these nTg groups. Cortical lesion volume was significantly reduced in Tg males compared to nTg males (P = 0.0137) and was unchanged in the Tg females compared to the nTg females. Neuronal loss was attenuated in the CA3 and LD in the Tg females compared to the nTg females (P = 0.0252 and P = 0.0244, respectively). A similar protection was not observed in the Tg males. Microglial activation paralleled the pattern of neuronal loss and was most consistently aligned with iron deposition in the cortex and hippocampus. No overt differences were found in the pattern of microglial activation or iron staining between nTg and Tg mice nor between genders. Our findings demonstrate that neuroprotection, afforded by overexpression of copper, zinc superoxide dismutase, exhibits both regional and gender specificity.

Therapeutic effects of environmental enrichment on cognitive function and tissue integrity following severe traumatic brain injury in rats

Postinjury environmental enrichment (EE) has been shown to alter functional and anatomical outcomes in a number of injury paradigms, including traumatic brain injury (TBI). The question of whether EE alters functional outcome following TBI in a model which produces overt histopathological consequences has not been addressed. We investigated this question using the severe, parasagittal fluid percussion injury (FPI) model. Rats (n = 7 per group, enriched and standard for behavior; n = 15 per group for histology) underwent severe (2.2-2.6 atm) FPI, with sham-operated rats (n = 7 per group, enriched and standard for behavior; n = 6 enriched, n = 3 standard for histology) serving as controls. Animals were allowed to recover for 11 days either in standard single housing or together (injured and sham) in an enriched environment consisting of a 92 x 61 x 77-cm ferret cage filled with various stimulatory objects. Consistent with earlier reports, injured animals recovering in the enriched environment showed significantly (P < 0.05) shorter latencies to find the platform in a Morris Water Maze task versus injured/standard animals on day 12 post-TBI. However, both injured groups showed significant deficits versus sham groups (P < 0.05). There were no differences between the sham/enriched and sham/standard groups. No significant group differences in swim speed were observed. At 14 days post-TBI, enriched animals had approximately twofold smaller lesion areas in regions of the cerebral cortex posterior to the injury epicenter (-4.5, -5.8, -6.8 mm relative to bregma; P < 0.05) compared to injured/standard animals. In addition, overall lesion volume for the entire injured cortical hemisphere was significantly smaller in animals recovering in the enriched environment. These results indicate that noninvasive environmental stimulation is beneficial in attenuating cognitive deficits and preserving tissue integrity in a TBI model which causes cerebral contusion and cell death.

Secondary hypoxemia exacerbates the reduction of visual discrimination accuracy and neuronal cell density in the dorsal lateral geniculate nucleus resulting from fluid percussion injury

The purpose of this study was to determine the impact of secondary hypoxemia on visual discrimination accuracy after parasagittal fluid percussion injury (FPI). Rats lived singly in test cages, where they were trained to repeatedly execute a flicker-frequency visual discrimination for food. After learning was complete, all rats were surgically prepared and then retested over the following 4-5 days to ensure recovery to presurgery levels of performance. Rats were then assigned to one of three groups [FPI + Hypoxia (IH), FPI + Normoxia (IN), or Sham Injury + Hypoxia (SH)] and were anesthetized with halothane delivered by compressed air. Immediately after injury or sham injury, rats in groups IH and SH were switched to a 13% O2 source to continue halothane anesthesia for 30 min before being returned to their test cages. Anesthesia for rats in group IN was maintained using compressed air for 30 min after injury. FPI significantly reduced visual discrimination accuracy and food intake, and increased incorrect choices. Thirty minutes of immediate posttraumatic hypoxemia significantly (1) exacerbated the FPI-induced reductions of visual discrimination accuracy and food intake, (2) further increased numbers of incorrect choices, and (3) delayed the progressive recovery of visual discrimination accuracy. Thionine stains of midbrain coronal sections revealed that, in addition to the loss of neurons seen in several thalamic nuclei following FPI, cell loss in the ipsilateral dorsal lateral geniculate nucleus (dLG) was significantly greater after FPI and hypoxemia than after FPI alone. In contrast, neuropathological changes were not evident following hypoxemia alone. These results show that, although hypoxemia alone was without effect, posttraumatic hypoxemia exacerbates FPI-induced reductions in visual discrimination accuracy and secondary hypoxemia interferes with control of the rat's choices by flicker frequency, perhaps in part as a result of neuronal loss and fiber degeneration in the dLG. These results additionally confirm the utility of this visual discrimination procedure as a sensitive, noninvasive means of assessing behavioral function after experimental traumatic brain injury.

Cognitive dysfunction and histological findings in rats with chronic-stage contusion and diffuse axonal injury

The Morris water maze (MWM) technique is well known as a prominent method of evaluating learning acquisition and memory retention impairments in rats. We previously reported on a modified fluid percussion device that is able to consistently produce experimental cortical contusion (CC) and diffuse axonal injury (DAI) in separate groups of rats. The purpose of the present protocol is to evaluate the differences in learning acquisition and memory retention impairments between these two types of injured rats in the chronic stage using the MWM technique. CC and DAI rats are respectively induced by lateral and midline fluid percussion. We also compare the histological differences between these two different types of traumatic brain injury. The results show statistically significant differences in learning acquisition impairment between the sham and CC rats and between the sham and DAI rats. However, a difference in memory retention impairment was expected to be seen only between the sham and DAI rats. Histologically, the loss of CA3 pyramidal cells in the hippocampus was observed ipsilaterally in the CC and bilaterally in DAI. Neuronal cell loss was observed in bilaterally in layer II of the entorhinal cortex in DAI, but not in CC.