TBI weight-drop model with variable impact heights differentially perturbs hippocampus-cerebellum specific transcriptomic profile

Modification of the height of a weight drop traumatic brain injury model that causes the formation of glial scar and cognitive impairment in rats

OBJECTIVE

Traumatic brain injury (TBI) is a chronic, progressive condition associated with permanent disabilities, particularly cognitive impairments. Glial scar formation following TBI is considered a contributing factor to these persistent disabilities. Currently, limited research exists on pharmacological interventions targeting glial scar prevention that require a standard weight drop TBI model for glial scar formation. Since there is no established standard TBI model for glial scar formation, this study aims to validate and modify the height of the weight drop model to identify glial scar formation and cognitive impairments.

METHODS

Fifteen male Sprague Dawley rats were randomly divided into sham, WD1, and WD2 groups. The weight drop model with a 10 g load was applied to the right exposed brain of the rats from a height of 5 cm (WD1) and 10 cm (WD2) using a modified Feeney's weight drop device. Cognitive impairments were confirmed using the novel object recognition (NOR) test with ethovision software on day 15. Subsequently, the rats were decapitated on day 16, and GFAP immunohistochemical staining was performed to confirm the presence of glial scarring.

RESULTS

The WD1 and WD2 groups exhibited a significant increase in glial scar formation compared to the sham group, with the WD2 group resulting in even more pronounced glial scar formation. Only the WD2 model caused statistically significant cognitive damage. The negative correlation coefficient indicates that an increase in GFAP + cells will decrease the cognitive function.

CONCLUSION

Modification of the height of the weight drop model, by dropping a weight of 10 g from a height of 10 cm (WD2 group) onto the right brain exposed of the rat has been proven to induce the formation of a glial scar and cognitive impairment.

Effects of repetitive mild traumatic brain injury on weight gain and chronic behavioral outcomes in male rats

To assess the long-term behavioral effects of repetitive mild traumatic brain injury (rmTBI), we employed a preclinical model of rmTBI and performed a battery of behavioral tests starting 14 weeks post-injury. Male Sprague-Dawley rats received four unilateral mild (6 m/s; 0.5 mm depth) controlled cortical impacts (CCI), centered 4 mm posterior and 3-4 mm lateral to the bregma, administered at five-day intervals. The animals' weights were monitored throughout the study. We tested the rats for anxiety-like (elevated plus maze, open field test), depression-like (forced swim test), locomotor (rotarod, open field test), and spatial learning and memory (Morris water maze (MWM)) behavioral deficits. Overall, a mild behavioral phenotype was observed. Significant deficits were observed with the MWM, indicating that our injury model disrupts spatial learning and memory. An interesting aspect of these data is a directional/visual component to the spatial learning and memory deficits dependent on the zone in which the trial began. With the injury being unilateral, there may be an imbalance in visual acuity that contributes to the observed deficits. Analysis of weight gain data demonstrated that rmTBI reduces weight during the period while injuries are occurring. This may represent another measure that can be tracked to determine injury severity and recovery. RNA-seq analysis demonstrated that gene expression at the chronic endpoint could distinguish between the experimental groups even with a mild behavioral phenotype. Future studies would include a more severe injury paradigm to promote longer-lasting behavior changes.

Models of traumatic brain injury-highlights and drawbacks

Traumatic brain injury (TBI) is the leading cause for high morbidity and mortality rates in young adults, survivors may suffer from long-term physical, cognitive, and/or psychological disorders. Establishing better models of TBI would further our understanding of the pathophysiology of TBI and develop new potential treatments. A multitude of animal TBI models have been used to replicate the various aspects of human TBI. Although numerous experimental neuroprotective strategies were identified to be effective in animal models, a majority of strategies have failed in phase II or phase III clinical trials. This failure in clinical translation highlights the necessity of revisiting the current status of animal models of TBI and therapeutic strategies. In this review, we elucidate approaches for the generation of animal models and cell models of TBI and summarize their strengths and limitations with the aim of exploring clinically meaningful neuroprotective strategies.

Dilation of the superior sagittal sinus detected in rat model of mild traumatic brain injury using 1 T magnetic resonance imaging

Introduction

Mild traumatic brain injury (mTBI) is a common injury that can lead to temporary and, in some cases, life-long disability. Magnetic resonance imaging (MRI) is widely used to diagnose and study brain injuries and diseases, yet mTBI remains notoriously difficult to detect in structural MRI. mTBI is thought to be caused by microstructural or physiological changes in the function of the brain that cannot be adequately captured in structural imaging of the gray and white matter. However, structural MRIs may be useful in detecting significant changes in the cerebral vascular system (e.g., the blood-brain barrier (BBB), major blood vessels, and sinuses) and the ventricular system, and these changes may even be detectable in images taken by low magnetic field strength MRI scanners (<1.5T).

Methods

In this study, we induced a model of mTBI in the anesthetized rat animal model using a commonly used linear acceleration drop-weight technique. Using a 1T MRI scanner, the brain of the rat was imaged, without and with contrast, before and after mTBI on post-injury days 1, 2, 7, and 14 (i.e., P1, P2, P7, and P14).

Results

Voxel-based analyses of MRIs showed time-dependent, statistically significant T2-weighted signal hypointensities in the superior sagittal sinus (SSS) and hyperintensities of the gadolinium-enhanced T1-weighted signal in the superior subarachnoid space (SA) and blood vessels near the dorsal third ventricle. These results showed a widening, or vasodilation, of the SSS on P1 and of the SA on P1-2 on the dorsal surface of the cortex near the site of the drop-weight impact. The results also showed vasodilation of vasculature near the dorsal third ventricle and basal forebrain on P1-7.

Discussion

Vasodilation of the SSS and SA near the site of impact could be explained by the direct mechanical injury resulting in local changes in tissue function, oxygenation, inflammation, and blood flow dynamics. Our results agreed with literature and show that the 1T MRI scanner performs at a level comparable to higher field strength scanners for this type of research.

Traumatic Brain Injury Induces Microglial and Caspase3 Activation in the Retina

Traumatic brain injury (TBI) is among the main causes of sudden death after head trauma. These injuries can result in severe degeneration and neuronal cell death in the CNS, including the retina, which is a crucial part of the brain responsible for perceiving and transmitting visual information. The long-term effects of mild-repetitive TBI (rmTBI) are far less studied thus far, even though damage induced by repetitive injuries occurring in the brain is more common, especially amongst athletes. rmTBI can also have a detrimental effect on the retina and the pathophysiology of these injuries is likely to differ from severe TBI (sTBI) retinal injury. Here, we show how rmTBI and sTBI can differentially affect the retina. Our results indicate an increase in the number of activated microglial cells and Caspase3-positive cells in the retina in both traumatic models, suggesting a rise in the level of inflammation and cell death after TBI. The pattern of microglial activation appears distributed and widespread but differs amongst the various retinal layers. sTBI induced microglial activation in both the superficial and deep retinal layers. In contrast to sTBI, no significant change occurred following the repetitive mild injury in the superficial layer, only the deep layer (spanning from the inner nuclear layer to the outer plexiform layer) shows microglial activation. This difference suggests that alternate response mechanisms play a role in the case of the different TBI incidents. The Caspase3 activation pattern showed a uniform increase in both the superficial and deep layers of the retina. This suggests a different action in the course of the disease in sTBI and rmTBI models and points to the need for new diagnostic procedures. Our present results suggest that the retina might serve as such a model of head injuries since the retinal tissue reacts to both forms of TBI and is the most accessible part of the human brain.

A Novel Laser-Based Zebrafish Model for Studying Traumatic Brain Injury and Its Molecular Targets

Traumatic brain injury (TBI) is a major public health problem. Here, we developed a novel model of non-invasive TBI induced by laser irradiation in the telencephalon of adult zebrafish (Danio rerio) and assessed their behavior and neuromorphology to validate the model and evaluate potential targets for neuroreparative treatment. Overall, TBI induced hypolocomotion and anxiety-like behavior in the novel tank test, strikingly recapitulating responses in mammalian TBI models, hence supporting the face validity of our model. NeuN-positive cell staining was markedly reduced one day, but not seven days, after TBI, suggesting increased neuronal damage immediately after the injury, and its fast recovery. The brain-derived neurotrophic factor (Bdnf) level in the brain dropped immediately after the trauma, but fully recovered seven days later. A marker of microglial activation, Iba1, was elevated in the TBI brain, albeit decreasing from Day 3. The levels of hypoxia-inducible factor 1-alpha (Hif1a) increased 30 min after the injury, and recovered by Day 7, further supporting the construct validity of the model. Collectively, these findings suggest that our model of laser-induced brain injury in zebrafish reproduces mild TBI and can be a useful tool for TBI research and preclinical neuroprotective drug screening.

Brain Trauma, Glucocorticoids and Neuroinflammation: Dangerous Liaisons for the Hippocampus

Glucocorticoid-dependent mechanisms of inflammation-mediated distant hippocampal damage are discussed with a focus on the consequences of traumatic brain injury. The effects of glucocorticoids on specific neuronal populations in the hippocampus depend on their concentration, duration of exposure and cell type. Previous stress and elevated level of glucocorticoids prior to pro-inflammatory impact, as well as long-term though moderate elevation of glucocorticoids, may inflate pro-inflammatory effects. Glucocorticoid-mediated long-lasting neuronal circuit changes in the hippocampus after brain trauma are involved in late post-traumatic pathology development, such as epilepsy, depression and cognitive impairment. Complex and diverse actions of the hypothalamic–pituitary–adrenal axis on neuroinflammation may be essential for late post-traumatic pathology. These mechanisms are applicable to remote hippocampal damage occurring after other types of focal brain damage (stroke, epilepsy) or central nervous system diseases without obvious focal injury. Thus, the liaisons of excessive glucocorticoids/dysfunctional hypothalamic–pituitary–adrenal axis with neuroinflammation, dangerous to the hippocampus, may be crucial to distant hippocampal damage in many brain diseases. Taking into account that the hippocampus controls both the cognitive functions and the emotional state, further research on potential links between glucocorticoid signaling and inflammatory processes in the brain and respective mechanisms is vital.

A role of Na+, K+ -ATPase in spatial memory deficits and inflammatory/oxidative stress after recurrent concussion in adolescent rats

Sports-related concussions are particularly common during adolescence, and there is insufficient knowledge about how recurrent concussions in this phase of life alter the metabolism of essential structures for memory in adulthood. In this sense, our experimental data revealed that seven recurrent concussions (RC) in 35-day-old rats decreased short-term and long-term memory in the object recognition test (ORT) 30 days after injury. The RC protocol did not alter motor and anxious behavior and the immunoreactivity of brain-derived neurotrophic factor (BDNF) in the cerebral cortex. Recurrent concussions induced the inflammatory/oxidative stress characterized here by increased glial fibrillary acidic protein (GFAP), interleukin 1β (IL 1β), 4-hydroxynonenal (4 HNE), protein carbonyl immunoreactivity, and 2',7'-dichlorofluorescein diacetate oxidation (DCFH) levels and lower total antioxidant capacity (TAC). Inhibited Na⁺,K⁺-ATPase activity (specifically isoform α_2/3) followed by K_m (Michaelis-Menten constant) for increased ATP levels and decreased immunodetection of alpha subunit of this enzyme, suggesting that cognitive impairment after RC is caused by the inability of surviving neurons to maintain ionic gradients in selected targets to inflammatory/oxidative damage, such as Na,K-ATPase activity.