Network Actions of Pentobarbital in the Rat Mesopontine Tegmentum on Sensory Inflow Through the Spinothalamic Tract

The recent discovery of a barbiturate-sensitive “general anesthesia switch” mechanism localized in the rat brain stem mesopontine tegmental anesthesia area (MPTA) has challenged the current view of the nonspecific actions of general anesthetic agents in the CNS. In this study we provide electrophysiological evidence that the antinociception, which accompanies the behavioral state resembling general anesthesia following pentobarbital (PB) microinjections into the MPTA of awake rats, could be accompanied by the attenuation of sensory transmission through the spinothalamic tract (STT). Following bilateral microinjections of PB into the MPTA spontaneous firing rate (SFR), antidromic firing index (FI), and sciatic (Sc) as well as sural (Su) nerve-evoked responses (ER) of identified lumbar STT neurons in the isoflurane-anesthetized rat were quantified using extracellular recording techniques. Microinjections of PB into the MPTA significantly suppressed the SFR (47%), magnitudes of Sc- (26%) and Su-ER (36%), and FI (41%) of STT neurons. Microinjections of PB-free vehicle control did not alter any of the above-cited electrophysiological parameters. The results from this study suggest that antinociception, which occurs during the anesthesia-like state following PB microinjections into the MPTA, may be due, in part, to (in)direct inhibition of STT neurons via switching mechanism(s) located in the MPTA. This study provides a provenance for investigating electrophysiologically the actions on STT neurons of other current agents used clinically to maintain the state of general anesthesia

Towards clinical management of traumatic brain injury: a review of models and mechanisms from a biomechanical perspective

Traumatic brain injury (TBI) is a major worldwide healthcare problem. Despite promising outcomes from many preclinical studies, the failure of several clinical studies to identify effective therapeutic and pharmacological approaches for TBI suggests that methods to improve the translational potential of preclinical studies are highly desirable. Rodent models of TBI are increasingly in demand for preclinical research, particularly for closed head injury (CHI), which mimics the most common type of TBI observed clinically. Although seemingly simple to establish, CHI models are particularly prone to experimental variability. Promisingly, bioengineering-oriented research has advanced our understanding of the nature of the mechanical forces and resulting head and brain motion during TBI. However, many neuroscience-oriented laboratories lack guidance with respect to fundamental biomechanical principles of TBI. Here, we review key historical and current literature that is relevant to the investigation of TBI from clinical, physiological and biomechanical perspectives, and comment on how the current challenges associated with rodent TBI models, particularly those involving CHI, could be improved

The liver X receptor agonist GW3965 improves recovery from mild repetitive traumatic brain injury in mice partly through apolipoprotein E.

Traumatic brain injury (TBI) increases Alzheimer's disease (AD) risk and leads to the deposition of neurofibrillary tangles and amyloid deposits similar to those found in AD. Agonists of Liver X receptors (LXRs), which regulate the expression of many genes involved in lipid homeostasis and inflammation, improve cognition and reduce neuropathology in AD mice. One pathway by which LXR agonists exert their beneficial effects is through ATP-binding cassette transporter A1 (ABCA1)-mediated lipid transport onto apolipoprotein E (apoE). To test the therapeutic utility of this pathway for TBI, we subjected male wild-type (WT) and apoE-/- mice to mild repetitive traumatic brain injury (mrTBI) followed by treatment with vehicle or the LXR agonist GW3965 at 15 mg/kg/day. GW3965 treatment restored impaired novel object recognition memory in WT but not apoE-/- mice. GW3965 did not significantly enhance the spontaneous recovery of motor deficits observed in all groups. Total soluble Aβ(40) and Aβ(42) levels were significantly elevated in WT and apoE-/- mice after injury, a response that was suppressed by GW3965 in both genotypes. WT mice showed mild but significant axonal damage at 2 d post-mrTBI, which was suppressed by GW3965. In contrast, apoE-/- mice showed severe axonal damage from 2 to 14 d after mrTBI that was unresponsive to GW3965. Because our mrTBI model does not produce significant inflammation, the beneficial effects of GW3965 we observed are unlikely to be related to reduced inflammation. Rather, our results suggest that both apoE-dependent and apoE-independent pathways contribute to the ability of GW3965 to promote recovery from mrTBI

Merging pathology with biomechanics using CHIMERA (Closed-Head Impact Model of Engineered Rotational Acceleration): a novel, surgery-free model of traumatic brain injury

Background: Traumatic brain injury (TBI) is a major health care concern that currently lacks any effective treatment. Despite promising outcomes from many preclinical studies, clinical evaluations have failed to identify effective pharmacological therapies, suggesting that the translational potential of preclinical models may require improvement. Rodents continue to be the most widely used species for preclinical TBI research. As most human TBIs result from impact to an intact skull, closed head injury (CHI) models are highly relevant, however, traditional CHI models suffer from extensive experimental variability that may be due to poor control over biomechanical inputs. Here we describe a novel CHI model called CHIMERA (Closed-Head Impact Model of Engineered Rotational Acceleration) that fully integrates biomechanical, behavioral, and neuropathological analyses. CHIMERA is distinct from existing neurotrauma model systems in that it uses a completely non-surgical procedure to precisely deliver impacts of prescribed dynamic characteristics to a closed skull while enabling kinematic analysis of unconstrained head movement. In this study, we characterized head kinematics as well as functional, neuropathological, and biochemical outcomes up to 14d following repeated TBI (rTBI) in adult C57BL/6 mice using CHIMERA. Results Head kinematic analysis showed excellent repeatability over two closed head impacts separated at 24h. Injured mice showed significantly prolonged loss of righting reflex and displayed neurological, motor, and cognitive deficits along with anxiety-like behavior. Repeated TBI led to diffuse axonal injury with extensive microgliosis in white matter from 2-14d post-rTBI. Injured mouse brains also showed significantly increased levels of TNF-α and IL-1β and increased endogenous tau phosphorylation. Conclusions Repeated TBI using CHIMERA mimics many of the functional and pathological characteristics of human TBI with a reliable biomechanical response of the head. This makes CHIMERA well suited to investigate the pathophysiology of TBI and for drug development programs.Applied Science, Faculty ofMechanical Engineering, Department ofOrthopaedics, Department ofPathology and Laboratory Medicine, Department ofMedicine, Faculty ofReviewedFacult

CHIMERA repetitive mild traumatic brain injury induces chronic behavioural and neuropathological phenotypes in wild-type and APP/PS1 mice

Background: The annual incidence of traumatic brain injury (TBI) in the United States is over 2.5 million, with approximately 3–5 million people living with chronic sequelae. Compared with moderate-severe TBI, the long-term effects of mild TBI (mTBI) are less understood but important to address, particularly for contact sport athletes and military personnel who have high mTBI exposure. The purpose of this study was to determine the behavioural and neuropathological phenotypes induced by the Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA) model of mTBI in both wild-type (WT) and APP/PS1 mice up to 8 months post-injury. Methods: Male WT and APP/PS1 littermates were randomized to sham or repetitive mild TBI (rmTBI; 2 × 0.5 J impacts 24 h apart) groups at 5.7 months of age. Animals were assessed up to 8 months post-injury for acute neurological deficits using the loss of righting reflex (LRR) and Neurological Severity Score (NSS) tasks, and chronic behavioural changes using the passive avoidance (PA), Barnes maze (BM), elevated plus maze (EPM) and rotarod (RR) tasks. Neuropathological assessments included white matter damage; grey matter inflammation; and measures of Aβ levels, deposition, and aducanumab binding activity. Results: The very mild CHIMERA rmTBI conditions used here produced no significant acute neurological or motor deficits in WT and APP/PS1 mice, but they profoundly inhibited extinction of fear memory specifically in APP/PS1 mice over the 8-month assessment period. Spatial learning and memory were affected by both injury and genotype. Anxiety and risk-taking behaviour were affected by injury but not genotype. CHIMERA rmTBI induced chronic white matter microgliosis, axonal injury and astrogliosis independent of genotype in the optic tract but not the corpus callosum, and it altered microgliosis in APP/PS1 amygdala and hippocampus. Finally, rmTBI did not alter long-term tau, Aβ or amyloid levels, but it increased aducanumab binding activity. Conclusions: CHIMERA is a useful model to investigate the chronic consequences of rmTBI, including behavioural abnormalities consistent with features of post-traumatic stress disorder and inflammation of both white and grey matter. The presence of human Aβ greatly modified extinction of fear memory after rmTBI.Applied Science, Faculty ofMedicine, Faculty ofOther UBCMechanical Engineering, Department ofMedicine, Department ofNeurology, Division ofPathology and Laboratory Medicine, Department ofReviewedFacult

Chronic Exposure to Androgenic-Anabolic Steroids Exacerbates Axonal Injury and Microgliosis in the CHIMERA Mouse Model of Repetitive Concussion

<div><p>Concussion is a serious health concern. Concussion in athletes is of particular interest with respect to the relationship of concussion exposure to risk of chronic traumatic encephalopathy (CTE), a neurodegenerative condition associated with altered cognitive and psychiatric functions and profound tauopathy. However, much remains to be learned about factors other than cumulative exposure that could influence concussion pathogenesis. Approximately 20% of CTE cases report a history of substance use including androgenic-anabolic steroids (AAS). How acute, chronic, or historical AAS use may affect the vulnerability of the brain to concussion is unknown. We therefore tested whether antecedent AAS exposure in young, male C57Bl/6 mice affects acute behavioral and neuropathological responses to mild traumatic brain injury (TBI) induced with the CHIMERA (Closed Head Impact Model of Engineered Rotational Acceleration) platform. Male C57Bl/6 mice received either vehicle or a cocktail of three AAS (testosterone, nandrolone and 17α-methyltestosterone) from 8–16 weeks of age. At the end of the 7^th week of treatment, mice underwent two closed-head TBI or sham procedures spaced 24 h apart using CHIMERA. Post-repetitive TBI (rTBI) behavior was assessed for 7 d followed by tissue collection. AAS treatment induced the expected physiological changes including increased body weight, testicular atrophy, aggression and downregulation of brain 5-HT1B receptor expression. rTBI induced behavioral deficits, widespread axonal injury and white matter microgliosis. While AAS treatment did not worsen post-rTBI behavioral changes, AAS-treated mice exhibited significantly exacerbated axonal injury and microgliosis, indicating that AAS exposure can alter neuronal and innate immune responses to concussive TBI.</p></div

Chronic AAS treatment in mice induces physiological changes.

<p>Prior to rTBI, mice were treated 5 d per week for 7 weeks with a cocktail of androgenic-anabolic steroids (AAS) or sesame oil vehicle (VH). Cohort size: VH: N = 22, AAS: N = 23. (A) Percent increase in body weight in AAS and VH-treated mice over time. (B) Comparison of weights of seminal vesicles (SV), testes (TT), and brain (BR) collected at 7 d post-rTBI. (C) Macroscopic size comparison of seminal vesicle, testes and brain. Scale bar = 1cm. In all graphs, data are presented as mean ± SEM values. Body weight data are analyzed by two-way repeated measures ANOVA followed by a Bonferroni post hoc test, tissue weight data were analyzed by two-tailed unpaired t test. For all graphs, *: <i>p</i> < 0.05, ***: <i>p</i> < 0.001, ****: <i>p</i> < 0.0001.</p

Quantitative analysis of the microglial response to rTBI.

<p>Microglial morphology was quantitatively assessed using fractal analysis. Graphs in the left column represent fractal dimension for microglial morphology in (A) olfactory nerve layer, (B) corpus callosum, (C) brachium of superior colliculus and (D) optic tract. Graphs in the right column (E-H) show number of Iba1-positive cells per mm² in the same white matter regions. For all graphs, * indicates a significant rTBI effect compared to the respective sham values and # indicates a significant treatment effect between rTBI groups. Data are analyzed by two-way ANOVA followed by a Tukey post-hoc test. For all graphs *: <i>p</i> < 0.05, **: <i>p</i> < 0.01, ***: <i>p</i> < 0.001, ****: <i>p</i> < 0.0001, #: <i>p</i> < 0.05, ##: <i>p</i> < 0.01.</p

Chronic AAS treatment does not exacerbate acute post-rTBI behavioral deficits.

<p>(A) Duration of loss of righting reflex (LRR) was assessed immediately following the sham or TBI procedure. (B) Composite neurological severity score (NSS) was assessed at 1 h and at 1, 2 and 7 d post-rTBI. (C) Motor performance was assessed on an accelerating rotarod at 1, 2, and 7 d post-rTBI. The graph depicts fall latency in seconds at baseline before rTBI and at three post-rTBI time points. (D) Thigmotaxis was quantified at 1 and 6 d post-rTBI and is represented as thigmotaxis index. (E) Aggressive behavior was assessed with the RIT at the 5^th (RIT # 1) and 6^th (RIT # 2) week following initiation of AAS treatment (pre-rTBI) as well as at 5 d (RIT # 3) post-rTBI. Graphs represent latency to initiate fighting by the resident mouse. Data in all graphs are presented as mean ± SEM. Data are analyzed by repeated measures general linear model. Legends and cohort sizes are consistent across all graphs.</p

Chronic AAS treatment in mice exacerbates post-rTBI axonal injury.

<p>Post-rTBI axonal damage was assessed with silver staining. Representative 40X-magnified images of corpus callosum, external capsule, septal-fimbrial area and optic tract of sham (left column) and VH- (middle column) and AAS-treated (right column) rTBI brains are depicted.</p