A novel rat model of heterotopic ossification after polytrauma with traumatic brain injury.

Neurological heterotopic ossification (NHO) is characterized by abnormal bone growth in soft tissue and joints in response to injury to the central nervous system. The ectopic bone frequently causes pain, restricts mobility, and decreases the quality of life for those affected. NHO commonly develops in severe traumatic brain injury (TBI) patients, particularly in the presence of concomitant musculoskeletal injuries (i.e. polytrauma). There are currently no animal models that accurately mimic these combinations of injuries, which has limited our understanding of NHO pathobiology, as well as the development of biomarkers and treatments, in TBI patients. In order to address this shortcoming, here we present a novel rat model that combines TBI, femoral fracture, and muscle crush injury. Young adult male Sprague Dawley rats were randomly assigned into three different injury groups: triple sham-injury, peripheral injury only (i.e., sham-TBI + fracture + muscle injury) or triple injury (i.e., TBI + fracture + muscle injury). Evidence of ectopic bone in the injured hind-limb, as confirmed by micro-computed tomography (µCT), was found at 6-weeks post-injury in 70% of triple injury rats, 20% of peripheral injury rats, and 0% of the sham-injured controls. Furthermore, the triple injury rats had higher ectopic bone severity scores than the sham-injured group. This novel model will provide a platform for future studies to identify underlying mechanisms, biomarkers, and develop evidence based pharmacological treatments to combat this debilitating long-term complication of TBI and polytrauma.

Mild Closed-Head Injury in Conscious Rats Causes Transient Neurobehavioral and Glial Disturbances: A Novel Experimental Model of Concussion.

Rodent models can provide insights into the most pertinent issues surrounding concussion. Nonetheless, the relevance of some existing models to clinical concussion can be questioned, particularly with regard to the use of surgery and anesthesia and the mechanism and severity of injury. Accordingly, we have co-developed an awake closed-head injury (ACHI) model in rats. Here, we aimed to create a temporal profile of the neurobehavioral and neuropathological effects of a single ACHI. Adolescent male rats were placed in a restraint bag and a steel helmet was positioned over the head such that the impact target was centered over the left parietal cortex. Once positioned on a foam platform, a cortical impactor was used to strike the helmet. Sham animals underwent the same procedure without impact. When compared with sham rats, those given a single ACHI displayed evidence of sensorimotor deficits and reduced exploratory behavior within the first 20 min post-injury; however, these effects were resolved after 24 h. A single ACHI impaired spatial memory on the Y-maze task at both 5 min and 24 h post-ACHI; however, no deficits were apparent at 48 h. Immunostaining revealed region-specific increases in ionized calcium-binding adaptor molecule 1 and glial fibrillary acidic protein expression at 3 days post-impact, with no differences found at either 1 or 14 days. Taken together, our findings indicate that a single ACHI results in transient neurobehavioral and glial disturbances and as such, this model may be a valuable tool for pre-clinical concussion research.

Diffusion MRI abnormalities in adolescent rats given repeated mild traumatic brain injury.

OBJECTIVE: Mild traumatic brain injury (mTBI) is a serious health concern in the adolescent population. Repeated mTBI may result in more pronounced deficits, and has been associated with long-term neurological consequences including neurodegeneration. As such, there is a critical need for the development of objective mTBI biomarkers to help guide medical management. Diffusion-weighted imaging (DWI) is an advanced magnetic resonance imaging (MRI) technique that may detect brain abnormalities after mTBI. Diffusion tensor imaging (DTI) is the most commonly applied DWI method, and initial studies have reported DTI changes in mTBI patients. Furthermore, new DWI methods (e.g., track-weighted imaging; TWI) are being developed that may also be sensitive to mTBIs, but remain to be comprehensively studied. METHODS: This study utilized the Awake Closed Head Injury (ACHI) model of mTBI to investigate changes in DTI and TWI following repeated mTBI in adolescent male and female rats. A total of four ACHI impacts, two/day over two consecutive days, were delivered beginning on postnatal day 25. At 1 day and 7 days postinjury, rats were euthanized and brains were collected for DWI analyses. RESULTS: Rats given repeated mTBI displayed changes in fractional anisotropy and radial diffusivity (i.e., DTI measures), as well as track density (i.e., TWI). INTERPRETATION: These findings are consistent with initial DTI findings in mTBI patients, suggest that TWI may complement DTI, support the utility of DWI measures as biomarkers in mTBI, and further validate the ACHI rat model of mTBI.

Elimination of vesicular zinc alters the behavioural and neuroanatomical effects of social defeat stress in mice.

Chronic stress can have deleterious effects on mental health, increasing the risk of developing depression or anxiety. But not all individuals are equally affected by stress; some are susceptible while others are more resilient. Understanding the mechanisms that lead to these differing outcomes has been a focus of considerable research. One unexplored mechanism is vesicular zinc - zinc that is released by neurons as a neuromodulator. We examined how chronic stress, induced by repeated social defeat, affects mice that lack vesicular zinc due to genetic deletion of zinc transporter 3 (ZnT3). These mice, unlike wild type mice, did not become socially avoidant of a novel conspecific, suggesting resilience to stress. However, they showed enhanced sensitivity to the potentiating effect of stress on cued fear memory. Thus, the contribution of vesicular zinc to stress susceptibility is not straightforward. Stress also increased anxiety-like behaviour but produced no deficits in a spatial Y-maze test. We found no evidence that microglial activation or hippocampal neurogenesis accounted for the differences in behavioural outcome. Volumetric analysis revealed that ZnT3 KO mice have larger corpus callosum and parietal cortex volumes, and that corpus callosum volume was decreased by stress in ZnT3 KO, but not wild type, mice.

Repeated mild traumatic brain injury can cause acute neurologic impairment without overt structural damage in juvenile rats.

Repeated concussion is becoming increasingly recognized as a serious public health concern around the world. Moreover, there is a greater awareness amongst health professionals of the potential for repeated pediatric concussions to detrimentally alter the structure and function of the developing brain. To better study this issue, we developed an awake closed head injury (ACHI) model that enabled repeated concussions to be performed reliably and reproducibly in juvenile rats. A neurological assessment protocol (NAP) score was generated immediately after each ACHI to help quantify the cumulative effects of repeated injury on level of consciousness, and basic motor and reflexive capacity. Here we show that we can produce a repeated ACHI (4 impacts in two days) in both male and female juvenile rats without significant mortality or pain. We show that both single and repeated injuries produce acute neurological deficits resembling clinical concussion symptoms that can be quantified using the NAP score. Behavioural analyses indicate repeated ACHI acutely impaired spatial memory in the Barnes maze, and an interesting sex effect was revealed as memory impairment correlated moderately with poorer NAP score performance in a subset of females. These cognitive impairments occurred in the absence of motor impairments on the Rotarod, or emotional changes in the open field and elevated plus mazes. Cresyl violet histology and structural magnetic resonance imaging (MRI) indicated that repeated ACHI did not produce significant structural damage. MRI also confirmed there was no volumetric loss in the cortex, hippocampus, or corpus callosum of animals at 1 or 7 days post-ACHI. Together these data indicate that the ACHI model can provide a reliable, high throughput means to study the effects of concussions in juvenile rats.

Prenatal ethanol exposure impairs temporal ordering behaviours in young adult rats.

Prenatal ethanol exposure (PNEE) causes significant deficits in functional (i.e., synaptic) plasticity in the dentate gyrus (DG) and cornu ammonis (CA) hippocampal sub-regions of young adult male rats. Previous research has shown that in the DG, these deficits are not apparent in age-matched PNEE females. This study aimed to expand these findings and determine if PNEE induces deficits in hippocampal-dependent behaviours in both male and female young adult rats (PND 60). The metric change behavioural test examines DG-dependent deficits by determining whether an animal can detect a metric change between two identical objects. The temporal order behavioural test is thought to rely in part on the CA sub-region of the hippocampus and determines whether an animal will spend more time exploring an object that it has not seen for a larger temporal window as compared to an object that it has seen more recently. Using the liquid diet model of FASD (where 6.6% (v/v) ethanol is provided through a liquid diet consumed ad libitum throughout the entire gestation), we found that PNEE causes a significant impairment in the temporal order task, while no deficits in the DG-dependent metric change task were observed. There were no significant differences between males and females for either task. These results indicate that behaviours relying partially on the CA-region may be more affected by PNEE than those that rely on the DG.

The Benefits of Exercise on Structural and Functional Plasticity in the Rodent Hippocampus of Different Disease Models.

In this review, the benefits of physical exercise on structural and functional plasticity in the hippocampus are discussed. The evidence is clear that voluntary exercise in rats and mice can lead to increases in hippocampal neurogenesis and enhanced synaptic plasticity which ultimately result in improved performance in hippocampal-dependent tasks. Furthermore, in models of neurological disorders, including fetal alcohol spectrum disorders, traumatic brain injury, stroke, and neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's disease exercise can also elicit beneficial effects on hippocampal function. Ultimately this review highlights the multiple benefits of exercise on hippocampal function in both the healthy and the diseased brain.

Impairments in hippocampal synaptic plasticity following prenatal ethanol exposure are dependent on glutathione levels.

Previous studies from our laboratory have shown that prenatal ethanol exposure (PNEE) causes a significant deficit in synaptic plasticity, namely long-term potentiation (LTP), in the dentate gyrus (DG) region of the hippocampus of male rats. PNEE has also been shown to induce an increase in oxidative stress and a reduction in antioxidant capacity in the brains of both male and female animals. In this study the interaction between LTP and the major antioxidant in the brain, glutathione (GSH), is examined. We show that depletion of the intracellular reserves of GSH with diethyl maleate (DEM) reduces LTP in control male, but not female animals, mirroring the effects of PNEE. Furthermore, treatment of PNEE animals with N-acetyl cysteine (NAC), a cysteine donor for the synthesis of GSH, increases GSH levels in the hippocampus and completely restores the deficits in LTP in PNEE males. These results indicate that in males GSH plays a major role in regulating LTP, and that PNEE may cause reductions in LTP by reducing the intracellular pool of this endogenous antioxidant.

Effects of Ethanol Exposure during Distinct Periods of Brain Development on Hippocampal Synaptic Plasticity.

Fetal alcohol spectrum disorders occur when a mother drinks during pregnancy and can greatly influence synaptic plasticity and cognition in the offspring. In this study we determined whether there are periods during brain development that are more susceptible to the effects of ethanol exposure on hippocampal synaptic plasticity. In particular, we evaluated how the ability to elicit long-term potentiation (LTP) in the hippocampal dentate gyrus (DG) was affected in young adult rats that were exposed to ethanol during either the 1st, 2nd, or 3rd trimester equivalent. As expected, the effects of ethanol on young adult DG LTP were less severe when exposure was limited to a particular trimester equivalent when compared to exposure throughout gestation. In males, ethanol exposure during the 1st, 2nd or 3rd trimester equivalent did not significantly reduce LTP in the DG. In females, ethanol exposure during either the 1st or 2nd trimester equivalents did not impact LTP in early adulthood, but following exposure during the 3rd trimester equivalent alone, LTP was significantly increased in the female DG. These results further exemplify the disparate effects between the ability to elicit LTP in the male and female brain following perinatal ethanol exposure (PNEE).