Un modèle Roman de lésions cérébrales traumatiques légères pour les jeunes rats
Summary
The modified weight-drop technique is an easy, cost-effective procedure used for the induction of mild traumatic brain injury in juvenile rats. This novel technique produces clinically relevant symptomology that will advance the study of mild traumatic brain injury (mTBI) and concussion.
Abstract
Despite growing evidence that childhood represents a major risk period for mild traumatic brain injury (mTBI) from sports-related concussions, motor vehicle accidents, and falls, a reliable animal model of mTBI had previously not been developed for this important aspect of development. The modified weight-drop technique employs a glancing impact to the head of a freely moving rodent transmitting acceleration, deceleration, and rotational forces upon the brain. When applied to juvenile rats, this modified weight-drop technique induced clinically relevant behavioural outcomes that were representative of post-concussion symptomology. The technique is a rapidly applied procedure with an extremely low mortality rate, rendering it ideal for high-throughput studies of therapeutics. In addition, because the procedure involves a mild injury to a closed head, it can easily be used for studies of repetitive brain injury. Owing to the simplistic nature of this technique, and the clinically relevant biomechanics of the injury pathophysiology, the modified weight-drop technique provides researchers with a reliable model of mTBI that can be used in a wide variety of behavioural, molecular, and genetic studies.
Introduction
Bien qu'il existe de nombreuses méthodes largement utilisé pour la génération de la forme modérée à sévère lésion cérébrale traumatique (TBI), très peu de techniques ont été développées pour induire doux, fermé blessures à la tête chez les rongeurs. Compte tenu du fait que les lésions cérébrales traumatiques légères (TCL) est trois fois plus fréquente que la lésion cérébrale modérée et sévère combinée 1, un modèle fiable de TCL est nécessaire pour faciliter la recherche concernant la physiopathologie, les résultats neurobiologiques et comportementales, et les stratégies thérapeutiques. Par exemple, en partie à cause des limitations de modèles animaux actuels 2, dans la dernière décennie, il ya eu plus de 200 échoué essais cliniques de médicaments pour le traitement de TBI 3. Lorsque les systèmes de modélisation sont générés pour les études de recherche translationnelle, l'applicabilité des résultats dépendent de la validité du modèle mis en œuvre. Pour l'étude de TCL / commotion cérébrale, un modèle animal fiable serait non seulement imiter la biomécanique forces responSible de blessure étiologie, mais également induire des symptômes compatibles avec ceux rapportés par la population cliniquement pertinente. En outre, parce que les enfants sont à risque particulièrement élevé pour les TCL, systèmes de modélisation optimale serait applicable aux jeunes et aux jeunes rongeurs, en plus de leurs équivalents adultes.
Analyses biomécaniques de circonstances dans lesquelles les athlètes ont subies mTBIs ou lésions cérébrales commotion indiquent que les facteurs prédictifs les plus critiques pour les blessures sont l'accélération rapide de la tête et les impacts à haute vitesse 4. La majorité des modèles de rongeurs actuellement employées pour l'induction de TBI permet peu ou pas de mouvement de la tête 5 (pour revue, voir 2). Le modèle présenté ici, délivre un impact à grande vitesse à la tête d'un rat juvénile physiquement effrénée qui est accompagné par une rotation de 180 ° et de chute libre qui se applique forces d'accélération / décélération à la tête et le corps du sujet. Tvoici deux principaux avantages associés à cette technique de la goutte de poids modifiée pour l'induction de TCL. Premièrement, le modèle produit commotion cliniquement pertinente comme symptomatologie sans causer aucun dommage manifeste au cerveau (pour une description complète des résultats comportementaux voir 6). Aussi compatible avec les rapports cliniques du syndrome post-commotion, cette technique poids-goutte modifiée produit des résultats hétérogènes. Bien que les effets de la TCL sont importants, il ya des variations importantes entre les rongeurs qui ont connu une TCL quand on l'examine de multiples mesures des résultats. Deuxièmement, la méthode permet l'étude de TCL répétitif 7. Comme la majorité des modèles de TBI existants infliger de telles blessures graves, il est souvent difficile d'induire une deuxième blessure, et presque impossible à étudier TBI répétitif sans d'importants dommages à l'ensemble du cortex.
Par conséquent, la principale raison pour utiliser la technique de la goutte de poids modifié pour le induction des TCL est de produire une blessure qui représente plus étroitement la physiopathologie et la symptomatologie de commotion cérébrale et répétitif TBI dans les populations juvéniles. Avec l'incidence croissante de TCL liés aux sports, les chutes et les accidents de la route, en particulier pendant l'enfance, ce modèle de rongeur unique de TCL fournit aux chercheurs un outil précieux pour l'étude de la lésion cérébrale commotion semblable qui peut être facilement appliquée à plusieurs succès paradigmes.
Protocol
Representative Results
Discussion
Reliable modelling systems are needed to effectively cultivate basic science research that has significant translational validity. In response to rising occurrences and popular media, the investigation of mTBI and concussion has become a priority in many disciplines. However, despite increased research, there have been only incremental improvements in therapeutic strategies and treatment options 3. This lack of progress may be partially due to a discrepancy between the modeling systems employed and actual injury etiology. The majority of studies utilized rodent models that failed to reproduce the important biomechanical forces and appropriate post-injury symptomology. The current human definition of mTBI specifies that the injury results from acceleration and deceleration forces associated with a blunt trauma 10. The modified weight drop technique described here is therefore an ideal model for the study of mTBI and concussion because it uses a glancing impact to cause rapid rotational acceleration and deceleration to the head of an unrestrained animal, mimicking the biomechanical forces identified in sports-related injuries and automobile accidents. In addition, this model is easily adapted to examine repetitive mTBI, a phenomena that is emerging as a serious medical and socioeconomic issue. Studies indicate that rodents may be exposed to a series of 10 distinct mTBIs with minimal mortality 7. Finally, the method is inexpensive and can be carried out rapidly, allowing for high-throughput examination of a many therapeutic compounds and treatment regiments.
Just as with any procedural technique, certain aspects of the protocol are particularly important to the generation of reliable results. First, the tin foil needs to be scored effectively. If the tin foil is not properly scored, the force imparted by the weight during the glancing impact will not be enough to propel the juvenile rat through the tin foil onto the collection sponge. In these situations, the rat will remain in the starting position (chest down on the tin foil) and the mTBI will result from the blunt trauma from the weight impacting the stationary head, not the rotational acceleration and deceleration desired. Second, during the induction of the mTBI and the sham injury, the level of anesthetic applied to each rat should be consistent. Owing to the fact that time-to-right is used as marker of mTBI, the researcher should try to ensure that animals receiving a mTBI and animals receiving a sham injury are exposed to similar levels of anesthetic. A major advantage to this technique over many other TBI procedures is the low level and duration of anesthesiology. However, the juvenile rat needs to be non-responsive to a toe or tail pinch to ensure they do not wake-up on the stage before the injury is induced. Finally, in order to maintain a consistent injury etiology, the positioning of the rat’s head is particularly important. Ideally the weight should impact the center of the dorsal surface of the head. Caution should be taken to avoid positioning the path of the weight too near the caudal/posterior portion of the head, as impacting the brainstem and cerebellum is associated with increased mortality and seizure activity.
Based upon the biomechanical pathophysiology of injury induction and the behavioural outcomes examined, the modified weight-drop technique appears to be a reliable model for the investigation of paediatric mTBI and concussion. Although preliminary studies of this novel model have assessed some basic molecular and structural changes 7 future studies will be needed to ascertain how the brain responds to a mTBI with this injury etiology. An in-depth analysis of the neuroanatomical and biological changes that occur at the cellular and epigenetic level would increase model validity and translational applicability. In addition to stimulating the generation of targeted pharmacological therapies, understanding the pathophysiological changes that occur in the brain in response to mTBI and concussion would also direct the research related to clinical biomarkers that have the ability to predict outcomes following injury.
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
The authors would like to thank Irene Ma, Rose Tobais, and Jong Rho for their technical assistance. Funding was provided to MJE by the Department of Pediatrics at the University of Calgary, the Alberta Children’s Hospital Foundation (ACHF) and the Alberta Children’s Hospital Research Institute (ACHRI). The Postdoctoral fellowship for RM was provided by ACHF.
Materials
| Brass Weights | Ginsberg Scientific | 7-2500-2 | Need to have metal loop attached to base |
| Alluminum Foil | Alcan | Available at most grocery stores | |
| Masking Tape | Commercially available | ||
| U-Shaped Plastic Stand | Constructed by Laboratory | ||
| Clamp Stand | Sigma-Aldrich | Z190357 | |
| Plastic Guide Tube | Could be constructed or purchased at a hardware store | ||
| Fishing Line | Angler 10lb | Purchased from a sporting goods retailer | |
| Isoflurane | Pharmaceutical Partners of Canada | DIN 02237518 | Inhalation Anesthetic |
| Topical Lidocaine (30ml) | Astra Zeneca | DIN 0001694 | Xylocaine Jelly 2% |
| Cotton Swabs | Commercially available | ||
| Heating Pad – 3 heat setting | Commercially available | ||
| Stop Watch | Sportline | L303 | Purchased from a sporting goods retailer |
| Video Camera | Sony | HDR-CX260V | |
| Sprague Dawley Rats | Charles River Laboratories | SAS SD 40 | Male and females ordered from Charles River Laboratories and pups bred in-house |
| Balance Beam | Constructed by Laboratory |
Riferimenti
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- Mychasiuk, R., Hehar, H., Farran, A., Esser, M. J. Mean Girls: Sex differences in the effects of mild traumatic brain injury on the social dynamics of juvenile rat play behaviour. Behavioural Brain Research. 259, (2014).
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