Severity Assessment in Rats Undergoing Subarachnoid Hemorrhage Induction by Endovascular Perforation or Corresponding Sham Surgery

INTRODUCTION: Animal models for preclinical research of subarachnoid hemorrhage (SAH) are widely used as much of the pathophysiology remains unknown. However, the burden of these models inflicted on the animals is not well characterized. The European directive requires severity assessment-based allocation to categories. Up to now, the classification into predefined categories is rather subjective and often without underlying scientific knowledge. We therefore aimed at assessing the burden of rats after SAH or the corresponding sham surgery to provide a scientific assessment. METHODS: We performed a multimodal approach, using different behavior tests, clinical and neurological scoring, and biochemical markers using the common model for SAH of intracranial endovascular filament perforation in male Wistar rats. Up to 7 days after surgery, animals with SAH were compared to sham surgery and to a group receiving only anesthesia and analgesia. RESULTS: Sham surgery (n = 15) and SAH (n = 16) animals showed an increase in the clinical score the first days after surgery, indicating clinical deterioration, while animals receiving only anesthesia without surgery (n = 5) remained unaffected. Body weight loss occurred in all groups but was more pronounced and statistically significant only after surgery. The analysis of burrowing, open field (total distance, erections), balance beam, and neuroscore showed primarily an effect of the surgery itself in sham surgery and SAH animals. Only concerning balance beam and neuroscore, a difference was visible between sham surgery and SAH. The outcome of the analysis of systemic and local inflammatory parameters and of corticosterone in blood and its metabolites in feces was only robust in animals suffering from larger bleedings. Application of principal component analysis resulted in a clear separation of sham surgery and SAH animals from their respective baseline as well as from the anesthesia-only group at days 1 and 3, with the difference between sham surgery and SAH being not significant. DISCUSSION/CONCLUSION: To our knowledge, we are the first to publish detailed clinical score sheet data combined with advanced behavioral assessment in the endovascular perforation model for SAH in rats. The tests chosen here clearly depict an impairment of the animals within the first days after surgery and are consequently well suited for assessment of the animals' suffering in the model. A definitive classification into one of the severity categories named by the EU directive is yet pending and has to be performed in the future by including the assessment data from different neurological and nonneurological disease models.