Severity assessment of complex and repeated intracranial surgery in rats

Abstract

Introduction Evidence-based grading of the impact of intracranial surgery on rat’s well-being is important for ethical and legal reasons. We assessed the severity of complex and repeated intracranial surgery in a 6-hydroxydopamine (6-OHDA) Parkinson’s rat model with subsequent intracranial electrode implantation, and in an intracranial tumor model with subsequent resection. Methods Stereotactic surgery was performed in adult male rats with the same general anesthesia and perioperative pain management. In the Parkinson’s model, Sprague Dawley (SD) rats received unilateral injection of 6-OHDA (n=11) or vehicle (n=7) into the medial forebrain bundle as first operation. After four weeks, neural electrodes were implanted in all rats as second operation. For tumor formation, BDIX/ UlmHanZtm (BDIX) rats (n=8) received frontocortical injection of BT4Ca cells as first operation, followed by tumor resection as second operation after one week. Multiple measures severity assessment was done two days before and four days after surgery in all rats, comprising clinical scoring, body weight and detailed behavioral screening. To include a condition with a known burden, rats with intracranial tumors were additionally assessed up to a predefined humane endpoint that has previously been classified as "moderate". Results After the first operation, only 6-OHDA injection resulted in transient elevated clinical scores, a mild long-lasting weight reduction and motor disturbances. After the second surgery, body weight was transiently reduced in all groups. All other parameters showed variable results. Principal Component Analysis showed a separation from the preoperative state driven by motor-related parameters after 6-OHDA injection, while separation after electrode implantation and more clearly after tumor resection was driven by pain-related parameters, although not reaching the level of the humane endpoint of our tumor model. Conclusion Overall, cranial surgery of different complexity only transiently and rather mildly affects rat’s well-being. Multiple measures assessment allows the differentiation of model-related motor disturbances in the Parkinson’s model from potentially pain-related conditions after tumor resection and electrode implantation.