A sensitive and reliable locomotor rating scale for open field testing in rats

Behavioral assessment after spinal cord contusion has long focused on open field locomotion using modifications of a rating scale developed by Tarlov and Klinger (1954). However, on-going modifications by several groups have made interlaboratory comparison of locomotor outcome measures difficult. The purpose of the present study was to develop an efficient, expanded, and unambiguous locomotor rating scale to standardize locomotor outcome measures across laboratories. Adult rats (n = 85) were contused at T7-9 cord level with an electromagnetic or weight drop device. Locomotor behavior was evaluated before injury, on the first or second postoperative day, and then for up to 10 weeks. Scoring categories and attributes were identified, operationally defined, and ranked based on the observed sequence of locomotor recovery patterns. These categories formed the Basso, Beattie, Bresnahan (BBB) Locomotor Rating Scale. The data indicate that the BBB scale is a valid and predictive measure of locomotor recovery able to distinguish behavioral outcomes due to different injuries and to predict anatomical alterations at the lesion center. Interrater reliability tests indicate that examiners with widely varying behavioral testing experience can apply the scale consistently and obtain similar scores. The BBB Locomotor Rating Scale offers investigators a more discriminating measure of behavioral outcome to evaluate treatments after spinal cord injury.