The Effect of Intrathecal Baclofen Injection on Muscle Stretch Reflex in Spinal Cord Injured Rabbit

ABSTRACT

OBJECTIVE: To develop an experimental model that is useful to evaluate the effect of antispastic medication administered intrathecally and to titrate the intrathecal baclofen effect quantitatively by using muscle stretch reflex. METHOD: Ten rabbits were laminectomized posteriorly and intrathecal catheter was inserted. Then the spinal cords were contused by 12.5 gx20 cm weight drop around 12th thoracic vertebra. After 8~12 days, muscle stretch reflex was measured before intrathecal baclofen injection (ITBI) and after ITBI 30 minutes, 60 minutes, and 120 minutes. Rabbits' triceps surae were dissected and stretched 5 mm at the rate of 2 mm/sec using a step motor. The change of muscle tension was graphed into the time (length)-tension curve. The slope in the time (length)-tension curve was defined as stiffness index (SI). RESULTS: The measurement of muscle stretch reflex was available in 5 of 10 spinal cord injured rabbits. The proportion of SI reduced significantly at 60 minutes and 120 minutes compared to baseline (p=0.005, p<0.001). CONCLUSION: Our data proved the antispastic effect of ITBI quantitatively by using muscle stretch reflex. We concluded that the quantitative measurement method of the antispastic effect of ITBI will be useful in evaluating antispastic effect by intrathecal administration of the other antispastic medications.