Graded crush of the rat optic nerve as a brain injury model: combining electrophysiological and behavioral outcome

In the present study, we have developed an animal model for central nervous system (CNS) damage using the graded crush injury of the adult rat optic nerve. This injury model has the following characteristics: (a) the injuries are reproducible; (b) the injuries can be created with controlled severity; and (c) variations in the severity of the injuries correlate with definable electrophysiological and behavioral outcomes. Self-closing forceps, modified by attaching a screw to the handle, were used as a lesion-causing device. Rat optic nerves were crushed in vitro. The severity of the injury, calibrated by a measured applied force, was determined, electrophysiologically, in vitro. Compound action potential was assessed and recorded by suction electrodes connected to both sides of the nerve. In vivo studies correlated the calibrated crush injuries with behavioral outcome. After severe crush (applied force: 205 g or higher), the rats were unable to orient towards visual stimuli presented in the visual field of the damaged nerve and only minor transient recovery was observed. After moderate crush (applied force: 120 g), however, there was a significant recovery of orienting performance up to the 6th postoperative day, followed by a gradual, secondary loss of function. In the mildly injured group (applied force lower than 30 g), functional improvement continued for up to 10 days and remained stable thereafter, with only minor secondary loss. This CNS graded injury model may be valuable to study the molecular and anatomical mechanisms underlying secondary degeneration and the potency of various posttraumatic treatments in leading to recovery of function.