The Weight-Drop Model of TBI

A weight-drop device was used to induce a closed-skull TBI as previously described (3, 25). The weight-drop device consisted of a guided- and weighted-rod with a blunt silicone-covered impact tip (3 mm diameter). Each mouse was placed in an anesthesia induction chamber containing 4% isoflurane for 2 min. Once anesthetized, mice were placed in a nose cone that maintained the anesthetic (2% isoflurane) for 3 min and administered 0.05 mg/kg of buprenorphine analgesic subcutaneously. Mice were given a sham or CTX muscle injury as described below, then a 2 cm incision was made along the midline of the scalp to reveal the intact skull. The mouse then removed from the nose cone, stabilized on the weight-drop device platform, the 215 g weighted-rod was released from a distance of 2.5 cm, and the impact tip made contact between the sagittal and coronal suture of the right hemisphere. The rod was retracted immediately after the impact occurred, and the scalp incision was sutured. The sham TBI procedure for the SHAM and CTX groups was identical to that described for the TBI procedure, except the weighted-rod was not released so that no impact occurred. Duration of apnea, loss of consciousness (i.e., hind-limb withdrawal to toe pinch), and self-righting reflex (latency to self-right) were recorded as indicators of acute injury severity (Table ​(Table1)1) (3, 26).

Acute injury measures.

TBI and MULTI groups had significantly longer apnea, unconsciousness (i.e., hindlimb withdrawal reflex to toe pinch), and self-righting reflex times (seconds ± SEM) than SHAM and CTX groups. There were no statistically significant differences between TBI and MULTI.