Figure 2.

Experimental closed-head impact injury in awake, unanaesthetized (anaesthesia-naïve) mice induces abrupt onset, transient course, and rapid resolution of neurobehavioural impairments that resemble human concussion. (A and B) Schematic of momentum transfer instrument before (A) and after (B) experimental closed-head impact injury. The developed instrument was designed for use with unanaesthetized C57BL/6 mice and is compatible with 100% survival without evidence of skull fracture; subdural, epidural, or subarachnoid haemorrhage; cervical trauma or spinal cord injury; commotio cordis or retinae; or post-traumatic apnoea. Animal subjects are secured across the thorax and positioned prone such that the head is in physical contact with a helmet analogue composed of an inner foam pad (P) and an outer hard shell (Sh) fixed to a mobile sled (S). Sled movement is constrained to linear translation by a low-friction monorail track (not shown). Sled motion is initiated by an operator-triggered computer program that actuates a solenoid valve, releases a bolus of pressurized gas, and accelerates a stainless-steel slug within the instrument barrel. Vent holes in the barrel convert slug motion to constant velocity. Sequential momentum transfer from the slug to a captive stainless-steel rod (R; known mass, m_r, empirically-determined velocity, v_r) and finally to the sled (S; known mass, m_s, empirically-determined velocity, v_s). Sled motion results in closure of the distal gap (G1), opening of the proximal gap (G2), and termination by the backstop (B). A detailed schematic of the developed instrument is shown in Supplementary Fig. 1A. (C) Head motion analysis (time-history plot) during experimental closed-head impact injury reconstructed from high-speed videographic records (100 000 fps; 100 kHz). Head position, acceleration, and jerk are plotted as a function of time after initiation of head motion (t = 0). Maximal head acceleration and jerk are observed within the first millisecond after impact. Experimental parameters were selected to kinematically match head motion in our blast neurotrauma mouse model (Supplementary Table 2). Blue dashed line, mean peak X-acceleration (n = 18 mice). Red dashed line, mean peak X-jerk (n = 18 mice). (D) Composite and subtest scores on the acute neurobehavioural response test battery (Supplementary Fig. 1B) assessed in awake unanaesthetized (anaesthesia-naïve) mice: (i) at pre-injury (baseline test); (ii) at 2 min after experimental closed-head impact injury (IMP) or exposure to the sham (no injury) control condition (CON) (post-injury test); and (iii) after a 3-h rest period (recovery test). Mice subjected to experimental impact injury showed significant decrements in composite scores and all three sub-test scores (open-field, inverted wire mesh, beam walk). IMP, n = 203 mice. CON; n = 117. Values represent means ± SEM. ***P < 0.001. Transient neurobehavioural impairments spanned multiple functional domains (including arousal, responsivity to environmental stimuli, locomotion, exploration, motor performance, habituation) that recapitulate features of concussion in humans (Supplementary Video 1). (E) Histogram and box-and-whiskers plot for population frequency distribution of composite scores on the acute neurobehavioural response test battery at baseline (pre-impact) and after first impact in awake (anaesthesia-naïve) mice exposed to experimental closed-head injury (n = 203). Baseline test: median score, 15; mean ± SEM, 14.9 ± 0.0 (white-bordered black inverted triangle). Impact 1 test: median score, 12; mean ± SEM, 11.6 ± 0.2 (black inverted triangle). (F) Histogram and box-and-whiskers plot for population (n = 203) frequency distribution of composite scores on the acute neurobehavioural response test battery after second impact and 3-h recovery. Impact 2 test: median score, 11; mean, 10.1 ± 0.2 (black inverted triangle). Recovery test: median score, 15; mean, 14.8 ± 0.0 (white-bordered black inverted triangle).