Motor and cognitive functional deficits following diffuse traumatic brain injury in the immature rat

To determine the motor and cognitive deficits following a diffuse severe traumatic brain injury (TBI) in immature Sprague Dawley rats (17 days), four groups of animals were injured at different severity levels using a new closed head weight drop model: (sham, severe injury [SI: 100 g/2 m], SH [SI + hypoxemia (30 min of an FiO2 of 8% posttrauma)], and ultra severe injury [US: 150 g/2 m]). Latency on beam balance, grip test performance, and maintenance of body position on an inclined board were measured daily after injury to assess vestibulomotor function. Cognitive function was assessed on days 11-22 using the Morris water maze (MWM). Balance beam latency and inclined plane body position were reduced in both SI and SH rats (n = 20) (p < 0.05 vs. sham) (maximally at 24 h), and lasted 3-4 day postinjury; however, SH did not differ from SI. In the US group (n = 10), motor deficits were profound at 24 h (p < 0.05 vs. all other groups) and persisted for 10 days. The groups did not differ on grip test. In cognitive performance, there were no differences between sham, SI, and SH. US, however, produced significant cognitive dysfunction (vs. sham, SI, and SH), specifically, greater latencies to find the hidden platform through 22 days. Swim speeds were not significantly different between any of the injury groups and shams. These data indicate that (1) beam balance, inclined plane and MWM techniques are useful for assessing motor and cognitive function after TBI in immature rats; (2) SI produces motor but not cognitive deficits, which was not augmented by transient hypoxia; and (3) US created a marked but reversible motor deficit up to 10 days, and a sustained cognitive dysfunction for up to 22 days after TBI.