Traumatic brain injury in late adolescent rats: effects on adulthood memory and anxiety.

The consequences of traumatic brain injury (TBI) sustained during late adolescence (7 weeks old) on spontaneous object recognition memory and on anxiety-like behaviors in the elevated plus maze were tested in rats during adulthood. Testing took place at 2 different postinjury times, in separate groups: 3 and 6 weeks, when animals were 10 and 13 weeks old, respectively. The rats were either submitted to controlled cortical impact injury, an experimental model of focal TBI with contusion, or were sham-operated. TBI animals failed to remember the familiar object and had a significantly lower performance than sham-operated animals, indicating memory disruption, when the retention delay was 24 hr, but not when it was 3 hr. TBI did not have any significant effect on the main anxiety-related behaviors, but it reduced time in the central platform of the elevated plus maze. The effects of TBI on memory and on anxiety-like behaviors were similar at the 2 postinjury times. In both TBI and sham-operated groups, animals tested 6 weeks after surgery had lower anxiety-related indices than those tested at 3 weeks, an effect that might be indicative of reduced anxiety levels with increasing age. In summary, focal TBI with contusion sustained during late adolescence led to object recognition memory deficits in a 24-hr test during adulthood but did not have a major impact on anxiety-like behaviors. Memory deficits persisted for at least 6 weeks after injury, indicating that spontaneous modifications of these functional disturbances did not take place along this time span.