Simvastatin and environmental enrichment effect on recognition and temporal order memory after mild-to-moderate...

The purpose of this study was to investigate the effect of mild-to- moderate (m-mod) traumatic brain injury (TBI) on spontaneous object (SO) recognition and temporal order (TO) memory in male Wistar rats and to compare the effects of environmental enrichment (EE) and simvastatin (Sim) on SO and TO memory post-injury.

A randomized repeated measure experimental design was used.

Seven days after arrival, animals received the injury or sham surgery. Using a Y-shaped maze, SO and TO memory was assessed in the two groups of animals at 6, 24, 48, 72 hours and 7, 14, 21 and 35 days post-surgery. Total time exploring each object and discrimination ratio were calculated and analysed. Then SO and TO memory were compared between two groups that received either Sim or EE for 2 hours daily starting 24 hours post-injury and a sham group that received saline for 14 days post-injury.

The results showed that the injury impaired SO and TO memory compared to the sham up to 35 days post-trauma. Injured animals exhibited familiarity preference, novelty aversion and impaired TO performance. EE improved the animals' SO recognition deficits 7 days post-injury after a shorter delay (1 minute) only and Sim reversed TO memory deficits 14 days post-injury after a longer delay (60 minutes).

Persistent SO and TO memory deficits follow TBI in animals; Simv and EE seem to be promising therapies of TBI memory deficits.