Effect of age in rats following middle cerebral artery occlusion

Despite the impressive increased understanding of the ischemic brain damage in general, the study of effects on different age groups, young versus old, using comparable ischemic insults is clearly lacking.

To investigate the mortality rate and neurological outcome among young and old rats, through a model of cerebral ischemia by middle cerebral artery occlusion (MCAO).

Twenty-three old (22-24 months of age) and 16 young (3-4 months of age) male rats underwent a MCAO procedure for 60 min. Surviving rats were randomly assigned to the 24-hour or 28-day resting group. The mortality rate and neurological outcome in different recovery time periods were determined for comparison between the young and old rats.

The overall mortality rate in old rats (43.5%) was significantly higher than that of the young rats (6.3%) (p = 0.01). The infarct volume for the 24-hour post-MCAO was 181.86 +/- 11.87 mm(3) for the young rats, and 204.64 +/- 27.18 mm(3) for the old rats. For the 28-day post-MCAO, the value was 91.16 +/- 3.59 mm(3) for the young rats, and 103.38 +/- 26.43 mm(3) for the old rats. A significant reduction in infarct volume is noted in both young (p < 0.01) and old (p < 0.05) rats after 28 days of recovery compared to that after 24 h of recovery. There was no meaningful difference in infarct volume between the young and old rats measured at 24 h or 28 days after the ischemic procedure. The right volume was larger than the left volume at 24 h post-MCAO for both the young and the old rats, whereas the quotient approached unity for the young rats at 28 days post-MCAO. For the old rats, the quotient was negative at 28 days post-MCAO, representing the ipsilateral hemisphere was smaller than the contralateral hemisphere.

The mortality risk to ischemic damage is greater for old rats. If an old rat survives the high-risk mortality in a short period after the MCAO procedure, the recovery would be of no difference to that of a young rat.