A single systemic transient hypotension induces long-term changes in rats' MRI parameters and behavior: relation to aging

The aim of this work was to examine whether a single 20-minute systemic hypotension induces short- and long-term changes in 12- and 18-month-old rat brain.

Age-related changes were determined after hemorrhagic hypotension over a 6-month period of investigation using holeboard testing, diffusion-weighted (DW) magnetic resonance imaging (MRI) and T2 and T2* relaxometry.

The results showed a short-term but significant reduction in the apparent diffusion coefficient (ADC) after hypotension, which was accompanied by an increase in T2 relaxation time and deterioration in rat locomotor activity and memory capacities. Thereafter, a transient pseudo-normalization was regained. However, a significant difference in ADC and T2 relaxation time between controls and rats with transient hypotension and in rat reference memory was noticeable at month 6 after injury. A significant negative linear correlation was detected between T2 relaxation time and reference memory capacity. With regard to the effect of cerebral aging, significant changes were found in hippocampal ADC, T2 and T2* relaxation times and in behavioral parameters in 18-month-old rats compared with 12-month-old animals.

It was demonstrated that even a single oligemic event induces long-term changes in rat brain. Increased T2 reflects memory reduction. In addition, it has been shown that DW-MRI technique allows a longitudinal in vivo assessment of short- and long-term changes in rat brain. Further MRI perfusion works and detailed histological investigations on brain structure are necessary to study whether MRI measurements adequately reflect structural changes in the brain.