Mild hypothermia fails to protect late hippocampal neuronal loss following forebrain cerebral ischaemia in rats

Abstract

Anaesthetized male rats (n = 86) from both Long-Evans strain (LES) (n = 43) and Wistar strain (WS) (n = 43) were utilized for the experiments. While three animals from each strain were used as control, 40 rats from each strain underwent up to 10 minutes forebrain ischaemia by bilateral common carotid artery (CCA) occlusion combined with systemic hypotension [Mean Arterial Blood Pressure (MABP) = 50 mm/Hg]. The animals from each strain were divided into four (n = 10) groups. In both strains, groups (n = 10) 1 and 2, temporalis muscle (TM) and body temperatures of the animals were kept at 36-37 degrees C during the experiments. The groups 1 and 2 were killed in 3 and 7 days after the ischaemic insult, respectively. The groups 3 and 4 were also killed 3 and 7 days after the ischaemic insult, but the forebrain ischaemia was carried out under mild cerebral hypothermia (TM temperature = 33 degrees C). Pyramidal neurons of the hippocampal CA1 region from each group was evaluated semiquantitatively. In WS, groups 1 and 2 showed moderate and severe neuronal loss in the CA1 region, respectively. However, in LES while the group 1 (3 days survival) did not show any neuronal loss, group 2 showed moderate neuronal loss of the CA1 region. While in group 3 (3 days survival, hypothermia) WS and LES, hypothermia protected the CA1 region, group 4 of LES showed mild neuronal loss. However WS, group 4 (7 days survival, hypothermia) showed severe neuronal loss of the CA1 region. It was concluded that mild hypothermia during ischaemic insults did not prevent the delayed postischaemic neuronal damage of the hippocampal CA1 region of both strains, and following 10 minutes forebrain ischaemia, male LES rats were found more resistant than male WS rats to neuronal loss of the CA1 region.