Neuroprotective Effects of Dexmedetomidine in the Gerbil Hippocampus after Transient Global Ischemia

Background: Cerebral ischemia induces a massive release of norepinephrine associated with neuronal death in the brain. It has been demonstrated that alpha2 -adrenoceptor agonists decrease the release and turnover of noradrenaline, and this might prove advantageous in counteracting the neurodegeneration in ischemic brain. Therefore, in the present study, the authors tested whether dexmedetomidine, a selective alpha2 -receptor agonist, has neuroprotective effects in a gerbil transient global ischemia model.

Methods: Ischemia was induced by bilateral carotid occlusion for 5 min in diethylether-anesthetized normothermic gerbils. Dexmedetomidine was administered subcutaneously in four different treatment paradigms (6-8 animals/group): 3 or 30 micro gram/kg 30 min before and thereafter at 3, 12, 24, and 48 h after the occlusion, or 3 or 30 micro gram/kg at 3, 12, 24, and 48 h after the occlusion. Control animals were subjected to forebrain ischemia but received only saline injections. One week after occlusion, animals were transcardially perfused for histochemistry. Neuronal death in the CA1 and CA3 regions of the hippocampus and in the hilus of the dentate gyrus was evaluated in silver-stained 60-micro meter coronal sections.

Results: Compared with saline-treated ischemic animals, dexmedetomidine at a dose of 3 micro gram/kg given before and continued after the induction of ischemia reduced the number of damaged neurons in the CA3 area (2 +/- 3 vs. 17 +/- 20 degenerated neurons/mm2; P <0.05). Also in the dentate hilus, the number of damaged neurons was reduced by dexmedetomidine (3 micro gram/kg) given before and continued after ischemia (5 +/- 7 vs. 56 +/- 42 degenerated neurons/mm2; P <0.01).