Mild hypothermia has no long-term impact on postischemic neurogenesis in rats.

BACKGROUND: Postischemic improvement of functional outcome by therapeutic hypothermia may be related to cerebral regeneration by postischemic neurogenesis. We investigated whether mild peri-ischemic hypothermia leads to a long-term increase in postischemic neurogenesis. METHODS: Seventy male sevoflurane-anesthetized Sprague Dawley rats were randomly assigned to the following treatment groups: normothermic ischemia, intraischemic hypothermia, and postischemic hypothermia with corresponding sham-operated controls. Fifteen naïve rats were investigated as reference for natural neurogenesis. Forebrain ischemia was induced by bilateral common carotid artery occlusion and hemorrhagic hypotension. In normothermic groups, the pericranial temperature was maintained at 37.5 degrees C. Animals in the hypothermic groups were cooled to a pericranial temperature of 33 degrees C for 45 min. All animals received 5-bromo-2-deoxyuridine for 7 days. Histopathological damage and 5-bromo-2-deoxyuridine-positive neurons of the hippocampus were analyzed after 28 days. RESULTS: Hypothermia had no impact on natural neurogenesis. Cerebral ischemia increased the number of new neurons regardless of pericranial temperature. Forty-five minutes of hypothermia beginning before ischemia diminished hippocampal injury to <10% in the CA1 and CA3 regions, whereas 45 min of postischemic hypothermia beginning after reperfusion did not reduce neuronal injury compared with normothermia. CONCLUSIONS: Neither intraischemic nor postischemic hypothermia affected the ischemia-induced increase in endogenous neurogenesis. Intraischemic hypothermia reduced hippocampal damage, whereas postischemic hypothermia as applied here did not prevent formation of histopathological injury. This indicates that, 28 days after cerebral ischemia, postischemic neurogenesis is not significantly increased by mild peri-ischemic hypothermia and not affected by the severity of histopathological damage.

Assessment of postischemic neurogenesis in rats with cerebral ischemia and propofol anesthesia.

BACKGROUND: Postischemic endogenous neurogenesis can be dose-dependently modulated by volatile anesthetics. The intravenous anesthetic propofol is used during operations with a risk of cerebral ischemia, such as neurosurgery, cardiac surgery, and vascular surgery. The effects of propofol on neurogenesis are unknown and, therefore, the object of this study. METHODS: Eighty male Sprague-Dawley rats were randomly assigned to treatment groups with propofol administration for 3 h: 36 mg x kg(-1) x h(-1) propofol with or without cerebral ischemia and 72 mg x kg(-1) x h(-1) propofol with or without cerebral ischemia. In addition, 7 rats with propofol administration for 6 h and 14 treatment-naive rats were investigated. Forebrain ischemia was induced by bilateral carotid artery occlusion and hemorrhagic hypotension. Animals received 5-bromo-2-deoxyuridine for 7 days. 5-Bromo-2-deoxyuridine-positive neurons were counted in the dentate gyrus after 9 and 28 days. Spatial learning in the Barnes maze and histopathologic damage of the hippocampus were analyzed. RESULTS: Propofol revealed no impact on basal neurogenesis. Cerebral ischemia increased the amount of new neurons. After 28 days, neurogenesis significantly increased in animals with low-dose propofol administered during cerebral ischemia compared with naive animals, whereas no significant difference was observed in animals with high-dose propofol during ischemia. Neuronal damage in the CA3 region was increased at 28 days with high-dose propofol. Postischemic deficits in spatial learning were not affected by propofol. CONCLUSIONS: Independent effects of propofol are difficult to ascertain. Peri-ischemic propofol administration may exert secondary effects on neurogenesis by modulating the severity of histopathologic injury and thereby regenerative capacity of the hippocampus.

Cerebral ischemia and neurogenesis: a two-time comparison.

BACKGROUND: This study compares the effect of mild and severe cerebral ischemia on neuronal damage and neurogenesis. METHODS: Sixteen Sprague-Dawley rats, anesthetized with 0.8 vol% halothane in O(2)/air, were subjected to forebrain ischemia by bilateral common carotid artery occlusion plus hemorrhagic hypotension (mean arterial blood pressure = 40 mmHg) for 8 (mild) or 13 (severe) min. Four non-ischemic animals were investigated as naïve controls. Bromodeoxyuridine (50 mg/kg), a marker of new cells, was administrated for seven consecutive postischemic days. After 28 days, animals were perfused with 4% paraformaldehyde and the brains were sliced. Histopathological damage of the hippocampus and the volume of the dentate gyrus were assessed by HE-staining. With immunohistochemistry BrdU-positve cells were detected in the dentate gyrus. The amount of new generated neurons was identified by double-immunofluorescence-staining of BrdU and neuronal marker (NeuN). RESULTS: In the CA-1 region of the hippocampus, mild ischemia induced damage up to 10% (HE-index 0.8 +/- 1.2) and severe ischemia up to 50% (HE-index 2.1 +/- 1.4). There was no histopathological damage in naïve control animals. The amount of new neurons was increased by 250% after mild insult and by 160% after severe insult compared to the naïve control animals. CONCLUSIONS: These data indicate that histopathological damage depends on the severity of the ischemic insult and that forebrain ischemia activates generation of new neurons. A mild ischemic challenge appears to be a more potent neurogenic stimulus than severe ischemia. The new neurons survive at least 28 days. This may relate to delayed histopathological and functional recovery after cerebral ischemia.

Sevoflurane affects neurogenesis after forebrain ischemia in rats.

BACKGROUND: The effect of sevoflurane on the neuroregenerative potential after neuronal injury is unclear. We investigated the effect of low and high concentrations of sevoflurane on endogenous neurogenesis after cerebral ischemia. METHODS: Anesthetized and ventilated rats were randomized to four different treatment groups. Groups 1 and 2: 1.4% sevoflurane; Groups 3 and 4: 2.8% sevoflurane. In Groups 1 and 3, no cerebral ischemia was induced (sham-operated). In Groups 2 and 4, 10 min of forebrain ischemia was induced by bilateral carotid artery occlusion plus hemorrhagic hypotension. Physiological variables were maintained constant. Bromodeoxyuridine was given as a marker of neurogenesis. After 28 days brains were perfused. Histopathological damage of the hippocampus was evaluated in hematoxylin and eosin (HE) stained sections using the HE-index (0 = no damage; 1 = 1%-10% damage; 2 = 11%-50% damage; 3 = 51%-100% damage). Immunohistochemistry was used to detect bromodeoxyuridine-positive neurons. Eight untreated rats were investigated as naive controls (Group 5). RESULTS: In neither sham-operated group was histopathological damage or change in neurogenesis observed compared to naive controls. In rats anesthetized with 1.4% sevoflurane, cerebral ischemia caused mild neuronal damage (HE-index of 0.64 +/- 0.84) and increased neurogenesis by 60% when compared with respective sham-operated animals; with 2.8% sevoflurane, the HE-index was 1.22 +/- 1.14, and the number of newly generated neurons increased by 230% when compared with respective sham-operated animals. CONCLUSION: The present data suggest that high concentrations of sevoflurane stimulate neurogenesis in the dentate gyrus after cerebral ischemia.