Prevention of Postischemic Hyperthermia Prevents Ischemic Injury of CA1 Neurons in Gerbils

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Abstract
Halothane-anesthetized Mongolian gerbils were submitted to 5-min bilateral carotid artery occlusion. After ischemia, halothane anesthesia was continued for various periods of up to 85 min, and the degree of CA1 neuronal injury was estimated 7 days later by counting the number of surviving pyramidal cells. During ischemia and postischemic halothane anesthesia, rectal and cranial temperature was kept at control level (37.7 and 37.0°C, respectively) using a feedback-controlled heating system. When anesthesia was discontinued after ischemia, transient hyperthermia occurred. In animals with 0- and 15-min postischemic halothane anesthesia, both cranial and rectal temperature rose by ∼1.5°C, and the number of surviving CA1 neurons amounted to <25% of control. After 45- or 85-min postischemic anesthesia, hyperthermia was significantly reduced and the number of surviving neurons increased to 65 and 89%, respectively. The protective effect of postischemic anesthesia was lost when anesthetized animals were submitted to the same hyperthermic profile as nonanesthetized ones, using a feedback-controlled heating system (16% surviving neurons in hyperthermia vs. 89% in normothermia, respectively). These observations demonstrate that postischemic anesthesia with 1% halothane protects against delayed neuronal death by preventing postischemic hyperthermia and not by its anesthetic effects.