NEUROSURGICAL ANESTHESIA SECTION EDITOR DAVID S. WARNER Mild Hypothermia, but Not Propofol, Is Neuroprotective in Organotypic Hippocampal Cultures John R. Feiner, MD, Philip E. Bickler, MD, PhD, Sergio Estrada, BS, Paul H. Donohoe, PhD, Christian S. Fahlman, PhD, and Jennifer A. Schuyler, BS Department of Anesthesia and Perioperative Care, University of California, San Francisco. The neuroprotective potency of anesthetics such as propofol compared to mild hypothermia remains un- defined. Therefore, we determined whether propofol at two clinically relevant concentrations is as effec- tive as mild hypothermia in preventing delayed neu- ron death in hippocampal slice cultures (HSC). Sur- vival of neurons was assessed 2 and 3 days after 1 h oxygen and glucose deprivation (OGD) either at 37°C (with or without 10 or 100 M propofol) or at an av- erage temperature of 35°C during OGD (mild hypo- thermia). Cell death in CA1, CA3, and dentate neu- rons in each slice was measured with propidium iodide fluorescence. Mild hypothermia eliminated death in CA1, CA3, and dentate neurons but propofol protected dentate neurons only at a concentration of 10 M; the more ischemia vulnerable CA1 and CA3 neurons were not protected by either 10 M or 100 M propofol. In slice cultures, the toxicity of 100 M N-methyl-d-aspartate (NMDA), 500 M glutamate, and 20 M -amino-5-methyl-4-isoxazole propionic acid (AMPA) was not reduced by 100 M propofol. Because propofol neuroprotection may involve gamma-aminobutyric acid (GABA)-mediated indi- rect inhibition of glutamate receptors (GluRs), the ef- fects of propofol on GluR activity (calcium influx in- duced by GluR agonists) were studied in CA1 neurons in HSC, in isolated CA1 neurons, and in cor- tical brain slices. Propofol (100 and 200 M, approxi- mate burst suppression concentrations) decreased glutamate-mediated [Ca 2+ ] i increases ([Ca 2+ ] i ) re- sponses by 25%–35% in isolated CA1 neurons and re- duced glutamate and NMDA [Ca 2+ ] i in acute and cultured hippocampal slices by 35%–50%. In both CA1 neurons and cortical slices, blocking GABA A re- ceptors with picrotoxin reduced the inhibition of GluRs substantially. We conclude that mild hypo- thermia, but not propofol, protects CA1 and CA3 neurons in hippocampal slice cultures subjected to oxygen and glucose deprivation. Propofol was not neuroprotective at concentrations that reduce gluta- mate and NMDA receptor responses in cortical and hippocampal neurons. (Anesth Analg 2005;100:215–25) T he neuroprotective qualities of propofol re- main controversial. Several studies have dem- onstrated neuroprotective effects of propofol in focal ischemia in intact animals (1– 4). Propofol reduces cell injury or injury surrogates in cellular preparations (5–9). In contrast, propofol failed to reduce postoperative neurologic deficits after car- diac surgery (10) and has failed to protect cells in some in vivo (11) and in vitro models (9,12) of cerebral ischemia. Propofol has properties that might be neuroprotective, including free radical scavenging (8), augmentation of -aminobutyric acid (GABA) receptor currents, and inhibition of N-methyl- d-aspartate (NMDA)-type glutamate receptor currents (13–15). The neuroprotective actions of propofol, if they exist, may involve interactions between GABA A re- ceptors and glutamate receptors. When activated by drugs such as propofol (16), GABA A receptors hy- perpolarize neurons and thus decrease the voltage- dependent current flow through NMDA receptors. The magnitude of this interaction has not been clearly defined. In addition, propofol inhibits NMDA receptors directly, although weakly. NMDA receptors expressed in Xenopus oocytes are slightly (30%) inhibited at clinical concentrations (35 M) of propofol (14). Orser et al. (15) reported the IC 50 of propofol on NMDA responses in cultured mouse neurons to be 160 M, a concentration that produces electroencephalogram (EEG) burst-suppression in humans. Supported, in part, by grants from the National Institutes of Health (RO1 GM 52212 to PEB) and the Genentech Foundation (to SE). Accepted for publication July 22, 2004. Address correspondence and reprint requests to Philip E. Bickler, MD, PhD, Sciences 255, Box 0542, University of California at San Francisco, 513 Parnassus Avenue, San Francisco, CA 94143– 0542. Address e-mail to bicklerp@anesthesia.ucsf.edu. DOI: 10.1213/01.ANE.0000142129.17005.73 ©2005 by the International Anesthesia Research Society 0003-2999/05 Anesth Analg 2005;100:215–25 215