Inhaled anesthetics have been shown to increase the aggregation of amyloid beta in vitro through the stabilization of intermediate toxic oligomers, which are thought to contribute to neurocognitive dysfunction in Alzheimer's disease. Inhaled anesthetics may escalate cognitive dysfunction through enhancement of these intermediate oligomer concentrations. We intermittently exposed 12-month-old Tg2576 transgenic mice and nontransgenic littermates to isoflurane and halothane for 5 days. Cognitive function was measured before and after anesthetic exposures using the Morris Water Maze; amyloid beta plaque burden and caspase-3 mediated apoptosis were quantified by immunohistochemistry. At 12 months of age, anesthetic exposure did not further enhance cognitive decline in the transgenic mice. Immunohistochemistry, however, revealed that the halothane-exposed Tg2576 mice had more amyloidopathy than the isoflurane treated mice or the nonexposed transgenic mice. Isoflurane exposure impaired cognitive function in the nontransgenic mice, implying an alternative pathway for neurodegeneration. These findings indicate that inhaled anesthetics influence cognition and amyloidogenesis, but that the mechanistic relationship remains unclear.

Background Experimental evidence suggests that anesthetics accelerate symptomatic neurodegenerative disorders like Alzheimer disease (AD). Since AD pathology precedes symptoms, we asked whether anesthetic exposure in the presymptomatic interval accelerates neuropathology and appearance of symptoms. Methods Triple transgenic Alzheimer mice exposed to the general aesthetics, halothane or isoflurane, at 2, 4 and 6 months of age, underwent water maze cognitive testing two months afterwards and their brains subsequently analyzed with ELISA, immunoblots, and immunohistochemistry for amyloid and tau pathology and biomarkers. Results Learning and memory improved after halothane exposure in the 2 month old group relative to controls, but no changes were noted in any isoflurane group. When gender was examined in all age groups, females exposed to halothane performed better than females exposed to isoflurane or controls. Thus, improvement in the 2 month exposure group is most likely due to a gender effect. Phospho-tau in the hippocampus was significantly increased two months after anesthesia, especially in the 6 month exposure group but changes in amyloid, caspase, microglia or synaptophysin were not detected. Conclusions These results indicate that exposure to two different inhalational anesthetics during the presymptomatic period of AD does not accelerate cognitive decline, two months later, and may cause a stress response, marked by hippocampal phosphorylated tau, resulting in preconditioning against the ongoing neuropathology, primarily in female mice.

Carbon monoxide (CO) exposure at high concentrations results in overt neurotoxicity. Exposure to low CO concentrations occurs commonly yet is usually sub-clinical. Infants are uniquely vulnerable to a variety of toxins, however, the effects of postnatal sub-clinical CO exposure on the developing brain are unknown. Apoptosis occurs normally within the brain during development and is critical for synaptogenesis. Here we demonstrate that brief, postnatal sub-clinical CO exposure inhibits developmental neuroapoptosis resulting in impaired learning, memory, and social behavior. Three hour exposure to 5 ppm or 100 ppm CO impaired cytochrome c release, caspase-3 activation, and apoptosis in neocortex and hippocampus of 10 day old CD-1 mice. CO increased NeuN protein, neuronal numbers, and resulted in megalencephaly. CO-exposed mice demonstrated impaired memory and learning and reduced socialization following exposure. Thus, CO-mediated inhibition of neuroapoptosis might represent an important etiology of acquired neurocognitive impairment and behavioral disorders in children.

BACKGROUND The number of elderly patients with frank or incipient Alzheimer’s disease (AD) requiring surgery is growing as the population ages. General anesthesia may exacerbate symptoms of and the pathology underlying AD, so minimizing anesthetic exposure may be important. This requires knowledge of whether the continuing AD pathogenesis alters anesthetic potency. METHODS We determined the induction potency and emergence time for isoflurane, halothane, and sevoflurane using the minimum alveolar anesthetic concentration for loss of righting reflex as an end point in 12- to 14-mo-old triple transgenic Alzheimer (3xTgAD) mice and wild type C57BL6 controls. 3xTgAD mice model AD by harboring three distinct mutations: the APPSwe, Tau, and PS1 human transgenes, each of which has been associated with familial forms of human AD. RESULTS The 3xTgAD mice exhibited mild resistance (from 8% to 30%) to volatile anesthetics but displayed indistinguishable emergence patterns from all three inhaled anesthetics. CONCLUSIONS These results show that the genetic vulnerabilities and neuropathology associated with AD produce a small but significant decrease in sensitivity to the hypnotic actions of three inhaled anesthetics. Emergence times were not altered.