Disruption of intracellular calcium homeostasis via abnormal and excessive activation of ryanodine receptors plays an important role in the neuropathology of Alzheimer’s disease. We investigated the therapeutic effect of dantrolene, a ryanodine receptor antagonist, on cognitive dysfunction and neuropathology in the triple transgenic Alzheimer mouse model (3xTg-AD). 3xTg-AD mice were treated with dantrolene from 2 to 13 months of age. Learning and memory were measured with the Morris Water Maze at 6, 10, and 13 months of age. Amyloid and tau neuropathology and biomarkers for synaptic dysfunction and neurodegeneration were examined in the brain using immunoblotting or immunohistochemistry. Dantrolene treatment for 11 months significantly reduced both memory deficits and amyloid plaque load in the hippocampus in 13 month old 3xTg-AD mice. Dantrolene treatment, however, had no effect on phosphorylated tau, phosphorylated or total GSK-3β, synaptic markers, or mitochondrial or cytosolic cytochrome C. Our results suggest that dantrolene significantly improves cognition in a murine model of Alzheimer’s disease and is associated with a reduction in amyloid plaque burden, forming the basis for a novel therapeutic approach for Alzheimer’s disease.

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In a maternal fetal rat model, we investigated the behavioral and neurotoxic effects of fetal exposure to isoflurane. Pregnant rats at gestational day 21 were anesthetized with 1.3% isoflurane for 6h. Apoptosis was quantified in the hippocampus and cortex at 2 and 18h after exposure in the fetal brain and in the postnatal day 5 (P5) pup brain. Spatial memory and learning of the fetal exposed pups were examined with the Morris Water Maze at juvenile and adult ages. Rat fetal exposure to isoflurane at pregnancy day 21 through maternal anesthesia significantly decreased spontaneous apoptosis in the hippocampal CA1 region and in the retrosplenial cortex at 2h after exposure, but not at 18h or at P5. Fetal exposure to isoflurane did not impair subsequent juvenile or adult postnatal spatial reference memory and learning and, in fact, improved spatial memory in the juvenile rat. These results show that isoflurane exposure during late pregnancy is not neurotoxic to the fetal brain and does not impair memory and learning in the juvenile or adult rat.

The commonly used general anesthetic isoflurane induces widespread neurodegeneration in the developing mammalian brain through poorly understood mechanisms. We have investigated whether excessive Ca 2ϩ release from the endoplasmic reticulum via overactivation of inositol 1,4,5-trisphosphate receptors (InsP 3 Rs) is a contributing factor in such neurodegeneration in rodent primary cultured neurons and developing rat brain. We also investigated the correlation between isoflurane exposure and cognitive decline in rats at 1 month of age. Our results show that isoflurane increases cytosolic calcium in the primary cortical neurons through release from the endoplasmic reticulum and influx from the extracellular space. Pharmacological inhibition of InsP 3 R activity and knockdown of its expression nearly abolishes the isoflurane-mediated elevation of the cytosolic calcium concentration and cell death in rodent primary cortical and hippocampal neurons. Inhibition of InsP 3 R activity by its antagonist xestospongin C significantly inhibits neurodegeneration induced by isoflurane at clinically used concentration in the developing brain of postnatal day 7 rats. Moreover, our results show that isoflurane activates ␤-site amyloid ␤ precursor protein-cleaving enzyme via activation of the InsP 3 R. We also noted that mice exposed to isoflurane during early postnatal development showed transient memory and learning impairments, which did not correlate well with the noted neuropathological defects. Taken together, our results suggest that Ca 2ϩ dysregulation through overactivation of the InsP 3 R may be a contributing factor in the mechanism of isoflurane-induced neurodegeneration in rodent neuronal cell culture and during brain development.