ASTROCYTIC GAP JUNCTIONAL COMMUNICATION DECREASES NEURONAL VULNERABILITY TO OXIDATIVE STRESS-INDUCED DISRUPTION OF CA2-DEATH( HOMEOSTASIS AND CELL)

We investigated the effect of uncoupling astrocytic gap junctions on n euronal vulnerability to oxidative injury in embryonic rat hippocampal cell cultures, Mixed cultures (neurons growing on an astrocyte monola yer) treated with 18-alpha-glycyrrhetinic acid (GA), an uncoupler of g ap junctions, showed markedly enhanced generation of intracellular per oxides (2,7-dichlorofluorescein fluorescence), impairment of mitochond rial function [(dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction], and cell death (lactate dehydrogenase release) following e xposure to oxidative insults (FeSO4 and 4-hydroxynonenal), GA alone ha d little or no effect on basal levels of peroxides, mitochondrial func tion, or neuronal survival. Intercellular dye transfer analyses reveal ed extensive astrocyte-astrocyte coupling but no astrocyte-neuron or n euron-neuron coupling in the mixed cultures, Studies of pure astrocyte cultures and microscope analyses of neurons in mixed cultures showed that the increased oxidative stress and cell death in GA-treated cultu res occurred only in neurons and not in astrocytes. Antioxidants (prop yl gallate and glutathione) blocked the death of neurons exposed to Fe SO4/GA. Elevations of neuronal intracellular calcium levels ([Ca2+](i) ) induced by FeSO4 were enhanced in neurons in mixed cultures exposed to GA. Removal of extracellular Ca2+ and the L-type Ca2+ channel block er nimodipine prevented impairment of mitochondrial function and cell death induced by FeSO4 and GA, whereas glutamate receptor antagonists were ineffective. Finally, GA exacerbated kainate-and FeSO4-induced in jury to pyramidal neurons in organotypic hippocampal slice cultures. T he data suggest that interastrocytic gap junctional communication decr eases neuronal vulnerability to oxidative injury by a mechanism involv ing stabilization of cellular calcium homeostasis and dissipation of o xidative stress.