Hydrogen sulfide (H2S), an endogenous gaseous mediator, has been shown to exert protective effects against damage to different organs in the human body caused by various stimuli. However, the potential effects of H2S on hypoxia-induced neuronal apoptosis and its mechanisms remain unclear. Here, we exposed mouse hippocampal neurons to hypoxic conditions (2% O-2, 5% CO2 and 93% N-2 at 37 degrees C) to establish a hypoxic cell model. We found that 4-h hypoxia treatment significantly increased intracellular reactive oxygen species (ROS) levels, and pretreatment with NaHS (a source of H2S) for 30 Min suppressed hypoxia-induced intracellular ROS elevation. The hypoxia treatment significantly increased cytosolic calcium ([Ca2+](i)), and pretreatment with NaHS prevented the increase in [Ca2+](i). Additionally, polyethylene glycol (PEG)-catalase (a H2O2 scavenger) but not PEG-SOD (an O-2(-) scavenger) conferred an inhibitory effect similar to H2S on the hypoxia-induced increase in [Ca2+](i). Furthermore, we found that pretreatment with NaHS could significantly inhibit hypoxia-induced neuronal apoptosis, which was also inhibited by PEG-catalase or the inositol 1,4,5-triphosphate (IP3) receptor blocker xestospongin C. Taken together, these findings suggest that H2S inhibits hypoxia-induced apoptosis through inhibition of a ROS (mainly H2O2)-activated Ca2+ signaling pathway in mouse hippocampal neurons. Crown Copyright (c) 2012 Published by Elsevier Inc. All rights reserved,