Effects of repeated hydrogen sulphide (H2S) exposure on learning and memory in the adult rat.

The effects of repeated exposure (125 ppm) of hydrogen sulphide (H2S) on learning and memory in the rat were investigated. A 16-arm radial arm maze (RAM) was used to examine neurobehavioural functioning in a series of three experiments. Experiment 1 involved training animals on a complex spatial maze task, prior to a 5-week period of exposure to H2S or a control gas mixture. Rats were tested for maze retention after each 5-day exposure period. It was determined that repeated H2S exposure had no effect on memory for a previously learned spatial task. Experiment 2 was conducted to determine whether H2S interferes with the acquisition of a novel spatial task. Naïve animals received daily maze training and exposure (H2S or control) sessions over an extended 11-week period (48 sessions). The results indicated that the groups were comparable on four of five measures of maze performance. H2S animals were impaired in their ability to find all of the reinforcers prior to the end of a trial, suggesting that H2S had an effect on performance rate, but not acquisition of the maze task. Finally, Experiment 3 was conducted to determine what role proactive interference might play in H2S-related brain impairment. Animals from the preceding experiment were trained on a new reversed contingency maze task. H2S animals made more overall arm entries than controls, suggesting that H2S may impair learning by increasing the animals' susceptibility to interference from irrelevant stimuli. The prefrontal cortex was discussed as a potential target site of H2S. The pathophysiological mechanisms underlying the effect of H2S on normal brain function have yet to be identified.