When Ken Lukowiak attended a meeting about a proposed gas well close to his hometown, he had no idea that it would trigger his most recent round of research. But he says that when a nurse pointed out that `kids downwind of wells tainted with hydrogen sulphide performed worse on exams than kids upwind', his interest was piqued. Could the gas well's bad-egg-smell impede a child's ability to learn? Although the stories were anecdotal, Lukowiak knew he had the perfect model system to test whether hydrogen sulphide affects memory, but not in children. Lukowiak works on memory in Lymnaea stagnalis, a humble snail that learns one simple task – remembering to keep its breathing orifice close – yet can teach us a huge amount about the mechanics of memory formation. Curious to know how his snail's memory performed after a dose of hydrogen sulphide, Lukowiak and his team began testing the molluscs and found that, worryingly, the anecdotal evidence held up to closer scrutiny (p. 2621).
But first Lukowiak needed to know how the snail's breathing responded to hydrogen sulphide exposure; after all, it seems to affect human respiration,so maybe it would affect the snails too. David Rosenegger monitored the snails' attempts to breathe through their breathing orifices, pneumostomes,when they were submerged in hypoxic water, and then compared their breathing behaviour when exposed to 100 μmol l–1 hydrogen sulphide. The snails attempted to breathe more often with their pneumostomes during the hydrogen sulphide treatment.
Knowing that hydrogen sulphide altered the snail's breathing patterns,Rosenegger went on to test the mollusc's ability to form long-term memories. Lukowiak explains that when Lymnaea are submerged in water, they usually breathe through their skins, unless the water is hypoxic; in which case, the molluscs extend their pneumostomes above the surface to supplement the meagre oxygen supply. But Lymnaea have the ability to learn to keep their penumostomes closed, even when the water is hypoxic, if gently tapped on the penumostome every time they try to open it. By using a specific pattern of training taps, Lukowiak knew that he could program the mollusc's long-term memory, and test hydrogen sulphide's effects.
After discussions with Sheldon Roth, a toxicologist, the team decided to expose the snails to environmental, but non-toxic, levels of hydrogen sulphide at various points during the training regime. Then Rosenegger waited a day before testing how well the snails remembered to keep their pneumostmes closed. While snails exposed to the 50 and 75 μmol l–1hydrogen sulphide had formed memories and kept their pneumostomes closed under hypoxic water, the snails exposed to 100 μmol l–1 hydrogen sulphide had no memory at all! And even though the snails exposed to lower doses could form memories, they didn't perform as well as untreated snails. Like the anecdotal children, Lukowiak's snails weren't doing well at school.
Lukowiak suspects that the noxious gas disrupts synaptic interactions in the tiny cluster of neurones that store the mollusc's memory, and hopes to identify the memory disruption mechanism soon. And as for the gas well close to his home? Given hydrogen sulphide's startling effects, he wonders whether the days of siting sour-gas well vents upwind of populated areas could be numbered.
