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Can aquatic snails better remember lessons learned when they are hopped up on methamphetamine? Barbara Sorg of Washington State University in Pullman teamed up with Ken Lukowiak of the University of Calgary Medicine to see if working with snails might provide clues as to why drug memories are so strong that they seem to draw addicts back into repetitive use and addiction.
The team experimented with so-called great pond snails, Lymnaea stagnalis. According to Lukowiak, the snails breathe through their skin when oxygen levels in the water are high, but when oxygen levels drop the snails extend breathing tubes above the water's surface to supplement their intake. Although humans have around 50 billion neurons in the brain devoted to memory and snails have only 20,000, the mechanisms are similar. According to Lukowiak, "Mother Nature is very conservative. Anything that works, she tends to repeat in other organisms even if highly more complex."
The team trained the snails to keep their breathing tubes closed, despite low oxygen levels, by poking them with a stick whenever they raised their tubes above the water level. Two training sessions of about an hour each were necessary for a snail to recall anything beyond 24 hours. So the team of scientists tested the snails to see if methamphetamines might heighten snail recall. Lacing the pond water with crystal meth, they repeated the lessons. When they tested the snails 24 hours later, the snails didn't seem to recall their lessons. But when they put methamphetamine in the water for the recall test, the snails performed exceptionally well. According to Lukowiak, "Only one training session was necessary to initiate long-lasting memory, whereas more typically the snail would need two or three to demonstrate similar recall."
Even doses of methamphetamine administered hours before training seemed to enhance memory, the team reported in the May 28 issue of the Journal of Experimental Biology. Sorg thinks this may demonstrate why it is so difficult for meth addicts to stay off drugs when they initiate memories of the "high" experience, either by using methamphetamine again or just putting themselves back in the environment where those memories were formed. The team also had difficulty negating or masking the lesson that drug-influenced snails learned. Sorg refers to strong drug-induced memories as pathological memories, "because they can initiate drug use even if the addict is determined not to repeat the behavior again."
