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  1. Terrapinzflyer
    Snails yield drug addiction clue
    View attachment 14898 In an unusual experiment, scientists have used pond snails to study the effects of methamphetamine, better known as crystal meth, on the brain.

    They discovered that the drug enhanced the creatures' abilities to learn and remember a task.

    This gives insight into how some addictive drugs produce memories that are hard to forget, and that can even cause addicts to relapse.

    The scientists described the discovery in the Journal of Experimental Biology.

    Barbara Sorg from Washington State University in the US led the research team. She explained that the snails provided a "simple model" enabling scientsts to examine the effects of drugs on an individual brain cell.

    "These drugs of abuse produce very persistent memories," explained Dr Sorg. "It's a learning process - drug addiction is learning unwittingly.

    "All of these visual, environmental and odour cues are being paired with the drug.

    So addicts might be able to kick their habit in a treatment centre, but when they return to their old haunts, all those cues trigger craving and relapse."

    The ultimate question, said Dr Sorg, is why is it so hard to forget these memories?

    To take the first step in answering that question, she and her team examined the effects of crystal meth on the snails, by comparing the performance of drugged and "un-drugged" snails in a simple breathing task.

    Learning to breathe

    The snails normally live in stagnant water and they breathe through their skin," explained Dr Sorg. "But when the water gets low in oxygen, they surface and open up a breathing tube.

    The scientists trained the snails not to surface by "poking" this breathing tube with a small stick.

    "They don't like that, said Dr Sorg, "so they learn through trial and error not to come up to the surface - they form a memory."

    The researchers found that if the snails were exposed to a low concentration of methamphetamine before the breathing task, this "primed them" to form a more persistent memory of it.

    The un-drugged snails would generally forget the task 24 hours after training. But methamphetamine-treated snails would retain the memory for longer.

    "The drug is not present in their system any longer, but something has happened in their cells that primes them for learning," said Dr Sorg.

    Having seen this drug-enhanced or "pathological" memory-making in action, the scientists now want to know what is changing within an individual brain cell.

    Dr Sorg's colleague, Professor Kenneth Lukowiak from the University of Calgary in Canada had previously identified the one critical cell, or neuron, in the brain of these snails that is crucial to learning and remembering how to regulate their breathing.

    This cell releases a signalling chemical called dopamine; a chemical that, in mammals, is involved in the brain circuitry associated with addiction.

    "That's why we decided [this snail] would be a good system to study," said Dr Sorg.

    "Now we want to look in that brain cell and find what has changed. It's a big task but some recent studies in our lab point to changes at the level of the cell's DNA that are caused by the drug."

    The researchers say that this work lays the foundations for ultimately targeting memory in the treatment of drug addiction and other disorders, such as post traumantic stress disorder.

    The ultimate idea would be to target specific memories - these pathological memories - to be forgotten or diminished.

    Dr Sorg concluded: "If we know something about how these memories are formed, and just as importantly, how they're forgotten, and if we can understand something about the process that promotes forgetting in a single cell, we might be able to translate that to higher animals, including humans."

    Professor George Kemenes from the University of Sussex, studies memory in molluscs in work that is funded by the UK's Medical Research Council.

    "Molecular level findings in snails can be highly instructive for learning and memory research in mammals, and can help us to understand how humans learn and remember," he said.

    "Ultimately, the humble snail could help prevent and treat memory disorders or even enhance normal memory."

    Hear more from the researchers on Science in Action on the BBC World Service on Friday 28 May.

    Friday, May 28 2010



  1. Synchronium
    Crystal meth (methamphetamine) is a highly addictive drug that seduces victims by increasing self-esteem and sexual pleasure, and inducing euphoria. But once hooked, addicts find the habit hard to break. Barbara Sorg from Washington State University, USA, explains that amphetamines enhance memory. 'In addiction we talk about the "drug memory" as a "pathological memory". It is so potent as to not be easily forgotten,' she explains. As memory plays an important role in addiction, Sorg wondered whether it might be possible to find out more about the effects of meth on memory by looking at the effect it has on a humble mollusc: the pond snail Lymnaea stagnalis.

    Lymnaea hold memories about when to breathe through their breathing tubes (pneumostomes) in a three neuron network, which is much simpler than the colossal circuits that hold our memories. Ken Lukowiak from University of Calgary, Canada, has been working on the mechanisms of memory formation in these snails for most of his career, so he and Sorg decided to team up to find out whether a dose of meth could improve the snails' memories in the way it does human memories. They publish their discovery that memories formed by snails under the influence of meth are harder to forget, which could help us to understand human addiction, on 28 May 2010 in The Journal of Experimental Biology.

    First Sorg and her students had to discover whether a dose of meth could affect the snails' breathing behaviour. According to Lukowiak, the snails breathe through their skins when oxygen levels are high, but when oxygen levels drop the snails extend their pneumostomes above the water's surface to supplement the supply. As the drug easily crosses the snail's skin, the team immersed the snails in de-oxygenated pond water spiked with meth, and watched to see how it affected their breathing. The snails stopped raising their pnemostomes at 1 and 3.3·μmol·l-1 meth, so having found a dose that altered the snail's behaviour, the team began testing its effects on the mollusc's long term memory.

    The team trained the snails to remember to keep their pneumostomes closed when oxygen levels were low by poking them with a stick every time they tried to open their pneumostomes. Giving the snails two training sessions separated by an hour, the team knew that the molluscs would hold the memory for over 24·h, but what would happen if they trained the snails in meth-laced water?

    Testing the snails in de-oxygenated pond water 24 hours later, the team were surprised to see that the snails seemed to have no recollection of their training, popping their pneumostomes above the water's surface. Maybe meth did not affect the snails' memories. But then Lukowiak remembered: 'If you put snails in a novel context even though they have memory they respond as if they don't have memory,' he says. Without meth in the water, the snails were ignoring their memory. However, when the team reintroduced meth to the test water, the snails suddenly remembered to keep their pneumostomes closed. This could explain why it's so hard for human addicts to kick the habit when returning to old haunts that trigger the addiction memory.

    Next the team wondered whether meth could improve the snails' memories. First they immersed the snails in meth-laced pond water, then they moved them into regular de-oxygented pond water and gave them a training session that the snails should only recall for a few hours. In theory the snails should have forgotten their training 24 hours later, but would the meth improve the snails' memories so they remembered to keep their pneomostomes closed a day later? It did. A dose of meth prior to training had improved the snails' memories, allowing them to recall a lesson that they should have already forgotten. And when the team tested whether they could mask the meth memory with another memory, they found that the meth memory was much stronger and harder to mask.

    So memories formed under the influence of meth seem to be harder to forget, possibly because the drug disrupts the mechanisms for forgetting, and could help us to understand how amphetamines enhance memory in humans.

    More information: Kennedy, C. D., Houmes, S. W., Wyrick, K. L., Kammerzell, S. M., Lukowiak, K. and Sorg, B. A. (2010). Methamphetamine enhances memory of operantly conditioned respiratory behavior in the snail Lymnaea stagnalis. J. Exp. Biol. 213, 2055-2065. http://jeb.biologists.org

    28th May, 2010
  2. Alfa
    But the conclusion that addiction, craving and psychoactive experience (on drugs that increase LTP) is learning is an unavoidable conclusion stemming from the invention of Long-Term Potentiation. LTP was invented in 1966.
    LTP is how you learn new things and various drugs increase LTP. Thereby drug use effectively imprints the psychoactive experience and has a long term affect on the psyche of the user.
    This is why drugs should be used as tools for personal development rather than recreational getaways. Drugs are quite the opposite of escapes from reality: they have a lasting effect on reality.

    I do find it odd they used snail breathing as a reference point because methamphetamine has a significant effect on breathing.
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