Wednesday, August 29, 2007

An enzyme that keeps old memories alive

Greg Miller writes a brief review of work by Shema et al. :
Many substances interfere with memory, as any hung-over partygoer can attest. But although booze and drugs can disrupt the making of new memories (such as the embarrassing antics at last night's party), they leave older memories intact. Neuroscientists think this is because, after a time, memories become wired into the brain in a way that makes them harder to wipe out: Long-term memories, in the generally accepted view, are maintained by structural changes to the synaptic connections between neurons.

The study [by Shama et al.] adds to other recent evidence that may challenge, or at least complicate, this view. A team of neuroscientists reports that injecting a drug that blocks an enzyme called protein kinase Mzeta (PKMzeta) into the cerebral cortex of rats makes the animals forget a meal that made them sick weeks earlier. The findings suggest that the continuing activity of PKMzeta is somehow necessary to maintain long-term memory, something that's not predicted by most current hypotheses on the mechanisms of memory. The work also hints at the possibility of future drugs that could tinker with memory--for therapeutic uses or for boosting brainpower.

"This is a somewhat mind-blowing conclusion," says David Glanzman, a neuroscientist at the University of California, Los Angeles. Enzymes similar to PKMzeta are known to be important in early stages of memory formation, Glanzman says, but most researchers had thought that these compounds were not needed to sustain memory once synaptic changes--such as the growth of new synapses or the strengthening of existing ones--had occurred.

...Going forward, it will be important to figure out how specific ZIP's memory-erasing effects are, says Lynn Nadel, a neuroscientist at the University of Arizona in Tucson. "It's possible that ZIP erases all learning, no matter how old," Nadel says. But if the drug works more selectively, it could one day have clinical applications, he says. For example, researchers and clinicians have been looking for compounds capable of eliminating the painful memories of trauma survivors (Science, 2 April 2004, p. 34). The flip side is cognitive enhancement, adds Richard Morris, a neuroscientist at the University of Edinburgh, U.K. "The next step might be to find out whether augmenting the action of PKMzeta can help sustain memories for longer than occurs normally."

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