Monday, October 27, 2008

Transsexuals, farts, stem cells and memory manipulation. Just another day...

From the news:
  • Australian study finds correlation between transsexuality and the gene coding a male hormone (androgen) receptor. Apparently, the long version of the gene has a less efficient product, and was found significantly more often in 112 male-female transsexuals compared to 258 control subjects. Which makes me wonder what this finding means to transsexuals, if anything at all...

  • Solomon Snyder, an interesting character in the history of neuroscience, stands behind a study linking the stink-inducing chemical in flatulence and blood pressure. Apparently the foul smell, hydrogen sulfide, can lower blood pressure significantly. Reported with a sort of childish glee by both the BBC and the CBC (and others)...

  • While Britain relaxes certain stem-cell laws, it is pointed out that Canada is the about the only country in the world that does not currently allow the use of animal eggs in the production of human embryonic stem cells. I would bet a hefty sum of cash that stem cell technology will cure at least some neurodegenerative disorders within my lifetime. However, it is up to legislators to determine whether it will be 10 years from now or 25...
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A very interesting piece from CBC reports on scientists who seem to succeed at wiping a specific memory from a rat. They do this by using mice who have a very fancy piece of genetic engineering on board. The scientists built a gene construct where they could make a certain protein become more abundant in certain areas of the brain through pharmacological manipulation. Then they tested if a mouse could remember a certain place by shocking him there, and seeing if he shows behavioural signs of fear the next time he gets put there.

By overexpressing the protein in question when the mouse was put back in the chamber, the researchers could effectively make the memory disappear. Now, as we all know, memory is a strange thing. It consists of four processes that we call "acquisition," "consolidation," "storage," and "retrieval," which we could equally call "getting," "coding," um, "storing," and "remembering." But it's more complicated than that - when a memory is brought back from storage to become part of conscious thought, it has to be re-encoded, and stored. Even worse, it becomes flexible while we remember it - numerous studies show memories are influenced by current emotions and knowledge, become mixed up with the present.

Instead of altering the memory, the overexpression of this protein (αCaMKII for those keeping track) seems to destroy the memory when it's being remembered, perhaps with a sort of excessive brain "noise" level that obliterates the memory signal during the process of recalling it. This paper is a tome, so I haven't been through it very thoroughly, but it's in an amazing journal (Neuron) and looks pretty watertight. Really an amazing study.

That being said, this is a bit of what a former colleague of mine calls a "sledgehammer" approach, because it lacks precision as a tool. Gene expression is affected through an enormous population of cells, so it could be the case that more than the memory being recalled is affected . Other limitations make it extremely tough to try pulling this off using similar methods in humans. Firstly, the behaviour is not very sophisticated, even for a mouse. More importantly, human memories - particularly the bad ones - are probably richer and more complex than those of mice, and will be consequently harder to "knock out."

The best part, however, is this very wise comment by senior author Joe Tsien: "All memories, including the painful emotional memories, have their purposes. We learn great lessons from those memories or experiences so we can avoid making the same kinds of mistakes again, and help us to adapt down the road."

Good advice, and wise words for the future of memory manipulation.

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