The Insulin-Like Hormone That Gives Rats a Memory Boost
A surprise to remember: Scientists have found that a naturally occurring hormone usually involved in cell repair is also present in the hippocampus of the brain, and when they extra doses of it to rats in their experiments, it appeared to greatly enhance the rats’ memory.
The hormone is called insulin-like growth factor II (IGF-II), and the fact that it showed up in the hippocampus (associated with memory and learning) made Cristina Alberini wonder if it could be a key player in memory formation. So she and her colleagues designed a test:
The team came up with a box that was lit on one side and unlit on the other. Rats that entered the dark side got a mild foot shock. The rats’ subsequent hesitation to return to the dark after getting shocked gave the scientists a measure of how well they remembered the traumatic event. [ScienceNOW]
The rats showed elevated IGF-II levels after the shock, but Alberini wanted to see whether tinkering with those levels could change the rats‘ ability to form and recall memories.
Some rats were then given an injection of IGF-II, in … the hippocampus. Even weeks later, rats that had received the IGF-II exhibited greater avoidance of the location than rats that had a control injection of another growth factor or saline solution.Â [Wall Street Journal]
In fact, Alberini says, the shot of IGF-II appeared to double the rats’ memory, based on their hesitancy to go over to the dark side. But the shot had to be given within 24 hours of the traumatic experience to work.
The team’s results, published today in Nature, offer a new piece of the consolidation puzzle, says neurobiologist Alcino Silva of the University of California, Los Angeles, who was not involved in the study. “We know a lot about the first few seconds of learning but not so much about the hours and days later,” he says. “Looking at this period is a big contribution. I’m envious, actually.” [ScienceNOW]
And, interestingly, the shot of IGF-II worked if it was injected into the hippocampus, but not if it was injected into the amygdala, which tends to be associated with fear. Now, Alberini says, she wants to see whether giving the protein supplement to the rats’ entire body works the way the hippocampus injection does. It’s the next step on the long research road to determining whether such a memory effect could appear in humans.