WASHINGTON, D.C.--Could this explain what gave cartoon hero Mighty Mouse the courage to fight evil? Researchers have found that flesh-and-blood mice lacking a particular gene are unusually brazen, venturing into wide open spaces and onto narrow bridges that their genetically normal kin avoid. The mutant mice also appear to have weaker memories of scary encounters than normal mice do.
The finding comes out of an effort to understand the mechanisms of fear by studying genes that are active in the lateral amygdala, a brain region crucial for learned fear responses. One gene that is especially busy is called stathmin, and in the new study, a team led by Gleb Shumyatsky of Rutgers University in Piscataway, New Jersey, took a look at the brains and behavior of mice engineered to lack that gene.
The stathmin knockout mice are relatively fearless. Not only do the mutant mice spend more time than do normal mice in exposed spaces, indicating a lack of innate fear, they're also less prone to freeze up in fear when they hear a tone that previously signaled an impending electric shock, indicating an impairment of fear learning. The deficit seems specific to fear, however: the mutants performed normally on a task that requires swimming mice to learn and remember the location of a submerged platform, the team reported here 16 November at the annual meeting of the Society for Neuroscience. The findings will also appear tomorrow in Cell.
The stathmin gene regulates the formation and breakdown of microtubules, filaments that provide structural support and help move proteins around inside cells. This study provides the first direct evidence that microtubules are involved in some kinds of learning and memory, Shumyatsky says, but he adds that their precise role is far from clear.
"This is a beautiful study," says Joseph LeDoux, a neuroscientist who studies the neural basis of fear at New York University in New York City. It's possible that the work will eventually lead to a better understanding of anxiety disorders, LeDoux says, but it's too early to make any specific conclusions. One idea, Shumyatsky says, is that is that individual differences in stathmin activity might determine people's anxiety set point--how jittery they are in general, and how strongly adverse events affect them. If only Mighty Mouse could volunteer a DNA sample...