Bozza's group has shown that the TAARs are extremely sensitive to amines -- a class of chemicals that is ubiquitous in biological systems and is enriched in decaying materials and rotting flesh. Mice and humans typically avoid amines since they have a strongly unpleasant, fishy quality.
Bozza's team, including the paper's lead authors, postdoctoral fellow Adam Dewan and graduate student Rodrigo Pacifico, generated mice that lack all 14 olfactory TAAR genes. These mice showed no aversion to amines. In a second experiment, the researchers removed only the TAAR4 gene. TAAR4 responds selectively to phenylethylamine (PEA), an amine that is concentrated in carnivore urine. They found that mice lacking TAAR4 fail to avoid PEA, or the smell of predator cat urine, but still avoid other amines.
"It is amazing to see such a selective effect," Dewan said. "If you remove just one olfactory receptor in mice, you can affect behavior."
The TAAR genes are found in all mammals studied so far, including humans. "The fact that TAARs are highly conserved means they are likely important for survival," Bozza said.
One idea is that the TAARs may make animals very sensitive to the smell of amines. Humans may have TAAR genes to avoid rotting foods, which become enriched in amines during the decomposition process. In fact, the TAARs may relay information to a specific part of the brain that elicits innately aversive behavior in animals.
Bozza's lab has recently shown that neurons in the nose that express the TAARs connect to with a specific region of the olfactory bulb -- the part of the brain that first receives olfactory information. This suggests that the TAARs may elicit hardwired responses to amines in mice, and perhaps humans.
"We hope th
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