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Mouse: I am not afraid
The innate tendency of mice to shy away from the smell of danger can be switched off by simply turning off certain receptors in the nose, even though the same mice can detect the smells and be taught to avoid them, says research published online in Nature. In the experiments, mice lacking these receptors were undeterred by the scent of rotting food or predators, which normal mice stay well clear of.
The mammalian olfactory system mediates various responses, including aversive behaviours to spoiled foods and fear responses to predator odours. In the olfactory bulb, each glomerulus represents a single species of odorant receptor. Because a single odorant can interact with several different receptor species, the odour information received in the olfactory epithelium is converted to a topographical map of multiple glomeruli activated in distinct areas in the olfactory bulb.
To study how the odour map is interpreted in the brain, Hitoshi Sakano and colleagues generated mutant mice in which olfactory sensory neurones in a specific area of the olfactory epithelium are ablated by targeted expression of the diphtheria toxin gene.
In experiments, mice lacking these receptors do not react normally to aversive smells, such as rotting food or the usually fearful scent of fox or snow leopard, but can be conditioned to be averse to them. This suggests the presence of dedicated systems for innate versus learned responses.
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