Japanese scientists have created genetically-modified mice that, shorn of their ability to sense dangerous smells, will even snuggle up to a kitten, according to a study released on Wednesday by the journal Nature.

The mice were engineered to lack specific nasal receptors that respond to the scent of rotting food or predators, in a project designed to help understand the mechanisms of smell.

The mice were able to detect these smells using other olfactory cells but, lacking the key pathway that triggered a “fear” warning to the brain, were quite undeterred by the presence of a cat or acids and other dangerous compounds.

However, the mice could be conditioned into realising that these smells meant danger, using classic laboratory methods of exposing them to the scents and to a painful irritant at the same time.

The researchers, led by the University of Tokyo’s Hitoshi Sakano, believe that the findings explain important differences in the olfactory bulb, the part of the forebrain where odours are perceived.

Inside the bulb are several thousand clusters of cells called glomeruli, which receive signals from the millions of receptor cells in the nose.

In mice, separate sets of glomeruli are used to receive warning smells, the paper suggests. One set is innate, and another set is for learned responses.