A direct line through the brain to avoid rotten food
Consuming putrid food can be lethal as it allows bacterial pathogens to enter the digestive system. To detect signs of decay and thus allowing us and other animals to avoid such food poisoning is one of the main tasks of the sense of smell. Behavioural scientists and neurobiologists at the Max Planck Institute for Chemical Ecology in Jena, Germany, have now for the first time decoded the neural mechanisms underlying an escape reflex in fruit flies (Drosophila) activated in order to avoid eating and laying eggs in food infected by toxic microorganisms. A super-sensitive and completely dedicated neural line, from olfactory receptor, via sensory neuron and primary brain neurons, is activated as soon as the tiniest amount of geosmin is in the air. Geosmin is a substance released by bacteria and mold fungi toxic to the fly. This stimulus overrides all other food odour signals, irrespective of how attractive they are on their own. Consequently, geosmin is a full STOP signal that prevents flies from eating and laying eggs in toxic food, similar to when we open the fridge and smell last week’s forgotten dinner.