The influence of early odour experience on the neural response of the olfactory bulb in laboratory mice.

In mice (strain NMRI) the influence of olfactory rearing conditions on the ontogenetic development of the bulbar electroencephalogram (EEG) was investigated. The cages of control animals were perfused continually with filtered air, whereas in the three experimental groups geraniol was added to the atmosphere at different times (group G0-13, from birth till day 13; group G0-6, from birth till day 6; group G6-12, from day 6 till day 12). At various ages the EEG of the bulbus olfactorius was studied by means of permanently implanted tungsten electrodes, and the neural response to nest odour and geraniol (10(-2) vol. %) was recorded. No differences were found between the groups regarding the overall development of the bulbar EEG, nor did the raising conditions affect the neural response to nest odour. However, in groups G0-13 and G6-12 a marked response to the odour of geraniol was recorded, while in the controls and the individuals that had experienced geraniol only during their first week of life, the bulbar response to this odourant did not differ from that obtained following stimulation with clean air. In the animals of group G0-13, which were investigated as adults (day 70), the prominent geraniol response was still recordable 2 months after the last contact with the odour. These results indicate that odours experienced during a sensitive period in the nest evoke neuronal alterations in the olfactory system of the mouse that facilitate processing of a known odourant.