The influence of permanent odor stimuli on the postnatal development of neural activity in the olfactory bulbs of laboratory mice.

Young laboratory mice were kept from birth in a surrounding with one dominating synthetical odor substance (geraniol, C10H18O; experimentals); the controls were bred under normal conditions. Between postnatal days 10 and 35 the development of the neural activity in the olfactory bulb and the response to the synthetical (geraniol) and a natural odor (nest material) were tested at 6 different stages of age. By means of a computer the total energy and the frequency composition (power spectra) of the electrophysiologically leaded potentials were analyzed at the time of stimulation and without stimulation. The developmental increment of neural activity was retarded at the experimentals, but the typical high-frequency waves (oscillations) appeared about 5-6 days earlier than in the controls. Both odor substances induced neural responses measured by energy and frequency changes in the power spectra. In controls none of the odors leads to noticeable changes in the composition of frequencies at days 10 and 14. Beginning at postnatal day 18 the odor substances of nest material evoked increasing neural reactions; at all stages of age geraniol induced only slight alterations in the power spectra. In the experimentals responses could be measured first at day 14. The changes in power spectra rapidly increased in the following 3 weeks and the responses to geraniol reached several times more intense levels than in the controls. The influence of permanent olfactory stimuli on the ontogenetic development of the olfactory bulb and the extreme plasticity of this system are discussed.