EOG responses in anesthetized freely breathing rats

In mammals, access of odor molecules to the olfactory receptor neurons is c ontrolled by respiratory activity. Thus, anesthetized, freely breathing rat s were used to record from the olfactory mucosa in the intact nasal cavity (electroolfactogram or EGG) so as to study global response characteristics to odor stimuli. During alternation of the inspiratory phases of odor sampl ing and expiratory phases, the response was a succession of individual EOG events synchronized with respiration. These were characterized by a steep d ecrease that started similar to 100-150 ms after the beginning of inhalatio n, reached its maximum at the transition between inspiration and expiration and was followed by a slower rise until the next inhalation. They were gre ater during the first respiratory cycles following odor stimulation onset. Thereafter their amplitudes decreased throughout odor delivery, but a signi ficant EOG signal was still present at the end of short (10 s) and long (60 s) odor presentations. Amplitude increased with odor concentration, but mu ch less than expected from concentration changes. Lastly, for some odors EO G responses persisted well beyond the end of stimulation. These results are in agreement with the respiratory synchronization of mitral cell activitie s observed during short odor presentations and long duration odor exposures . They underline again the importance of taking into account the respirator y activity in studies on the functioning of the olfactory system.