INITIAL EVENTS OF THE ELECTRO‐OLFACTOGRAM

A voltage change between the surface of the olfactory mucosa and any other point on a frog is produced by a smell. This is called the electro-olfactogram or EOG and often includes two components. These were first described by 0ttoson.l The major component is a large negative voltage swing of the mucosa surface with respect to an indifferent electrode elsewhere. The negative peak typically occurs 0.8 second after the onset of the stimulus. This voltage is maintained at a level somewhat lower than the peak for the duration of a prolonged stimulus, or falls back to the long-term base line with a longer time constant than the rising phase for a short puff of odorized air. The peak amplitude is proportional to the number of stimulus molecules per unit time reaching the mucosa for any particular stimulus. This is true for a fairly wide range of stimulus strengths above a threshold value and below a saturation value. The amplitude of the peak voltage decreases with the number of stimulus puffs if they are closely spaced. The peak amplitude is constant if the stimuli are separated by intervals of from 30 seconds to 5 minutes, depending upon the particular substance being used for the stimulus. The other component of the EOG is a voltage swing, usually positive and small, occurring before the large negative swing. It was characterized by Ottoson as having an amplitude independent of stimulus strength. In the case of n-butanol, this initial positive deflection does not occur if there is no water vapor present with the butanol. The amplitude of the positive swing increases as the temperature of the stimuli is increased, and this increases the amount of water vapor and butanol arriving at the mucosa per puff. Ottoson also saw indications of the positive swing when his electrode was touching nonolfactory tissue. He concluded that this transient was an artifact, possibly due to some effect of water either on the tissue or on the electrode, or on both. I have come to somewhat different conclusions about the early events associated with the EOG and this paper presents the results of some experiments using a wide variety of stimulating substances.