Responses of olfactory bulb neurons to repeated odor stimulations in awake freely-breathing rabbits.

Thirty-one olfactory bulb neurons were recorded in the olfactory bulbs of unanaesthetized rabbits during repeated stimulations. Their single-unit activity associated with the inspiratory phases of the respiratory cycles and that associated with the expiratory phases were processed separately. When responses were classified into 3 types, i.e., excitation, inhibition and null, it was found that a large number of neurons presented variable responses to repeated stimulations with the same stimulus. However, the passage from one type to another was found to be limited: responses by excitation or inhibition to the first stimulation turned into null responses only; null responses turned into either excitation or inhibition. Inspiration- and expiration-related responses were also subjected to a principal component analysis in order to determine whether changes in responses were compatible with a reliable coding of the qualitative properties of a stimulus. The results indicated that the repeated presentations of an odorant induced fairly similar profiles of activity across the set of neurons while different odorants induced clearly discriminable profiles. It is concluded that repeated stimulations do not blur the characteristic features of the across-neuron profile of response of an odorant in the olfactory bulb despite the variability of the responses of the neurons which compose the profile.