OLFACTORY-BULB OUTPUT CELL TEMPORAL RESPONSE PATTERNS TO INCREASING ODOR CONCENTRATIONS IN FREELY BREATHING RATS

This study compares the single-unit responses of 74 mitral/tufted cell s recorded in freely breathing rats to step increases of the intensity of five odorants from 2 x 10(-4) to 10(-1) of saturated vapor pressur e. It reveals a stability of the responses of these olfactory bulb out put cells. Olfactory stimulation has frequently been shown to produce a strong patterning of mitral/tufted cell discharges highly correlated with respiration. In this study, cells were generally found to show t he same response type to two consecutive concentrations, and only a fe w cells switched their response from excitation to suppression or vice versa. Their firing peak and/or trough occupied the same position in a high proportion of respiratory cycles recorded during a stimulation, and they remained significantly time-locked to the same respiratory e poch for the next higher concentration. Increasing odor concentration did not cause the mean firing frequency of individual cells during a p eak to change appreciably between successive or extreme concentrations . By contrast, it tended to shift their maximum frequency during this peak towards an earlier respiratory cycle after stimulation onset. The se results are compared with data reported in other electrophysiologic al studies and with results given by olfactory bulb models before bein g discussed for their implications in odor coding.