Modulation of the multiunit responses of the olfactory bulb and respiratory activity as a function of the significance of odors in freely moving rats
Cattarelli, M.; Pager, J.; Chanel, J.
Journal de Physiologie 73(7): 963-984
1977
ISSN/ISBN: 0021-7948 PMID: 614410 Document Number: 112575
Multiunit electrical mitral cell activity of the olfactory bulb was recorded with the respiratory activity from freely moving rats stimulated by several biologically meaningful (alarming, reassuring) and neutral odors. The rats were given food and water ad lib. The recording tips of bipolar stainless steel electrodes were placed in the ventral mitral cell layer of 1 olfactory bulb, under oscilloscope control. Respiratory activity was recorded from 2 macroelectrodes screwed into the skull above the other olfactory bulb. Recordings were performed 8 days after surgery. The rat was placed in a cylindrical Perspex cage with a continuous airflow. During the test period, the airflow was either deodorized between 2 stimulations or odorized during the stimulations. Seven stimuli were delivered, each lasting 10 s, every 2 min. The stimuli were the odors of feces (alarming, fox; neutral, lion; and reassuring, grouped rats),or of usual food, citral, isoamyl acetate and deodorized air for the sham stimulations. The respiratory frequency and the sniffing duration and latency were measured. The summated mitral cell activity recorded during the stimulations was interpreted as positive or negative responses (increased or decreased activity) or as a lack of response (no significant modification of the trace). The respiratory frequency increased significantly during stimulations by reassuring (grouped rats) or neutral odors (usual food, isoamyl acetate). No significant change was elicited by alarming (fox) or aversive (citral) odors. The longest sniffing durations were obtained for those odors bearing a marked biological meaning : fox or grouped rats. The sniffing behavior seemed to be correlated with the animal internal state determined by the corresponding cues. Different patterns of multiunit responses were obtained according to the biological meaning of the odor. Habituation was observed as a decreased ratio of positive responses to ten successive identical stimulations. Habituation was minimal for the odors of fox and grouped rats. Increase, decrease or no change of the bulb responses and of respiratory activity were not always concomitant. Sniffing behavior was not systematically correlated with positive bulb responses. Respiratory activity and bulb responses to the 1st stimuli, were mainly associated with general arousal of the animal. Bulb responses then displayed a differential habituation corresponding to the affective tone of odors. The operation of at least 2 modulating systems with common central relays was suggested.