Single cell recording in the rat olfactory bulb

Abstract

The purpose of this investigation was to determine if there are unique odor components in the goal box of a straight alleyway following rewarded and nonrewarded trials. Behavioral research has convincingly demonstrated that unless the goal box is cleaned between animals a pattern of slow running on nonreward trials and fast running on reward trials soon develops. The explanation for these patterned responses has been that the rat emits an odor in the goal box, depending on the presence or absence of reward, which allows following conspecifics to predict the upcoming goal event before reaching the end of the alleyway. Behavioral research has been unable to determine if there are unique odors associated with each type of goal event, if there is only one odor of varying concentration, or if only one odor is present and the cue for the other condition is merely the absence of that odor. Twenty-eight female Sprague Dawley rats were used as subjects for the recording. Subjects were immobilized with Flaxidil and single cell responses recorded from the mitral cell layer of the olfactory bulb. Odor stimuli used for the recording were: paper from the goal box of a straight alleyway in which eight rats had received two reward trials (R-paper), or two nonrewarded trials (N-paper), and paper to which urine (U-paper) or food (F-paper) had been added. Subjects were tested with each stimuli three times, clean air was presented between each of the 12 stimulus presentations. A change of firing rate by a cell of 20% or greater from the clean air baseline firing rate was considered a significant change. A total of 187 cells were recorded from, and 178 of these were used in the data analysis. Unique changes in firing rate response of a single cell to the stimuli (different for one stimulus than for the other three) were found in 25 cells for the N-paper, 26 cells for the R-paper, 22 cells for the U-paper, and 31 for the F-paper. Similar changes in firing rate of a single cell were found in 20 cells for N and R-paper, 17 cells for N and U-paper, 6 for N and F-paper, 11 for R and U-paper, 7 for R and F-paper, and 11 for all four stimuli. The results of this study strongly suggest that there are unique odors in the goal box as a result of nonreward and reward trials. It further suggests that these R and N odors are different from the odors of food or urine, and that R and N odors are possibly very similar in chemical structure.