Similarity of granular-induced inhibitory periods in pairs of neighboring mitral / tufted cells. BUONVISO, N., M.A. CHAPUT and F. BERTHOMMIER. Physiologie Neurosensorielle. CNRS - Univ. Lyon 1. 69622 Villeurbanne cedex, France, ICP-INPG. Avenue F[acute]elix Viallet. 38031 Grenoble cedex.
APStracts 3:0121N, 1996.
SUMMARY AND CONCLUSIONS
1 ? - ? Neighboring mitral/tufted cells have been previously shown to present temporal correlations of their firings, related to the respiratory rhythm, particularly under odor stimulation. This occurs despite the existence of a powerful inhibitory control exerted by granule cells onto mitral/tufted cells. In the present study, we hypothesized that neighboring mitral cells can present granular-induced inhibitory periods with similar latencies and durations and that such a similarity would preserve them from a possible suppression of their temporal correlations. 2 ? - ? To test this hypothesis, we analyzed the latencies and durations of the inhibitory periods induced by granular activation in pairs of simultaneously recorded neighboring mitral cells. The activation of granule cells was achieved by electrical stimulation of the different pathways known to directly activate granule cells (LOT, AC and PC). Data from this group were compared to those of a control group composed of distant cells also recorded simultaneously. 3 ? - ? Results first show that the latencies to onset of inhibition or to recovery were more frequently similar in neighboring cells than in control cells and that this similarity was enhanced by odor stimulation. Second, the probability that 2 cells exhibit similar inhibitory periods (i.e. similar latencies to both onset and to recovery) in response to electrical stimulation of LOT, AC or PC was significantly higher in neighboring- than in control cells. Third, only neighboring cells were found to present similar inhibitory periods in response to the stimulation of all of the 3 structures. 4 ? - ? Granular activation was also found to modify the temporal patterns of individual mitral cells. However, although these patterns were not systematically modified similarly in neighboring mitral cells, they remained perfectly synchronized with 0 delay if they were already synchronous without electrical stimulation. On the contrary, if patterns were spontaneously uncorrelated, electrical stimulation never produced a synchronization of their firings, even if their temporal relationships could be profoundly modified. 5 ? - ? These results show that neighboring mitral cells can receive granular-induced inhibition with similar latencies and durations with a probability much higher than control cells. Such similarities allow neighboring mitral cells to preserve their temporal correlations in spite of the powerful inhibitory input from granule cells. Functional hypothesis about the role of the cortical feed-back projections onto the bulb are discussed. 

Received 22 February 1996; accepted in final form 22 May 1996.
APS Manuscript Number J131-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96