HETEROGENEOUS CHARACTERISTICS OF MITRAL CELLS IN THE RAT OLFACTORY-BULB

The spontaneous firing activity of olfactory bulb mitral cells and the ir response, to intrabulbar infusion of GABA(A) receptor antagonist bi cuculline were studied in ovariectomized, urethane-anesthetized female rats. Mitral cells recorded in the absence of specific stimuli and na sal airflow displayed three distinct patterns of spontaneous fifing: h igh-frequency bursts with relatively long silent periods; high-frequen cy bursts without accurately defined silent periods; continuous. Infus ion of bicuculline (0.2 nmol) into the bulb yielded inconsistent resul ts on spontaneous firing and its inhibition evoked by electrical stimu lation of the lateral olfactory tract. Of 32 cells tested, the spontan eous firing rate increased for 24, decreased for 6, and was not altere d for 2. Likewise, of 18 cells tested, the poststimulus inhibitory per iod shortened for 12, lengthened for 4, and not altered for 2. An incr eased dose (0.4 nmol) of bicuculline produced dose-response relationsh ips simply without any reversal effect. These results suggest that the heterogeneity of mitral cells exists in the context of local interneu ronal circuitry in the bulb.