In vivo whole-cell recording of odor-evoked synaptic transmission in the rat olfactory bulb.

One of the first steps in the coding of olfactory information is the transformation of synaptic input to action potential firing in mitral and tufted (M/T) cells of the mammalian olfactory bulb. However, little is known regarding the synaptic mechanisms underlying this process in vivo. In this study, we examined odor-evoked response patterns of M/T and granule cells using whole-cell recording in anesthetized, freely breathing rats. We find that odor-evoked excitatory responses in M/T cells typically consist of bursts of action potentials coupled to the approximately 2 Hz respiration rhythm. Odor-evoked, rhythmic M/T cell excitation is reliable during odor presentation (2-4 sec); in contrast, both excitatory responses of granule cells and M/T cell lateral inhibition adapt quickly after the first respiration cycle in the presence of odorants. We also find that the amplitude and initial slope of odor-evoked synaptic excitation play an important role in regulating the timing of M/T cell spikes. Furthermore, differences in odor concentration alter the shape of odor-evoked excitatory synaptic responses, the latency of M/T cell spikes, and the timing of M/T cell lateral inhibition.