Odor-evoked calcium signals in dendrites of rat mitral cells

Mitral cell dendrites do more than passively integrate and convey synaptic potentials to the soma, they release transmitter onto local interneurones to mediate recurrent and lateral inhibition. Several mechanisms may control the level of dendritic intracellular calcium ([Ca²⁺]) and define timing for dendritic release. Here we investigated in vivo, how odor controls calcium dynamics in mitral cell dendrites by combining intracellular recording and two-photon microscopy imaging of [Ca²⁺]. During odor stimulation, two types of [Ca²⁺] changes accompany membrane potential oscillations that are phase-locked with the respiratory cycle: (i) one is graded and parallels the membrane potential, even below the threshold for action potential firing; (ii) a second is transient, triggered by sodium action potentials that invade the entire dendritic tree. These results indicate that mitral cell dendritic compartments are synchronized by action potentials and suggest that the efficacy of dendritic synapses is finely tuned by odor-evoked graded changes in [Ca²⁺].