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 t o 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 type s of [Ca2+] changes accompany membrane potential oscillations that are phas e-locked with the respiratory cycle: (i) one is graded and parallels the me mbrane 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 dendriti c compartments are synchronized by action potentials and suggest that the e fficacy of dendritic synapses is finely tuned by odor-evoked graded changes in [Ca2+].