Dendritic calcium activity precedes inspiratory bursts in preBotzinger complex neurons

Medullary interneurons of the preBötzinger complex assemble excitatory networks that produce inspiratory-related neural rhythms, but the importance of somatodendritic conductances in rhythm generation is still incompletely understood. Synaptic input may cause Ca2+accumulation postsynaptically to evoke a Ca2+-activated inward current that contributes to inspiratory burst generation. We measured Ca2+transients by two-photon imaging dendrites while recording neuronal somata electrophysiologically. Dendritic Ca2+accumulation frequently precedes inspiratory bursts, particularly at recording sites 50–300 μm distal from the soma. Preinspiratory Ca2+transients occur in hotspots, not ubiquitously, in dendrites. Ca2+activity propagates orthodromically toward the soma (and antidromically to more distal regions of the dendrite) at rapid rates (300–700 μm/s). These high propagation rates suggest that dendritic Ca2+activates an inward current to electrotonically depolarize the soma, rather than propagate as a regenerative Ca2+wave. These data provide new evidence that respiratory rhythmogenesis may depend on dendritic burst-generating conductances activated in the context of network activity.