Dendritic Calcium Activity Precedes Inspiratory Bursts in preBötzinger Complex Neurons

Abstract

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.