Somatic and proximal dendritic Ca2+ dynamics in inspiratory preBotzinger Complex neurons.

Abstract

PreBötzinger Complex (preBötC) neurons are interconnected and postulated to underlie respiratory rhythm generation. Each inspiration results from preBötC neurons firing a synchronous burst of action potentials on top of a 10–20 mV, 0.3–1 s inspiratory drive potential. The mechanisms for inspiratory drive generation remain unknown. We tested whether somatic and proximal dendritic [Ca2+] increases during inspiratory drive. We used whole cell recording and a CMOS camera coupled to an intensifier to detect single neuron Ca2+ signals with high temporal resolution (1 kHz) in neonatal rat medullary slice preparations, recording simultaneously the integrated rhythmic hypoglossal nerve activity (∫XIIn). In neurons loaded with Fluo‐4, we were able to resolve somatic and proximal dendritic Ca2+ transients associated with each AP. We isolated the inspiratory drive potential after preventing APs by blocking Na+ channels with intracellular QX‐314. In the absence of APs, we did not detect somatic or proximal dendritic Ca2+ signals contributing to the inspiratory drive potential. Our data suggest that during inspiration somatic and proximal dendritic Ca2+ transients are mainly the consequence of Ca2+ influx through VGCCs during backpropagating APs. We propose that if Ca2+ influx contributes to inspiratory drive formation is through Ca2+ transients happening at distal dendrites by synaptic events that modulate/activate drive currents. However, we recognize the possibility that extremely low level or highly localized [Ca2+] transients, undetectable with our current technology, could be present.