K+ and Ca2+ dependence of inspiratory-related rhythm in novel “calibrated” mouse brainstem slices

Recently developed transversal newborn rat brainstem slices with “calibrated” rostrocaudal margins unraveled novel features of rhythmogenic inspiratory active pre-Bötzinger complex (preBötC) neural networks (Ballanyi and Ruangkittisakul, 2009). For example, slice rhythm in physiological (3 mM) superfusate K+ is depressed by modestly raised Ca2+ and restored by raised K+. Correspondingly, we generated here calibrated preBötC slices from commonly used newborn C57BL/6 mice in which rostrocaudal extents of respiratory marker structures, e.g., the inferior olive, turned out to be smaller than in newborn rats. Slices of 400-600 μm thickness with likely centered preBötC kernel (“m-preBötC slices”) generated rhythm in 3 mM K+ and 1 mM Ca2+ for several hours although its rate decreased to <5 bursts/min after >1 h. Rhythm was stable at 8-12 bursts/min in 6-7 mM K+, depressed by 2 mM Ca2+, and restored by 9 mM K+. Our findings provide the basis for future structure-function analyses of the mouse preBötC, whose activity depends critically on a “Ca+/K+ antagonism” as in rats.