Stochastic activation among inspiratory cells in the pre-Bötzinger complex of the rat medulla revealed by Ca(2+) imaging

In the pre-Bötzinger complex of the ventral medulla (preBötC), a variable pattern of inspiratory neuronal output and synchronous activation of inspiratory cells can be observed. However, it is not well known whether cellular activation patterns among inspiratory cells are variable or fixed. Here, we evaluated the activation sequence of inspiratory cells during individual rhythmic bursts using calcium imaging. Onset timing and peak timing of calcium fluctuations during rhythmic bursts in individual inspiratory cells were used to evaluate the activation sequence. The sequences of both timings changed stochastically in individual rhythmic bursts, although the sequences differed between the two timings even within the same rhythmic burst. The weak correlation between these two timings might indicate that the two parameters reflect different physiological events. Furthermore, a subset of inspiratory cells was found to initially activate in the sequences of successive rhythmic bursts. These results suggest that rhythmic activation of inspiratory cells occurs with a degree of loose regularity but is not invariable with respect to the sequence of either onset or peak timing.