Purinergic signaling mediates neuroglial interactions to generate sighs

Abstract

Sighs prevent the collapse of alveoli in the lungs, initiate arousal under hypoxic conditions, and even express sadness and relief. Sighs are periodically superimposed on normal breaths, known as eupnea. Implicated in the generation of these rhythmic behaviors is the preBötzinger complex (preBötC)1. Yet how this small microcircuit can produce two rhythms with strikingly different periodicities remains unresolved. Our computational simulations predict that sighs are generated by the coincidence of two temporally distinct calcium oscillations and are in agreement with experimental evidence suggesting that astrocytes drive sigh behavior through slower, extrinsically driven calcium oscillations that link the eupnea and sigh rhythms. We found that purinergic signaling is necessary to generate spontaneous and hypoxia- induced sighs, and photo-activation of preBötC astrocytes is sufficient to elicit sigh activity. We conclude that sighs are an emergent property of the preBötC network generated by neuroglial interactions, where the distinct modulatory responses of neurons and glia allow for both rhythms to be independently regulated.

Sigh breathing rhythm depends on intracellular calcium oscillations in a population of inspiratory rhythmogenic preBötzinger complex neurons in mice

“…S1C). A parallel experiment employed the highly selective P2Y 1 antagonist MRS2279 because recent evidence in preprint form purports that gliotransmission specifically via P2Y 1 receptors is obligatory for sigh rhythmogenesis in vitro (17). Bath-applied 20 μM MRS2279 had no effect on either inspiratory or sigh rhythm (inspiratory rhythm: 0.20 ± 0.04 Hz in control vs. 0.26 ± 0.06 Hz in MRS2279, p = 0.13; sigh rhythm: 0.86 ± 0.45 min -1 in control vs. 0.61 ± 0.28 min -1 in MRS2279, p = 0.26) (Fig.…”

“…We conclude that glia and gliotransmission are not mandatory for sigh rhythmogenesis because attenuating purinergic P2Y signaling, the dominant means by which astrocytes interact with preBötC neurons (30–32), did not preclude or modify sigh rhythmogenesis. A recent report in preprint form showed that blocking gliotransmission at P2Y 1 receptors stops the sigh rhythm in vitro but does not stop sighs in adult mice (17). Our conclusion is not incompatible – purinergic gliotransmission is ultimately unnecessary for sigh behavior – but our data in vitro are incongruous.…”

“…One possibility is that two discrete rhythmogenic mechanisms are embodied in different cell populations, neural and/or non-neural (17). Astrocytes can generate intracellular Ca 2+ oscillations and gliotransmission via purinergic P2 receptors modulates inspiratory preBötC rhythms (30)(31)(32), which suggests astrocytes communicating with preBötC neurons via purinergic P2 receptors is a feasible mechanism for sigh rhythmogenesis.…”

“…First, the literature is contradictory regarding whether dichotomous eupnea-and sighspecialized neuron populations exist in the preBötC (15,16); furthermore, a more recent report suggests that preBötC astrocytes are sigh rhythmogenic (17). Second, experimental data are unsupportive regarding a rhythmogenic role for INaP in inspiration (18)(19)(20)(21)(22).…”

Transcriptomes of Electrophysiologically Recorded Dbx1-derived Inspiratory Neurons of the preBötzinger Complex in Neonatal Mice

“…For example, regarding inspiration, intracellular Ca 2+ signaling in the context of SOCE could recruit Ca 2+ -activated non-specific cationic current (ICAN), which profoundly contributes to inspiratory burst pattern [29][30][31] , consistent with the role of Type-2 neurons. Sigh breaths, which occur at lower frequencies but are two-fold larger in magnitude 32 are likely also to involve Ca 2+ signaling and possibly SOCE mechanisms that recruit ICAN 33 .…”