Preinspiratory calcium rise in putative pre‐Bötzinger complex astrocytes

Abstract

Key points• Autonomic respiratory rhythm is essential to maintain lives and is generated in the lower brainstem. The ventrolateral medullary region, called the pre-Bötzinger complex (preBötC), is the kernel for respiratory rhythm generation. Despite previous extensive studies focusing on neurons, the mechanism of how respiratory rhythm is generated has not been fully understood.• Here we show that non-neuronal glial cells (a subset of putative astrocytes) in the preBötC are periodically activated preceding inspiratory neuronal activity, periodic activity of putative astrocytes persists during blockade of neuronal activity, and stimulation of astrocytes in the preBötC induces inspiratory neuronal firings.• These findings together with the previous report that blockade of astrocytic metabolism abolishes inspiratory neural output suggest that astrocytes are functionally involved in respiratory rhythm generation.• These results will help us better understand how respiratory rhythm is generated and how respiratory output is disturbed in various pathological conditions. AbstractThe neural inspiratory activity originates from a ventrolateral medullary region called the pre-Bötzinger complex (preBötC), yet the mechanism underlying respiratory rhythmogenesis is not completely understood. Recently, the role of not only neurons but astrocytes in the central respiratory control has attracted considerable attention. Here we report our discovery that an intracellular calcium rise in a subset of putative astrocytes precedes inspiratory neuronal firing in rhythmically active slices. Functional calcium imaging from hundreds of preBötC cells revealed that a subset of putative astrocytes exhibited rhythmic calcium elevations preceding inspiratory neuronal activity with a time lag of approximately 2 s. These preinspiratory putative astrocytes maintained their rhythmic activities even during the blockade of neuronal activity with tetrodotoxin, whereas the rhythm frequency was lowered and the intercellular phases of these rhythms were decoupled. In addition, optogenetic stimulation of preBötC putative astrocytes induced firing of inspiratory neurons. These findings raise the possibility that astrocytes in the preBötC are actively involved in respiratory rhythm generation in rhythmically active slices.

Astrocytes release prostaglandin E2 to modify respiratory network activity

“…Under control conditions, astrocytes displayed a low oscillating frequency (1.1 ± 0.5 cycles/min in the preBö tC (n = 22 slices) vs. 1.1 ± 0.4 cycles/min in the pFRG/RTN (n = 19 slices); difference not statistically significant), similar to that described previously for active astrocytes (Grass et al, 2004;Schnell et al, 2011;Okada et al, 2012;Oku et al, 2016). The frequency displayed by the .…”

“…It has also become evident that astrocytes are involved in respiratory behavior. The preBö tzinger Complex (preBö tC), a brainstem respiratory center (Grass et al, 2004), contain electrically active astrocytes, that exhibit rhythmic calcium (Ca 2+ ) oscillations associated with the respiratory-related neuronal rhythm (Schnell et al, 2011;Okada et al, 2012). Further, brainstem astrocytes respond to changes in blood gas levels (Angelova et al, 2015), especially in the chemosensitive region the parafacial respiratory group/retrotrapezoid nucleus (pFRG/RTN) (Huckstepp et al, 2010).…”

Brainstem mechanisms underlying the cough reflex and its regulation

“…Fellin 2009). It has been proposed that astrocytes in the respiratory network may contribute to the characteristic of inspiratory activity (Hulsmann et al, 2000;Schnell et al, 2011;Okada et al, 2012;Oku et al, 2016) and play a crucial role in central chemoreception within the RTN (Gourine et al, 2010;Guyenet et al, 2016). The finding that ozone-induced pulmonary inflammation results in a specific activation of vagal afferents that induces astroglial cellular alterations in the NTS (Chounlamountry et al, 2015 also for further Refs.)…”

An astrocyte-dependent mechanism for neuronal rhythmogenesis

“…In most instances, the potential contribution of astrocytes, the most abundant type of cells in the brain, is largely ignored. Only in respiration has it been shown that astrocytes play a significant role by detecting pH changes in the blood and modulating neuronal firing in return 6,7 . Several ionic conductances endow neurons with rhythmogenic abilities.…”