Preinspiratory calcium rise in putative pre-Botzinger complex astrocytes

Key points Autonomic respiratory rhythm is essential to maintain lives and is generated in the lower brainstem. The ventrolateral medullary region, called the pre-Botzinger complex (preBotC), 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 preBotC are periodically activated preceding inspiratory neuronal activity, periodic activity of putative astrocytes persists during blockade of neuronal activity, and stimulation of astrocytes in the preBotC 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. Abstract The neural inspiratory activity originates from a ventrolateral medullary region called the pre-Botzinger complex (preBotC), 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 preBotC 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 preBotC putative astrocytes induced firing of inspiratory neurons. These findings raise the possibility that astrocytes in the preBotC are actively involved in respiratory rhythm generation in rhythmically active slices.