Persistence of inspiratory rhythm in calibrated newborn rat pre‐Bötzinger complex slices upon blockade of store‐mediated calcium signaling

Abstract

It is not clear which roles calcium release from cellular stores and subsequent modulation of ion channel activities play in generation of inspiratory rhythm by the bilaterally organized pre‐Bötzinger complex (preBötC) in the lower brainstem.We studied this in transversal newborn rat brainstem slices with anatomically defined location of the <200 μm thin preBötC using suction electrode recording of inspiratory‐related neural population activity combined with contralateral multiphoton/confocal imaging of free cytosolic calcium (Cai). In 400 μm thick slices with centered or caudally exposed preBötC, inspiratory rhythm was not perturbed during 20 min bath‐application of the sarcoplasmic/endoplasmic reticulum calcium ATPase blocker cyclopiazonic acid (CPA, 50 μM) and remained unchanged for further >1 h after return to control solution. In 400 or 700 μm thick slices with caudally exposed preBötC, persistence of rhythm during 50 μM CPA was accompanied by a major Cai rise in presumptive astrocytes (soma diameter ~10 μm) imaged in slice depths of up to 100 μm. Contrary, CAP caused a minor increase in Cai baseline in larger (15–25 μm) neighboring cells that showed inspiratory‐related Cai rises, thus likely representing inspiratory preBötC neurons. CPA attenuated astrocytic Cai rises due to glutamate (0.5 mM) and blocked (oscillatory) Cai rises in response to the metabotropic glutamate receptor agonist t‐ACPD (25 μM), whereas a major and modest response of preBötC neurons to glutamate or t‐ACPD, respectively, persisted in CPA.Our findings indicate that CPA causes store‐mediated calcium release in astrocytes and impairs their metabotropic calcium signaling, whereas inspiratory bursting of preBötC neurons is independent of such calcium stores.Supported by CIHR, AHFMR, CFI‐ISRIP, CIHR‐MFN Health