Multiphoton calcium imaging of methylxanthine‐reversal of opioid depression of inspiratory‐related pre‐Bötzinger complex rhythm in newborn rat brainstem slices

Abstract

Breathing depression by opioids is reversed by methylxanthines (e.g. theophylline). Opioids block Ca2+ channels while methylxanthines cause Ca2+ release from cellular stores at high doses. We studied in newborn rat brainstem slices with 2photon imaging whether opioid block of inspiratory center pre‐Bötzinger Complex (preBötC) and its recovery by theophylline involved cytosolic Ca2+ change.DAMGO blocked bursting and related Ca2+ rises in most preBötC neurons. Ca2+ baseline fell by ~10% in these cells, but not in presumed astrocytes. Theophylline and phosphodiesterase‐4 (PDE4) blocker Rolipram restored rhythm with no effect on Ca2+ baseline. Ca2+ store blocker cyclopiazonic acid did not raise the baseline in preBötC neurons, but in astrocytes. Ca2+ rises became irregular upon block of L‐type Ca2+ channels with nifedipine or Ni2+(0.1mM) without effect on Ca2+ baseline or rhythm. At 2.5mM, Ni2+ blocked rhythm and Ca2+ baseline fell by 10%.SummaryOpioid depression is associated with a Ca2+ fall in preBötC cells that is not due to block of L‐type Ca2+ channels whereas actions of methylxanthines or PDE4 blockers do not involve a major change in Ca2+.Supported by CIHR, AHFMR, CFI‐ISRIP, MFN Health