Neuropharmacology

Biography

Biography: Petr Tvrdik

Abstract

Microglia are highly reactive to tissue injury. In response to focal damage, microglia extend their processes toward the compromised tissue. The cell motility aspects of this behaviour have been characterized, but the intracellular events, particularly the Ca2+ responses, have not been systematically studied in microglia due to technical difficulty. Here, we used live two-photon imaging in the PC::G5-tdT reporter mouse expressing the genetically encoded Ca2+ indicator GCaMP5G and fluorescent marker tdTomato in cortical microglia. We found that spontaneous Ca2+ transients in microglial somas and processes were generally low (only 4% of all microglia showing transients within 20 min), but baseline activity was markedly increased when the animals were subcutaneously injected with LPS 12 h before imaging. When challenged with focal laser injury, an additional surge in Ca2+ activity (up to 67%) was observed in the somas and protruding processes, particularly in close proximity to the damaged tissue. Notably, coherent and simultaneous Ca2+ rises in multiple microglial cells were occasionally detected in LPS and bicuculline-treated animals. We have demonstrated that Ca2+ transients were predominantly mediated via purinergic receptors. We also compared the speed of process extension in BAPTA-AM and the purinergic receptor antagonist PPADS-treated animals and showed that BAPTA-AM significantly slowed the process protrusion, but PPADS did not. This study illustrates the suitability of the PC::G5-tdT mouse reporter for investigations of microglial physiology.