Cintia Sokvári

We have previously shown that neuromodulatory actions on astrocytes can elicit metabotropic glutamate- and N-methyl-D-aspartate receptor-dependent tonic changes in excitability in the mesopontine region. Although in vitro experiments explored robust effects, the in vivo significance of our findings remained unknown. In this project, chronic chemogenetic activation of mesopontine astrocytes and its actions on movement, circadian activity, acoustic startle and spatial memory were tested. The control group of young adult male mice where mesopontine astrocytes expressed only the mCherry fluorescent tag was compared to the group expressing the hM3D(Gq) chemogenetic actuator. Chronic chemogenetic astrocyte activation reduced the amplitude of the acoustic startle reflex and increased the locomotion speed in the resting period. Gait alterations were also demonstrated but no change in the spatial memory was explored. As a potential background of these findings, chronic astrocytic activation decreased the cholinergic neuronal number to 54% and reduced the non-cholinergic neuronal number to 76% of the control. In conclusion, chronic astrocytic activation and the consequential decrease in the neuronal number led to disturbances in movement and circadian activity resembling brainstem-related symptoms of progressive supranuclear palsy, raising the possibility that astrocytic overactivation is involved in the pathogenesis of this disease.

The Piezo1 mechanosensitive ion channel is abundant on several elements of the central nervous system including astrocytes. It has been already demonstrated that activation of these channels is able to elicit calcium waves on astrocytes, which contributes to the release of gliotransmitters. Astrocyte- and N-methyl-D-aspartate (NMDA) receptor-dependent slow inward currents (SICs) are hallmarks of astrocyte–neuron communication. These currents are triggered by glutamate released as gliotransmitter, which in turn activates neuronal NMDA receptors responsible for this inward current having slower kinetics than any synaptic events. In this project, we aimed to investigate whether Piezo1 activation and inhibition is able to alter spontaneous SIC activity of murine neocortical pyramidal neurons. When the Piezo1 opener Yoda1 was applied, the SIC frequency and the charge transfer by these events in a minute time was significantly increased. These changes were prevented by treating the preparations with the NMDA receptor inhibitor D-AP5. Furthermore, Yoda1 did not alter the spontaneous EPSC frequency and amplitude when SICs were absent. The Piezo1 inhibitor Dooku1 effectively reverted the actions of Yoda1 and decreased the rise time of SICs when applied alone. In conclusion, activation of Piezo1 channels is able to alter astrocyte–neuron communication. Via enhancement of SIC activity, astrocytic Piezo1 channels have the capacity to determine neuronal excitability.