Characterization of a novel transgenic mouse model to investigate brain-wide activation of astrocyte Gq signaling.

Astrocytes sense and modify neuronal activity, and accumulating evidence suggests a role for these cells in the modulation of neuroinflammation and cognition. Most experiments investigating the in vivo role of astrocytic signaling use viral vectors to drive astrocyte-specific expression of receptors in localized regions of the brain. However, viral vector-mediated delivery of receptors can lead to off-target inflammation and impact neurogenesis, neuronal function and behavior. Here, we used transgenic mice expressing Cre-inducible hM3Dq, a designer receptor exclusively activated by designer drugs (DREADD), to target the Gq-coupled receptor hM3Dq specifically in astrocytes without the use of viral transduction. We showed that in vitro administration of clozapine N-oxide to primary astrocytes derived from astro-hM3Dq mice increased intracellular calcium levels. Similarly, acute in vivo activation of astrocytic hM3Dq induced time-dependent changes in resting-state brain function as well as increased c-Fos expression throughout the brain. Acute astrocyte-specific hM3Dq activation increased synthesis of cortical mRNA of proinflammatory cytokines TNF, IL-1β and IL-6, while chronic activation did not greatly impact proinflammatory cytokine expression. Importantly, however, acute global activation of astrocyte-specific hM3Dq did not adversely affect behavior in a battery of tasks. Taken together, we conclude that the astro-hM3Dq mouse line can serve as a reliable model for studying the brain-wide role of astrocytic muscarinic and Gq signaling in neuroinflammation, behavior and neuronal activity, mitigating the potential negative effects associated with the use of viral transduction.