Interrogating the Spatiotemporal Landscape of Neuromodulatory GPCR Signaling by Real-Time Imaging of cAMP in Intact Neurons and Circuits

Modulation of neuronal circuits is key to information
processing in the brain. The majority of neuromodulators
exert their effects by activating G-proteincoupled
receptors (GPCRs) that control the production
of second messengers directly impacting
cellular physiology. How numerous GPCRs integrate
neuromodulatory inputs while accommodating diversity
of incoming signals is poorly understood. In
this study, we develop an in vivo tool and analytical
suite for analyzing GPCR responses by monitoring
the dynamics of a key second messenger, cyclic
AMP (cAMP), with excellent quantitative and spatiotemporal
resolution in various neurons. Using this imaging
approach in combination with CRISPR/Cas9
editing and optogenetics, we interrogate neuromodulatory
mechanisms of defined populations of
neurons in an intact mesolimbic reward circuit and
describe how individual inputs generate discrete
second-messenger signatures in a cell- and receptor-
specific fashion. This offers a resource for studying
native neuronal GPCR signaling in real time.