Protocol for monitoring neurotransmitter release upon projection-specific activation in mouse dorsal raphe nucleus via in vivo fiber photometry

Fiber photometry is powerful for monitoring in vivo neural activity and neurotransmitter dynamics. Here, we present a protocol for synchronized fiber photometry recordings and optogenetic activation to measure neurotransmitter release using genetically encoded fluorescent biosensors in the mouse dorsal raphe nucleus. We outline detailed steps for stereotaxic virus injection, fiber-optic cannula implantation, and synchronized fiber photometry and optogenetics. Additionally, we describe histological validation and analysis of photometry data. These steps can be adapted for tracking various neurotransmitters in other brain circuits. For complete details on the use and execution of this protocol, please refer to Song et al.