The impact of fast and slow dopamine signaling revealed by new fluorescence lifetime technologies

Dopamine signaling is essential for learning, motivation, and movement, and is involved in disorders such as Parkinson’s disease, addiction, and schizophrenia. These disorders can involve disruptions in dopamine signaling on both fast (seconds) and slow (minutes to days) timescales. Current technologies mainly measure fast, relative dopamine signaling and are limited in detecting slow dopamine dynamics and downstream cellular signaling. Understanding the interaction between fast and slow dopamine signaling is important because these processes are believed to drive neuronal changes underlying neurological and psychiatric disorders.
In this dissertation, I developed methods that, for the first time, enable simultaneous measurement of fast and slow dopamine changes in the brains of freely moving animals. These methods include: 1) devices that measure fluorescence lifetime, and 2) genetically encoded sensors that report molecular changes in the brain through fluorescence lifetime signals. The newly developed systems, FLIP and FLIPR, allow fluorescence lifetime measurements with high precision and speed in freely moving mice. In addition, new dopamine and calcium fluorescence lifetime sensors were developed and characterized.
These technologies were subsequently applied to investigate how dopamine influences brain signaling and behavior. Together, the findings in this thesis provide a foundation for future research into dopamine function, neurological and psychiatric disorders, and the development of new therapeutic approaches.
Main findings of this dissertation include:
• FLIP was developed as a fiber-based fluorescence lifetime system capable of measuring dopamine-dependent protein kinase A (PKA) signaling in freely moving mice.
• dLight3.8 was developed as a genetically encoded dopamine sensor with both fluorescence intensity and fluorescence lifetime responses.
• FLIPR was developed as a next-generation fluorescence lifetime system that is 1000 times faster and capable of picosecond precision measurements, enabling simultaneous detection of fast and slow dopamine dynamics.
• A new calcium fluorescence lifetime sensor, LifeCamp, was developed to measure neuronal activity and basal calcium levels across fast and slow timescales.
• Dopamine signaling in the tail of the striatum was found to regulate exploratory and risk-taking behavior depending on hunger state.
• Distinct dopamine-dependent PKA signaling mechanisms in D1 and D2 neurons were shown to contribute to different phases of learning.
• Slow dopamine changes were found to regulate both downstream neuronal signaling and motivational behavior.