In vivo imaging of the coupling between neuronal and CREB activity in the mouse brain

Sensory experiences exert long-term modifications of neuronal circuits and behavior. Neuronal activity is relayed from active synapse to the nucleus, where dedicated transcription pathways are recruited. Previous research has demonstrated that the synapse-nucleus axis is vital for regulation of learning, injury repair and development in the central nervous system. However, it has not been possible to precisely determine the interplay between neuronal activity patterns and transcription factor activity. We have engineered a new FRET biosensors which allows us to image in vivo signaling of CREB, a transcription factor important for synaptic plasticity, using 2-photon fluorescence lifetime imaging (2pFLIM). Combination of red-shifted CREB sensor and GCaMP imaging allowed simultaneous imaging of CREB and calcium dynamics at single cells. With this approach, we explored how experience shapes the interplay between CREB and neuronal activity in the visual cortex of awake mice. We found that dark rearing augmented the sensitivity and persistence of visually evoked CREB activity, thereby shifting the threshold for neuronal activity-transcription coupling. We are currently combining this technique with imaging of endogenous signaling protein in intact cortical circuits. These experiments will allow to unravel the transcriptional dynamics underlying experience-dependent plasticity in the brain.