Greater emphasis on the study of intact cellular networks in their physiological environment has led to rapid advances in intravital imaging in the central nervous system, while the peripheral system remains largely unexplored. To assess large networks of sensory neurons we selectively label primary afferents with GCaMP6s and visualise their functional responses in vivo to peripheral stimulation. We show that we are able to monitor simultaneously the activity of hundreds of sensory neurons with sensitivity sufficient to detect, in most cases, single action potentials with a typical rise time of around 200 milliseconds, and an exponential decay with a time constant of approximately 700 milliseconds. Using this sensitive technique we are able to show that large scale recordings demonstrate the recently disputed polymodality of nociceptive primary afferents with between 40-80% of thermally sensitive DRG neurons responding also to noxious mechanical stimulation. We also specifically assess the small population of peripheral cold fibres and demonstrate significant sensitisation to cooling after a model of sterile and persistent inflammation, with significantly increased sensitivity already at decreases of 5oC when compared to uninflamed responses. This not only reveals interesting new insights into the (patho)physiology of the peripheral nervous system but also demonstrates the sensitivity of this imaging technique to physiological changes in primary afferents.

Large scale in vivo recording of sensory neuron activity with GCaMP6