In vivo and ex vivo imaging of nociceptor expression and activity

Abstract

Our ability to perceive nociceptive pain is crucial to respond to harmful stimuli: it warns us about noxiously hot or cold objects. Sensory nerve endings that respond to pain (nociceptors) initiate an electrical signal in the periphery and transport it to the dorsal horn and eventually to higher brain centers. The detection of noxious stimuli involves the expression of nociceptive ion channels in sensory nerve endings, such as transient receptor potential (TRP) channels. Recently we found that the acute response to noxious heat relies on the functional expression of TRPV1, TRPM3 and TRPA1 in sensory nerve endings. Calcium imaging on isolated dorsal root ganglia (DRG) is a widely accepted model to study the involvement of TRP channels in acute pain responses. However, DRGs are clusters of nerve cell bodies, present in the dorsal root of spinal nerves, far away from the skin where the physiological stimulus detection take place. We use two different optical measurement protocols to study ion channel activity in sensory neurons: an in vivo-protocol to image DRGs and an in tissue-protocol to visualize intact skin measurements. A cre-dependent GCaMP3 mouse line is used. These mice express the genetically encoded calcium indicator GCaMP3 in specific somatosensory neurons. Using this technique, we study the role of TRP channels in different pain models, such as inflammation.