The development of novel techniques utilizing the advantages of light has created an optical revolution for neuroscience research. Controlling and probing neuronal function with light has provided unprecedented insights by being able to manipulate many neurons simultaneously in intact circuits and living organisms.
In my dissertation research, I used novel optical methods to probe the cellular permeability of sensory neuron populations. Primary nociceptive afferents detect, modulate and integrate many pain-related stimuli. Sensory information is transmitted from the periphery through the dorsal root ganglia along labeled lines coding for sensory modalities and receptive fields. Recently, our understanding of sensory processing has been expanded by the discovery of neuronal interactions both on the level of peripheral nerve endings and in the spinal cord. Here I report a crosstalk between injured and intact neuronal population after peripheral nerve injury. This communication is revealed at the somata of sensory neurons distant from the site of injury and correlates with permeability changes of both injured and intact nociceptor populations after injury. I devised a sensitive probe to measure the activity of nociceptive cells in intact tissue using a photoswitch molecule. Transient Receptor Potential (TRP) ion channel are a major class of molecular sensors detecting painful stimuli. I show that TRPA1, a member of the TRP family, is necessary for this crosstalk which is limited to petidergic, slow conducting C fibers. In addition, electrical activity of nociceptive fibers alone is sufficient to mimic similar permeability changes as nerve injury. Injury induced hyperexcitability of sensory fibers and TRP channel dysfunction have been implicated with conditions of pain hypersensitivity, chronic and neuropathic pain. I therefore propose that this crosstalk might contribute to adaptions of pain signaling in various disease states.
Photoswitch molecules have found many experimental applications in neuroscience research. However, the exact mechanism by which they function remains unclear. Therefore, another part of my research focused on studying interactions of the photoswitchable compound QAQ with the model potassium channel Shaker. I investigated the affinity of both QAQ isomers to the open Shaker channel and surprisingly found that block is not voltage-dependent. Further, I analyzed the effects of use-dependent inhibition and report that QAQ does not associate with closed channels. However, once channels are opened, QAQ does interfere with the kinetics of the gate slowing down the closing of the channel.
