Chronic pain syndromes are to a large extent due to maladaptive plastic changes in the CNS. A CNS area particularly relevant for such changes is the spinal dorsal horn, where inputs from nociceptive and non-nociceptive fibers undergo their first synaptic integration. This area harbors a sophisticated network of interneurons, which function as a gate-control unit for incoming sensory signals. Several different types of interneurons can be distinguished based e.g. on their neurotransmitter and neuropeptide content. Despite more than 40 years of research, our knowledge about the integration of these neurons in dorsal horn circuits and their contribution to sensory processing is still very limited. This proposal aims at a comprehensive characterization of the dorsal horn neuronal network under normal conditions and in chronic pain states with a focus on inhibitory interneurons. A genome-wide analysis of the gene expression profile shall be made from defined dorsal horn interneurons genetically tagged with fluorescent markers and isolated by fluorescence activated cell sorting. A functional characterization of the connectivity of these neurons in spinal cord slices and of their role in in vivo sensory processing shall be achieved with optogenetic tools (channelrhodopsin-2), which permit activation of these neurons with light. Finally, behavioral analyses shall be made in mice after diphteria toxin-mediated ablation of defined interneuron types. All three approaches shall be applied to naïve mice and to mice with inflammatory or neuropathic pain. The results from these studies will improve our understanding of the malfunctioning of sensory processing in chronic pain states and will provide the basis for novel approaches to the prevention or reversal of chronic pain states.
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