Agashkov K. Cellular and network mechanisms of nociceptive signal processing in the spinal cord and genetically engineered modification as a novel tool for a treatment of neuropathic pain syndrome

The dissertation is devoted to the study of the functioning of the neuronal networks of the dorsal horn of the spinal cord and their contribution to the processing and transmission of nociceptive signals to supraspinal structures. For the first time, the role of different types of spino-parabrachial neurons (SPN) of the lamina I in the transmission of specific nociceptive information was established and the molecular and cellular mechanisms underlying this specificity were identified. Lamina I SPN’s play a key role in the processing of pain signals and is an almost exclusive group of cells that transmit nociceptive signals from the spinal cord to the brain. Here, to identify the molecular and cellular mechanisms involved in the coupling of input and output signals in rat lamina I SPN, a novel whole spinal cord preparation was used, which allows experiments with intact cells and ensures the integrity of network connections in the dorsal corner. We found that most SPNs receive a small number of direct nociceptive inputs from C-fibers and generate one action potential in response to a saturating afferent stimulus, thus acting as a simple signal transmitter from the primary afferents. However, 69% of all action potentials induced by afferent stimulation in the entire population of SPN originate from a small fraction (19%) of neurons. These neurons receive a large number of direct inputs from Aδ and C fibers, generate powerful butst of AP’s in response to stimulation of primary afferents, and effectively integrate local network activity through NMDA-dependent mechanisms. We have found that they amplify and integrate the nociceptive input signal, encoding its intensity by increasing the number of generated APs. In this work, we also used subpial delivery of viral vectors to the dorsal horn of the spinal cord of mice. These vectors are based on the use of capsides of adeno-associated viruses, which carry the genes glutamate decarboxylase and vesicular GABA transporter. Thus, local excitatory neurons that were infected with these viruses began to synthesize and secrete the inhibitory GABA transmitor. As a result of the introduction of high concentrations of viral constructs, there was a significant decrease in the pain mechanosensitivity of control mice. At the cellular level, dorsal horn neurons showed a general decrease in excitatory synaptic activity, an increase in inhibitory synaptic activity. The administration of viral constructs in the spinal cord of mice with damaged sciatic nerve, led to complete disappearance of neuropathic pain symptoms in the absence of side effects. Thus, we identified important mechanisms involved in the processing of nociceptive signals in the dorsal spinal cord and tested a novel therapeutic approach that can be used in the treatment of chronic neuropathic pain.