It has become increasingly evident that astrocytes actively participate in neurophysiology, as well as contribute to the development and progression of a number of neurological disorders. Astrocytes are the most numerous cells in brain and spinal cord (~50% of all CNS cells) and associate with all cellular elements;a single astrocyte can envelop as many as 100,000 synapses. Astrocytes play a critical role in regulating neuronal excitability through their ability to buffer extracellular K+ and take up synaptically released glutamate. Interference with either of these properties leads to neuronal hyperexcitability. Astrocytes also exhibit Gs-, Gi-, and Gq-linked G-protein coupled receptors (GPCRs) regulating a host of second messenger cascades. Increases in astrocytic Ca2+ lead to the release gliotransmitters including glutamate, ATP, PGE2, and D-serine. Each of these gliotransmitters plays an important role in regulating neuronal excitability in the spinal cord and the first three are thought to be involved in the sensitization of nociceptive neurons in chronic pain. Astrocytes exhibit calcium oscillations and intercellular calcium waves that enable them to synchronize neuronal activity through the release of gliotransmitters. Further, reactive astrocytes release a number of factors thought to sensitize nociceptive neurons including NGF, NO, proinflammatory cytokines, and prostaglandins. While research in the field of chronic pain has focused primarily on mechanisms intrinsic to nociceptive neurons, more recent studies suggest that chronic pain derives, in part, from the activation of microglia and astrocytes. Given the prominent role of astrocytes in the regulation of neuronal excitability, it is not surprising that there is an excellent correlation between the development of chronic pain and the appearance of reactive astrocytes. Pharmacological as well as genetic studies indicate that blocking astrocytic activation blocks the maintenance of certain forms of chronic pain. Experiments within this proposal will take advantage of an experimental tool kit composed of electrophysiological and confocal imaging techniques, together with genetically modified lines of mice to study the role of astrocytes in chronic pain.
In Specific Aims 1 and 2, we will determine if astrocytic properties known to modulate neuronal excitability are altered in the setting of chronic pain. These studies will include analyses of potassium buffering and glutamate uptake as well as the ability of astrocytes to modulate neuronal excitability through the release of gliotransmitters. It is becoming increasing clear that inflammatory processes are involved in a number of neurological diseases, including chronic pain.
In Specific Aim 3 we will test the hypothesis that the activation of astrocytic NF:B, a proinflammatory transcription factor, is important in the development or maintenance of chronic pain.
