Regulation of Cocaine Use by Astrocyte Voltage-Gated Channels

Project Summary/Abstract Significant investigative effort over the past three or four decades has been devoted to uncovering neuronal mechanisms that regulate substance use, including the use of cocaine. Notable progress in this effort includes evidence that dysregulation of neuronal signaling after cocaine exposure may rely on plasticity within non- neuronal cells. A particularly large share of attention has been paid to astrocytes, fueled by early demonstrations that a variety of brain insults from trauma to neurodevelopmental disorders profoundly alter astrocyte morphology. Cocaine exposure impacts astrocyte cytoskeleton, changing the size and shape of astrocyte cell bodies, processes, and proximity to synapses. Additionally, cocaine triggers changes in the astrocyte ability to initiate and maintain propagation of Ca2+ waves that have established themselves as a prototypical signature of “active” astrocyte signaling. Much less is understood about cocaine effects on astrocyte K+ responses, a key feature of neuroglial interface whereby astrocyte permeability to K+ maintains ion homeostasis in the extracellular space following neuronal extrusion of K+ ions during action potentials. We provide the first, to our knowledge, evidence that astrocyte K+ channels are affected by and contribute to development of cocaine use in the rat self-administration model. This novel form of plasticity involves astrocytic voltage-gated potassium channels, a surprising finding given that voltage-gated channels rely on membrane excitability for activation whereas astrocytes are traditionally perceived as ‘non-electrically excitable’. We present preliminary data that the voltage-gated KCNQ channels in astrocytes of the nucleus accumbens shell (NAc) are rapidly and dose-dependently up-regulated by extracellular dopamine, that KCNQ channel activity influences astrocyte Ca2+ responses after cocaine self-administration, and that attenuation of cocaine-seeking by KCNQ inhibition requires functional NAc astrocytes. We propose to use standard pharmacological techniques along with newer molecular approaches, electrophysiology, and Ca2+ imaging to further describe astrocyte KCNQ channel contribution to cocaine use. Our hypothesis is that KCNQ channels regulate astrocyte Ca2+ signaling to impact acquired cocaine-seeking behavior as well as its reinstatement after extinction. Within this hypothesis, we explore contribution of neuronal KCNQ channels, relevance of astrocyte Ca2+ compartmentalization to transmembrane and endoplasmic reticulum domains, and cocaine impact on expression of distinct KCNQ subtypes. We predict that astrocyte KCNQ activity, independent of neuronal KCNQ channels, influences generation of intracellular Ca2+ signals by membrane-proximal sources and that inhibition of astrocyte KCNQ activity pharmacologically or by virus-mediated knock-down attenuates cocaine seeking and cue-induced reinstatement. The results of this experimentation lay the foundation for work to investigate contribution of astrocyte K+ channels to neuroglial coupling. For example, cocaine-induced up-regulation of astrocyte K+ uptake is expected to increase K+ buffering throughout the astrocyte syncytium with implications for homeostatic regulation of signaling within related neuronal circuits. Similarly, changes in astrocyte K+ may influence Ca2+ dependent release of neurotransmitter molecules, cytokine production, and secretion of extracellular vesicles or other signals to influence neuronal output and cocaine-associated behavior. Manipulation of molecular targets within astrocytes will promote understanding of dynamic roles of these cells in the healthy brain and enhance development of novel cell-type specific tools to mitigate cocaine use.