Functional consequences of cocaine self-administration on astrocytes

Project Summary/Abstract Accumulating evidence has identified nucleus accumbens astrocytes as salient targets of drug abuse. For example, numerous studies indicate that rat self-administration of multiple drug classes results in impaired glutamate homeostasis, as well as decreased structural features and synaptic colocalization of nucleus accumbens astrocytes. Preliminary data for this proposal reveal that male rat accumbens astrocytes exhibit striking (~40%) reductions in surface area, volume, and synaptic colocalization 45 days after 10 days of long- access (6h/d) cocaine self-administration. These findings suggest loss of physiological function of astrocytes as regulators of neural circuits. However, the mechanism(s) driving these observations are unknown, as are the consequences to neural function. We hypothesize that astrocyte pathology underscores the neural adaptations and increased measures of craving observed across prolonged abstinence (also known as incubation). Accordingly, the goal of this proposal is to define the relationship between cocaine self- administration and the onset of astrocyte dysfunction in the nucleus accumbens, as well as the relationship between astrocyte dysfunction, synaptic transmission, and behavior. Aim 1 will assess the effects of operant cocaine self-administration on evoked Ca2+ responses in accumbens astrocytes as a function of both self- administration and abstinence, and will determine the functional significance of astrocyte Ca2+ to cocaine seeking behaviors. Aim 2 will examine how cocaine self-administration affects the ability of astrocytes to negatively regulate excitatory synaptic transmission in D1 and D2 receptor-positive medium spiny neurons. Lastly, Aim 3 will establish the role of dopamine and G protein-mediated astrocyte signaling in the pathological effects of cocaine on accumbens astrocyte structure. For each aim, we will evaluate endpoints as a function of time across abstinence. These objectives will collectively be accomplished by leveraging a multimodal approach that spans cellular physiology to circuit analysis and animal behavior, combining rat cocaine self- administration with high-resolution imaging of fluorescently-labeled astrocytes, acute slice imaging of Ca2+- labeled astrocytes using a photoconvertible Ca2+ indicator (astro-CaMPARI2), astrocyte DREADD stimulation, astrocyte Ca2+ depletion using an astrocyte-expressed PMCA2 Ca2+ pump, whole cell patch-clamp electrophysiology, neuronal subtype-specific analyses using Drd1a-Cre and Drd2-Cre transgenic rats, and fluorescent imaging of an adenosine biosensor GRABAdo. Collectively, these studies will define the relationship between astrocyte dysfunction across abstinence from cocaine self-administration with neural physiology and behavior.