Project Grant F32NS151755

ELUCIDATING THE ROLE OF ASTROCYTES IN HOMEOSTATIC PLASTICITY - PROJECT SUMMARY/ABSTRACT. NEURAL CIRCUITS MUST BALANCE PLASTICITY AND STABILITY TO SUPPORT LEARNING AND MEMORY. HEBBIAN PLASTICITY CAN STRENGTHEN SYNAPSES BASED ON ACTIVITY BUT CAN DESTABILIZE CIRCUITS IF LEFT UNCHECKED. HOMEOSTATIC PLASTICITY COUNTERACTS THIS BY RESTORING NETWORK STABILITY WHILE SIMULTANEOUSLY PRESERVING CHANGES THAT UNDERLIE LEARNING AND MEMORY. DESPITE EXTENSIVE RESEARCH ON NEURONAL MECHANISMS OF HOMEOSTATIC PLASTICITY, THE CONTRIBUTIONS OF ASTROCYTES, GLIAL CELLS WITH BROAD SPATIAL AND TEMPORAL INFLUENCE, REMAIN POORLY UNDERSTOOD. ONE OF THE MOST IMPACTFUL ROLES OF ASTROCYTES TO PROPER CIRCUIT FUNCTION IS THE REGULATION OF EXTRACELLULAR GLUTAMATE, WHICH OCCURS THROUGH UPTAKE. THEIR UNIQUE MORPHOLOGY AND INTEGRATIVE PROPERTIES SUGGEST A CRITICAL ROLE IN CIRCUIT-WIDE HOMEOSTATIC REGULATION. THIS PROPOSAL INVESTIGATES HOW ASTROCYTES CONTRIBUTE TO HOMEOSTATIC PLASTICITY, FOCUSING ON THEIR STRUCTURAL REMODELING, ABILITY TO SENSE EXTRACELLULAR GLUTAMATE, AND UPTAKE OF EXTRACELLULAR GLUTAMATE DURING HOMEOSTATIC PLASTICITY IN THE MOUSE VISUAL CORTEX. AIM 1 WILL DETERMINE HOW ASTROCYTE STRUCTURE AND FUNCTION CHANGE DURING HOMEOSTATIC PLASTICITY. EXPANSION MICROSCOPY WILL BE USED TO QUANTIFY THE PERISYNAPTIC ASTROCYTIC PROCESS (PAP) COVERAGE OF AND ASTROCYTIC GLUTAMATE TRANSPORTER, GLT1, DISTRIBUTION PROXIMAL TO SYNAPSES. FUNCTIONAL IMAGING WITH OPTICAL GLUTAMATE SENSORS AND GENETICALLY ENCODED VOLTAGE INDICATORS (GEVIS) WILL BE USED TO ASSESS GLUTAMATE CLEARANCE AND ASTROCYTE MEMBRANE DEPOLARIZATION DURING VISUAL DEPRIVATION, A PARADIGM WHICH INDUCES ROBUST HOMEOSTATIC PLASTICITY IN THE VISUAL CORTEX. AIM 2 WILL ELUCIDATE THE ROLE OF ASTROCYTIC GLUA2-CONTAINING AMPA RECEPTORS (GLUA2-AMPARS) IN HOMEOSTATIC PLASTICITY. USING ASTROCYTE-SPECIFIC GRIA2 KNOCKOUT ANIMALS AND WITH DRUGS ACUTELY RESTRICTED BY TETHERING (DART)-BASED PHARMACOLOGICAL EXPERIMENTS, THIS AIM WILL ASSESS HOW GLUA2-AMPARS INFLUENCE ASTROCYTE MEMBRANE ACTIVITY AND CONTRIBUTE TO HOMEOSTATIC PLASTICITY. THIS WORK WILL DEFINE NOVEL ASTROCYTIC MECHANISMS UNDERLYING HOMEOSTATIC PLASTICITY AND ESTABLISH ASTROCYTES AS ACTIVE PARTICIPANTS IN MAINTAINING CIRCUIT STABILITY. BY INTEGRATING STRUCTURAL, FUNCTIONAL, AND MOLECULAR APPROACHES, THE PROPOSED RESEARCH WILL ADVANCE UNDERSTANDING OF HOW MULTIPLE CELL TYPES WORK IN CONCERT TO PRESERVE CIRCUIT FUNCTION. THIS WORK WILL PROVIDE NOVEL INSIGHTS INTO HOW ASTROCYTES ARE AN INTEGRAL PART OF SYNAPTIC COMPUTATION, AND WILL FURTHER INFORM THE BROADER UNDERSTANDING OF LEARNING, MEMORY, AND DEVELOPMENTAL DISORDERS.