Grant: Discovery Grants Program - Individual

Rationale: Neuromodulators affect signal-to-noise and frequency transmission within a neural circuit by effects on cortical inhibition. As many neuromodulators are released in an extrasynaptic volume manner where degradation/uptake and the confines of the complex CNS limit diffusion distance, we ask the question - Do astrocytes rapidly extend neuromodulator actions to every synapse? Astrocytes are ideally situated to extend neuromodulator effects given that each astrocyte can 1) ensheath over 100,000 synapses, 2) release ATP/adenosine known to affect inhibition, 3) regulate extracellular potassium that can affect excitability and 4) express receptors for all neuromodulators. Understanding the role astrocytes play in neuromodulator-mediated regulation of behavioral state will highlight their importance in psychiatric and neurodegenerative conditions. Here, we explore the hypothesis that astrocytes extend neuromodulatory influence via alterations in calcium dynamics, release of purines, and potassium homeostasis. Aim 1 will examine neuromodulator effects on spontaneous and evoked postsynaptic currents in isolation by whole-cell patch-clamp of layer II neurons in cortical slices. Use of a GAPDH inhibitor and various purinergic agonists/antagonists will help us better understand the role astrocyte glycolysis and purinergic signaling play in neuromodulator-mediated changes to cortical networks. Direct astrocyte patch dialysis with a calcium chelator will further enable direct assessment of any astrocytic role without affecting surrounding cells or synapses. Aim 2 will assess the role of purine release and regulation of extracellular potassium in neuromodulator-mediated effects on inhibition. Fast scan cyclic voltammetry will assess neuromodulator effects on ATP/adenosine release. Potassium ion-selective electrodes will be used to measure neuromodulator-mediated effects on both baseline and activity-mediated changes in extracellular potassium. Aim 3 will use two-photon imaging to assess neuromodulator influence on astrocyte calcium dynamics in cortical slices using genetically-encoded calcium indicators delivered by an adeno-associated virus. We will assess both the threshold (number of stimulations at 20-50 Hz) and dynamics (speed/distance/oscillations) of evoked calcium events under control and neuromodulator conditions. Significance: Astrocyte dysfunction, stress and neuromodulator loss correlate with development of neurodegenerative and psychiatric disorders. Understanding the role of astrocytes in coordination of network responses under physiological conditions is a necessary first step to understanding pathology associated with stress, neurodegeneration, and psychiatric disorders. Furthermore, these studies support a fundamental shift in psychiatry that typically focuses on neural circuits to that of neuron-glia interactions, potentially expanding the basis for pharmacological treatment.