Astrocyte Neuron Interactions in Synchronous Bursting Behavior

Faculty #7
Discipline: Biological Sciences
Subcategory: STEM Research

Karla Sanchez - Delaware State University
Co-Author(s): Melissa Harrington and Murali Temburni, Delaware State University

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Establishing functional neuronal networks during brain development requires synchronous oscillatory activity among neurons. However, the mechanisms of synchronization are not fully understood. Current models of neuronal synchronous activity assume that it is a process intrinsic to neurons. Evidence that glial cells particularly astrocytes modulate synchronous activity in networks of neurons is accumulating — for example during sleep, during prodromal oscillations preceding spreading depression, and the slow inward currents (SICs) resulting in synchronous activity in hippocampal neurons, thalamus and nucleus accumbens. Astrocytes participate in neuronal communication by releasing ‘gliotransmitters’ like glutamate, ATP and D-serine. We hypothesize that astrocyte-neuron interactions are crucial for the development of synchronous activity seen in the developing vertebrate brain. We tested this hypothesis by establishing pure and mixed (astrocyte and neuronal) cultures from the developing chicken brain (optic tectum) and recording total neuronal activity using the multi-electrode array system, MED64. Pure neuronal cultures were obtained by treating cultures with the mitotic inhibitor 5-fluorodeoxyuridine (FUdR) which kills mitotically active astrocytes but spares post-mitotic neurons. Neurons were kept alive in the absence of astrocytes by supplementing the culture medium with 50% astrocyte conditioned medium. Mixed cultures of astrocytes and neurons show random spiking activity in one week and synchronous activity in two weeks whereas pure neuron only cultures show random spiking activity without synchronization even after two weeks – thus clearly establishing a role for astrocytes in the development of synchronous activity. To further confirm the involvement of astrocytes we have reintroduced astrocytes into the randomly spiking pure neuronal cultures after synchronous activity was observed in the control mixed cultures. We observed an immediate increase in spiking activity which synchronized within a week of reintroduction of astrocytes into the FUdR treated pure neuronal cultures. To further dissect the molecular pathways involved, we are targeting GPCR pathways within astrocytes that mediate intracellular Calcium release. Activation of these G-protein coupled receptors by their respective neurotransmitters mobilizes intracellular calcium release leading to exocytosis of either glutamate or ATP. We are expressing dominant negative peptides designed to disrupt downstream signaling pathways of these receptors and thereby calcium mobilization and exocytosis of gliotransmitters in chick embryo astrocytes.

Funder Acknowledgement(s): NSF HBCU-UP Research Initiation Award (HRD-1401026); NIH COBRE pilot award (1P20GM103653-01A1).

Faculty Advisor: None Listed,