Abstracts

Rationale: Astrocytes are crucial to clearing extracellular glutamate released during synaptic transmission. Glutamate uptake shapes extracellular neurotransmitter dynamics, which in turn contribute to glutamate receptor activation, synaptic plasticity, and synaptogenesis. Pathologically altered glutamate uptake is associated with hyperexcitability, excitotoxicity, and seizure. It is known that during CNS development, glutamate transport becomes more robust. How neonatal insult affects the functional maturation of astrocytes, however, is largely unknown. Methods: To address this question, we have developed a novel technique, Laser Scanning Astrocyte Mapping (LSAM), which combines glutamate transport current (GTC) recording from astrocytes, with laser scanning photostimulation. LSAM enables the measurement of both the glutamate responsive domain of a single astrocyte, and the spatial heterogeneity of glutamate clearance kinetics within that domain. Results: Using LSAM, we have investigated whether astrocyte maturation is perturbed the neonatal freeze lesion (FL) model of developmental cortical malformation. The FL model is associated with both reactive astrocytosis and in vitro hyperexcitability. We have found that 4 weeks following FL, astrocytes respond to glutamate from a larger spatial domain than in the sham lesioned brain. Furthermore, these same cells clear glutamate faster in distal, as compared to proximal processes, a functional phenotype of neonatal astrocytes. Lastly, the developmental shift in glutamate transporters from GLAST-dominated clearance at neonatal timepoints to GLT-1-dominated clearance at mature timepoints, is disrupted following FL. Conclusions: These findings show neonatal cortical FL has significant effects on the functional maturation of astrocytes and that LSAM is a powerful new approach to probe astrocyte function with subcellular precision.