Identification of astrocytes in the MNTB. (A) Fluorescence image showing a principal neuron and a neighboring astrocyte of a GFAP-eGFP mouse, both cells filled with Alexa 594 via the patch pipettes. The top picture shows the red channel, displaying both cells, as well as the tips of both recording pipettes. The middle picture shows the green channel, displaying eGFP fluorescence only in the astrocyte. The bottom picture shows the overlay of eGFP and Alexa fluorescence only in the astrocyte. Bar, 20 µm (refers to all pictures). (B) Representative current profile. Membrane currents were evoked by 50-ms voltage steps ranging from −160 mV to +40 mV, from a holding potential of −70 mV. Note the typical passive response of astrocytes compared with the sodium currents observed in neurons. (C) Current-voltage (IV) relationship from the neuron and the astrocyte shown in B. IV relationship showed a linear pattern in astrocytes and a delayed rectification in neurons. (D) Astrocytes respond to KA and D-Asp. Voltage-clamp recording of an astrocyte clamped to −70 mV. Bath application of KA (0.5 mM) induced inward currents. The response was blocked when CNQX (50 µM) was preincubated and co-applied with KA (0.5 mM). D-Asp (0.5 mM) elicited an inward current too, this response was reduced when TBOA (100 µM) was preincubated and co-applied with D-Asp (0.5 mM). The application bars on the top correspond to all applications. (E) Summary of the effect of CNQX on KA and TBOA on D-Asp currents. The amplitudes of KA and D-Asp currents were normalized, showing the relative reduction induced by CNQX (n = 5) and TBOA (n = 6). Data are the mean ± SEM. Asterisks represent significant differences (*, P = 0.01; **, P = 0.001).