Fig. 2.

Glutamate responses in astroglial cells of the hippocampus. Within the hippocampus of TgN(GFAP-EGFP) transgenic mice two different astroglial cell populations can be distinguished by fluorescence intensities due to different levels of green fluorescent protein (EGFP) expression. These two cell populations respond to glutamate either by activation of glutamate transporters or AMPA-type glutamate receptors. (A) Confocal laser scanning microscopy of a hippocampal section obtained from TgN(GFAP-EGFP) mice and immunostained for the glutamate transporter GLT-1 (red). Astroglial cells (green) with different morphology can be readily distinguished, isolated and electrophysiologically characterized. (B) In two of the EGFP-positive astrocytes, rapid application of glutamate (left, postnatal day 9) or AMPA (right, postnatal day 15) evoked fast transient and completely desensitizing [τ (inactivation time constant) = 6 and 8.2 ms, respectively] inward currents that were completely inhibited by AMPA receptor antagonists GYKI53655 or NBQX. (C) In another EGFP-positive cell (postnatal day 13), the control response to glutamate (left) was enhanced two-fold in the presence of cyclothiazide (CTZ; right). (D) Cells with numerous processes and brightest fluorescence levels do not express functional AMPA receptors but possess functional glutamate transporters, since kainate cannot elicit currents while an inward current can still be observed in the presence of the selective AMPA receptor blocker NBQX. A: F. Kirchhoff, personal observations; B–D: modified from Matthias et al. (2003).