Male Sprague Dawley rats, 3 weeks of age, were anaesthetized and perfused transcardially with with Ringer’s solution (37°C), followed by 4% paraformaldehyde (PFA) in PBS (37°C, pH 7.4). Tissue was sectioned (100 µm thick) using a vibratome, and injected with a BX50WI microscope (Olympus, Melville, NY) and, using infrared differential interference contrast videomicroscopy,cells with a small diameter soma (approx. 7–11µm) in the stratum radiatum of CA1 were located and impaled with glass micropipettes filled with 5% aq. Lucifer Yellow. The astrocytes were filled using a 0.5 Hz pulses of current until all of the processes were brightly fluorescent. After several astrocytes were filled, a slice was placed in the 4% PFA overnight at 4°C. Slices were then imaged after coverslipping in Gelvatol. Confocal images were acquired with a BioRad Radiance2000 (Hercules, CA) attached to a Nikon E600FN (Kanagawa, Japan) microscope equipped with a Nikon (Tokyo, Japan) 60x oil objective (NA 1.4). Additional details are provided in Bushong EA, Martone ME, Ellisman MH. Maturation of astrocyte morphology and the establishment of astrocyte domains during postnatal hippocampal development. Int J Dev Neurosci. 2004 Apr;22(2):73-86.