Male Sprague Dawley rats were anesthetized 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 either 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, and subsequently immunostained. 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) 60× oil objective (NA 1.4). Optical z resolution is 0.25µm. 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.