Determination of the fine organization of actin networks is important for understanding different functional aspects of the central nervous system (CNS) such as plastic events. Early studies investigating the localization of actin filaments at the ultrastructural level relied on structural methods or antibodies raised against actin isoforms. More recently, many investigators have employed the actin-binding peptide phalloidin conjugated to various fluorescent molecules. By conjugating phalloidin to the fluorophore eosin, we have been able to localize f-actin at the electron microscopic level using photooxidation of diaminobenzidine (DAB) by eosin. The goal of this study is to provide a better description of the cellular and subcellular localization of actin filaments at the light and electron microscopy level based on the high binding affinity of phalloidin for actin and utilizing this novel method.

Tissues were obtained from male Sprague Dawley rats that were perfused transcardially under deep anesthesia with normal rat Ringer's solution at 35°C followed by fixative. The fixative contained 4 % paraformaldehyde and different concentrations of glutaraldehyde, ranging from 0.1- 2.5%. Sections of cerebellum, striatum and hippocampus which were cut at a thickness of 50-80 μm with a Vibratome were incubated with phalloidin-eosin in a solution of 0.05% in 0.5% cold water fish gelatin/50mM glycine-PBS (“working buffer”) for 2 hrs. As a control, phalloidin-eosin was omitted for one set of tissues.