Hippocampal neuron cultures were prepared as previously reported [6]. In brief, the hippocampuses were dissected out from mouse embryos at 16 days in utero. The tissues were then incubated for 20 min at 37°C in MEM (minimum essential medium) modified for suspension culture (Life Technologies) plus 0.25% trypsin (Life Technologies). The dissociated hippocampal neurons were plated on glass coverslips coated with a confluent monolayer of mouse cortical astrocytes obtained as described below. The neurons were maintained at 37°C in a humidified atmosphere with 5% CO2. Cortical astrocytes dissociated from newborn mouse cortices were grown in culture flasks at 37°C in a humidified atmosphere with 5% CO2 until confluent. The cells were exposed to 10-5 M cytosine arabinoside (Sigma) and cultured for additional 12–24 hrs at 37°C. After remove of the media with cellular debris, the cells were used for coating coverslips.