Neonatal rats aged from 1 to 3 days (P1 to P3 rats) were sacrificed by decapitation, using procedures recommended by the animal care committee of Université Laval. Their hippocampi were then dissected. Hippocampal cells were dissociated enzymatically and mechanically (trituration through a Pasteur pipette). A papain solution (; Worthington, Freehold, New Jersey) containing -free HBSS, cysteine (Sigma), DNase 1 (type IV; Sigma), 25 mM NaHCO3, penicillin ()/streptomycin (), 1 mM sodium pyruvate, and glucose was used. After dissociation, cells were washed and centrifuged in a Neurobasal medium containing BSA ( and , respectively), Pen/Strep, glucose, pyruvate, and DNase1 (as above). They were plated on poly-d-lysine-coated Aclar coverslips at high density ( coverslip). Growth media () consisted of a mixture of Neurobasal medium and B27, supplemented with penicillin/streptomycin (; ), and 0.5 mM Glutamax (Thermo Fisher Scientific, Waltham, Massachusetts). Cytosine -d-arabinofuranoside (Ara-C) (; Sigma, St. Louis, Missouri) was added 24 h after plating to reduce the number of non-neuronal cells. After 4 days in vitro (DIV), half of the growth medium was replaced twice a week by a medium containing no Ara-C.