Ten P0 pups were decapitated, the entire brain was exposed and bulbs removed and dissected out in cold (+4°C) Leibowitz L‐15 medium (Sigma‐Aldrich, Saint Louis, Missouri, USA). Subsequently, collected olfactory bulbs were digested twice in fresh minimum essential medium‐H (MEM‐H; Sigma‐Aldrich, Saint Louis, Missouri, USA) containing 0.03% collagenase (Sigma‐Aldrich, Saint Louis, Missouri, USA) and 0.25% trypsin (Sigma‐Aldrich, Saint Louis, Missouri, USA) for 15 min at 37°C. Suspension was mechanically triturated and filtrated through a 80 μm nylon filter and centrifuged at 600 g for 10 min. Cells were suspended with fresh complete Dulbecco's modified Eagle's medium (DMEM, Sigma‐Aldrich, Saint Louis, Missouri, USA) supplemented with 10% foetal bovine serum (FBS, Sigma‐Aldrich, Saint Louis, Missouri, USA), 2 mM L‐glutamine (Sigma‐Aldrich, Saint Louis, Missouri, USA), penicillin (50 U/ml, Sigma‐Aldrich, Saint Louis, Missouri, USA) and streptomycin (50 mg/ml, Sigma‐Aldrich, Saint Louis, Missouri, USA) and plated in 25 cm2 flasks. Cytosine arabinoside (Sigma‐Aldrich, Saint Louis, Missouri, USA) at final concentration of 10−5 M was added 24 hours (hrs) after plating to reduce the number of dividing fibroblasts. After two passages, purity of OECs was verified by using immunofluorescence with p75 and S‐100 (data not shown). Media were replaced twice a week for three passages and then cultures were used to collect the conditioned medium. OEC‐CM was removed from the cultures and filtered through a membrane filter (0.22 μm pore diameter) to remove cells and debris.