Persistent neuronal responsiveness to the OB chemoattractant(s). A, Effect of a P4 cortical explant on cells migrating from an E16 LGE explant. B, Effect of a P4 OB explant on cells migrating from an E16 LGE explant. C, Effect of a P4 OB explant on cells migrating from a P8 SVZa explant. D, Effect of a P4 OB explant on cells migrating from a P11 SVZa explant. E, Effect of a P4 OB on cells migrating from a P15 SVZa explant. Scale bar, 100 μm. F, The proximal/distal (P/D) ratios of cell numbers were counted from 25 P4 cortical and 21 P4 OB cocultures with E16 LGE explants, 16 cortical and 33 OB cocultures with P4 SVZa explants, 32 cortical and 30 OB cocultures with P8 SVZa explants, 24 cortical and 21 OB cocultures with P11 SVZa explants, and 25 cortical and 24 OB cocultures with P15 SVZa explants. The difference between cortical and OB cocultures was statistically very significant (p < 0.0001).