Endogenous cortical proliferation is enhanced following FGF-2 gene delivery. (a) Endogenous proliferation occurs infrequently in the naive entorhinal cortex. Newly generated cells labeled by BrdU administration over 48 hours are indicated by the arrow and shown at higher magnification in the inset. (b) Intracerebral saline injection prior to BrdU treatment produced no visible increase in proliferation in the entorhinal cortex. (c) Injection of adenovirus expressing the reporter gene LacZ produced little effect on proliferation in the entorhinal cortex. (d) Adenovirus-mediated gene delivery of FGF-2 produced a substantially increased proliferation in the entorhinal cortex.