Free-floating basal forebrain sections were processed as previously described.29 (link),30 (link) Briefly, for assessment of cholinergic neuron marker colocalization, sections were incubated for 48 hours at 4°C in a primary antibody cocktail of goat anti-ChAT (Millipore), TrkA (Millipore), and p75NTR (Millipore). To assess cholinergic neuron marker colocalization with BrdU, tissue was similarly incubated in a primary antibody cocktail of goat anti-ChAT (Millipore), rabbit anti-NeuN (Millipore, Cat. #MABN140), and mouse anti-BrdU (Millipore). Sections were then incubated for 2 hours at room temperature in the secondary antibody cocktail (rabbit Alexa Fluor 594, mouse Alexa Fluor 488, and goat Alexa Fluor 350; Invitrogen, Carlsbad, CA). Immunofluorescent images were obtained using a DS-RiZ scope (Nikon Inc., Melville, NY) and colocalization quantified using NIS Elements AR46 (Nikon Inc.).