Fig. 1. Neural cell proliferation declines in relation to age in the mouse olfactory mucosa. A, Coomassie Blue staining of proteins on SDS PAGE and Western blotting of ß-actin. Olfactory mucosa extracts were obtained from mice ranging in age from 1 day (d) to 8.5 months (m). B, kinetics of basal cell proliferation and olfactory neuron production by Western blotting experiments. PCNA serves as a marker for the proliferative state of basal cells; GAP 43, ß3 tubulin, and OMP serve as markers of differentiating and mature olfactory neurons. Western blotting was realized with the same lysates as that in A. The densitometric profiles are given for PCNA (•) and OMP ({square}). Neural cell proliferation and mature neuron production have opposite kinetics.