Fig. 3. Lithium inhibits neurite extension more effectively than differentiation. PC12 cells were treated with NGF in the presence of LiCl (2.5-10 mM) or NaCl (10 mM) or in control conditions. After three DIV, cultures were examined and the proportion of cells bearing one or more processes greater in length than one cell diameter (A) and the average neurite length in the field (B) were determined. At least 100 cells were analysed for each condition from each of four independent experiments. The levels of MAP1B and MAP1B-P in these cultures were determined by immunoblot analysis (D). Immunoblots were quantified and protein levels were normalised to controls. The levels of MAP1B-P are expressed as a proportion of MAP1B levels (C). Results are means±s.e.m. from four independent experiments. Note the close correlation between the Li⁺-induced inhibition of MAP1B phosphorylation and neurite extension.