Histochemistry of rat brain tissue used monoclonal anti-BrdU, 1:250 (Novocastra), rat monoclonal anti-BrdU, 1:250 (Accurate), mouse monoclonal anti-NeuN (1:200; Chemicon), mouse monoclonal anti-TuJ1, 1:500 (gift of A. Frankfurter) and rabbit polyclonal anti-TUC-4, 1:10,000 (gift for S. Hockfield).