Antibodies used in this study were as follows: rabbit anti-Er81 [14], rabbit anti-Pea3 [14], rabbit anti-PV [14], rabbit anti-eGFP (Molecular Probes, Eugene, Oregon, United States), rabbit anti-Calbindin, rabbit anti-Calretinin (Swant, Bellinzona, Switzerland), rabbit anti-CGRP (Chemicon, Temecula, California, United States), rabbit anti-vGlut1 (Synaptic Systems, Goettingen, Germany), rabbit anti-Brn3a (gift from E. Turner), rabbit anti-TrkA and -p75 (gift from L. F. Reichardt), rabbit anti-Runx3 (Kramer and Arber, unpublished reagent), rabbit anti-Rhodamine (Molecular Probes), mouse anti-neurofilament (American Type Culture Collection, Manassas, Virginia, United States), sheep anti-eGFP (Biogenesis, Poole, United Kingdom), goat anti-LacZ [14], goat anti-TrkC (gift from L. F. Reichardt), and guinea pig anti-Isl1 [14].