PlexinB1 expression changes as a function of age within GnRH-1 neurons. (a and b) Photomicrograph of a nasal explant labeled for GnRH-1 (brown) and peripherin (blue) at 7 div. From 3 to 7 div, GnRH-1 neurons migrate from the olfactory pit epithelia (OPE), following olfactory axons to the midline and off the explant into the periphery. At 7 div, a large population of GnRH-1 neurons is located in the periphery of the explant (b). Panel b is an enlarged view of the box in panel a. (c) Summary of the percentage of GnRH-1 neurons expressing each transcript (PlexinB1, PlexinB2, and GnRH-1) by single-cell RT-PCR analysis. (d) Representative gel of PCR products from individual GnRH-1 cells at different in vitro time points. (e) Approximately 60% of the examined migratory GnRH-1 neurons (n = 8) expressed PlexinB1, whereas only 9% of the postmigratory cells (n = 11) were positive for PlexinB1. PlexinB2 mRNA was not detected in GnRH-1 neurons at any stage analyzed. *, significantly different from other time points (P < 0.005). Statistical significance was determined using Wilcoxon-Mann-Whitney nonparametric test. Em, E17.5 embryo; NMC, nasal midline cartilage; W, water. Bars: (a) 200 μm, (b) 20 μm.