Fig. 1. Developmental regulation of TrkB (A-A'), TrkC (A), Ret (B-B'), GFR1 (B) and GFR2 (B) mRNA expression in the mouse LC, as assessed by in situ hybridization with ³⁵S-labeled riboprobes from embryonic day (E) 13 to postnatal day (P) 0. Dark-field pictures in A' and B' show TrkB and Ret hybridization, respectively. Note the intense Ret signal in the mesencephalic nucleus of the trigeminus, in the lower-left corner of B'. High magnification bright field pictures of representative cells of the main dark field pictures are presented in the upper-left corner of A' and B'. Adjacent sections hybridized with a DIG-labeled TH riboprobe were used to identify the position of the LC (bright field pictures in A'' and B''). The hybridization signal for each of the ³⁵S-labeled probes was measured using NIH Image in: (1) the area occupied by the LC; (2) in the vicinity of the LC to control for background signal in the tissue; (3) in the tissue-free area of the fourth ventricle. The background value of the tissue-free area was subtracted from the labeling values in the LC area and the non-labeled control tissue, before statistical comparison and graph plotting. Values represent the mean±s.e.m. of 4 measures per section in 3 sections per animal in 3 animals per condition. Statistical analysis of the in situ signal showed that all time points in A and B, except for the GFR1 signal at E15 and the TrkC signal at P0, signals were significantly higher than the tissue background signal (P<0.05, paired t-test). Scale bar: 100 µm.