Pattern of RA-regulated transcription in the hippocampus detected using the RARE/LacZ RA reporter mouse. RA reporter gene expression in the hippocampus was detected by immunostaining for the beta-galactosidase reporter protein. A greater number of cells of the dentate gyrus are labeled in the infrapyramidal versus the suprapyramidal blade (A and B: beta-galactosidase immunostaining in red and nuclei labeled with bisbenzamide in blue). A greater number of beta-galactosidase positive cells were also evident in the proximal versus distal halves (B). When numbers of beta-galactosidase positive cells were counted in the two blades, counting separately those in the proximal and distal halves arbitrarily divided at the centre point (as shown in B), a significant difference was evident between the two blades in both proximal and distal halves (C). A significant difference was also evident between the distal and proximal portions of the infrapyramidal and suprapyramidal blade (C). When RARE/LacZ animals were injected with 30 mg/kg RA over 3 days to generate homogenous levels of RA throughout the hippocampus, this resulted in similar activation of the RA reporter in the infrapyramidal and suprapyramidal blades (D and E) significantly shifting the ratio of numbers of beta-galactosidase positive cells from its normal value of 1.3–0.9 (F). Scale bars: A, B, D, and E, 90 μm. (C) Suprapyramidal versus infrapyramidal blade in the distal part of the dentate gyrus, n = 3, one way ANOVA, P < 0.0001, Tukey's posthoc test, P < 0.05 (*), Suprapyramidal versus infrapyramidal blade in the proximal part of the dentate gyrus, n = 3, one way ANOVA, P < 0.0001, Tukey's posthoc test, P < 0.01 (**), Infrapyramidal and suprapyramidal blade in the distal dentate gyrus versus infrapyramidal and suprapyramidal blade respectively in the proximal part of the dentate gyrus, n = 3, one way ANOVA, P < 0.0001, Tukey's posthoc test, P < 0.001 (***). (F) Control-treated infrapyramidal/suprapyramidal blade ratio versus RA-treated infrapyramidal/suprapyramidal blade ratio, n = 3, Student's unpaired t test, P < 0.05 (*). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]