16 Histochem Cell Biol (2012) 137:11–24 Fig. 1 Comparative single ISH for NPY and serotonin receptors in different brain areas. Both CISH (a) and FISH (c) signals are strong and clear for NPY mRNA in the DG. e, g Signal intensities of 5-HT2C mRNA-reactive neurons in the La range from high-to- moderate in CISH (e), equivalent signals are found in HS-TSA-FISH (g). i, m CISH signals for 5-HT1A mRNA are of moderate and low intensity but clearly identiﬁable with high signal-to-noise ratio in granule cells of the DG (i) and in neurons of the BL (m), respectively. k, o Corresponding HS-TSA-FISH signals are weak in the DG 123 granule cells with high background of multiple ﬂuorescent dots in the hilus (k), and dispersed between nuclei in the BL (o), preventing unequivocal identiﬁcation of labeled cells in the latter. Sense controls in CISH are virtually devoid of labeling (b, f, j, n), but contain occasional small ﬂuorescent dots in HS-TSA-FISH (arrows in d, h, I, p). In all FISH images (third and fourth column) nuclei were stained using DAPI. Scale bars in (a, c, e, g, i, k, m, o) are also valid for (b, d, f, h, j, l, n, p), respectively