Figure 6. Oxytocin peptide (OXT) is not produced locally in taste tissue.

A. RT-PCR was carried out on vallate papilla (t1), two samples of vallate and foliate taste buds (t2, t3), non-taste lingual epithelium (nt, negative control), and brain (br, positive control). Primers selective for OXT (top), PLCβ2 (middle) and β-actin (bottom) were tested in parallel for each sample. The expected PCR product and size in basepairs are indicated at right. B,C. Validating the anti-OXT antibody. Coronal sections of brain from heterozygous (Oxt +/−) or knockout (Oxt −/−) mice, fixed and processed in parallel for OXT-immunostaining (red). Sections through the hypothalamus reveal a cluster of OXT-positive neurons in the Paraventricular Nucleus (PVN), in Oxt +/− but not in Oxt −/− mouse. In C, the PVN is shown at higher magnification. D. Cryosections of vallate papillae from the same Oxt +/− and Oxt −/− mice as in B,C, immunostained with the same anti-OXT antibody (green). These sections were also immunostained with anti-Tyrosine Hydroxylase (TH, red) to reveal nerve fibers. Vertical arrows point at the apical pore of two taste buds in each panel. No specific immunofluorescence for OXT was detected in taste buds, adjacent epithelium, or nerve fibers. The faint green fluorescence in these images is identical in tissues from Oxt +/− and −/− mice and thus, cannot be attributed to OXT. Certain primary and secondary antibodies, even those well-validated in other tissues, do yield similar faint non-specific background staining in taste tissue. The “gold standard” test [58] in knockout tissue demonstrates that it is non-specific. Scale bars are 50 µm for B and 20 µm for C, D.