Fig. 5. Ca²⁺-sensing receptors (Ca-SR) in goldfish olfactory epithelium. (A) Immunocytochemistry with rabbit antiserum to an epitope of the external domain of puffer fish Ca-SR. There is a relatively low concentration of receptors in the cells of the outermost layer of the epithelium (e) of a primary lamella with isolated, apparently migratory receptor-type cells (some indicated by open arows) staining more intensely, indicating a much higher receptor content. Magnification x350. (B) Negative control reaction in which the specific primary antibody was replaced by normal rabbit serum. No reaction was detected in any cells of the olfactory epithelium. Magnification x350. (C) In situ hybridisation of Ca-SR with a DIG-labelled oligonucleotide probe, showing abundant hybridisation in the basal layer of the olfactory epithelium (open arrows). Magnification x350. (D) A negative control in situ hybridisation in a similar area of epithelium to that in C; the specific oligoprobe was omitted from the reagents. There was no reaction in any olfactory tissue cells. Magnification x350.