Developmental changes in the distribution of calretinin-immunoreactive cells in human fetal nasal epithelium

Immunoreactivity of the calcium binging protein calretinin is often used as a marker of olfactory neurons. Although the immunoreactivity and density of olfactory neurons are known to change between developmental stages in the human fetus, previous descriptions have been limited to the olfactory epithelium and/or the nasal septum and have not included the entire nasal cavity. Using horizontal semi serial sections of heads of six mid-term fetuses (9-15 weeks of gestation), we examined the topographical anatomy of calretinin-positive olfactory neurons. By 9 weeks of gestation, the distribution of calretinin-positive cells reached levels inferior to the developing inferior meatus. By 12 weeks, concentrations in the inferior end had reached the level of the inferior meatus and the middle meatus carried abundant positive cells. However, by 15 weeks, calretinin positive cells were restricted to levels superior to the middle meatus and in the vomeronasal organ. Placode-derived cells are initially distributed antero-inferiorly along the nasal epithelium, but most lose their calretinin immunoreactivity. They might differentiate into the neuroendocrine cells embedded between nasal respiratory epithelial cells. The final differentiation of calretinin-positive cells was likely to require connection to the olfactory bulb and accessory bulb.