The human vomeronasal organ. Part II: prenatal development

Abstract

During the 20th century, the human vomeronasal organ (VNO) has been controversial regarding its structure, function, and even identity. Despite reports that provide evidence for its presence throughout prenatal and postnatal ontogeny, some studies and numerous textbooks declare its absence in late fetal and postnatal humans. To that end, the present study was designed to establish firmly whether the human VNO is homologous with that of other mammals and whether it degenerates (partially or completely) or persists throughout prenatal development. Fifty human embryos and fetuses (33 d to 32 wk fertilisation age) and 2 neonates were examined by light microscopy. Four embryonic primates (mouse lemurs) were examined for a comparison of VNO embryogenesis. The presence or absence and structural characteristics of the VNO and supporting tissues are described. The first appearance of the VNO was in the form of bilateral epithelial thickenings of the nasal septum, the vomeronasal primordium. The primordia invaginated between 37 and 43 d of age and formed the tubular VNO. The tubular VNO was located dorsally at a variable distance from, but was always spatially separated from the paraseptal cartilages. The mouse lemurs examined in this study and other reports from the literature indicate that the human VNO resembles that of primates having functional VNOs until just after a tubular VNO is formed. Examination of the VNO and adjacent tissues suggested that the VNO may lose receptor cells and corresponding vomeronasal nerves and become a ciliated, pseudostratified epithelium between " 12 and 14 wk of age. Our findings indicate the prenatal human VNO goes through 3 successive stages : early morphogenesis, transformation (of the epithelium), and growth. These observations indicated that (1) all embryonic humans develop a vomeronasal organ which is homologous with the VNOs of other mammals, but which has become displaced and highly variable in relative location during embryogenesis ; (2) the human vomeronasal organ does not degenerate prenatally, but very likely loses the functional components of the vomeronasal complex of other mammals ; and (3) the remnant of the human VNO persists until birth and beyond.

Development of the neurons controlling fertility in humans: new insights from 3D imaging and transparent fetal brains

“…Here, we show that during human fetal development the VNO and the AOB are indeed anatomically connected, since NRP2-immunoreactive vomeronasal fibers project to the dorsal OB, as reported in rodents (Cloutier et al, 2002). The VNO also contains strongly Ki67-positive and SOX2-positive putative neurogenic precursors, in agreement with the increase in volume of the human fetal VNO epithelium with age and its persistence at least until birth (Bhatnagar and Smith, 2001;Smith and Bhatnagar, 2000).…”

“…In humans, the olfactory placodes develop as thickenings of the ectoderm on the ventrolateral sides of the head around the fifth week of gestation (Muller and O'Rahilly, 2004). Although there is general agreement about the existence of a VNO in the human embryo (Smith and Bhatnagar, 2000), very little information is available about its development and molecular signature. Here, we first observed that the placodes invaginate at Carnegie stage (CS) 16 (∼39th day of gestation) to form simple olfactory pits (Fig.…”

Embryonic and Postnatal Differentiation of Olfactory Epithelium and Vomeronasal Organ in the Syrian Hamster

“…Fine structure of the olfactory epithelium (OE) and vomeronasal organ (VNO) has been well-documented on various species of amphibians [6,9,17,[19][20][21], reptiles [10,18] and mammals [1,3,[14][15][16]. Details in their developmental changes have also been well-documented in various species [4,7,8,19,[23][24][25][26].…”

“…Details in their developmental changes have also been well-documented in various species [4,7,8,19,[23][24][25][26]. Since the VNO is embryologically derived from the nasal placode as is the OE [13].…”

Ontogeny of the nasopalatine duct in primates

“…As mammals with highly dependent infants and (usually) patent NPDs, primates appear to contradict this view. It should be noted that Wöhrmann-Reppening and Barth-Mü ller's (1994) hypothesis specifically focuses on prenatal events pertaining to the juncture of the NPD and VNO duct (see Smith and Bhatnagar (2000) for further details on this development in prenatal mouse lemurs). Previous studies (Coppola et al, 1993;Coppola and Millar, 1994), as well as the current results, indicate that patency of the communication of the VNO with the nasal cavity (directly or indirectly via the NPD) may occur prenatally in some mammals or perinatally in others, regardless of the precociality/atriciality of the infants.…”