Vomeronasal

The vomeronasal organ (VNO), located in the nose, is a small chemical sensing stmcture associated with odors and behavioral effects. The vomeronasal system, which is made up of the VNO and a portion of the brain s limbic system, is stmcturaHy independent of the olfactory and nervous terminalis systems in the nose. It may, however, interact with these systems in a manner dependent on prior experience or learning, and therefore be direcdy related to the association of smells and experiences. This independent chemosensory system in the nose may prove to open doors to new learning associated with the sense of smell and human behavior. 

Sensory (vomeronasal) tentacular-apparatus in Caecilians (Apodan amphibian, Gymniophiona) (from Badenhorst, 1978). 

In its central projections the vomeronasal pathway, distinguished by a unique lectin-affinity, ascends to an accessory olfactory bulb, while dorsal and ventral pathways supply the dorsal and ventral regions of the main olfactory bulb (Saito and Taniguchi, 2000). The AOS (but not the MOS) of salamanders displays considerable diversity in the... 

Fig. 2.7 Salamander nasal cavity TS — anterior to entry of naso-lacrimal duct. LD = lateral diverticulum NSE = non-sensory epithelium VNE = vomeronasal epithelium MOE = olfactory epithelium and RP = reflective pigment (after Dawley, 1988).

Fig. 2.11 (a) Dissection of VNC — Mouse Lemur (Microcebus murinus). Cl-C3 = Para-septal cartilage bars LV = ventral vein NC = arterioles/capillary network SV = dorsal vein and VNw = ventral wall (from Schilling, 1970). Vomeronasal complex in murine Rodents. Comparison of LS with TS in Rat (b) LS (horizontal). VV = vascular sinus arrow = venous diverticulum = VN lumen and NE = neuroepithelium (from Larriva-Sahd, 1994). (c) TS (coronal). G = glands RFE = non-sensory epithelium (from Mendoza, 1993). 

Fig. 2.12 Vomeronasal complex Reptiles, TS Snake, (a) Drawing of Amphibolurus muricatus. skeletal elements in yellow (from Broom, 1895). (b) Generalised diagram of epithelial types L = lateral and M= medial (from Rehorek, 1998). (c) VNC, Primitive mammal junction of vomeronasal duct (VNd), with naso-palatine (Stenson s) duct (N-Pd) in Spiny Anteater (Short-nosed Echidna) brown = skeletal elements — septal and para-septal cartilages (from Broom, 1895).

Fig. 2.13 Vomeronasal complex plan views and diagrams of VNO and adnexae (secretory and vascular). Left Bat — generalised (from Cooper and Bhatnagar, 1976) arrow = sensory epithelium. Right Slow Loris (from Hedewig, 1980a) scale bar 100 pm.

PI. 2.3 Vomeronasal neuroepi(helium in Prosimian mid-sensory zone in adult Lemur catta—-uniform lining, x40O (Evans, unpubl.). 

Fig. 2.19 Central pathways and nuclei, (a) Frog AOS Pl/Pm = lateral and medial pallium EP = post, olfactory eminence and nSm = medial Septal nucleus (from Kratskin, 1995). Reptiles and mammals-—afferent pathways from AOB to amygdala nuclei (Cortical C3 and Medial M), with tertiary connections to other central nuclei in hypothalamus (MPOA, VMH and PMN) (from Johnston, 2000). (b) Snake AOS Second-order projection of accessory fibres nAOT - nucleus of AOT AM = anterior amygdala and nSph = nucleus Sphericus. (c) Mammal AOS Projection sites of vomeronasal fibres in cortex and hypothalamus (from Johnston, 1998).

The operation of each part of the vomeronasal sense, from the semiochemicals of frogs to the prevention of pregnancy in mice, is further considered in Chaps. 5 and 7. 

Field and laboratory bioassay of chemosignals from related sympatric and allopatric species (overlapping and discrete distributions) are essential to an understanding of the relatedness or otherwise of functionally active compounds. The semiochemicals involved in speciation surely utilise the main and vomeronasal senses, but their relative contributions cannot be predicted at present. 

The origin of the nervous tissue which comprises the sensory epithelium of the vomeronasal organ is in the anterior neural crest, from which the anterior neurogenic placode appears at the rostral tip (Fig. 4.1). 

In the posterior glands of the nasal septum and in the vomeronasal glands an odorant-binding protein (OBP-II), as expected, increases... 

The vasculature is established by the 18th day of gestation in rats, and comes from the arterial supply as the anterior cerebral vessel, eventually entering the basal lamina via septal tributaries of the olfactory artery (Szabo, 1988). Unlike the MOE, the organ s capillaries penetrate in loops into the neuroepithelium. Blood from the vomeronasal complex arrives for collection in the vomeronasal vein, as described earlier [Fig. 2.11(a)]. The establishment of the highly vascular columnar complexes seen in the ophidian organ has not been correlated with functional development (c.f. Wang and Halpem, 1980 Holtzman and Halpem, 1990). 

The binding of an odourant to the 7-trans-membrane receptors (GPCR) found on the olfactory cilia and vomeronasal microvilli is considered in Chap. 6. The model visualised in PI. 5.1 represents the... 

Fig. 5.7(a) Vomeronasal pump (vasomotor activation and control of VN fluid contents) reciprocal compression/relaxation of lumenal and vascular volumes, vi/ve = internal/ external simus vessels, (a) Fluid intake — lumen expanded/vessels relaxed — pressure drops, (b) Fluid expulsion — lumen compressed/vessels expanded — pressure rise (from Schilling, 1970). 

Both primitive and advanced forms have been examined for vomeronasal excitation. The turtle VN nerve was the subject of EOG recordings elicited by small organic molecules and by specific signal compounds (Tucker, 1963 Hatanaka, 1987). The simple arrangement of the chelonian accessory area (Fig. 2.8) allows air or liquid delivery hence the preferred odourant vehicle varies with habitat across the aquatic or terrestrial turtles, and the land tortoises (Chap. 1 and Halpem, 1992). 

Table 5.1 Occurrence of adult human vomeronasal structures. 

Coding region of the vomeronasal (V1R) gene, as expressed in human MOE neurones (from Rodriguez et al., 2000). 

Fig. 6.1 Interrelationships of chemoreceptors internal (neurotransmitters) and external chemosignals. Phylogenetic connections for sequences in transmembrane (Fig. 6.2) domains Nos. = bootstrap values from 100 Megaline searches (based on majority consensus tree). Invertebrate — DrOR fruit-fly, CeOR nematode vertebrate — FOR fish, LOR (1 2) lamprey, MOR mouse VR (1 2) vomeronasal (from Dryer and Berghard, 1999).

Fig. 6.2 Topology of GPCRs for the main classes of chemoreceptors. Group A vomeronasal (V1R and V2R) and Group B olfactory (OR) and taste (T1R) (from Tirindelli, 1998 Hoon, 1999 Gilbertson, 2000).

The mechanism which operates to select the functional member of an allele pair during neuronal maturation is not known for vomeronasal... 

Temporal alterations in peripheral chemoreceptors are rare in vertebrates, but this group provides an example of transient enhancement of signal capture efficiency. The Red-backed salamander (Plethodon cinereus) shows dimorphic and seasonal VNO volume fluctuations. Males always possess a significantly larger vomeronasal area, and both... 

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