Stimulus access

4B Prenatal occlusion of nostrils in man nasal plug formation (luring foetal life (c.f. Schaeffer, Fig. b, 1910) mid-term 16/17 weeks/HC, 96 pm (Museum No, 62/ 1048 U.B.). 

In mart, an overlooked feature is the occurrence of mucoid-like plugs in the foetal nostrils (Schaeffer, 1910). The presence of this blockage can be confirmed by endoscopic inspection in utero these plugs seem likely to affect free amniotic flow, since they appear to be reinforced by a folded membranous gathering at the nasal vestibule (PI. 4B). A degree of restriction of fluid access to the VN aperture, which is immediately caudal to the nostril aperture, and is patent in foetal life, may be a protective feature (Jordan, 1972). The timing of the dissolution of these sealant devices prior to parturition is regrettably not known. 

Later in intra-uterine life, the human infant is susceptible to early chemical prompting, but again the affector route is not known with certainty. Neonatal discrimination in favour of familiar (maternal) amniotic fluid is demonstrable, suggesting that the foetus already has active chemosensory capacities (Schaal, 1998). Smell and taste are operative in the near full-term foetus since it shows detection of about 120 mg/day maternal intake of anethole (as anise condiments) within a few days before parturition this exposure induced subsequent preferential responses by babies to anethole (Schaal et ai, 2000). The human neonate is not likely to have its organ as a fully functioning chemosensor, 

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Fig. 5.6 Deafferentation of AOS by blockage of stimulus access. Prevention of VN output by injection of tissue cement seals lumen of (1) N-Pd (oral entry) and (2) VNd (nasal entry) (from Dorries et al., 1997).

A previously unexplained observation of a link between nose and gonads — the so-called naso-genital relationship — can now be placed in context. Removal of the relay site for the pump-regulator (see above) by extirpation of the sphenopalatine ganglion was found to result in a state of pseudo-pregnancy (Rosen et al, 1940). Interruption of stimulus access would clearly prevent most uptake through loss of control over the pump. A diestrous state would be induced (Sec. 5.3 below) attributable to the lack of male urinary semiochemicals. 

An adaptive association of Flehmen with fluid-sampling is shown where related modifications to the stimulus-access system, such as anatomical and behavioural anomalies, appear. The F. sequence is inconspicuous and ducts reduced in two African Alcephaline antelopes the Topi (Damaliscus iunatus) and Coke s Hartebeest (Alcephalus... 

Coppola D.M. and Millar L.C. (1994). Stimulus access to the accessory olfactory system in the prenatal and perinatal rat. Neuroscience 60, 463-468. 

Coppola D.M. and O Connell R.J. (1989). Stimulus access to olfactory and vomeronasal receptors in utero. Neuroscience Lett 106, 241-248. 

Meredith M. (1982). Stimulus access and other processes involved in nasal chemosensory function potential substrates for neuronal and hormonal influence. In Olfaction and Endocrine Regulation (Breipohl W., ed.). IRL Press, London, pp. 223-248. 

Meredith, M. and O Connell (1979) Efferents control of stimulus access to the hamster vomeronasal organ. J. Physiol. 286, 301-316. 

Stimuli gain access to the organ via the incisive foramen in the roof of the mouth or the nasal cavity. The vomeronasal pump, described for the hamster by Meredith and O Connell (1979), aids in moving molecules into the organ. This way the animal can control stimulus access and its intensity. Experiments... 

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