Nasal cavity accessibility

Prevention of access is the least intrusive method since it need not have any irreversible consequences for the afferent pathway. The common entrance to both olfactory systems in newts is easily closed-off by plugging the nostrils (Kikuyama et al., 1997). A potentially reversible method threaded plugs into the NP canal of cats via the nasal cavity (Verbeme, 1980). This procedure produced a slight effect on male chemoinvestigation of urine and or scent marks. The advantages of avoiding tissue disturbance then, have to be offset by the lack of any estimate of the effectiveness of the blockade, especially if reversible. Tissue cement injections into the N-Pd can be applied to the larger... 

Transsphenoidal pituitary microsurgery Surgery through the nasal cavity to access the pituitary gland through the sphenoid bone. 

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... 

Although the vomeronasal system is specialized to detect stimuli in a liquid environment, it probably is not functional in utero, at least in mice. Fluorescent microspheres were not taken up by the vomeronasal organ as the access canal is not open yet in utero. In rats, by contrast, the canal is open before birth and the microspheres can be taken up. The olfactory epithelium of the main olfactory system plays a greater role prenatally, as evidenced by the uptake of radiolabeled 2-deoxyglucose (Coppola and Coltrane 1994). Fetal mice respond to amyl acetate and isovaleric acid delivered into the nasal cavity through a tiny cannula (Coppola, 2001). In both rats and mice, the main olfactory system, and not the vomeronasal system, appears to mediate prenatal olfaction (Coppola, 2001). 

A primary function of the nasal cavity is olfaction. The location of the olfactory mucosa, recessed on the roof of the respiratory passage, means that it is accessed only by diffusion of volatile or airborne substances in inhaled air. The specialized epithelium features sensitive olfactory neurons that provide a direct link to the CNS. The structural features of the epithelium and potential for drug delivery are considered in detail in Section 19.6.1. 

The olfactory region located in the poorly accessible recessed roof of the nasal passages offers the potential for certain compounds to circumvent the blood-brain barrier and enter into the brain [48]. The olfactory sensory cells are in contact with both the nasal cavity and the CNS and this neuronal connection constitutes a direct pathway to the brain. By utilizing this pathway drugs would not only circumvent the blood-brain barrier, but also avoid any hepatic first-pass effect and degradation in the blood compartment, a particularly important issue in the case of peptide drugs. 

What happens at the instant when an odor-active molecule comes in touch with our nasal cavity 205 The first interaction of odorant molecules takes place in the olfactory receptor neurons, which are embedded in the pseudostratified columnar epithelium (or simply, olfactory epithelium), which is located in the posterior nasal cavity in the case of mammals. Olfactory sensory neurons express receptor proteins on the surface membrane of the cilia, which gain access to the extracellular region covered with mucus. The airborne odorants are dissolved into the mucus, bind with the receptors, and then the receptor protein triggers a signal transduction cascade. This results in the opening of the cation channel that would depolarize the sensory neuron and eventually elicit a train of action potentials in the axon. The olfactory axon leads to the olfactory bulb through basal lamina and lamina propria. 

The strong constitutive expression of this antigen led us to question whether it might be related to continuous chemoreceptive activities of the VNO. To determine whether our Fos-like immunoreactivity was dependent upon chemical stimulation of the VNO, we closed one nostril of mice and after 2 weeks to 16 months sacrificed them and performed immunohisto-chemistry. Naris closure is thought to effectively block the access of both odorants and outside air flow to the nasal cavity. It is also believed that it blocks chemicals from the environment from entering the VNO (see Meredith, 1991). In naris closure mice, the closed side of the VNO, regardless of the time-span after closure (2 weeks to 16 months), showed no... 

As Morgan and Curran (1995) pointed out, constitutive expression by members of the Fos family may be related to constant activity of a tissue. Such constant activity may result from extrinsic or intrinsic stimuli, or both. To investigate the possibility that our Fos-like immunoreactivity might be due to continual sensory stimulation, we employed naris closure to inhibit access of stimulus chemicals to the VNO. Since the opening of the VNO in rodents is on the floor of the nasal cavity inside the nostril (Wysocki, 1979 Gar-rosa. Coca Mora, 1986), and this opening appears to be the only access for stimuli... 

For more than a half century now Boron Neutron Capture Therapy (BNCT) has had potential as a treatment against cancers in difficult-to-access areas of the body. Targets are principally maUgnant brain tumors called glioblastoma multiformehvX also include head and neck cancers involving the Up, mouth, nasal cavities, lymph nodes, sinuses, pharynx, and larynx. How does BNCT work As we know from Table 14.2, boron has two important isotopes, boron-11 (80.22%) and boron-10 (19.78%). It turns out that when B-10 is bombarded with slow or so-called thermal neutrons, an excited, unstable form of boron-11 is formed that immediately disintegrates to produce alpha particles and lithium-7. This process is shown in Equation 14.18. 

Access from the oral cavity to the nasal cavity is necessary for retronasal olfaction, but it is not sufficient. As suggested, it is conceivable that odorants could reach the nasal cavity from the mouth but not arrive at the olfactory epithelium at all, or at least not in a quantity per unit time that would be sufficient to partition into the mucous covering of that sensory epithelium, activate relevant populations of olfactory receptor neurons, and... 

The human buccal mucosae of the oral cavity, i.e., the buccal and the sublingual epithelia, offer a robust and easily accessible area for systemic delivery and the advantage of low enzymatic activity (Lee et al., 1987 Yamamoto et al, 1990). Unfortunately, the multilayered buccal barrier is relatively thick and dense, and proteinaceous substances are not readily absorbed via this route. Thus, permeability of insulin via this route has been calculated to be 12 orders of magnitude less than via the nasal route (Harris and Robinson, 1990). 

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