Olfactory system tract

Neuromodulatory transmitter inputs to PC. Darkfield photomicrographs showing the distribution of dopaminergic (a), noradrenergic (b), and serotonergic (c) fibers revealed respectively with immunohistochemistry for tyrosine hydroxylase (TH), dopamine-j8-hydroxylase (DBH), and serotonin (S-HT). Abbreviations Endo, endopiriform nucleus lot, lateral olfactory tract. Reprinted from Handbook of Chem. Neuroanat. Integrated Sys. CNS, Vol. 12, Part III, Chapter III, The Olfactory System, M. Shipley et al., pp. 469-573, 1996, with permission from Elsevier, Ltd... 

The AOB has direct projections to the amygdala, specifically to the medial and posterior cortical nuclei, the bed nucleus of the stria terminalis and the nucleus of the accessory olfactory tract. These pathways may be involved in the processing of pheromonal information. Neurons in the AOB targets express gonadal steroid receptors and thus may be modulated directly by circulating hormones. The efferent connections of the accessory olfactory system are summarized in Fig. 22. 

Orientation via chemical cues may be more important in some species than in others. For example, Oldham (1966, 1967) studied homing and orientation in American toads Bufo americanus) and green frogs Rana clamitans). Oldham (1966) partially destroyed the olfactory tracts of 99 American toads and used 99 intact toads treated as operational controls. An additional 112 toads were left untreated. The toads were then transported to a point of land between two pools. About the same frequencies of returns occurred to the pools. Oldham concluded that olfaction was not necessary for orientation and homing in American toads. However, since only a portion of the olfactory system was destroyed, it is possible that olfaction was still involved in homing and orientation. 

Dopamine is an intermediate product in the biosynthesis of noradrenaline. Furthermore it is an active transmitter by itself in basal ganglia (caudate nucleus), the nucleus accumbens, the olfactory tubercle, the central nucleus of the amygdala, the median eminence and some areas in the frontal cortex. It is functionally important, for example in the extra-pyramidal system and the central regulation of emesis. In the periphery specific dopamine receptors (Di-receptors) can be found in the upper gastrointestinal tract, in which a reduction of motility is mediated, and on vascular smooth muscle cells of splanchnic and renal arteries. Beside its effect on specific D-receptors, dopamine activates, at higher concentrations, a- and -adrenoceptors as well. Since its clinical profile is different from adrenaline and noradrenaline there are particular indications for dopamine, like situations of circulatory shock with a reduced kidney perfusion. Dopamine can dose-dependently induce nausea, vomiting, tachyarrhythmia and peripheral vasoconstriction. Dopamine can worsen cardiac ischaemia. 

It is possible that systemic absorption of airborne aluminum occurs via the lungs, gastrointestinal tract after mucociliary clearance from the respiratory tract (ICRP 1994), or via the olfactory tract. Gitelman et al. (1995) found a better correlation between respirable aluminum air concentrations and urinary... 

Mesolimbic tract From the midbrain ventral tegmental area to the nucleus accumbens, olfactory tubercle, and parts of the limbic system. Arousal, memory, stimulus processing, locomotor activity, motivational behavior. Hyperactivity implicated in positive symptoms. 

Fig. 3 Vomeronasal system. Schematic representation of a rodent nasal cavity and brain (lateral view). Accessory olfactory bulb (AOB) mitral cells project to vomeronasal and extended amygdala. Inset The VNO is a bilateral tubular structure located at the base of the nasal septum. VSNs that express the same V1R or V2R converge on a small number of glomeruli in the AOB. Sensory neurons located in the apical layer of the epithelium project to the anterior part of the AOB, whereas those present in the basal layer project to the posterior part. MOE main olfactory epithelium, MOB main olfactory bulb, BSTMPM posteromedial bed nucleus of the stria terminalis, MEA medial amygdaloid nucleus, BACfF bed nucleus of the accessory olfactory tract, PMCO posteromedial cortical amygdaloid area...

Respiratory Effects. Respiratory tract irritation has been reported at concentrations as low as 216 ppm in volunteers exposed for 45 minutes to 2 hours (Rowe et al. 1952). At concentrations of >1,000 ppm, tetrachloroethylene is intensely irritating (Carpenter 1937 Rowe et al. 1952). Changes in pulmonary function tests were not observed in four male volunteers exposed to 0, 20, 100, or 150 ppm tetrachloroethylene for 7.5 hours/day, 5 days/week, for 1 week at each exposure concentration (Stewart et al. 1981). Exposure of mice to 300 ppm of tetrachloroethylene (300 ppm) for 6 hours/day for 5 days has resulted in degeneration of the olfactory and respiratory mucosa (Aoki et al. 1994). Respiratory effects were not reported in animals after oral exposure (NCI 1977). Environmental exposure to tetrachloroethylene in air or water is unlikely to pose a risk to the respiratory system. 

Figure 2. Schematic diagram of the nasal cavities and forebrain of a salamander, illustrating the central projections of the olfactory and vomeronasal systems in dorsal view. Anterior is toward the top of the figure, and only ipsilateral projections are shown. The medial (A) and lateral (B) olfactory tracts arise from the olfactory bulb. (C) The extra-bulbar ol ctory pathway bypasses the olfactory bulb and projects directly to the anterior preoptic area. (D) The accessory olfactory bulb, which receives input from the vomeronasal organ, projects to the lateral amygdala (la). Other abbreviations apoa = anterior preoptic area dp = dorsal pallium Ip = lateral pallium mp = medial pallium ma = medial amygdala s = septum sir = striatum. Based on descriptions in Hetrick, 1927,1933,1948 Kokoros and Northcutt, 1977 and Schmidt and Roth, 1990.

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