Olfactory nuclei, anterior

The output axons of the bulb emerge from its caudolateral aspect to make up the lateral olfactory tract leading to the AOS tertiary structures, most immediately the anterior olfactory nucleus. 

Among the seven families of serotonin receptors, only the 5-HT3 receptors are ligand-gated ion channels, whereas all others are G protein-coupled receptors (Barnes and Sharp 1999). 5-HT3 receptors are rather unselective cation channels with a high permeability for Ca2+ (Ronde and Nichols 1998). In the central nervous system, they are expressed abundantly in the neocortex, the anterior olfactory nucleus, the hippocampus, and the amygdala. In addition, 5-HT3 receptors are present in the caudate putamen and the nucleus accumbens, and, at high levels, in the brain stem (Parker et al. 1996 Morales et al. 1998 Chameau and van Hooft 2006). 

The clue to this transition seems to be found in the sense of olfaction. Early in the course of AD, degeneration occurs in the entorhinal cortex-hippocampal-subicular complex (Price and Morris, 1999). The olfactory bulb, particularly the anterior olfactory nucleus, shows numerous neurofibrillary tangles (NFTs). Odor identification deficits during life may be associated with NFTs in the hippocampus (Wilson et al., 2007). 

Architecture of the MOB (A, B) and primary olfactory cortex (POC, C). A and B Coronal section (Nissl stain) of the rat MOB at low (A) and high (B) magnifications. C Coronal section through the rat brain showing several structures of the POC. Abbreviations ac, anterior commissure Acb, nucleus accumbens AONvp, anterior olfactory nucleus, ventroposterior division DP, dorsal peduncular cortex IL, infralimbic cortex Pir, piriform cortex SEL, subependymal layer Scale bar in A and C = 1 mm. Modified from Handbook of Chem. Neuroanat. Integrated Sys. CNS, Vol. 12, Part III, Chapter III, The Olfactory System, M. Shipley etal., pp. 469-573,1996, with permission from Elsevier... 

Major connections of the main olfactory system. Axons of MOB mitral/tufted cells (circles in the EPL and MCL, respectively) project as the LOT to synapse in a number of structures collectively referred to as primary olfactory cortex (POC). Centrifugal inputs to MOB include feedback projections from POC as well as inputs from subcortical forebrain and brainstem neuromodulatory cell groups. Abbreviations AON, anterior olfactory nucleus DP, dorsal peduncular cortex Ent, entorhinal cortex IG-AHC, indusium griseum-anterior hippocampal continuation LC, locus coeruleus NDB, nucleus of the diagonal band PeCo, periamygdaloid cortex PC, piriform cortex RN, raphe nuclei (dorsal and median raphe) TT, taenia tecta Tu, olfactory tubercle... 

Ohm TG, Muller H, Braak E. 1991. Calbindin-D-28k-like immunoreactive structures in the olfactory bulb and anterior olfactory nucleus of the human adult Distribution and cell typology-partial complementarity with parvalbumin. Neuroscience 42 823-840. 

Schoenfeld TA, Macrides F. 1984. Topographic organization of connections between the main olfactory bulb and pars externa of the anterior olfactory nucleus in the hamster. J Comp Neurol 227 121-135. 

Watanabe K, Kawana E. 1984. Selective retrograde transport of tritiated D-aspartate from the olfactory bulb to the anterior olfactory nucleus, pyriform cortex and nucleus of the lateral olfactory tract in the rat. Brain Res 296 148-151. 

Abbreviations Al = primary auditory area ac = anterior commissure Acc = accumbens nucleus AON = anterior olfactory nucleus BF = barrel field BLA = basolateral nucleus of the amygdala CAl = cornu ammonis 1 CA3 = cornu ammonis 3 cc = corpus callosum Cg = cingulate area CPu = caudate-putamen DCb = deep cerebellar nuclei DCo = dorsal cochlear nucleus DG = dentate gyrus DMV = dorsal motor nucleus of the vagus nerve ECu = external cuneate nucleus EP = external plexiform layer ER = entorhinal cortex f = fornix Fa = facial nucleus fa = facial nerve fr = fasciculus retroflexus G1 = glomerular layer GPe = (external segment of the)... 

The axons of the external tufted cells project mainly to other sites in the same olfactory bulb (Schoenfeld et al. 1985). Middle and deep tufted cells also have local collaterals in the ipsilateral bulb but most of them appear to project out of the olfactory bulb to the anterior olfactory nucleus and other rostral olfactory cortical structures (Schoenfeld et al. 1985 Scott, 1986). The intrabulbar collaterals of the superficial tufted cells form... 

The axons of the mitral cells give off collaterals within the bulb in the internal plexiform and granule cell layers (Mori et al. 1983). The main axons course predominantly in the lateral olfactory tract which forms at the level of the AOB. These caudally directed axons give off collaterals in the anterior olfactory nucleus (AON) and other regions of olfactory cortex (Figs. 13, 18, 19). Tufted cells collateralize to an even greater extent in the bulb than mitral cells. The intrabulbar association pathway formed by CCK-ergic tufted cells was discussed earlier. 

MOB projects to several structures of the ipsilateral hemisphere, including the superficial plexiform layer of the anterior olfactory nucleus, piriform, periamygdaloid and lateral entorhinal cortices, taenia tecta, the anterior hippocampal continuation, in-dusium griseum and the olfactory tubercle (Figs. 14, 18, 19). Collectively, the regions directly innervated by the output of the MOB have been referred to as primary olfactory cortex (De Olmos et al. 1978). Most of these projections have been reported in several species (for review, cf. Shipley and Adamek, 1984). A recent study has also shown a... 

Abbreviations ACo = anterior cortical amygdaloid nucleus AOB = accessory olfactory bulb Me = medial amygdaloid nucleus AON = anterior olfactory nucleus (m = medial division) PCo = posterior cortical amygdaloid nucleus BST = bed nucleus of the stria terminalis DHR = dorsal hippocampal rudiment DPC = dorsal peduncular cortex DR = dorsal raphe nucleus Ent = entorhinal cortex LC = locus coeruleus LPO = lateral preoptic area MOB = main olfactory bulb MnR = median raphe BAOT = nucleus of the accessory olfactory tract NLOT = nucleus of the lateral olfactory tract DB = nucleus of the diagonal band PeCo = periamygdaloid cortex Pir = piriform cortex Tu = olfactory tubercle TT = taenia tecta... 

The main olfactory bulb projects to a collection of structures referred to collectively as primary olfactory cortex (De Olmos et al. 1978). These structures may be usefully divided into three groups (A) the anterior olfactory nucleus (Fig. 15) (B) rostral olfac-... 

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