Anterior olfactory nucleus AON

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. 

Female hamsters with transections of the lateral olfactory tract (LOT efferents and afferents of MOB and AOB) at the level of the anterior olfactory nucleus (AON) are not anosmic, but do show very little interest in male and female odors (Petrulis et al., 1999). This result indicates that chemosensory structures caudal to the cut, such as Pir, MeA and LEnt, are critical for female hamster sex odor preferences and interest in conspecific odors. Removing the VNO has no effect on a female s preferential investigation of male volatile odorants from a male versus a female s odor but did reduce the overall amount of investigation of male flank scent when direct contact was allowed (Petrulis et al., 1999). It appears that, similar to male hamsters, preferential attraction by females toward opposite sex odors at a distance is mediated by the MOS but that the VNS may play a role in chemoinvestigation in circumstances where direct contact with odorants is allowed. 

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... 

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)... 

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... 

Abbreviations AON, anterior olfactory nucleus mAChR, muscarinic cholinergic receptor nAChR, nicotinic cholinergic receptor alpha and beta adrenergic receptors NMDA, N-methyl-D-Aspartate receptor AMPA, a-amino-hydroxy-5-methyl-4-isoxazolepropionic acid receptor GABAa/b, gamma aminobutyric acidreceptor. 

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