Lateral olfactory tract

The two main olfactory tracts [Fig. 2.19(a)] comprise an ipsilateral bundle — in the lateral olfactory tract (LOT) — and some contralateral fibres in the anterior olfactory habenular tract (AOHT). The input from the MOS and AOS shows no inter-familial differences in the final brain locations, apart from minor anatomical variants (Schmidt, 1990). 

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. 

Rajendren G. and Dominic J. (1986). Effect of bilateral transection of the lateral olfactory tract on the male-induced implantation failure (Bruce effect) in mice. Physiol Behav 36, 587-590. 

Fig. 4 Odor map in the zebrafish olfactory bulb. Amino acids and nucleotides are received mostly by V2R-type olfactory receptors on microvillous OSNs and are represented in the lateral region of the OB. In contrast, bile acids are received by OR-type olfactory receptors on ciliated OSNs and are represented in the medial region of the OB. LOT lateral olfactory tract, MOT medial olfactory tract...

Different from mammals, in which the mitral cells send axons from the OB to the olfactory cortex through a single tract (the lateral olfactory tract, LOT), there are two major bundles in the secondary olfactory pathways of fish the LOT and the medial olfactory tract (MOT). From the results of neuroanatomical, electrophysiological, and behavioral experiments in cod, goldfish, and carp (Doving and Selset 1980 Stacey and Kyle 1983 Kyle et al. 1987 Sorensen et al. 1991 Hamdani et al. 2000, 2001a, b, 2002 Hamdani and Doving 2003, 2006 Weltzien et al. 2003), the... 

Hamdani EH, Stabell OB, Alexander G, Doving KB (2000) Alarm reaction in the crucian carp is mediated by the medial bundle of the medial olfactory tract. Chem Senses 25 103-109 Hamdani EH, Alexander G, Doving KB (2001a) Projection of sensory neurons with microvilli to the lateral olfactory tract indicates their participation in feeding behaviour in crucian carp. Chem Senses 26 1139-1144... 

Hamdani EH, Kasumyan A, Doving KB (2001b) Is feeding behaviour in crucian carp mediated by the lateral olfactory tract Chem Senses 26 1133-1138 Hansen A, Finger TE (2000) Phyletic distribution of crypt-type olfactory receptor neurons in fishes. Brain Behav Evol 55 100-110... 

The basic circuitry of the MOB. Axons of ORNs travel in the ONL and synapse in the GL on the dendrites of mitrai ceiis (MC), tufted ceiis (externai tufted ceii, ET middie tufted ceii, MT), and generic juxtagiomeruiar (JG) neurons, which include perigiomeruiar ceiis (PG), ET ceiis, and short axon ceiis (SA). SA ceiis interconnect different giomeruii. There are serial and reciprocal synapses between the apicai dendrites of mitral/tufted cells and the processes of JG neurons. Superficial tufted cells (ST) are located in the superficial EPL or at the GL-EPL border. The lateral dendrites of mitral/tufted cells form serial and reciprocal synapses with the apical dendrites of granule cells (GC) in the EPL. GCs are located in the GCL and the MCL. The axons of mitral/tufted cells project locally to GCs (not shown) and also to primary olfactory cortex via the lateral olfactory tract (LOT). The bulb also contains other populations of interneurons neurons, including the van Gehuchten cells (VG) within the EPL... 

Cholinergic Actions in MOB Only limited information is available about cholinergic actions in MOB. Electrical activation of NDB has been reported to depress (Nickell and Shipley, 1988a) or increase (Kunze et al., 1991, 1992) mitral cell activity indirectly via primary effects on GABAergic GCs. NDB stimulation also reduced the field potential in the MOB caused by stimulation of the anterior commissure (Nickell and Shipley, 1993), an effect mediated by presynaptic inhibition of anterior commissure terminals via muscarinic receptors. One interpretation of these results is that cholinergic input to MOB may function to modulate interhemispheric transmission of olfactory information. In this regard, it is noteworthy that anterior commissural fibers are required for access and recall of olfactory memories between the two hemispheres. Infusion of ACh into MOB was reported to reduce paired-pulse depression of lateral olfactory tract (LOT)-evoked field potentials recorded in the GCL. This effect was attributed to... 

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... 

Collins GG, Probett GA. 1981a. Aspartate and not glutamate is the likely transmitter of the rat lateral olfactory tract fibres. Brain Res 209 231-234. 

Ffrench-Mullen JM, Koller K, Zaczek R, Coyle JT, Hori N, et al. 1985. N-Acetylaspartyiglutamate Possible role as the neurotransmitter of the lateral olfactory tract. Proc Natl Acad Sci USA 82 3897-3900. 

Satou M, Mori K, Tazawa Y, Takagi SF. 1983b. Monosynaptic and disynaptic activation of pyriform cortex neurons by synchronous lateral olfactory tract volleys in the rabbit. Exp Neurol 81 571-585. 

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. 

Commercial PCB Mixtures. Administration of single, high doses (500 and 1,000 mg/kg) of a mixture of Aroclor 1254 and 1260 to adult male rats reduced serotonin levels in the frontal cortex and hippocampus, increased serotonin in the lateral olfactory tract, and had no effect in the hypothalamus and brainstem (Seegal et al. 1986a). A correlation between the direction of the changes (increase or decrease) and changes in PCB levels in the different areas could not be made. In a similar study, there was a dose-... 

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. 

Fig. 13. Basic olfactory network. Schematic of the networks linking the olfactory bulb and primary olfactory cortex. Olfactory nerve axons (ON) terminate in the glomeruli (glom) onto mitral (m) and tufted (t) cells which project via the lateral olfactory tract (LOT) to layer la of primary olfactory cortex to terminate on the dendrites of layer Il-III pyramidal (p) cells. Layer 11-111 pyramidal cells in rostral olfactory cortex project to layer Ib in caudal olfactory cortex and vice versa. Olfactory cortical pyramidal cells also send reciprocal projections back to the olfactory bulb. Thus olfactory bulb output is continuously modified by feedback from areas it targets. Inhibitory interneurons in olfactory bulb and olfactory cortex (shown in gray) modulate network function. Neurons in the ipsilateral (AONi) and contralateral anterior olfactory nuclei (AON) link olfactory networks in the two hemispheres via the anterior commissure.

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... 

Piriform cortex (Fig. 15 C-D 17 A-F), also referred to as pyriform or prepyriform cortex, is a phylogenetically old, paleocortical structure. PC is located along the entire length of the lateral olfactory tract at the ventrolateral convexity of the base of the cortex. PC is thicker and more elaborate caudally than it is rostrally. PC is allocortical, having only two-three cellular layers and is thinner and less complex than the neocortex which has six layers. Haberly and Price (1978b) divided the piriform cortex into 3 layers that are further subdivided on the basis of cytoarchitecture and afferent connections. 

Commissural projections to the contralateral PC originate nearly exclusively from layer II neurons and travel in the anterior commissure [AC]. These projections innervate more posterior parts of the contralateral PC as well as nearby olfactory cortical sites (periamygdaloid cortex, lateral entorhinal cortex, anterior cortical nucleus, nucleus of the lateral olfactory tract) (Haberly and Price, 1978a,b). The caudally-directed commissural projections arise almost entirely from rostral layer lib neurons. However, there are shorter, less extensive commissural projections from caudal PC that target rostrally adjacent regions. This pathway arises mostly from deep layer III neurons although there is a modest contribution from layer II neurons. 

It is believed that many of the neurons in PC receive EAA inputs either from the lateral olfactory tract and/or from cortico-cortico connections within PC. Furthermore, elec-trophysiological studies show a role for EAA receptors in PC. Recent autoradiographic, in situ, and immunocytochemical evidence suggests that layer II PC contains an extensive amount of AMPA and kainate receptor subtypes, while layers la and II stain for NMD A receptors (Petralia and Wenthold, 1994 Monaghan et al. 1985 Wisden and Seeburg, 1993 Gall et al. 1990 Petralia and Wenthold, 1992, van den Pol et al. 1994 and Molnar et al. 1993). Further study of the cellular identification of these receptors within PC is necessary. 

MeAa medial nucleus of the amygdala, anterior part MeApd medial nucleus of the amygdala, posterodorsal part MeApv medial nucleus of the amygdala, posteroventral part NLOT nucleus of the lateral olfactory tract ONL olfactory nerve layer... 

McDonald, A.J. (1983) Cytoarchitecture of the nucleus of the lateral olfactory tract, a Golgi study in the rat. Brain Res. Bull.. 10, 497-503. 

Mori, K., Kogure, S. and Takagi, S.F. (1977) Alternating responses of olfactory bulb neurons to repetitive lateral olfactory tract stimulation. Brain Res., 133, 150-155. 

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