Projections to olfactory cortex

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 

Shipley, J.H. McLean, L.A. Zimmer and M. Ennis MAIN OLFACTORY SYSTEM 

Major connections of the main (MOB) and accessory (AOB) bulbs with cortical (gray panels) and subcortical structures (ellipses). Output projections of MOB and AOB shown by solid lines reciprocal and centrifugal projections to MOB and AOB are shown by gray lines. Cortical areas comprising the primary and accessory olfactory cortex are indicated by squares. 

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 

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Recently, the neuropeptide, corticotropin releasing factor (CRF), has been demonstrated in mitral and some tufted cells using both immunocytochemistry (Fig. 1 IB) and in situ hybridization in the rat (Imaki et al. 1989). CRF fibers were also observed in the molecular layer of the piriform cortex. This finding is consistent with CRF being a releasable neural peptide in mitral cells since mitral cells synaptically terminate in the molecular layer of the piriform cortex. A similar localization of CRF has been reported in the squirrel monkey suggesting that this peptide may be a conserved transmitter/ modulator in the mitral/tufted cells of many mammals (Bassett et al. 1992). Finally, calretinin, a calcium binding protein, has been shown by immunohistochemistry to be localized in mitral cells (Jacobowitz and Winsky, 1991). Transmitter candidates for mitral and tufted cells are discussed further in 2.5.3., Projections to olfactory cortex. 

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