Periamygdaloid cortex

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 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... 

As noted by de Olmos et al. (1978), there are several transitional regions (including periamygdaloid cortex) between the piriform cortex and the entorhinal cortex and between olfactory cortices and neocortex. These transitional regions have been described in detail previously (De Olmos et al. 1978) and the reader is referred to that paper for additional information. Caudal to the piriform and periamygdaloid cortices is the entorhinal cortex. This cortex is divided into medial, lateral and intermediate divisions and has six layers. 

In the hamster, neurons in the rostral to caudal levels of piriform cortex terminate from superficial to deep in the GCL of MOB, respectively. However, this gradual shift in termination is not as apparent in the rat. The periamygdaloid cortex and NLOT terminate in the deep GCL (Luskin and Price, 1983). In summary, it would appear that most of the afferent projections to MOB from the AON project most heavily to the ipsilateral GCL. 

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. 

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... 

The caudolateral part of AON is continuous through transitional zones with the piriform cortex, which in turn gives way caudally to periamygdaloid and transition cortices and then the lateral entorhinal cortex. Collectively, these cortical structures comprise the entire temporal cortical mantle ventral to the rhinal sulcus. 

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