Lateral entorhinal cortex

Kohler, C. Chan-Palay, V. Haglund, L. and Steinbusch, H.W.M. Immunohistochemical localization of serotonin nerve terminals in the lateral entorhinal cortex of the rat Demonstration of two separate patterns of innervation from the midbrain raphe. Anat Embryol 160 121-129, 1980. 

Strong parvalbumin immunoreactivity is present in layer 4 of the primary somatosensory cortex. SMl-32 immunoreactivity formed distinctive patches in layer 4 of the barrel field and forelimb and hindlimb regions. The primary auditory area was identified on the basis of reduced calbindin immunoreactivity in the deep layers. All the auditory areas were marked by the presence of SMl-32 positive cells in the superficial layers. AChE marked the location of the prelimbic and agranular insular cortices. NADPH-diaphorase assisted in defining the agranular insular, perirhinal, and retrosplenial granular cortices. Additionally, NADPH-diaphorase immunoreactivity indicated the ventral part of the medial entorhinal cortex. Calretinin immunoreactivity assisted in delineation of the lateral entorhinal cortex where the outer part of layer one is densely stained. 

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. 

The main olfactory bulb sends a projection to the entire extent of piriform, peri-amygdaloid and lateral entorhinal cortex (see above. Outputs of MOB). This projection terminates in the superficial half of layer I, layer la. Both mitral and tufted cells project to the rostral parts of AON and piriform cortex while the projection to more caudal parts of olfactory cortex becomes progressively dominated by mitral cells (Schoenfeld and Macrides, 1984). 

Piriform cortex, lateral entorhinal cortex and the transitional cortical areas project heavily back to the olfactory bulb (Figs. 13,14, 18,19). The projections are heavier from the rostral than the caudal parts of primary olfactory cortex in rat and mouse (Shipley and Adamek, 1984). A few cells in the posterolateral and medial cortical amygdaloid areas may project to the MOB (Shipley and Adamek, 1984). These feedback projections to the olfactory bulb arise mainly from pyramidal neurons in layers II and III in primary olfactory cortex. 

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. 

The entorhinal cortex receives a substantial input from the MOB (Broadwell, 1975 De Olmos et al. 1978 Kosel et al. 1981 Shipley and Adamek, 1984). In turn, the medial and lateral entorhinal cortex projects to the dentate gyrus and CA fields of the hippocampus (Hjorth-Simonsen, 1972 Steward, 1976). Recent studies show that MOB projections to entorhinal cortex make direct contact with stellate cells located in layer II that in turn project via the perforant path to the hippocampus (Schwerdtfeger et al. 

For the majority of cases of individual discrimination and recognition, it is likely that the main olfactory system is the primary system involved and that higher-order olfactory processing areas are essential. Thus one would expect that projection areas of the main olfactory system should be involved in individual discrimination. Recent neurophysiological studies of the anterior piriform cortex indicate a role for this region in discrimination of learned odors, including odors of mixtures (Wilson, 2002 Wilson and Stevenson, 2003). In one set of lesion studies we showed that one area that may be important for discrimination of individual odors is the lateral entorhinal cortex and the surrounding para-hippocampal area (peri-rhinal cortex, temporal cortex, and subiculum). 

In the human brain, the knowledge of the distribution of the mRNAs coding for 5-HT3A and 5-HT3B receptor subunits is much more limited. By in situ RT-PCR, the co-localization of both subunit mRNAs in a population of neurons in monkey lateral amygdala, and entorhinal cortex and in pyramidal cells of the human cerebral cortex (163) has been described. 

Fig. 21. Summary diagram of the laminar distribution of dopaminergic fibers in different fields of the rat cortex. Adapted from Fallon and Loughlin (1987). Abbreviations ACd, dorsal anterior cingulate ENT1, lateral entorhinal PF, prefrontal PIR, piriform RSg, granular retrosplenial SR, suprarhinal.

However, these results have been questioned, and are not considered reliable (Seeman and Van Tol, 1995). More specific radioligands have been developed recently. Using the new D4 dopamine receptor radioligand [3H]NGD-94-l, D4 dopamine receptors were identified in the hippocampus, hypothalamus, dorsal medial thalamus, entorhinal cortex, insular cortex, prefrontal cortex and lateral septal nucleus (Primus et al., 1997 Lahti et al., 1998). In contrast to the distribution of DrD3 dopamine receptors, no binding was seen in the basal ganglia. These results correspond to the distribution of D4 dopamine receptor mRNA. 

As emphasized by Cajal (1911) and later corroborated by Lor-ente de No (1934), the main input to the dentate gyrus is from the entorhinal cortex (but also perirhinal cortex, among others) by way of a fiber system called the perforant path. It is the major input to the hippocampus. The axons of the perforant path arise principally in layers II and III of the entorhinal cortex, with minor contributions from the deeper layers IV and V. Axons... 

The subiculum curves anteriorly and laterally to wrap around the posterior extension of the dentate gyrus. It borders the medial entorhinal cortex and field of CAl (Figure 6.1). The subiculum can be divided into three distinct cytoarchitectural areas. The parasubiculum borders the medial entorhinal cortex and contains moderately packed medium-sized cells. Next to the parasubiculum is presubiculum, which is characterized by a superficial lamina of densely packed small cells. The subiculum proper is the third distinct area. It borders anterolaterally to the field of CAl and has a loosely packed pyramidal cell layer and a wide molecular layer. 

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