Piriform cortex pyramidal cells

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The cytoarchitecture of NLOT (Fig. 17C) has been studied extensively by McDonald (1983). It is considered an anterior part of the amygdala. NLOT can be subdivided into 3 layers on the basis of Nissl preparations a superficial plexiform layer I which contains a few small and medium-sized cells, a layer II which contains many tightly packed cells, and layer III located dorsal to layer II and containing fairly large, loosely packed cells. Most cells of NLOT are medium-sized pyramidal shaped with extensive spines on secondary and distal dendrites. According to McDonald (1983), layers I and II appear similar in connections to the piriform cortex while layer III seems to be a closely related subcortical area. Many neurons of layers II and fewer neurons of layer III project to the olfactory bulb (de Olmos et al. 1978 Shipley and Adamek, 1984). In addition to olfactory bulb projections, many axons of NLOT neurons make up the stria terminalis and cross to the contralateral piriform cortex, olfactory tubercle, lateral nucleus of the amygdala, and bed nucleus of the stria terminalis (de Olmos, 1972). Afferent connections to NLOT arise mainly from olfactory related areas and the basolateral nucleus of the amygdala. 

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. 

Fig. 26. Pyramidal cells in piriform cortex. A and B, Photomicrograph (A) and reconstruction (B) of a intracellularly filled layer II pyramidal neuron In PC. The short apical dendritic arbor is characteristic of layer 11 pyramidal cells. C and D. Another example of a layer II pyramidal neuron. E and F. Low (E) and high power (F) photomicrographs and reconstruction of a layer III pyramidal neuron. Note the profusion of spines connected by necks to the basal dendritic trunks of this pyramidal cell. Scale bar in A, B and E = 100 /tm bar in F = 20 jum.

Results from binding and in situ hybridization studies in the piriform cortex suggest that 5-HTia receptors are located on the dendrites of pyramidal cells (layer II) and also on intrinsic cells of layer III (Pompeiano et al. 1992). In the entorhinal cortex, the... 

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