Main olfactory bulb mitral cell layer

Fig. 3 Vomeronasal system. Schematic representation of a rodent nasal cavity and brain (lateral view). Accessory olfactory bulb (AOB) mitral cells project to vomeronasal and extended amygdala. Inset The VNO is a bilateral tubular structure located at the base of the nasal septum. VSNs that express the same V1R or V2R converge on a small number of glomeruli in the AOB. Sensory neurons located in the apical layer of the epithelium project to the anterior part of the AOB, whereas those present in the basal layer project to the posterior part. MOE main olfactory epithelium, MOB main olfactory bulb, BSTMPM posteromedial bed nucleus of the stria terminalis, MEA medial amygdaloid nucleus, BACfF bed nucleus of the accessory olfactory tract, PMCO posteromedial cortical amygdaloid area...

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). 

HT,a receptor is found mainly in the external plexiform layer. On the other hand, the mRNA for the S-HTja receptor has been shown by in situ hybridization to be in the mitral cell and external plexiform layers (Pompeiano et al. 1994) and more precisely, in mitral and tufted cells (McLean et al. 1994). This leads one to speculate that the dendrites or cell bodies of olfactory bulb output cells receive serotonergic input via... 

Central/Tertiary structures The fish olfactory bulb is a fourlayered structure much as in higher vertebrates. Within the 2nd layer, the first synapse for olfactory input is on the dendrites of the mitral cells (MC). About 1000 ORN axons converge on one MC, a ratio similar to mammals. The MC output, from cells at various levels, leads into several glomeruli and receives (inhibitory) input from granule cells. The latter also innervate a distinct cell type in the MC layer of teleosts — the ruffed cells (RC), with which they have reciprocal synapses [Fig. 2.18(a)] both relay cells send ascending fibres to forebrain centres (Kosaka and Hama, 1982). The RC are unlike the MC since they are not stimulated by the ORNs directly. Their interactions (Chap. 5) may contribute to the processing of pheromonal stimuli (Zippel, 2000). The main bulbar pathways project to several nuclei in the forebrain via two ipsilateral tracts, the lateral and medial [Fig. 2.18(b)], the latter mediates sexual behaviour and the former probably other behaviours (Hara,... 

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. 

---