HT inputs to the piriform cortex

As with the other monoamines, a comprehensive study of 5-HT inputs to PC has not been undertaken. Anterograde and retrograde tracing studies have demonstrated a rich 

Our recent immunocytochemical studies indicate that the 5-HT innervation of the cortex exhibits less interlaminar specificity than NE terminals and is, in general, complimentary to that of NE inputs (Fig. 27). The serotonergic innervation of PC is very heavy by comparison to DA and NE. 5-HT fibers are especially heavy in layers I and III and the endopiriform nucleus. The density of 5-HT fibers progressively decreases in the deeper parts of layer III. Layer II by contrast, is sparsely innervated. 5-HT fibers in all layers are relatively short, with a tortuous, convoluted orientation and exhibit more varicosities than NE or DA fibers. As with NE, there is little variation of 5-HT fiber distribution or density at different rostrocaudal levels of PC. 

Less information is available concerning the 5-HT receptor subtypes present in parts of the olfactory system other than in the olfactory bulb. However, it is clear that the 

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 

There is no known extrinsic DA innervation of the olfactory bulb. As noted above, however, the MOB contains several hundred thousand intrinsic juxtaglomerular DA neurons 

---