MULTIPLE SIGNAL TRANSDUCTION EVENTS AND MODULATION OF OLFACTORY RESPONSES IN MOUSE OLFACTORY SENSORY NEURONS Yu, Yiqun In the mammalian olfactory system, one olfactory sensory neuron (OSN) expresses a single olfactory receptor (OR) gene. I studied two subsets of mouse OSNs, hereafter refered to as Ho-OSNs and AB-OSNs, in intact mouse olfactory turbinates using calcium imaging. Both of Ho-OSNs and AB-OSNs were located in the most ventral olfactory receptor zone. Ho-OSNs were specifically responsive to 2-heptanone (Ho), heptaldehyde (H) and cis-4-heptenal (cH). Dose-dependent analysis indicated that their responses to individual odorant was saturated within one logarithm unit of concentrations, a typical characteristic of isolated OSNs. Binary mixture and crossadpatation studies showed that these three odorants bound to the same binding sites in Ho-OSNs. However, these three structurally similar odorants activated distinct signaling pathways in Ho-OSNs. In detail, 2-heptanone-evoked intracellular calcium elevation was mediated by AC-cAMP signaling, while heptaldehyde triggered the PLC-DAG pathway. The cis-4-heptenal-evoked [Ca2+]i increases resulted from a combination of cAMP mediated activation and suppression involving PLC signaling. Furthermore, the PLCmediated intracellular calcium alteration was independent of IP3 signaling. A further complexity is that these olfactory receptors were able to interact with other types of Gprotein coupled receptors (GPCRs), such as purinergic receptors. I determined that both the P2X3 and P2Y2 receptor subtypes were expressed in Ho-OSNs. Application of purinergic agonists elevated [Ca2+]i increases in Ho-OSNs. It was discovered that the ATP-induced calcium response required either intracellular or extracellular calcium, while depletion of intracellular calcium stores blocked the UTP-evoked [Ca2+]i increases. Purinergic agonists were able to modulate the odor response in Ho-OSNs, and purinergic antagonist experiments showed that modulation of heptaldehyde-induced calcium responses was due to activation of P2X3 receptor subtypes while heptanone-induced calcium responses was not. Although AB-OSNs were found adjacent to Ho-OSNs, they had complete separate response profiles. AB-OSNs were sensitive to acetophenone (Ace) and benzaldehyde (Ben). In AB-OSNs, both acetophenone and benzaldehyde activated the PLC signaling pathway. Pharmacological characterization indicated that in AB-OSNs, P2X1 and P2Y2 receptors were present, which is different from that in Ho-OSNs. P2X and P2Y agonists modulated odorant responses in AB-OSNs. Purinergic signaling differentially regulated the various odorant responses in AB-OSNs. The acetophenoneevoked [Ca2+]i increases were negativly modulated through activation of the P2Y2 receptor, while the calcium response induced by benzaldehyde was modulated by P2X1 receptor activation. Collectively, these studies suggest that a complex signaling mechanism exists in OSNs, which has important implications for understanding the mechanism of information process in the olfactory system. Ph.D. in Biology, July 2012 Zhang, Chunbo 2012-04-30 2012-07 Dissertation application/pdf islandora:9206 http://hdl.handle.net/10560/2947 BIOL / Biology Illinois Institute of Technology en In Copyright http://rightsstatements.org/page/InC/1.0/ Restricted Access