2004 — 2006 |
Mobley, Arie Sitthichai |
F31Activity Code Description: To provide predoctoral individuals with supervised research training in specified health and health-related areas leading toward the research degree (e.g., Ph.D.). |
Olfaction in the Lolliguncula Brevis
DESCRIPTION (provided by applicant): In general, olfactory receptor neurons (ORNs) are bipolar with an apical dendrite containing cilia or microvilli and a basal unmyelinated axon. In the squid, Lolliguncula brevis, five morphological variations on this general theme have been described. Preliminary data suggests a correlation between morphology and metabolite profiles in squid ORNs. Previous work in our lab has shown that a single squid ORN responds to two odors with opposing currents, suggesting activation of different odorant receptors and signal transduction pathways. Thus, this application is based on the hypotheses that: 1) squid ORN subtypes will have different but overlapping odor specificities; and 2) regardless of ORN subtype, odor-evoked excitatory responses will use a cAMP-mediated transduction pathway. Specific Aim 1 will establish the odor specificities of squid ORN subtypes. Specific Aim 2 will show that odors eliciting a depolarizing response in squid ORN subtypes are transduced by the same cAMP-mediated transduction pathway. Data will be analyzed for correlation between the transduction pathway, ORN metabolite profile, and odor specificities. The sense of smell contributes greatly to quality of life and is important as a warning against spoiled foods, gas leaks, or smoke. Recently, there have been several studies correlating the loss of smell with early onset of Alzheimer's and Parkinson's diseases. These diseases imply that there is a greater need to understand the olfactory system.
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0.979 |
2009 — 2010 |
Mobley, Arie Sitthichai |
F32Activity Code Description: To provide postdoctoral research training to individuals to broaden their scientific background and extend their potential for research in specified health-related areas. |
Mechanisms of Embryonic Olfactory Sensory Neuron Axon Targeting
DESCRIPTION (provided by applicant): The cascade of mechanisms that regulate the outgrowth of axons from olfactory sensory neurons (OSNs) and their precise targeting to specific glomeruli in the olfactory bulb remain controversial. While the odor receptors expressed by the OSNs are strongly implicated, there are conflicting reports pertaining to the functional transduction cascade downstream from the odor receptors. An absence of functional activity induced by naris closure, or deletion of a member of the transduction cascade, adenylyl cyclase 111, can have significant effects on the organization of OSN axons and their target glomeruli. However, perturbation of the cyclic nucleotide gated (CNG) channel that is the target of cAMP within the cascade results in little perturbation of axon outgrowth/targeting. Recent findings suggested that cAMP may contribute to OSN axon outgrowth, independent of CNG channel opening, by entering the nucleus and regulating gene expression. My goal is to explore an alternative hypothesis: that 1(h), the current generated by), contributes to OSN depolarization/ excitation and in the absence of the CNG channel can underlie axon outgrowth, coalescence, and formation of glomeruli. I propose a series of studies that will establish the spatio-temporal framework of HCN subunit expression, quantify developmental transients in subunit expression, directly test the effect of HCN on axon outgrowth and branching, and finally, explore how the absence of the HCN1 subunit affects OSN convergence and targeting. The data will have significant implications for developmental disorders such as Kallman's syndrome, and more generally for understanding developmental dynamics and cell-cell interactions during the initial development of sensory systems.
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1.009 |
2012 — 2014 |
Mobley, Arie Sitthichai |
R03Activity Code Description: To provide research support specifically limited in time and amount for studies in categorical program areas. Small grants provide flexibility for initiating studies which are generally for preliminary short-term projects and are non-renewable. |
Activity Dependent Mechanisms of Olfactory System Development
DESCRIPTION (provided by applicant): During development, the olfactory sensory neuron (OSN) axons navigate through the mesenchyme, coalesce with other axons expressing the same odorant receptor, and converge into a glomerulus in a topographically defined region of the olfactory bulb (OB). Although considerable effort has been made, the mechanisms regulating these events are not well understood. My long- term goal is to understand the mechanisms mediating this progression. Currently I am interested in the role that functional activity has in these events. This application focuses on the contribution of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel activity to olfactory development. The HCN channel current Ih was first characterized in cardiac pacemaking activity; the channels are found extensively in the central nervous system. HCN channels are gated by cAMP, which can affect channel kinetics depending on which of the four HCN subunits (HCN1-4) are present. The cyclic nucleotide binding domain of HCN channels make them good candidates for affecting the cAMP activity recently implicated in olfactory system development (Imai et al., 2006, Zou et al., 2007, Chesler et al., 2007). The following aims are designed to determine the role of HCN channels in OSN axon outgrowth, growth cone activity, coalescence and glomerular formation. We previously showed an upregulation of the HCN2 subunit during development (Mobley et al., 2010). Specific Aim 1 examines the mechanisms underlying the role of HCN2, which is strongly modulated by cAMP, in development. I will employ in utero electroporation of the olfactory epithelium to introduce a plasmid expressing GFP and HCN2 shRNA targeting OSNs. This original technique adapted to the nasal cavity will enable visualization of OSN axon behavior in vivo and may have a lasting influence on future studies of OSN dynamics. Specific Aim 2 examines the role of HCN channels and membrane potential in growth cone lamellipodia formation. Guidance signal-induced cAMP signaling is important for OSN axon growth cone targeting and coalescence. Elsewhere in brain cyclic nucleotide signaling is implicated in growth cone dynamics, though the role of HCN channels has not been explored (Ming et al., 1997; Maritan et al., 2009; Murray et al., 2009). Thus, our analyses of HCN mediated growth cone dynamics in OSNs would not only impact olfactory system development but on developmental mechanisms throughout the brain. Specific Aim 2 will challenge OSNs in vitro with membrane potential changes and HCN channel blockers to measure changes in growth cone lamellipodia and filopodia. Demonstrating a role for HCN channels in growth cone dynamics would impact a much larger field than olfactory research and provide new avenues for investigating activity dependent mechanisms of olfactory system development. The results of these studies may provide mechanisms for OSN axon targeting during development such as age-dependent subunit regulation and membrane potential-induced growth cone dynamics. The experiments proposed here may have broad implications for Ih channelopathies including sinus bradycardia, epilepsy, and peripheral neuropathic pain. PUBLIC HEALTH RELEVANCE: This proposal seeks to determine how hyperpolarization-activated cyclic nucleotide-gated (HCN) channels influence development of the olfactory system. This study will expand our understanding of how activity- dependent mechanisms influence axon growth cone dynamics, coalescence and glomerular formation during development, and may apply to the study of olfactory deficiencies such as Kallman syndrome. In turn, these results may apply broadly to cardiac pacemaking, sinus bradycardia, some forms of epilepsy and neuropathic pain, in which HCN channels are implicated.
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1.009 |