Studies On Adenosine-mediated Neuromodulation In The Enteric Nervous System

Although the role of adenosine in the inhibition of acetylcholine release from myenteric neurons of the small intestine is firmly established, the classification and characteristics of such receptors have not been adequately described. Unlike in the central nervous system, it is not clear if heterogeneity of adenosine receptors exists, or if nucleoside-mediated inhibition of the release of other neuromediators occurs in the enteric nervous system. The studies reported in this thesis were directed at these questions.;Adenosine recognition sites were characterized in ligand binding studies at purified myenteric varicosities. The receptor nature of the binding sites labelled by selective adenosine analogs is supported by the saturability of binding, the good correlation between binding affinity and biological activity (ie. inhibition of Ach release) as well as the potency of adenosine receptor antagonists in displacing their specific binding.;Evidence was obtained for the presence of a heterogeneous population of adenosine receptors on enteric nerve endings. The data is consistent with the presence of A{dollar}\sb1{dollar}-like adenosine receptors with affinity for both N{dollar}\sp6{dollar}- and 5{dollar}\sp\prime{dollar}- substituted adenosine analogs, as well as A{dollar}\sb2{dollar} adenosine receptors with affinity only for 5{dollar}\sp\prime{dollar}-N-ethylcarboxamide adenosine. The A{dollar}\sb2{dollar} receptor may be present in higher concentrations on enteric nerve endings.;Adenosine mediated inhibition of tachykinin release was demonstrated using cholecystokinin (CCK-8) and field-stimulated responses of atropinized guinea pig ileal strips. The data obtained indicates that the same adenosine receptor inhibits the release of both acetylcholine and tachykinins.;The presence of substantial quantities of alpha-neurokinin, substance P, met-enkephalin, leu-enkephalin and gastrin releasing polypeptide (GRP) in this synaptosomal preparation suggested its possible utility in functional studies on modulation of release of endogenous peptides by nucleosides. The finding of both potassium evoked- and GRP mediated-release of several neuropeptides from crude synaptosomal suspensions support this contention

Electromagnetic form factors of the Delta baryon

We develop a methodology that enables us to extract accurately the electromagnetic Delta form factors and their momentum dependence. We test our approach in the quenched approximation as a preparation for a study using dynamical fermions. Our calculation of the four form factors covers pion masses between about 410 MeV and 560 MeV on lattices with a size of 2.9 fm and a lattice spacing 0.09 fm. From the form factors we are able to obtain estimates of the magnetic moment and the charge radius of the Delta, which we compare to existing experimental and theoretical results.Our non-zero result for the electric quadrupole form factor signals a deformation of the Delta, pointing to an oblate charge distribution

Nucleon and Nucleon to Delta Axial form factors from Lattice QCD

We present results on the nucleon axial vector form factors $G_A(q^2)$ and $G_p(q^2)$ in the quenched theory and using two degenerate flavors of dynamical Wilson fermions for momentum transfer squared from about 0.1 to about 2 GeV^2 and for pion masses in the range of 380 to 600 MeV. We also present results on the corresponding N to Delta axial vector transition form factors $C_5^A(q^2)$ and $C_6^A(q^2)$ using, in addition to Wilson fermions, domain wall valence quarks and dynamical staggered sea quarks provided by the MILC collaboration.Comment: 7 pages, 4 figures, talk presented at the XXV International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, German

Axial Nucleon to Delta transition form factors on 2+1 flavor hybrid lattices

We correct the values of the dominant nucleon to Delta axial transition form factors CA_5 and CA_6 published in C. Alexandrou et.al., Phys. Rev. D 76,094511 (2007). The analysis error affects only the values obtained when using the hybrid action in the low Q^2 regime bringing them into agreement with those obtained with Wilson fermions.Comment: 1+2 pages, 2 figures, 1 Table, Erratum to C. Alexandrou et.al., Phys. Rev. D 76, 094511 (2007

Critical Biot Number of a Periodic Array of Rectangular Fins

We consider the heat transfer problem associated with a periodic array of rectangular fins subjected to convection heat transfer with a uniform heat transfer coefficient. Our analysis differs from the classical approach as (i) we consider two-dimensional (2D) heat conduction and (ii) the wall, to which the fins are attached, is included in the analysis

Projected [1H,15N]-HMQC-[1H,1H]-NOESY for large molecular systems: application to a 121kDa protein-DNA complex

We present a projected [1H,15N]-HMQC-[1H,1H]-NOESY experiment for observation of NOE interactions between amide protons with degenerate 15N chemical shifts in large molecular systems. The projection is achieved by simultaneous evolution of the multiple quantum coherence of the nitrogen spin and the attached proton spin. In this way NOE signals can be separated from direct-correlation peaks also in spectra with low resolution by fully exploiting both 1H and 15N frequency differences, such that sensitivity can be increased by using short maximum evolution times. The sensitivity of the experiment is not dependent on the projection angle for projections up to 45° and no additional pulses or delays are required as compared to the conventional 2D [1H,15N]-HMQC-NOESY. The experiment provides two distinct 2D spectra corresponding to the positive and negative angle projections, respectively. With a linear combination of 1D cross-sections from the two projections the unavoidable sensitivity loss in projection spectra can be compensated for each particular NOE interaction. We demonstrate the application of the novel projection experiment for the observation of an NOE interaction between two sequential glycines with degenerate 15N chemical shifts in a 121.3kDa complex of the linker H1 histone protein with a 152bp linear DN