Inhibitory activity of nociceptin/orphanin FQ on capsaicin-induced bronchoconstriction in the guinea-pig

In vivo studies were conducted in the guinea-pig to investigate the activity of the selective ORL1 receptor agonist nociceptin/orphanin FQ against capsaicin-induced bronchoconstriction, a response mediated by the release of tachykinins from pulmonary sensory nerves. Anesthetized guinea-pigs were ventilated with a rodent ventilator and placed in a whole-body plethysmograph, and pulmonary resistance (R(L)) and dynamic lung compliance (C(Dyn)) were monitored. Intravenous administration of nociceptin/orphanin FQ (0.3 mg/kg) inhibited the capsaicin-induced bronchoconstriction. The new nonpeptide ORL1 receptor antagonist 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H-benzimidazol-2-one (J-113397) administered intravenously (1 mg/kg) produced a significant blockade of the inhibitory effect of nociceptin/orphanin FQ (0.3 mg/kg) on capsaicin-induced bronchoconstriction, whereas the nonselective opioid receptor antagonist naloxone (1 mg/kg) had no effect. Nociceptin/orphanin FQ (0.3 mg/kg) did not affect the bronchoconstriction induced exogenously by the tachykinin NK2 receptor agonist [beta-ala8]-neurokinin A (4-10). We conclude that nociceptin inhibits in vivo capsaicin-evoked tachykinin release from sensory nerve terminals in the guinea-pig by a prejunctional mechanism. This inhibitory action does not involve activation of opioid receptors.     

The neutralist, the fly and the selectionist

The neutralist-selectionist debate was a staple of molecular evolution and population genetic discourse in the 1970s and 1980s. It waned thereafter, without resolution, as it has taken time to understand what DNA data can reveal about the subject. Recent developments using DNA data from Drosophila melanogaster show that natural selection is pervasive to an extent that is surprising to some former neutralists. It is now known that natural selection acts on synonymous variation, and that linkage effects between selected sites are shaping patterns of variation over large pieces of the genome.     

Population genetics of Caenorhabditis elegans: the paradox of low polymorphism in a widespread species

Caenorhabditis elegans has become one of the most widely used model research organisms, yet we have little information on evolutionary processes and recent evolutionary history of this widespread species. We examined patterns of variation at 20 microsatellite loci in a sample of 23 natural isolates of C. elegans from various parts of the world. One-half of the loci were monomorphic among all strains, and overall genetic variation at microsatellite loci was low, relative to most other species. Some population structure was detected, but there was no association between the genetic and geographic distances among different natural isolates. Thus, despite the nearly worldwide occurrence of C. elegans, little evidence was found for local adaptation in strains derived from different parts of the world. The low levels of genetic variation within and among populations suggest that recent colonization and population expansion might have occurred. However, the patterns of variation are not consistent with population expansion. A possible explanation for the observed patterns is the action of background selection to reduce polymorphism, coupled with ongoing gene flow among populations worldwide.     

Speciation and inversions: chimps and humans

A new set of models has resurrected a role for chromosomal inversions in the formation of new species. Traditional models, which are generally considered to be unlikely in most cases, had imagined that inversions might aid speciation by directly causing low hybrid fitness. In contrast, the newer models focus on the effect that inversions have on local recombination rates. A test of these models found a strikingly high rate of amino-acid substitution within regions where humans and chimpanzees differ by inversions, suggesting perhaps that our ancestral species underwent a divergence process in which gene flow and inversions played a key role. However, it remains uncertain whether this interesting finding is actually consistent with the proposed model.     

Physicochemical characterization of bovine retinal arrestin

The native conformation of bovine retinal arrestin has been characterized by a variety of spectroscopic methods. The purified protein gives rise to a near uv absorption band centered at 279 nm which results from the absorbance of its 14 tyrosine and one tryptophan residue. The extinction coefficient for this absorption band was determined to be 38.64 mM-1, cm-1 using the tyrosinate-tyrosine difference spectrum method; this extinction coefficient is ca. 17% lower than the previously reported value, and provides estimates of protein concentration which are in good agreement with estimates from the Bradford colorimetric assay. When native arrestin is purified to homogeneity, it displays a fluorescence spectrum which is dominated by tyrosine emission with no discernible contribution from tryptophan. Observation of the tyrosine-like fluorescence is dependent on the purity and structural integrity of the protein. Denaturation of arrestin by guanidine hydrochloride results in a diminution of tyrosine fluorescence and the concomitant appearance of a second fluorescence maximum at ca. 340 nm, presumably due to the single tryptophan residue. Thermal denaturation of arrestin leads to a conformation characterized by a broad fluorescence band centered at ca. 325 nm. Study of the arrestin fluorescence spectrum as a function of temperature indicates that the thermal denaturation is well modeled as a two-state transition with a transition midpoint of 60 degrees C. Temperature-dependent far uv circular dichroism studies indicate that changes in secondary structure occur coincident with the change in fluorescence. Studies of the temperature dependence of arrestin binding to light-adapted phosphorylated rhodopsin shows a strong correlation between the fluorescence spectral features of arrestin and its ability to bind rhodopsin. These data suggest that the relative intensities of tyrosine and tryptophan fluorescence are sensitive to the structural integrity of the native (i.e., rhodopsin binding) state of arrestin, and can thus serve as useful markers of conformational transitions of this protein. The lack of tryptophan fluorescence for native arrestin suggests an unusual environment for this residue. Possible mechanisms for this tryptophan fluorescence quenching are discussed.