The effect of corticosterone on standard metabolic rates of small passerine birds

Summary Resting metabolic rates of Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) and pine siskins (Carduelis pinus) were evaluated at thermoneutral temperatures before and after administration of corticosterone (B) at physiological doses. There was no effect of B on basal metabolic rate of either species, but nocturnal metabolic rate varied significantly less over the 3-h period of measurement in B-treated sparrows and siskins than in control birds. These results, coupled with observations of caged birds, suggest that corticosterone has no direct effect on avian resting metabolism but does reduce the responsiveness of birds to external stimuli and thus promotes nocturnal restfulness.Abbreviations B corticosterone - VO ₂ rate of oxygen consumption - T ₃ tri-iodothyromine - T ₄ tetra-iodothyronine, thyroxine     

Purification and characterization of the DNA-binding protein Ner of bacteriophage Mu

The construction is described of a plasmid (pL-ner) which directs the high-level production of the bacteriophage Mu Ner protein in Escherichia coli. The protein, recovered in the soluble cellular fraction, was susceptible to in vivo proteolytic processing, in many host strains, but not in E. coli B, a natural lon- prototroph. A simple purification method is described which takes advantage of the basic nature of the protein. The purified protein was shown to be physically and chemically homogeneous and to have an amino acid sequence identical to that predicted for the authentic protein. The protein was also shown to have in vitro biological activity, as measured by specific binding to a DNA fragment containing the consensus Ner-binding sequence, and in vivo biological activity as the protein produced by the pL-ner plasmid allowed lysogenic-like maintenance of a Mu prophage c mutant unable to synthesise a functional Mu repressor.     

Botryosphaeriaceae associated with Acacia heterophylla (La Réunion) and Acacia koa (Hawaii)

Acacia koa and A. heterophylla are commonly occurring native trees on the Hawaiian Islands and La Réunion, respectively. A recent phylogenetic study suggested that A. heterophylla renders A. koa paraphyletic, and that the former likely arose from the Hawaiian Islands around 1.4 million years ago. An intriguing question is whether their microbiota is similar, although they occur naturally in two very distant geographical locations. In this study, we compared the fungi in the Botryosphaeriaceae isolated from natural populations of A. koa and A. heterophylla. These fungi were chosen because they commonly occur on woody plants and some are important pathogens. They are also known to have been moved globally on asymptomatic plant materials. Isolates were identified based on comparisons of DNA sequence data for the rDNA-ITS, TEF1-α and β-tubulin loci. Ten Botryosphaeriaceae species were identified, of which four species were specific to A. koa from the Hawaiian Islands and five to A. heterophylla in La Réunion. Only one species, Neofusicoccum parvum, which is known to have a wide global distribution, was common to both hosts. The overall results of this study suggest that although A. koa and A. heterophylla share a recent evolutionary history, they have established independent microbiota, at least in terms of the Botryosphaeriaceae.     

High-resolution three-dimensional structure of reduced recombinant human thioredoxin in solution

The solution structure of recombinant human thioredoxin (105 residues) has been determined by nuclear magnetic resonance (NMR) spectroscopy combined with hybrid distance geometry-dynamical simulated annealing calculations. Approximate interproton distance restraints were derived from nuclear Overhauser effect (NOE) measurements. In addition, a large number of stereospecific assignments for beta-methylene protons and torsion angle restraints for phi, psi, and chi 1 were obtained by using a conformational grid search on the basis of the intraresidue and sequential NOE data in conjunction with 3JHN alpha and 3J alpha beta coupling constants. The structure calculations were based on 1983 approximate interproton distance restraints, 52 hydrogen-bonding restraints for 26 hydrogen bonds, and 98 phi, 71 psi, and 72 chi 1 torsion angle restraints. The 33 final simulated annealing structures obtained had an average atomic rms distribution of the individual structures about the mean coordinate positions of 0.40 +/- 0.06 A for the backbone atoms and 0.78 +/- 0.05 A for all atoms. The solution structure of human thioredoxin consists of a five-stranded beta-sheet surrounded by four alpha-helices, with an active site protrusion containing the two redox-active cysteines. The overall structure is similar to the crystal and NMR structures of oxidized [Katti, S. K., LeMaster, D. M., & Eklund, H. (1990) J. Mol. Biol. 212, 167-184] and reduced [Dyson, J. H., Gippert, G. P., Case, D. A., Holmgren, A., & Wright, P. (1990) Biochemistry 29, 4129-4136] Escherichia coli thioredoxin, respectively, despite the moderate 25% amino acid sequence homology. Several differences, however, can be noted. The human alpha 1 helix is a full turn longer than the corresponding helix in E. coli thioredoxin and is characterized by a more regular helical geometry. The helix labeled alpha 3 in human thioredoxin has its counterpart in the 3(10) helix of the E. coli protein and is also longer in the human protein. In contrast to these structural differences, the conformation of the active site loop in both proteins is very similar, reflecting the perfect sequence identity for a stretch of eight amino acid residues around the redox-active cysteines.     

Changes in plasma levels of testosterone during male-male interactions in the song sparrow,Melospiza melodia: time course and specificity of response

Summary Previous investigations have shown that malemale interactions over territory boundaries result in an increase in plasma levels of testosterone (T). In order to determine the time course of this increase following an agonistic challenge, male song sparrows, Zonotrichia (= Melospiza) melodia, were exposed to simulated territorial intrusions. Responding males were captured at intervals after onset of the intrusion for up to 60 min. Plasma levels of T were elevated by 10 min after onset of the challenge, and remained high in birds sampled 10–60 min after onset of the intrusion. In addition, plasma levels of luteinizing hormone (LH) increased and were significantly elevated after 10 min of stimulation. The results suggest that at least the prolonged elevation of T secretion precipitated by a male-male interaction was mediated via an increase in LH release. However, the initial surge of T levels in plasma may be LH independent. p Investigations of captive birds confirmed that circulating LH and T levels increased when male song sparrows were challenged by a conspecific male. Challenges involving a male house sparrow, Passer domesticus, had no effect suggesting that responses to male intrusions were species characteristic and not a result of general arousal. Further, auditory stimuli (vocalizations) alone, and visual stimuli (a devocalized male) alone were less effective in stimulating an increase in secretion of T than a combination of auditory and visual stimuli.Abbreviations DHT dihydrotestosterone - LH luteinizing hormon; - T testosterone     

Sporothrix eucalypti (sp. nov.), a shoot and leaf pathogen ofEucalyptus in South Africa

A species ofSporothrix was consistently isolated from leaf spots and serious shoot infections on a clone ofEucalyptus grandis in Northern Natal, South Africa. The fungus was morphologically distinct from other species in the genus and is consequently described as a new taxon,S. eucalypti. Sporothrix eucalypti was shown to be highly virulent in pathogenicity tests on a number ofE. grandis clones. Significant differences amongst susceptibility of clones were also detected in these tests.Sporothrix eucalypti represents a new pathogen ofEucalyptus that has the potential to cause substantial damage to this host in South Africa and probably elsewhere in the world.     

Assessment of oral candidiasis in patients with respiratory disease and efficacy of a new nystatin formulation.

Fifty consecutive patients with respiratory diseases who developed oropharyngeal candidiasis were assessed clinically and microbiologically before and after seven days'' treatment with nystatin suspension or pastilles (a new formulation). In 45 patients in whom microbiology yielded positive results there was frequent associated use of oral corticosteroids, antibiotics, sedatives, and inhaled corticosteroid, while in a few patients atropine analogues may have predisposed to infection. Dentures were worn by 32 of the infected patients. Concomitant treatment of dentures in chronically infected patients appeared to improve the therapeutic response. Pastilles and suspension were equally efficacious both clinically and microbiologically. The potential for enhanced drug delivery to the oropharynx suggests that nystatin pastilles may be useful in patients in whom poor compliance seems likely.     

Sex-specific variation in brown-headed cowbird immunity following acute stress: a mechanistic approach

There is some discrepancy in the literature regarding whether acute stress is immunostimulatory or immunosuppressive. Studies of domesticated (laboratory and food) animals and humans typically indicate that acute stress is immunostimulatory, whereas studies of non-domesticated species document both immunostimulatory and immunosuppressive results. Few studies have examined the mechanisms responsible for changes in immune activity in species other than those classically used in laboratory research. We examined the effect of both acute stress and exogenous corticosterone (CORT) on the bactericidal capacity (BC) of blood plasma from captive, wild-caught brown-headed cowbirds (Molothrus ater) to determine if CORT is responsible for changes in levels of immune activity. We conducted "stress tests" in which we handled birds to elicit a stress response and then measured the birds' total CORT and BC at 30 or 90 min post-stressor. We also conducted non-invasive tests in which we administered exogenous CORT by injecting it into mealworms that were fed to the cowbirds remotely. Total, free, and bound CORT levels, corticosteroid binding globulins (CBGs), and BC at 7 or 90 min post-mealworm ingestion were measured. Both males and females exhibited significant increases in total CORT following handling stress and the administration of exogenous CORT. Experimental males and females also exhibited a significant increase in CBG capacity at 7 min post-mealworm ingestion compared to controls. Male cowbirds exhibited a significant decline in their BC following both handling stress and the administration of exogenous CORT whereas female cowbirds exhibited no decline under either condition. Female CBG levels were not different than those of males, suggesting that differences in BC could be due to differences between the sexes in the number of corticosteroid receptors which, along with CBGs, regulate the stress response. Female cowbirds may modulate their stress response as an adaptive life-history strategy for maximizing current reproduction.     

Rapid inhibition of female sexual behavior by gonadotropin-inhibitory hormone (GnIH)

Gonadotropin-releasing hormone (GnRH) is largely responsible for the initiation of sexual behaviors; one form of GnRH activates a physiological cascade causing gonadal growth and gonadal steroid feedback to the brain, and another form is thought to act as a neurotransmitter to enhance sexual receptivity. In contrast to GnRH, gonadotropin-inhibitory hormone (GnIH) inhibits gonadotropin release. The distribution of GnIH in the avian brain suggests that it has not only hypophysiotropic actions but also unknown behavioral actions. GnIH fibers are present in the median eminence (ME) and are in apparent contact with chicken GnRH (cGnRH)-I and -II neurons and fibers. In birds, cGnRH-I regulates pituitary gonadotropin release, whereas cGnRH-II enhances copulation solicitation in estradiol-primed females exposed to male song. In the present study, we determined the effects of GnIH administered centrally to female white-crowned sparrows. A physiological dose of GnIH reduced circulating LH and inhibited copulation solicitation, without affecting locomotor activity. Using rhodaminated GnIH, putative GnIH binding sites were seen in the ME close to GnRH-I fiber terminals and in the midbrain on or close to GnRH-II neurons. These data demonstrate direct effects of GnIH upon reproductive physiology and behavior, possibly via separate actions on two forms of GnRH.