A new method for deriving steady-state rate equations suitable for manual or computer use.

A method is reported for the separation of S-adenosyl-3-methylthiopropylamine and other basic compounds in the eye of the sea catfish (Arius felis) by ion-exchange chromatography on CM-Sephadex. One of the basic compounds was isolated in crystalline form and was shown to be S-adenosyl-3-thiopropylamine by chemical and spectroscopic characterizations and by comparison with a synthetic sample.     

Characterization of a potent biotin-conjugated CRF analog and the response of anterior pituitary corticotropes

A biotin-conjugated synthetic corticotropin releasing factor (B-CRF) was prepared and characterized. Its biological activity and binding affinity were compared with that of unlabeled synthetic CRF. Both forms of the releasing factor were equipotent in in vitro studies measuring the release of corticotropin (ACTH) (ED50 = 1 nM). The IC50 in the binding assays was 1.5 nM for CRF and 4 nM for B-CRF. Dual avidin-biotin peroxidase complex stains were then used in pituitary monolayer cultures to visualize receptivity to the releasing factor and to confirm opiocortin storage in the target cells. All corticotropes showed stain for B-CRF. The percentage of cells that were double-labeled for ACTH and CRF increased with the dose of B-CRF during a four hour incubation period. The CRF stain was abolished, however, when an excess of unlabeled CRF was added to compete with B-CRF. The distribution of the B-CRF and ACTH stains varied in the cells with the time of exposure to the analog. These studies show that biotin-conjugate CRF is a potent analog that can be demonstrated cytochemically on cells identified immunocytochemically as corticotropes. It can be used to follow important events associated with CRF stimulation including the rapid internalization of CRF coupled with the mobilization of corticotropin stores and the formation of cellular processes.     

Climate drivers alter nitrogen availability in surface peat and decouple N2 fixation from CH4 oxidation in the Sphagnum moss microbiome

Peat mosses (Sphagnum spp.) are keystone species in boreal peatlands, where they dominate net primary productivity and facilitate the accumulation of carbon in thick peat deposits. Sphagnum mosses harbor a diverse assemblage of microbial partners, including N₂-fixing (diazotrophic) and CH₄-oxidizing (methanotrophic) taxa that support ecosystem function by regulating transformations of carbon and nitrogen. Here, we investigate the response of the Sphagnum phytobiome (plant + constituent microbiome + environment) to a gradient of experimental warming (+0°C to +9°C) and elevated CO₂ (+500 ppm) in an ombrotrophic peatland in northern Minnesota (USA). By tracking changes in carbon (CH₄, CO₂) and nitrogen (NH₄-N) cycling from the belowground environment up to Sphagnum and its associated microbiome, we identified a series of cascading impacts to the Sphagnum phytobiome triggered by warming and elevated CO₂. Under ambient CO₂, warming increased plant-available NH₄-N in surface peat, excess N accumulated in Sphagnum tissue, and N₂ fixation activity decreased. Elevated CO₂ offset the effects of warming, disrupting the accumulation of N in peat and Sphagnum tissue. Methane concentrations in porewater increased with warming irrespective of CO₂ treatment, resulting in a ~10× rise in methanotrophic activity within Sphagnum from the +9°C enclosures. Warming's divergent impacts on diazotrophy and methanotrophy caused these processes to become decoupled at warmer temperatures, as evidenced by declining rates of methane-induced N₂ fixation and significant losses of keystone microbial taxa. In addition to changes in the Sphagnum microbiome, we observed ~94% mortality of Sphagnum between the +0°C and +9°C treatments, possibly due to the interactive effects of warming on N-availability and competition from vascular plant species. Collectively, these results highlight the vulnerability of the Sphagnum phytobiome to rising temperatures and atmospheric CO₂ concentrations, with significant implications for carbon and nitrogen cycling in boreal peatlands.     

A critique of the contributions of immunoperoxidase cytochemistry to our understanding of pituitary cell function, as illustrated by our current studies of gonadotropes, corticotropes and endogenous pituitary GnRH and TRH

Summary The peroxidase-antiperoxidase technique has been used to study sites of pituitary hormone storage and binding. Some recent findings from our laboratory show that the technique can make intriguing contributions to our understanding of pituitary cell function. In serial ulbra-thin sections, one can identify two or three hormones in a given cell. During pre-pubertal development, gonadotropes may contain adrenocorticotropin immunoreactivity. Brain releasing hormones may be stored or sequestered in granules of cells they stimulate. This report includes a discussion andcritique of our recent findings and interpretations which must be considered before one draws any conclusions about their biological significance.     

Local Interactions Lead to Pathogen-Driven Change to Host Population Dynamics

Individuals tend to interact more strongly with nearby individuals or within particular social groups. Recent theoretical advances have demonstrated that these within-population relationships can have fundamental implications for ecological and evolutionary dynamics [1], [2], [3], [4], [5], [6], [7], [8], [9], [10] and [11]. In particular, contact networks are crucial to the spread [12], [13] and [14] and evolution [8], [9], [11] and [15] of disease. However, the theory remains largely untested experimentally [16]. Here, we manipulate habitat viscosity and thereby the frequency of local interactions in an insect-pathogen model system in which the virus had previously been shown to have little effect on host population dynamics [16] and [17]. At high viscosity, the pathogen caused the collapse of dominant and otherwise stable host generation cycles. Modeling shows that this collapse can be explained by an increase in the frequency of intracohort interactions relative to intercohort interactions, leading to more disease transmission. Our work emphasizes that spatial structure can subtly mediate intraspecific competition and the effects of natural enemies. A decrease in dispersal in a population may actually (sometimes rather counterintuitively) intensify the effects of parasites. Broadly, because anthropological and environmental change often cause changes in population mixing, our work highlights the potential for dramatic changes in the effects of parasites on host populations.