P.F. van Bergen

Stable carbon isotope changes during artificial charring of propagules

Abstract Charred organic remains are ubiquitous in the archaeological and fossil record and are often used to interpret past environments and climate. This study focuses on the physical and chemical alteration that takes place during heating (i.e. charring). Modifications to the internal and external morphology were noted alongside the change in molecular and stable carbon isotope signature. Molecular analyses were undertaken using direct temperature resolved mass spectrometry and the stable carbon isotopes determined using isotope ratio mass spectrometry. The results of this study document a general enrichment in 13 C/ 12 C composition of charred material which could reflect the changes observed in both the molecular composition and the relative proportions of the molecules formed. These results indicate that spurious results might be inferred when comparing the stable carbon isotope signature of charred/charcoalified material with uncharred organic matter

A hypotensive and bradycardic action of γ2-melanocyte-stimulating hormone (γ2-MSH) microinjected into the nucleus tractus solitarii of the rat

In conscious and urethane-anesthetized rats intravenously (i.v.) administered γ2-melanocyte-stimulating hormone (γ2-MSH), a melanotropin derived from the precursor peptide pro-opiomelanocortin (POMC), has been shown to induce a pressor response combined with a tachycardia. A site of action within the hindbrain, e.g. the nucleus tractus solitarii (NTS) or the area postrema (AP), has been suggested.In order to test the postulate that γ2-MSH acts within these hindbrain regions, the peptide was microinjected into various parts of the NTS and into the AP of urethaneanesthetized rats and blood pressure (BP) and heart rate (HR) were measured.Injection of γ2-MSH (100–500 pmol) into the NTS resulted in a dose-dependent decrease in BP and HR rather than in the expected pressor and tachycardic response which is generally found in conscious and urethane-anesthetized rats following i v. administration of the peptide. With respect to the depressor and bradycardic effect the melanotropin was far more potent when injected into the pars commissuralis than into the medial part of the NTS. The responses were maximal after 3–4 min and lasted for about 15 min. γ2-MSH had no effect when injected into the AP. It is noteworthy that also a hypotensive and bradycardic effect for γ2-MSH is found in pentobarbitalanesthetized rats following i.v. administration. Therefore, we conclude that in addition to a pressor and tachycardic response γ2-MSH can elicit an opposite effect by interaction with structures within a discrete region in the NTS, the pars commissuralis. The occurrence of these different cardiovascular responses to γ2-MSH is not necessarily surprising: in fact, the direct application of γ2-MSH at the NTS-site may directly activate inhibitory pathways, whereas i.v. injection allows the peptide to reach other (brain) areas involved in cardiovascular regulation as well. A depressor effect after i.v. administration of γ2-MSH can be unmasked during deep anesthesia with pentobarbital which might blunt the stimulating effects by depression of sympathetic outflow.

CARBON AND OXYGEN ISOTOPE DENDROCHRONOLOGY IN SUB-FOSSIL BOG OAK TREE RINGS - A PRELIMINARY STUDY

SUMMARY Isotope dendroclimatology is a relatively new field investigating en vironmental factors that control the radial growth of trees. Tree-ring series of sub-fossil bog oaks can be dated from sites across northwest Europe indicating that the environmental change(s) were regional rather than local. Bog oaks show characteristic periods of suppressed growth thought to have resulted from changes in the hydrological status of bogs towards either wetter or drier conditions. This study investigates relative changes in stable carbon (δ13C) and oxygen (δ18O) isotope content in phases of suppressed and normal growth in three bog oaks dated as c. 200 BC to 150 AD from Zwolle, eastern Netherlands. Bog oaks show no clear relationship between tree-ring width and isotopic composition although one tree exhibited relatively depleted values of 13 C and 18 O with suppressed growth. Suppressed ring growth is characterised by the formation of earlywood only, possibly as a result of hydrologic alterations that limited the formation of latewood, which would otherwise have locked up a detectable signal in stable isotopic shift.

A study on possible modulating and direct effects of γ2-MSH and ACTH-(1–24) on the cardiovascular system of the rat

In conscious rats, γ2-melanocyte-stimulating hormone (γ2-MSH) dose-dependently increases blood pressure and heart rate, whereas adrenocorticotropin-(1–24) [ACTH-(1–24)] dose-dependently decreases blood pressure, an effect which was accompanied by a reflectory tachycardia. As the exact mechanism involved in these cardiovascular effects of the two melanocortins is as yet not known, we undertook a series of experiments to investigate the possibility that these peptides have modulating or direct effect on the cardiovascular system of the rat. In pithed rats γ2-MSH, administered intravenously (i.v.) in doses of 5–200 nmol/kg, had no significant effect on systolic and diastolic blood pressure and on heart rate, whereas ACTH-(1–24), 5–500 nmol/kg, i.v., dose-dependently decreased blood pressure and increased heart rate. Infusion of γ2-MSH, 10–8 M, or ACTH-(1–24), 10–6 M, in the isolated perfused rat heart did not significantly affect left ventricular pressure or coronary flow. Pretreatment with either γ2-MSH or ACTH-(1–24) did not modify the responsiveness of the myocardium and coronary vasculature to salbutamol and phenylephrine. Neither γ2-MSH nor ACTH-(1–24) did affect the vascular contractile machinery of skinned vascular smooth muscles of the rabbit with respect to Ca2+ handling in the cell, as measured by its sensitivity to exogenously applied Ca2+. γ2-MSH had no effect on blood pressure and heart rate in pithed rats in which postganglionic sympathetic outflow was stimulated by 1,1-dimethyl-4-phenylpiperazinium (DMPP), nor in pithed rats in which preganglionic sympathetic outflow was stimulated electrically. A dose of 15 nmol/kg ACTH-(1–24) had no significant influence on preganglionic outflow to the cardiac and vascular structures in pithed rats. These data show that γ2-MSH does not exert its cardiovascular effects via a peripheral site of action at the level of the vascular system and the heart, nor directly on pre- or postganglionic sympathetic outflow. These results are in support for the notion that the peptide acts via a brain region localised outside the blood-brain barrier. The acute depressor effect of ACTH-(1–24), however, seems to be due to a direct effect on the vasculature in the periphery.

The problematic systematic position of Ceratostratiotes Gregor (Hydrocharitaceae ?) – morphological, anatomical and biochemical comparison with Stratiotes L.

Abstract. The enigmatic fossil taxon Ceratostratiotes sinjanus (Kerner) Bužek has been considered as either a Hydrocharitaceae seed (monocot) or a Ceratophyllaceae fruit (dicot). The co-occurrence of seeds of Stratiotes kaltennordheimensis (Zenker) Keilhack (Hydrocharitaceae) and Ceratostratiotes in Early Miocene sediments in Langau (Lower Austria) enabled comparisons of morphological-anatomical features and lignin compositions, independent of diagenetic biases. The biochemistry of the Ceratostratiotes seed coat wall is not monocotyledon-like and is dissimilar to that of the co-occurring Stratiotes testae. In contrast, the Ceratostratiotes seed coat anatomy resembles that of Hydrocharitaceae genera with the micropyle and raphe being very similar to those in seeds of Stratiotes. Although the horizontal arrangement of the Ceratostratiotes spines is different from the longitudinal arrangement of the surface ridges in Stratiotes kaltennordheimensis and the spines in Blyxa (Hydrocharitaceae), the spine structures are very similar. A mixture of similarities and differences characterizes the morphological-anatomical features. Thus the systematic affinity of Ceratostratiotes still remains enigmatic.

The Shearwater Field – understanding the overburden above a geologically complex and pressure-depleted high-pressure and high-temperature field

Abstract The Shearwater Field, located in Block 22/30b in the UK Central Graben, remains one of the best-known fields in the UK Continental Shelf (UKCS). At the time of the initial development, Shearwater represented one of the most complex and technically challenging high-pressure and high-temperature (HPHT) developments of its kind in the North Sea. During the early life of the field, pressure depletion resulted in compaction of the Fulmar reservoir, leading to mechanical failure of the development wells. The compaction also resulted in weakening of the overburden due to an effect known as stress arching. Over time, this resulted in in situ stress changes in the overburden which have been observed from 4D seismic datasets and are in line with geomechanical modelling. This is particularly true for the Hod Formation in the Chalk Group, and resulted in the need to make changes to infill well design, including the use of new drilling technologies, to ensure safe and effective well delivery. The insights presented here, which relate to the understanding of pore pressure and fluid fill in the overburden, and how the overburden has responded to stress changes over time, are of relevance to current and future HPHT field developments in both the UK North Sea and elsewhere.