Showing papers by "University of Liverpool published in 1981"

Free Ca2+ increases in exponential phases during mouse oocyte activation.

Abstract: A dramatic rise in cytoplasmic free Ca2+ concentration has been shown to occur during fertilization and artificial activation in the oocytes of both the medaka fish1 and sea urchin2. Indirect evidence has implicated Ca2+ in the parthenogenetic activation of mammalian oocytes. Mouse oocytes can be activated by the intracellular injection of Ca2+ but not Mg2+ (ref. 3), and hamster oocytes by exposure to the calcium ionophore, A23187 (ref. 4). We report here measurements of cytoplasmic free Ca2+ during the artificial activation and fertilization of single mouse oocytes injected with the Ca2+-sensitive photoprotein aequorin. Free Ca2+ rises exponentially from a resting level of below 0.1 µM to >5 µM over a period of 10–30 min. A series of oscillatory Ca2+ transients precedes this Ca2+ rise during fertilization, but not during artificial activation.

Inter-animal olfactory cues in operant drug discrimination procedures in rats

Abstract: Olfactory cues from prior subjects in operant chambers were shown to be an effective stimulus which rodents could use to direct lever selection in a typical operant drug discrimination (DD) paradigm. Such cues persisted for very long periods of time (16h), and were deposited after very short (5 min) operant sessions. In extinction tests inter-animal olfactory cues exerted very strong stimulus control over lever selection. Furthermore, such cues were not specific to individual rodent subjects but were generalizable between subjects. Inter-animal cues directing lever selection could be abolished by cleaning operant manipulanda with a 10% alcohol solution. Reanalysis of some DD data previously reported by one of the authors (Goudie 1977) indicated that this specific earlier study (and by implication perhaps other studies) might have been confounded by inter-animal cues. In a DD study with nicotine it was found that the drug cue was antagonized by mecamylamine for all subjects except those who had a reliable olfactory cue from prior subjects to direct lever selection (subjects who possessed both an olfactory and a drug cue to direct lever selection responded in a way suggesting that the exteroceptive olfactory cue controlled behaviour rather than the interoceptive drug cue). These findings indicate that inter-animal olfactory cues could be of considerable methodological significance in DD studies. The possible significance of such cues has not previously been reported upon in detail, and in reports of many DD studies there do not appear to be explicit indications that interanimal cues have been adequately controlled.

Clinical Implications of Enzyme Induction and Enzyme Inhibition

Abstract: The pharmacological effect of a drug is partly dependent upon its concentration at its site of action, which in turn is partly dependent upon its rate of elimination. The rate of elimination of many lipophilic drugs is governed by the activity of the hepatic microsomal mixed-function oxidases. Consequently any alteration in the activity of these enzymes may result in a modification of drug action. A wide range of chemically unrelated substances may stimulate the activity of the mixedfunction oxidases by enzyme induction. The drugs most frequently encountered as enzymeinducing agents in man are barbiturates, rifampicin and Phenytoin. Enhancement of drug metabolism by ethanol, tobacco smoking and diet may also involve enzyme induction. Enzyme induction is normally associated with a reduction in drug efficacy but may also alter the toxicity of certain substances. Enzyme induction has been assessed in man by measuring changes in the pharmacokinetics of a marker drug, or changes in the disposition of endogenous compounds such as γ-glutamyltranspeptidase, D-glucaric acid and 6β-hydroxycortisol. The therapeutic problems associated with enzyme inhibition have received much less attention than those associated with enzyme induction. The effect on the rate of elimination of a particular drug will depend upon the fraction of the dose that is normally metabolised by the inhibited enzyme and on the affinity of the enzyme for the drug and the inhibitor. An alteration in the dosage schedule is usually only necessary for drugs with a small therapeutic ratio.

New vertebrate brain–gut peptide related to a molluscan neuropeptide and an opioid peptide

Abstract: Peptides related to mammalian hormones and neuropeptides are known to occur widely in invertebrate nervous systems1–11. It seems plausible to suppose that peptides which have hitherto been found only in invertebrate nervous systems might also have representatives that function as hormones or neuroregulators in vertebrates. However, this idea has yet to be rigorously tested. Recently, Boer et al.12 described immunohistochemical studies in which antisera to a peptide isolated from molluscan ganglia, Phe-Met-Arg-Phe-NH2 (FMRFamide)13, revealed nerve fibres in the brain of the mouse and a teleost fish. This tetrapeptide is of particular interest in that its amino acid sequence is related to that of the C-terminal tetrapeptide of cholecystokinin (CCK) and gastrin (Trp-Met-Asp-Phe-NH2), and is identical to the primary sequence of the C-terminal tetrapeptide of an enke-phalin-related heptapeptide, Tyr-Gly-Gly-Phe-Met-Arg-Phe-OH, recently isolated from bovine adrenal medulla and striatum and known to be a potent opioid agonist14–16. It is not known whether the material identified by Boer et al. corresponds to these previously identified vertebrate peptides. We present here evidence from radioimmunoassay and immunohistochemical studies that FMRFamide-like material occurs in central nervous system and gut endocrine cells of vertebrates. The material is distinguishable in properties and distribution from presently known peptides related to CCK or Met-enkephalin, and we propose that it be added to the list of substances thought to have dual roles as gut hormones and central neuroregulators17,18.

The influence of season and barnacles on the algal colonization of Patella vulgata exclusion areas

Abstract: Patella vulgata were excluded from barnacle dominated areas at Port St Mary, Isle of Man by wire fences attached to the rock in September 1977, December 1977, April 1978 and July 1978. The sequences of algal colonization of these exclusion areas differed markedly with season: in autumn diatoms were followed directly by Fucus, in winter and spring diatoms were followed by green algae and then Fucus, and in late summer Fucus sporelings arose directly on the barnacles. There was no evidence that the initial stages were necessary for the subsequent recruitment of Fucus.

Dung fly struggles: Evidence for assessment strategy

Abstract: 1. Dung fly males guard their females from other males while the female oviposits. Occasionally an attacker grasps the female and a struggle for the possession of female begins. These contests obey ‘war of attrition’ rules. Outcomes and durations of struggles were analysed with respect to the various asymmetries present in the contests, using a technique that tests how the two opponents shift their fighting strategies in accordance with variations in a particular asymmetric feature. 2. In struggles, the attacking male is almost invariably larger than the guarding male (the ‘owner’). Males do not appear to play strategies that are fixed in relation to their own size, but play strategies that depend on their size relative to that of their opponent. No significant difference was found between struggle durations for two small opponents and those for two large opponents, though both were significantly different from large versus small opponents. As the relative size of the owner increases, the persistence of the attacker decreases significantly. That of the owner probably increases (though this is not proven). 3. The female's size relative to the owner's size also exerts a significant effect on the outcome. The larger the female, the greater the probability of takeover. This arises from a greater persistence of the attacker. The ‘resource holding power’ (RHP) of the owner is therefore considered to be influenced both by his size relative to that of the attacker and by his size relative to that of this female. In addition, the owner may have an inherent RHP advantage due to his initial grasp on the female. This may contribute to the fact that only 20–25% of struggles end in takeover despite the fact that the attacker is larger than the owner. 4. Another effect that must contribute to the low frequency of take-overs concerns the fact that the mean value of winning (the resource value) is higher for the owner than for the attacker. Resource value relates mainly to the number of eggs that remain to be laid at the time of the struggle. Though the owner may be unable to monitor this directly, there is a strongly significant negative correlation between owner's persistence and the time he had spent guarding. Thus he escalates as resource value increases. In contrast, attackers appeared to be unable to estimate resource value; their persistence was independent of the female's egg content. 5. The data strongly support the notion that dung flies assess RHP and resource value in contests and alter their fighting strategies accordingly. We discuss the data in relation to recent theoretical developments in the study of assessment strategy.

Human Trophoblast-Specific Surface Antigens Identified Using Monoclonal Antibodies*

Abstract: Mouse monoclonal antibodies have been produced against syncytiotrophoblast plasma membrane preparations isolated from term human placentas. Of 20 positive clones, two antibodies (H309, H318) were directed against the Cγ2 domain of IgG, one (H312) was directed against albumin, and another (H303) was directed against a further normal human serum component (not transferrin). One monoclonal antibody (H310) recognized an antigenic epitope restricted to trophoblast and lymphocytes: this antibody did not inhibit mitogenic or allogeneic stimulation of lymphocytes. Two monoclonal antibodies (H315 and H317) reacted with trophoblast-specific antigenic determinants. The H315 antigen was present on first trimester syncytiotrophoblast, unlike the H317 antigen.

Vigilance and Flock Size in Brent Geese: The Edge Effect

Abstract: We report a test of the hypothesis that the commonly observed decline in vigilance with increasing flock size in birds is a result of the greater vigilance of birds on the edge of the flock (due to their greater risk of predation rather than to the influence of flock size per se). Greater vigilance by edge birds would produce this effect because as flock size increases the proportion of birds on the perimeter of the flock declines. Observations on wild flocks of dark-bellied brent geese (Branta bernicla bernicla) support the hypothesis. Zusammenfassung Bei einer Reihe von Vogeln nimmt der wachsame Anteil des Schwarmes mit der Schwarmgrose ab. Lazarus (1978) nahm an, das dies die Folge erhohter Wachsamkeit der Randvogel gegenuber Raubern ist (wegen der hoheren Feind-Gefahrdung), da der Anteil von Vogeln am Schwarmrand mit der Schwarmgrose abnimmt. Um diese Hypothese zu prufen, wurde die Zeit, die die Vogel in Kopf hoch-, Kopf extrem hoch- und Kopf unten-Haltungen ver-brachten, bei Rand- und Zentrumsvogeln weidender Schwarme von Ringel-gansen (Branta bernicla bernicla) gemessen. Randvogel verbrachten wesentlich mehr Zeit in der Kopf hoch- und weniger in der Kopf unten-Position als Vogel im Schwarmzentrum, jedoch gab es in der extremen Kopf hoch-Position keinen bedeutenden Zeitunterschied. Diese Beobachtungswerte, ein Schwarm-formindex und ein Mas fur den Individuenabstand im Schwarm waren Grundlage eines Modells um zu prufen, wie weit der Randeffekt allein die Schwarm-grose—Wachsamkeitsbeziehung erklaren kann. Vom Modell abgeleitete Kurven pasen gut zu den Daten, abgesehen von einer Uberschatzung der Wach-samkeitswerte in einem kleinen Bereich der Schwarmgrose. Die Folgen der Verletzung der Annahmen des Modelles wurden erortert. Der Rand/Mitte-Unterschied kann kaum dadurch erklart werden, das Wachsamkeit eher der Entdeckung von Artgenossen oder Weideflachen als der von Raubern dient.

Dating of post‐glacial landforms in the central howgills

Abstract: Little is known of Holocene landform development in Upland Britain. This paper describes a site at Middle Langdale in the Howgill Fells of Cumbria where large, but now stabilized and inactive gullies cut through periglacial material. At the base of the gullies large debris cones have buried earlier alluvial sediments on the valley floor. On these sediments and buried by the debris cones is a well-developed organic soil from which two 14C dates have been obtained in an attempt to estimate the age range of the soil. These dates range from 2580±55 years BP for the fine particulate fraction from the base of the organic horizon to 940±95 years BP for fossil rootlets from the uppermost organic layer, immediately below the overlying debris cones. The pollen evidence suggests that the valley floor site was initially dominated by alder carr and later by a Juncus marsh with birch, alder and hazel nearby. The pollen, from the surrounding upland area suggests woodland on the valley sides, dominated by oak and elm that was later replaced by a more open environment rich in heath species and in which disturbed ground species were present. The magnetic evidence indicates a stable local environment during soil formation but shows a sudden inwash of unweathered debris at the top of the buried soil. The evidence suggests that the valley floor was geomorphologically stable throughout the period of soil formation, although there was a local change in valley floor vegetation and a reduction of woodland cover on the valley sides at sometime during the period. The evidence then points to major geomorphological changes; a wave of soil erosion, gully development and debris cone deposition, perhaps following the Scandinavian introduction of sheep farming in the tenth century A.D.

Effects of Not Knowing the Order of an Autoregressive Process on the Mean Squared Error of Prediction—I

Abstract: Given a realization of T consecutive observations of an autoregressive process, x, of unknown order m, a process of an arbitrary order p is assumed to be fitted for predicting the future values of another process [xtilde](t), where [xtilde](t) is independent of xt but otherwise has identical probabilistic structure. The mean squared error of prediction when the autoregressive coefficients are estimated by least squares is obtained to terms of order T -1. The bias in estimating the autoregressive coefficients is examined. The results are illustrated for three processes with m = 2 by considering fitting of a process with p = 1.

The mechanism of zinc tolerance in grasses

Abstract: The mechanism of zinc tolerance in non‐tolerant and tolerant clones of Deschampsia caespitosa and Anthoxanthum odoratum has been investigated. Analysis of non‐tolerant and tolerant clones of these two grasses showed that the tolerant roots accumulated more zinc than the non‐tolerant ones. The zinc contents of the shoots of both clones were similar and contained less zinc than the roots. Compartmental flux analysis using 65Zn suggested that both clones of D. caespitosa were capable of actively pumping zinc across the plasmalemma into the external medium. However, only the tolerant clone was capable of actively pumping zinc out of the cytoplasm of root cells into vacuoles when exposed to levels of zinc up to 1mM, this process was inhibited above 0.1mM zinc in the non‐tolerant clone. Analysis of D. caespitosa for organic acids showed that only the tolerant clone, grown in the presence of zinc accumulated high levels of malic acid. Cytoplasmic sensitivity to zinc was measured by estimating the effect...

Cancer of the larynx and other occupational hazards of mustard gas workers.

Abstract: An attempt was made to tract 511 men and women who manufactured mustard gas during the 1939-1945 war. Despite limitations in the identifying data available, 428 (84%) were traced to the end of 1974. The numbers of deaths from all neoplasms combined (45) and from all other causes (136) were slightly greater than those expected from national death rates, but not significantly so. Two deaths were attributed to carcinoma of the larynx and one to carcinoma of the trachea, compared with an expected number of 0.40 (P less than 0.02). Carcinoma of the larynx was also mentioned on the death certificate of another man. Seven subjects are known to have developed cancer of the larynx, compared with 0.75 expected (P less than 0.001). Excess mortality was also observed from cancer of the lung, pneumonia and accidents, but the excesses were small and difficult to interpret.

Mechanism of Metal Tolerance in Higher Plants

Abstract: A number of higher plants have evolved populations with the ability to grow and flourish in soils containing elevated levels of trace metals. These populations are said to be metal tolerant. This character has been found amongst both wild and crop species. Wild species often show differentiation into ecotypes which can vary in their degree of tolerance; some cultivars of various crop species also show variation in their degree of tolerances.