Effects of Excitatory Amino Acids on Cerebral Oxygen Consumption and Blood Flow in Rat

This investigation tested the importance of excitatory amino acids' effects on regional cerebral O₂ consumption and the concomitant changes in cerebral blood flow (rCBF) in isoflurane anesthetized rats. In the glutamate or N-methyl-D-aspartate (NMDA) groups, 10^–2 M glutamate or NMDA was topically applied to the right cortex and the left cortex was used as a control. One mg/kg dizocilpine maleate (MK-801), a non-competitive NMDA receptor antagonist, was administered (iv) to the MK-801 group and saline was given to the control group. Cortical rCBF was determined using ¹⁴C-iodoantipyrine and regional O₂ extraction was measured microspectrophotometrically. Cerebral O₂ consumption increased 77% after glutamate (contralateral cortex: 9.0 ± 1.1 ml O₂/min/100 g, glutamate treated cortex: 15.9 ± 3.9), while a 46% increase was observed with the same concentration of NMDA (contralateral cortex: 9.8 ± 2.0, NMDA treated cortex: 14.3 ± 5.5). After MK-801, the O₂ consumption decreased to 37% of the control value (control cortex: 7.0 ± 1.3, MK-801 treated cortex: 2.6 ± 3.9). MK-801 significantly decreased cerebral O₂ extraction from 7.1 ± 1.3 ml O₂/100 ml (control cortex) to 5.3 ± 0.6 (MK-801 treated cortex). However, there was no significant difference in cerebral O₂ extraction between treated and contralateral cortex in either the glutamate or NMDA groups. The increase in O₂ consumption caused by glutamate or NMDA was coupled with increased rCBF. Glutamate increased rCBF from 95 ± 5 ml/min/100 g (contralateral cortex) to 165 ± 31 (treated cortex), while NMDA increased rCBF from 114 ± 12 (contralateral cortex) to 178 ± 60 (treated cortex). MK-801 decreased O₂ consumption with a lesser decrease of rCBF. The rCBF was 48 ± 9 in the MK-801 treated cortex and 99 ± 22 in the control cortex. Some substances produced by the activation of NMDA receptors may be related to the coupling of cerebral metabolism and blood flow, since after blockade of NMDA receptors with MK-801, this relationship is uncoupled. These findings suggest that glutamatergic processes have a major effect on cerebral O₂ consumption and that this is at least partly due to NMDA receptors.     

Effect of breast self-examination techniques on the risk of death from breast cancer

OBJECTIVE: To measure the effect of breast self-examination (BSE) technique and frequency on the risk of death from breast cancer. DESIGN: Case-control study nested within the Canadian National Breast Screening Study (NBSS). SETTING: The Canadian NBSS, a multicentre randomized controlled trial of screening for breast cancer in Canadian women. SUBJECTS: The case subjects were 163 women who had died from breast cancer and 57 women with distant metastases. Ten control subjects matched by 5-year age group, screening centre, year of enrolment and random allocation group were randomly selected for each case subject. EXPOSURE MEASURES: Self-reported BSE frequency before enrolment in the NBSS, annual self-reports of BSE frequency during the program and annual objective assessments of BSE technique. OUTCOME MEASURES: Odds ratios (ORs) associated with BSE practice were estimated by conditional multiple logistic regression modelling, which permitted control of covariates. RESULTS: Relative to women who, when assessed 2 years before diagnosis, examined their breasts visually, used their finger pads for palpation and examined with their 3 middle fingers, the OR for death from breast cancer or distant metastatic disease for women who omitted 1, 2 or 3 of these components was 2.20 (95% confidence interval [CI] 1.30 to 3.71, p = 0.003). The OR for women who omitted 1 of the 3 components was 1.82 (95% CI 1.00 to 3.29, p = 0.05), for those who omitted 2 of the 3 components, 2.84 (95% CI 1.44 to 5.59, p = 0.003), and for those who omitted all 3 components, 2.95 (95% CI 1.19 to 7.30, p = 0.02). The results remained unchanged after adjustment for potential confounders. CONCLUSION: The results, obtained with the use of prospectively collected data, suggest that the performance of specific BSE components may reduce the risk of death from breast cancer.     

Sex determination in Actinidia. 1. Sex-linked markers and progeny sex ratio in diploid A. chinensis

 First results from two strategies aimed at elucidating the genetics of sex in the dioecious genus Actinidia Lindl. (Actinidiaceae) support the hypothesis that sex-determining genes are localized in a pair of chromosomes which, although cytologically indistinguishable, function like an XX/XY system with male heterogamety. A. chinensis Planch., a close relative of the kiwifruit [A. deliciosa (A. Chev.) CF Liang et AR Ferguson], has diploid and tetraploid races. Bulk segregant analysis to find sex-linked markers revealed two markers whose inheritance patterns in three diploid families showed X and Y linkage and indicated that the male is the heterogametic sex. Some recombination between the markers and the sex-determining loci was also demonstrated. Sex ratios in 12 progenies from controlled crosses varied around 1:1, as expected for an XX/XY system. Received: 20 December 1995 / Revision accepted: 24 April 1997     

The carotenoids of eggs of wild and farmed Atlantic salmon, and their changes during development to the start of feeding

The only carotenoid detected in newly fertilized eggs of wild Atlantic salmon, Salmo salar, from western Scotland was astaxanthin at a concentration [μg carotenoid g^?1 wet wt of eggs, mean ±S.D. (number of parental females)] of 6.2±1.2(7) in 1982, 6.4±1.8(20) in 1983, and 7.6 ± 13(6) in 1984. In eggs of farmed Atlantic salmon the only carotenoid detected was canthaxanthin at concentrations which varied significantly between farms depending on the level of synthetic canthaxanthin in the broodstock diet. Thus on two farms using feed with 50 μgg^?1, the levels were 11.8 ± 3.4(7) and 12.3 ± 2.9(6), while on two farms using 75μgg^?1 the levels were 18.7 ± 5.0(9) and 21.2 ± 2.7(21). The levels in eggs of one-seawinter fish (grilse) did not differ from those of two-seawinter fish reared on the same farm and diet. During development from newly fertilized egg to fry at the end of yolk-sac absorption, the quantity of carotenoid present per individual decreased, presumably as a result of metabolism. Despite large differences in quantity present, the quantity so metabolized was fairly constant at 2–4 μg carotenoid g^?1 original egg weight for eggs from two-seawinter farmed and wild salmon, except that in eggs from farmed grilse it was 7 μg g^?1. In fry from wild eggs, 99.14% of the remaining carotenoid was present in the integument (skin and fins) as astaxanthin, astaxanthin monoester and astaxanthin diester. In fry from farmed salmon eggs, 47 ± 8% of the carotenoid present was found in the unused yolk oil droplets and in the liver, and 37 ± 6% was found in the integument as canthaxanthin and an unidentified metabolite of canthaxanthin. These findings explain visible colour differences between fry from wild parents and fry from canthaxanthin-fed farmed parents, particularly in the fins, liver and residual oil droplets. The canthaxanthin metabolite was also found, together with canthaxanthin, in the skin of farmed adults fed canthaxanthin. Preliminary tests showed it to be unchanged by saponification but reduced by sodium borohydride. For eggs from the three farms incubated under the same conditions in the same season, percentage mortality both to the eyed stage and between hatching and first feeding varied significantly between farms, but percentage mortality between the eyed stage and hatching did not do so. Results combined from two seasons for eggs from three farms and one wild source showed that egg mortality between fertilization and the eyed stage was not significantly different between wild and farmed salmon, but mortality between the eyed stage and hatching, and between hatching and first feeding, were both significantly higher in farmed salmon than in wild salmon. Such differences could not be explained simply by the large differences in egg carotenoid content, but were almost certainly due to factors such as broodstock nutrition, broodstock management, and stripping and fertilization procedures.     

Differences in larval feeding behavior correlate with altered developmental strategies in two parasitic wasps: implications for the size-fitness hypothesis

Parasitoid wasps have long been favored organisms for fundamental studies on reproductive strategies and life-history evolution. Progeny allocation models designed with parasitoids in mind assume that offspring develop by consuming most or all of the resources available from a single host, and that size is the most important factor affecting offspring fitness. Many parasitoids exhibit host usage patterns consistent with these assumptions, but our recent observations suggested that endoparasitic wasps in the family Braconidae often do not. To investigate how differences in host usage patterns might affect developmental strategies, we compared two related braconids with contrasting host usage patterns. Apanteles carpatus consumed virtually all host tissues during immature development, whereas Microplitis demolitor fed exclusively on host hemolymph and consumed a relatively small proportion of available host resources. Development time of M. demolitor was unaffected by host size, whereas development time of A. carpatus was much longer in small hosts than in large hosts. On the other hand, offspring size in M. demolitor correlated strongly with host size, but it correlated only weakly with host size in A. carpatus . Our results collectively suggest that selection has favored rapid development at the potential cost of reduced size in M. demolitor , and increased size at the potential cost of increased development time in A. carpatus . Tissue feeding appears to be more prevalent among parasitoids overall, but hemolymph feeding is the predominant pattern of host usage in several subfamilies of endoparasitic braconids. We argue that the relative importance of offspring size and development time will be influenced by host ecology and the effects of selected traits on parasitoid survival.     

Soil community composition drives aboveground plant–herbivore–parasitoid interactions

Soil organisms can influence higher trophic level aboveground organisms, but only very few studies have considered such effects. We manipulated soil community composition of model grassland ecosystems by introducing nematode communities, microorganisms, neither or both groups. Above ground, aphids ( Rhopalosiphum padi ) and parasitoids ( Aphidius colemani ) were introduced, and we measured individual performance and population dynamics of plants, aphids and parasitoids. In microcosms with nematode inoculations either with or without microorganism inoculation, aphids offspring production was significantly reduced by 31%. Aphid populations on both host plants Agrostis capillaris and Anthoxanthum odoratum were lowest in microcosms with combined nematode and microorganism inoculations. Opposite results were found for parasitoids. While the number of emerged parasitoids did not differ between treatments, parasitoid mortality and the proportion of males were significantly lower in microcosms with nematode and microorganism inoculations. Parasitized aphids were significantly larger in microcosms with nematodes inoculated. Plant biomass did not differ, but in the preferred host plant A. odoratum , foliar phenolic content was reduced in the presence of nematodes, and also the concentration of amino acids in the phloem. This study shows that the composition of the soil community matters for aboveground multitrophic interactions.     

Comparative phylogeographies of six species of hinged terrapins (Pelusios spp.) reveal discordant patterns and unexpected differentiation in the P. castaneus/P. chapini complex and P. rhodesianus

Using up to 2117 bp of mitochondrial DNA and up to 2012 bp of nuclear DNA, we analysed phylogeographic differentiation of six widely distributed species of African hinged terrapins (Pelusios spp.) representing different habitat types. Two taxa each live in savannahs or in forests and mesic savannahs, respectively, and the remaining two species occur in intermediate habitats. The species living in forests and mesic savannahs do not enter dry savannahs, whereas the savannah species may occur in dry and wet savannahs and even in semi‐arid steppe regions. We found no obvious correlation between habitat type and phylogeographic pattern: one savannah species (P. rhodesianus) shows phylogeographic structure, i.e. pronounced genetic differences among geographically distinct populations, and the other (P. nanus) not. One species inhabiting forests and mesic savannahs (P. carinatus) has phylogeographic structure, the other (P. gabonensis) not. The same pattern is true for the two ecologically intermediate species, with phylogeographic structure present in P. castaneus and absent in P. chapini. Nuclear evidence suggests that the latter two taxa with abutting and partially overlapping ranges are distinct, while mtDNA is only weakly differentiated. Pelusios castaneus shows pronounced phylogeographic structure, which could reflect Pleistocene range interruptions correlated with the fluctuating forest cover in West and Central Africa. Our results do not support the recognition of an extinct subspecies of P. castaneus for the Seychelles. Pelusios carinatus contains two well supported clades, which are separated by the Congo River. This species is closely related to P. rhodesianus, a taxon consisting of two deeply divergent mitochondrial clades. One of these clades is paraphyletic with respect to P. carinatus, but the two clades of P. rhodesianus are not differentiated in the studied nuclear markers and, again, paraphyletic with respect to P. carinatus. Using mtDNA sequences from the type material of P. rhodesianus, we were able to allocate this name to one of the two clades. However, owing to the confusing relationships of P. rhodesianus and P. carinatus, we refrain from taxonomic decisions.