Temporal characterization of growth of fathead minnow (Pimephales promelas) larvae during sublethal hydrogen cyanide exposure

Growth of fathead minnow yolk sac larvae was characterized from changes in dry weight and total content and concentrations of RNA, DNA and protein in fish exposed to a sublethal level of HCN (58 micrograms/l) and in age matched controls. Cyanide toxicosis occurred within 24 hr of exposure as evidenced by significant reductions in protein and RNA content and RNA/DNA ratio of larvae. After 96 hr exposure to HCN, larvae exhibited the same growth rate and protein synthetic rate (RNA/DNA) as control fish. HCN toxicosis and recovery is rapid and at least partial tolerance to HCN develops within 96 hr of exposure in larval fathead minnows.     

Pre-exposure affects the olfactory response of Drosophila melanogaster to menthol

A modification of the trap assay (Woodard et al., 1989) was used to evaluate the response of Drosophila melanogaster (Meigen) to food media containing menthol. Dose-response curves for flies to mentholic foods were produced for flies that had been pre-exposed to menthol, during development and adult life, and flies that had not been exposed to menthol before the assay. Mentholic food media were less attractive to Drosophila than plain food medium. Rearing flies on a medium containing menthol reduced their aversion to some concentrations of menthol. The rearing effect was not simply due to lowered general activity levels resulting from developing in a medium containing menthol. There was a threshold concentration of menthol in the rearing medium below which we found no induced behavioural change.     

Contribution of midbody channels to embryogenesis in the mouse

Summary We have examined the persistence of midbody channels during the second, third, and fourth cleavage cycles of the mouse using immunofluorescence to map the distribution of midbody microtubule bundles in intact embryos. Electron microscopy showed these bundles to be a characteristic feature of midbodies throughout the interphase period. In recently-divided embryos at each cleavage stage the number of midbodies was half the number of blastomeres, and declined towards zero as the next cleavage approached. This indicated to us that the only midbodies present in each stage were those which had arisen in the immediately-preceding division. Of those blastomeres which were in mitosis at the time of fixation, less than 4% were connected via a midbody to another blastomere, demonstrating that persistence of midbodies beyond a single cleavage cycle is a rare event. We conclude that midbody channels in our embryos are likely to connect only pairs of sister blastomeres because midbodies do not persist through multiple cleavage cycles. Midbody channels cannot, therefore, be regarded as providing extensive cell coupling in advance of the onset of gap junctional communication.     

Proteins secreted by day-16 to -18 bovine conceptuses extend corpus luteum function in cows

Corpus luteum function, interoestrous interval and spontaneous uterine PGF-2 alpha (PGF) production were evaluated in 9 cyclic Holstein cows (3/group) after intrauterine injections of pooled conceptus secretory proteins, 5 beta-pregnan-3 alpha-ol-20-one, or homologous serum proteins on Days 15.5 through 21 after oestrus. A significant extension of corpus luteum lifespan and interoestrous interval were detected in cows treated with conceptus secretory proteins compared to the other 2 groups. CL lifespan and interoestrous interval were not different (P greater than 0.25) between 5 beta-pregnan-3 alpha-ol-20-one and control groups. Evaluation of spontaneous PGF responses suggested that proteins synthesized and secreted by the bovine conceptus accommodate luteal maintenance during early gestation via an attenuation of endometrial PGF production.     

The stimulation of hepatic gluconeogenesis by acetoacetate precursors. A role for the monocarboxylate translocator

The regulation of the gluconeogenic pathway from the 3-carbon precursors pyruvate, lactate, and alanine was investigated in the isolated perfused rat liver. Using pyruvate (less than 1 mM), lactate, or alanine as the gluconeogenic precursor, infusion of the acetoacetate precursors oleate, acetate, or beta-hydroxybutyrate stimulated the rate of glucose production and, in the case of pyruvate (less than 1 mM), the rate of pyruvate decarboxylation. alpha-Cyanocinnamate, an inhibitor of the monocarboxylate transporter, prevented the stimulation of pyruvate decarboxylation and glucose production due to acetate infusion. With lactate as the gluconeogenic precursor, acetate infusion in the presence of L-carnitine stimulated the rate of gluconeogenesis (100%) and ketogenesis (60%) without altering the tissue acetyl-CoA level usually considered a requisite for the stimulation of gluconeogenesis by fatty acids. Hence, our studies suggest that gluconeogenesis from pyruvate or other substrates which are converted to pyruvate prior to glucose synthesis may be limited or controlled by the rate of entry of pyruvate into the mitochondrial compartment on the monocarboxylate translocator.     

Inhibition of uterine prostaglandin-F2 alpha production by bovine conceptus secretory proteins

The effect of bovine conceptus secretory proteins (CSP) on uterine prostaglandin (PG)-F2 alpha production was evaluated in dairy cattle following injection of estradiol-17 beta. Intrauterine injections of dialyzed serum proteins (Control, n = 5) or CSP (n = 5) were administered from days 15 through 18 post-estrus. Following intrauterine treatments on day 18, all cows were injected with E2 (3 mg) to stimulate uterine PGF2 alpha production. Plasma concentrations of progesterone (P4) and 15-keto-13,14-dihydro-PGF2 alpha (PGFM) were determined by RIA. The PGFM responses following E2 challenge were decreased (p less than 0.01) for cows receiving CSP versus serum proteins into the uterine lumen. Individual PGFM, P4 and cycle length responses are discussed. Data suggest that proteins secreted by the bovine conceptus suppress uterine PGF2 alpha production during pregnancy recognition in the cow.     

Diatom constraints on the position of the Antarctic Polar Front in the middle part of the Pliocene

The relative percentages of diatom taxa in 5 deep-sea cores (DSDP 266, ODP 699A, ODP 747A, ODP 751 A, and Eltanin Core 50-28) from the Southern Ocean are determined for an interval centered on 3.1 to 2.9 Ma in the middle part of the Pliocene. This climatically warm interval, which is being studied by the PRISM Project of the U.S. Geological Survey, coincides with a proposed interval of major deglaciation of East Antarctica. The maximum southerly position of the Antarctic Polar Front between 3.1 and 3.0 Ma is inferred from these diatom studies, the presence of calcareous nannofossils in the sediments, and sedimentologic and micropaleontologic information from the literature. It is suggested that the Antarctic Polar Front may have migrated by as much as 6 ° of latitude further to the south in the southeastern Atlantic and Indian Oceans during this Pliocene warm interval but probably lay close to its present day position in the southwest Atlantic and Drake Passage. Summer sea surface temperatures are inferred to have been no more than 3 °–4 °C warmer than present at latitudes between 55 ° and 60 °S.     

Localization of sequences regulating ancestral and acquired sites of esterase6 activity in Drosophila melanogaster

We have broadly defined the DNA regions regulating esterase6 activity in several life stages and tissue types of D. melanogaster using P- element-mediated transformation of constructs that contain the esterase6 coding region and deletions or substitutions in 5' or 3' flanking DNA. Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and the primary sequences regulating its activity lie between -171 and -25 bp relative to the translation initiation site: deletion of these sequences decrease activity approximately 20-fold. Hemolymph activity is also modulated by four other DNA regions, three of which lie 5' and one of which lies 3' of the coding region. Of these, two have positive and two have negative effects, each of approximately twofold. Esterase6 activity is present also in two male reproductive tract tissues; the ejaculatory bulb, which is another ancestral activity site, and the ejaculatory duct, which is a recently acquired site within the melanogaster species subgroup. Activities in these tissues are at least in part independently regulated: activity in the ejaculatory bulb is conferred by sequences between -273 and -172 bp (threefold decrease when deleted), while activity in the ejaculatory duct is conferred by more distal sequences between -844 and -614 bp (fourfold decrease when deleted). The reproductive tract activity is further modulated by two additional DNA regions, one in 5' DNA (-613 to -284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to +2731 bp; threefold decrease when deleted) that probably overlaps the adjacent esteraseP gene. Collating these data with previous studies suggests that expression of EST6 in the ancestral sites is mainly regulated by conserved proximal sequences while more variable distal sequences regulate expression in the acquired ejaculatory duct site.