Postmortem Changes in Rat Brain: Studies on Membrane-Bound Enzymes and Receptors

The relationship between the stability of potential neurochemical markers and autolysis time was studied at 4 degrees C and 25 degrees C using postmortem brain samples from two rat strains. In general, qualitatively similar results were obtained with either N/Nih or Sprague-Dawley rats; however, quantitative differences were often observed, particularly in regard to benzodiazepine receptor changes. For every enzyme activity or binding property examined, no significant change was found when brains were kept at 4 degrees C for up to 72 h prior to freezing at -70 degrees C. Na,K-ATPase and low-affinity Ca-ATPase activities were also stable in brains kept at 25 degrees C for up to 72 h. Mg-ATPase activity was reduced in brains kept at 25 degrees C for 24 and 48 h. [3H]Guanidinoethylmercaptosuccinic acid [( 3H]GEMSA) binding to enkephalin convertase in the cytosol was not significantly changed in brains kept at 25 degrees C; however, a small increase was seen for [3H]GEMSA binding to the membrane fraction at 24, but not 48 and 72 h postmortem. [3H]Quinuclidinyl benzilate [( 3H]QNB) binding to muscarinic cholinergic receptors decreased in brains kept at 25 degrees C for 72 h. Opioid receptor binding also decreased in brains kept at 25 degrees C. Using [3H]2-D-alanine-5-D-leucine enkephalin to label delta opioid receptors, a statistically significant decrease in binding was observed as early as 6 h postmortem, and was completely abolished after 72 h at 25 degrees C. In contrast, [3H]naloxone binding was unchanged after 24 h at 25 degrees C, but was decreased after 48 and 72 h.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolism and excretion of acetylchromenes by the migratory grasshopper

The extent of metabolism and excretion of three acetylchromenes (two toxic, one relatively nontoxic) were examined in adult migratory grasshoppers (Melanoplus sanguinipes) following topical administration. Both the total amount excreted (parent plus metabolites) and the proportion of parent compound in the excreta were inversely correlated with contact toxicity. Both toxic and nontoxic acetylchromenes are rapidly absorbed from the cuticle, with maximum excretion of parent and metabolite chromenes from 4 to 8 h posttreatment in each case. Much of the applied compounds (60–80%) apparently remains within the insect, and cannot be recovered by extraction of the insect. Metabolites formed result from simple oxidative and reductive transformations. For all of the compounds tested (including the allatocidin precocene II), the major mode of metabolism results from aliphatic hydroxylation of one of the geminal methyl groups on the chromene. No conjugated metabolites were found in the excreta.     

HISTORICAL VERSUS SELECTIONIST EXPLANATIONS IN EVOLUTIONARY BIOLOGY

Abstract— Evolutionary changes require historical explanations, yet these are limited by the evolutionary processes we entertain and investigate. Using phylogenetic analysis, adaptation and natural selection can be tested as historical claims, but this is appropriate only in those special cases where change follows the scheme of one character-one function, singled out in new environmental circumstances. Systematic treatment of the evolutionary origin of characters (in particular, origin through ecological and developmental flexibility) lies outside the scope of selectionist explanations. Structural hypotheses about regularities in the directions of change, also analyzed phylogenetically, expand the scope of historical explanation to include the origin of characters, yet retain the view of organisms as passive and constrained objects of evolutionary change. Historical biology needs to encompass both the active responses of organisms and the construction by organisms of their own environments. For this to be realized will require changes in the concepts and practices of evolutionary biology, including a re-examination of the Lamarckian theme that the active responses of organisms have evolutionary significance—the rarity of individual-to-individual transmission of "acquired" characters does not disprove the possibility of their frequency increasing in a population.     

Regional mapping panel for human chromosome 17: Application to neurofibromatosis type 1

A somatic cell hybrid mapping panel was constructed to localize cloned DNA sequences to any of 15 potentially different regions of human chromosome 17. Relatively high-resolution mapping is possible for 50% of the chromosome length in which 12 breakpoints are distributed over approximately 45 megabases, with an average spacing estimated at 1 breakpoint every 2-7 megabases. This high-resolution capability includes the pericentromeric region of 17 to which von Recklinghausen neurofibromatosis (NF1) has recently been mapped. Using 20 cloned genes and anonymous probes, we have tested the expected order and location of panel breakpoints and confirmed, refined, or corrected the regional assignment of several cloned genes and anonymous probes. Four markers with varying degrees of linkage to NF1 have been physically localized and ordered by the panel: the loosely linked markers myosin heavy chain 2 (25 cM) to p12----13.105 and nerve growth factor receptor (14 cM) to q21.1----q23; the more closely linked pABL10-41 (D17S71, 5 cM) to p11.2; and the tightly linked pHHH202 (D17S33) to q11.2-q12. Thus, physical mapping of linked markers confirms a pericentromeric location of NF1 and, along with other data, suggests the most likely localization is proximal 17q.     

Influence of Phosphate on the Growth and Nodulation Characteristics of Rhizobium trifolii

The growth and nodulating characteristics of Rhizobium trifolii 6 and 36 differed under different external phosphate conditions. Under growth conditions designed to deplete the internal phosphate content of the rhizobia, strain 6 maintained a generation time of 5 h during the exponential phase over two cycles of growth in phosphate-depleted medium. In contrast, the generation time of strain 36 was extended from 3.5 to 9.8 h over two cycles of phosphate-depleted growth, although the organism eventually achieved the same cell density and cellular phosphate content as that of strain 6 at stationary phase. Phosphate-depleted strain 6 required 0.51 ± 0.08 μM phosphate to commence proliferation, whereas phosphate-depleted strain 36 required 0.89 ± 0.04 μM phosphate under the same conditions. Phosphate-depleted strain 6 maintained viability when exposed to external phosphate concentrations subcritical for growth to occur, whereas phosphate-depleted strain 36 lost viability within 48 h when exposed to medium containing phosphate at concentrations subcritical for growth. Phosphate-depleted strain 36 was inferior to phosphate-depleted strain 6 at nodulating subterranean clover (Trifolium subterraneum L. cv. Mt. Barker) by taking 2 to 4 days longer to develop nodules in phosphatedepleted plant grown medium at pH 5.5. Nodulation by phosphate-depleted strain 36 was accelerated either by including phosphate in the plant growth medium at pH 5.5 or by raising the solution pH of phosphate-depleted plant growth medium to pH 6.5. External phosphate and pH effects were not observed on the nodulating capabilities of phosphate-depleted strain 6 or on luxury phosphate-grown cells of either strain. Phosphatedepleted strains 6 and 36 proliferated to a similar extent on the rhizoplanes even under stringently low external P_i concentrations. The phosphatase activities of both phosphate-depleted strains were significantly (P = 0.05) higher at pH 6.5 than at pH 5.5, and the activity of strain 6 was significantly higher (P = 0.05) than that of strain 36 at pH 5.5 and 5.0.     

Kinetics of Butyrate, Acetate, and Hydrogen Metabolism in a Thermophilic, Anaerobic, Butyrate-Degrading Triculture

Kinetics of butyrate, acetate, and hydrogen metabolism were determined with butyrate-limited, chemostat-grown tricultures of a thermophilic butyrate-utilizing bacterium together with Methanobacterium thermoautotrophicum and the TAM organism, a thermophilic acetate-utilizing methanogenic rod. Kinetic parameters were determined from progress curves fitted to the integrated form of the Michaelis-Menten equation. The apparent half-saturation constants, K_m, for butyrate, acetate, and dissolved hydrogen were 76 μM, 0.4 mM, and 8.5 μM, respectively. Butyrate and hydrogen were metabolized to a concentration of less than 1 μM, whereas acetate uptake usually ceased at a concentration of 25 to 75 μM, indicating a threshold level for acetate uptake. No significant differences in K_m values for butyrate degradation were found between chemostat- and batch-grown tricultures, although the maximum growth rate was somewhat higher in the batch cultures in which the medium was supplemented with yeast extract. Acetate utilization was found to be the rate-limiting reaction for complete degradation of butyrate to methane and carbon dioxide in continuous culture. Increasing the dilution rate resulted in a gradual accumulation of acetate. The results explain the low concentrations of butyrate and hydrogen normally found during anaerobic digestion and the observation that acetate is the first volatile fatty acid to accumulate upon a decrease in retention time or increase in organic loading of a digestor.     

Effect of Bacteriophage on Colonization of Sugarbeet Roots by Fluorescent Pseudomonas spp

The colonization potential of two fluorescent Pseudomonas strains (M11/4, B2/6) that exhibit antifungal activity in vitro was studied on the roots of sugarbeet plants in a clay loam soil. The cell density of the introduced bacteria declined on the root system over a 16-day test period in nonsterile soil. Strain B2/6 declined at a significantly faster rate compared with M11/4. This loss in viability and difference in colonization ability between M11/4 and B2/6 was not observed in sterile soil. Nutrient deprivation induced by indigenous microorganisms was excluded as a key factor involved in the decline of the introduced bacteria on the basis that strains M11/4 and B2/6 retained viability when subjected to nutrient starvation conditions over a 16-day period. Experiments designed to test whether antagonism by indigenous microorganisms was responsible for the decline in the introduced fluorescent Pseudomonas sp. population revealed the presence of large numbers of bacteriophage in the soil capable of lysing strain B2/6. Reconstitution experiments carried out with sugarbeet seedlings inoculated independently with strains M11/4 and B2/6 and grown in sterile soil to which a soil phage filtrate had been added showed a significant decrease in the viability of strain B2/6 relative to M11/4. Phage antagonistic toward strain B2/6 were detected in 43% of soils taken from the major sugarbeet growing regions of Ireland.     

The prickly-pears (Opuntia spp., Cactaceae): A source of human and animal food in semiarid regions

The Cactaceae contain many economically promising species primarily in the genus Opuntia. This genus appears to have its center of genetic diversity in Mexico where it is widely used as fodder, forage, fruit, and a green vegetable. In southwestern United States, the prickly-pears have been considered as both weeds and valuable forage plants. During the frequent, unpredictable droughts, propane torches known as “pear burners” are used to singe the spines off cactus pads so that they can be eaten by livestock. Although spineless varieties of Opuntia can be consumed directly by domestic livestock, they are extremely susceptible to herbivory by wildlife. The Cactaceae possess Crassulacean Acid Metabolism, which can be four- to five-fold more efficient in converting water to dry matter than the most efficient grasses. Some Opuntia strains grow rapidly with fresh-fruit yields of 8,000–12,000 kg/ha/ yr or more and dry-matter vegetative production of 20,000–50,000 kg/ha/yr.