Impulse pattern generation in a crayfish abdominal postural motoneuron

Journal of Comparative Physiology A - It is concluded that burst formation is endogenous to the motoneuron andnot strongly dependent on patterned presynaptic input.     

Nucleotide sequences of HS-α satellite DNA from kangaroo rat dipodomys ordii and characterization of similar sequences in other rodents

The most common repeated nucleotide sequences of the highly repetitive satellite HS-α fraction from kangaroo rat Dipodomys ordii was determined using ribosubstitution methods. This sequence was α nucleotides long and represented about 25% of the total HS-α satellite DNA, while the remaining DNA was composed of sequence variants related to the most common sequence. The sequences of the commonest of these variants are reported. Furthermore, the most common repeated sequence was identical to that reported for the α satellite of guinea pig Cavia porcellus. The α satellites of guinea pig, Cavia porcellus, pocket gopher, Thomomys bottae and antelope ground squirrel, Ammospermophilus leucurus, are shown to have sequences in common with the kangaroo rat. This implies that the simplest repeated sequences of mammalian satellite DNAs may persist over much longer evolutionary times than previously thought.Attempts to explain the very rapid quantitative changes in satellites whose sequence is strongly conserved have led us to consider that they might have a role in sympatric speciation. Among the novel features of the model presented is that fluctuations in satellites could be due to “speciation genes.” Such genes would confer a strong selective advantage in certain situations, and could explain the many puzzling instances in which large numbers of new related species have appeared over a short evolutionary span.     

Carrier-mediated Uptake of Arginine and Urea by Volvox carteri f. nagariensis

Volvox carteri f. nagariensis takes up arginine via a high affinity, highly specific carrier, whereas carriers for neutral and acidic amino acids cannot be detected (even in nitrogen-starved cultures). Exogenous arginine is accumulated against a steep concentration gradient and is incorporated into protein with high efficiency, but it is not catabolized to any significant extent and will not serve as a nitrogen source adequate to support growth. Urea is also taken up by a saturable carrier, but several lines of evidence indicate that the arginine and urea carriers are distinct and different. Preexposure to arginine suppresses arginine uptake while stimulating urea uptake. The K_i values observed for reciprocal, competitive inhibition of uptake by arginine and urea are orders of magnitude different from the respective K_m values for uptake. The two uptake systems show entirely different patterns of sensitivity to inhibition by structural analogs. Finally, the V_max values for arginine and urea uptake fluctuate independently (but in a regular pattern) during the asexual life cycle. The fluctuations of urea uptake activity are of considerable magnitude and appear to be linked to key phases of the developmental program.     

Combination v. sequential therapy with melphalan, 5-fluorouracil and methotrexate for advanced ovarian cancer.

The results of a national clinical trial to compare combination and sequential chemotherapy for stage III or IV ovarian cancer are reported. Of the 253 patients from 16 centres across Canada who were admitted to the trial 13 were excluded from the analysis. All the patients were observed for 2 to 5 years from entry into the trial. There were no differences in response to therapy or in survival between the patients treated with melphalan followed by 5-fluorouracil and then by methotrexate in high dosage and the patients treated with the same agents in combination. Patients with minimal residual disease after resection of stage III ovarian cancer had a good prognosis. Other favourable prognostic factors were age (less than 55 years), performance status (90% or 100% on the Karnofsky scale) and histologic grade of the tumour.     

The life history and host specificity of theEchium borer,Phytoecia coerulescens [Col.: Cerambycidae]

The cerambycid stem borerPhytoecia coerulescens (Scopoli) is a possible biological control agent for the weedEchium plantagineum L. in Australia. The adult beetle oviposits at the base of stems ofEchium spp. and a few otherBoraginaceae. The larva damages the flower stem by boring both upwards and downwards and eventually, at the end of the season, girdling the stem at its base. It overwinters in the rootstock of its host plant. It does not attack plants of agricultural importance in the field and host restriction to a small group of boraginaceous plants was confirmed in the laboratory, withEchium spp. as principal hosts. It is therefore considered thatP. coerulescens is a safe agent to introduce into Australia for the control ofE. plantagineum.     

Antimetabolic activities of 2-fluoro-L-histidine.

2-Fluoro-L-Histidine inhibits protein synthesis in various cell cultures, as measured by ³H-leucine incorporation. This histidine analog also inhibits the cytopathogenicity of a number of RNA and DNA viruses in primary and continuous cell cultures; it blocks the transformation of normal mouse (MO) cells by murine sarcoma virus, and partially suppresses the release of murine leukemia virus by a continuously infected mouse cell line (JLSV5). In human skin fibroblasts, it reduces the interferon-inducing capacity of poly(I)·poly(C). Inhibition of cell protein synthesis may be the common cause of the various effects. 4-Fluoro-L-histidine is essentially inert in all of the test systems examined.     

Comparison of fatty acid oxidation in mitochondria and peroxisomes from rat liver

Oxygen uptake with succinate or palmitoyl-CoA as substrates can be measured in rat liver mitochondria that have been isolated by sucrose density gradient centrifugation providing the fractions are diluted with a 30 mM phosphate buffer rather than with an isotonic medium. Separate assay procedures were used to measure peroxisomal and mitochondrial β-oxidation of palmitoyl-CoA in the fractions of a sucrose gradient used to separate these organelles. A preliminary estimate of the ratio of palmitoyl-CoA oxidation by the mitochondrial fraction relative to the surviving peroxisomes from livers of male rats was 3.2.     

Rates of synthesis and source of glycolate in intact chloroplasts

Summary Intact chloroplasts capable of high rates of CO₂ assimilation completely oxidized 3-phosphoglycerate and dihydroxyacetone phosphate to glycolate when CO₂ concentrations were low. Bicarbonate was converted first into products of the Calvin cycle and then into glycolate. Under high oxygen and at high pH values CO₂ fixation and glycolate formation ceased before bicarbonate was exhausted. This is interpreted as the consequence of a depletion of ribulose diphosphate (RuDP) at the oxygen compensation point, where oxygen consumption by glycolate formation and oxygen evolution by phosphoglycerate reduction balance each other. Depletion of RuDP by glycolate formation is proposed to play a role in the Warburg effect. The maximum rate of glycolate synthesis observed with dihydroxyacetone phosphate as substrate was 35 mol mg^-1 chlorophyll h^-1 at 20°C. This may not reflect the maximum capacity of chloroplasts for glycolate synthesis. Dithiothreitol and catalase, which prevent accumulation of oxygen radicals or H₂O₂ during carbon assimilation, increased glycolate formation. H₂O₂ was inhibitory. Other inhibitors of glycolate formation were glyceraldehyde and carbonylcyanide p-trifluoro-methoxphenylhydrazone. From the sensitivity of glycolate synthesis to uncoupling and the ATP requirement of RuDP formation it is concluded that glycolate originated from RuDP. Different induction periods of carbon fixation and glycolyte formation suggested that glycolate synthesis is not only regulated by the ratio of oxygen to CO₂ but also by another factor.