The association between amount of red muscle and mobility in fishes: A statistical evaluation

Synopsis It is commonly accepted that more active fishes have a greater proportion of red muscle in their trunk musculature than do less active fishes. Further, the proportion of red muscle has been used to classify fish species into functional groups reflecting different activity patterns. Nevertheless, existing measures of both red muscle and mobility have several limitations, and the relationship between these parameters has never been evaluated quantitatively. Using data from the literature, we demonstrate a positive, statistical association between the proportion of red muscle in the caudal peduncle of marine fishes and a qualitative measure of mobility (categorization as sedentary vs. mobile based on natural-history accounts). Analyses of the frequency distribution of the proportion of red muscle also provide evidence for two subdistributions. However, this bimodality does not correspond with sedentary vs. mobile or sit-and-wait vs. active search dichotomies.     

Physiological roles of animal succinate thiokinases Specific association of the guanine nucleotide-linked enzyme with haem biosynthesis

The discovery of two distinct succinate thiokinases in mammalian tissues, one (G-STK) specific for GDP/GTP and the other (A-STK) for ADP/ATP, poses the question of their differential metabolic roles. Evidence has suggested that the A-STK functions in the citric acid cycle in the direction of succinyl-CoA breakdown (and ATP formation) whereas one role of the G-STK appears to be the re-cycling of succinate to succinyl-CoA (at the expense of GTP) for the purpose of ketone body activation. A third metabolic participation of succinyl-CoA is in haem biosynthesis. This communication shows that in chemically induced hepatic porphyria, when the demand for succinyl-CoA is increased, it is the level of G-STK only which is elevated, that of A-STK being unaffected. The results implicate G-STK in the provision of succinyl-CoA for haem biosynthesis, a conclusion which is further supported by the observation of a high G-STK/A-STK ratio in bone marrow.     

Comparison of the roles of Ostracods and Cladocerans in regulating community structure and metabolism in freshwater microcosms

Laboratory microcosms were used to compare the effects of the littoral ostracod Cypridopsis vidua and the planktonic cladoceran Daphnia magna on community structure and metabolism. Filter-feeding by cladocerans, both in the presence and absence of ostracods, greatly reduced the abundance of planktonic algae when D. magna reached peak density around day 50; rotifers and euglenids were then limited to flocculent matter on the container bottom. Both net production and community respiration rates decreased as community composition changed. Microcosms containing ostracods as the only microcrustacean showed little reduction in total algal numbers but the otherwise dominant alga, Scenedesmus spp., was replaced by Ankistrodesmus spp. when peak ostracod density was reached around day 100. Rotifers were completely eliminated but euglenids were able to coexist with ostracods. Ostracods impacted community metabolism less than cladocerans, but depressed respiration slightly more than net production.     

Degradation of 4-hydroxyphenylacetate by Xanthobacter 124X

Xanthobacter 124X when grom on 4-hydroxyphenylacetate was able to hydroxylate this compound yielding homogenisate. Ring fission of this latter compound gave maleylacetoacetate which was isomerized to fumarylacetoacetate. The isomerase involved resembled maleylacetoacetate isomerases in Gram-negative bacteria in that glutathione was required for activity. Fumarate and acetoacetate were both detected as products of the hydrolysis of fumarylacetoacetate.     

Dopamine Metabolites in Rat Cisternal Cerebrospinal Fluid: Major Contribution from Extrastriatal Dopamine Neurones

The interpretation of central 3,4-dihydroxyphenylethylamine (dopamine, DA) metabolism, as indicated by determinations in rat cisternal CSF, was investigated using intrastriatal injection of the DA neurotoxin 6-hydroxydopamine (6-OHDA) and intraperitoneal injection of the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4). DA turnover was subsequently determined by measurement of the rate of accumulation of total 3,4-dihydroxyphenylacetic acid and homovanillic acid (DOPAC + HVA) in the CSF after probenecid was given. Two days later the rats were killed, and metabolism of DA and 5-hydroxytryptamine (5-HT) was investigated by determining levels of the amines and their metabolites in brain regions. Although 6-OHDA greatly decreased striatal DA metabolism, this was not paralleled by DA turnover as indicated by CSF, as this fell only moderately and approximately in parallel with results for the brain as a whole. 5-HT metabolism was essentially unaltered. DSP4 considerably depleted noradrenaline and caused smaller decreases of 5-HT metabolism in some regions. However, DA metabolism was not significantly affected, either in brain or CSF, which suggests that noradrenaline neurones make only a small contribution to central DA metabolism. Results as a whole suggest that DOPAC and HVA concentrations in rat cisternal CSF reflect whole brain DA metabolism and derive predominantly from DA neurones in extrastriatal regions of the brain.     

Investigation of Dopamine Content, Synthesis, and Release in the Rabbit Retina In Vitro: I. Effects of Dopamine Precursors, Reserpine, Amphetamine, and l-DOPA Decarboxylase and Monoamine Oxidase Inhibitors

The basal catecholamine content of rabbit retina was determined by liquid chromatography with electrochemical detection (LC-EC) and 3,4-dihydroxyphenylethylamine (dopamine, DA) found to be the major catecholamine. The immediate DA precursor, 3,4-dihydroxyphenylalanine (L-DOPA), and the metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), were also detected at about 2.8% and 17% of DA levels, respectively. When added exogenously, L-tyrosine did not increase the rate of DA synthesis over the basal level. In contrast, exogenous L-DOPA led to a 3.5-fold increase in DA, and to a 20-fold increase in DOPAC content. The monoamine oxidase inhibitors pargyline and (-)-deprenyl differentially affected the degradation of DA, since 100 microM pargyline was apparently more effective than 100 microM (-)-deprenyl. Reserpine and (+/-)-amphetamine each induced a Ca2+-independent decrease of DA stores. The separate actions of reserpine and (+/-)-amphetamine in lowering tissue DA levels were additive, suggesting two separate pools of DA available for release from presynaptic stores. The present study demonstrates that the LC-EC technique may be used to investigate the modulation of the synthesis and release of retinal DA in vitro, without the prior uptake of radiolabelled transmitter.     

Differentiation among populations of Sedum wrightii (Crassulaceae) in response to limited water availability: water relations,CO2 assimilation,growth and survivorship

Summary Sedum wrightii is one of only a few species in the Crassulaceae for which there is evidence for a high degree of variability in the ratio of daytime to nighttime CO₂ assimilation. There are both environmental and genetic components to this variability. S. wrightii grows over a wide altitudinal gradient. The purpose of this study was to compare low, intermediate, and high altitude populations with respect to the degree of CAM expression and the capability to tolerate limited water availability. We utilized clonallyreplicated genotypes of plants from each population in common environment greenhouse experiments. Genetic differences among the populations were found in long-term water use efficiency, in 24 hour CO₂ exchange patterns, in biomass ¹³C values, in carbon allocation, and in water status and ultimately survival during prolonged drought. The differences among the populations appear to be closely related to differences in the native habitats. The low altitude, desert plants had the greatest ability to grow and survive under conditions of limited water availability and appear to have the greatest shift to nighttime CO₂ uptake during periods without water, while the high altitude plants had the poorest performance under these conditions and appear to shut down net carbon uptake when severely water limited.     

Mannitol metabolism in cultured plant cells

Non-structural storage carbohydrates were measured in 9-day-old barley ( Hordeum vulgare L. cv. Brant) primary leaves. Accumulation rates of starch, sucrose and total non-structural carbohydrates (TNC) were approximately linear when measured between 2- and 12-h of light. Progressively higher TNC accumulation rates were observed at higher irradiance levels (i.e., comparing 250, 550 and 1050 ·mol m⁻² s⁻¹). Synthesis of a low-molecular-weight fructan also was enhanced by high irradiances. Low irradiance treatments decreased leaf sucrose levels and there was a corresponding increase in the lag period preceding starch synthesis in the light. Increased starch accumulation rates were usually observed when sucrose concentrations were high. These and other results suggested that cytosolic sucrose concentrations affected starch metabolism in the chloroplast. However, sucrose accumulation rates increased and starch storage decreased when barley seedlings were transferred from 20 to 10°C during the light period. Lowering the night temperature from 20 to 10°C for a single dark period 8-days after planting increased the TNC content of barley primary leaves at the beginning of day nine. In this experiment, TNC accumulation rates of treated and untreated leaves were similar. Changes in the accumulation rate of TNC were usually observed within 2- to 4-h after barley seedlings were exposed to altered environmental conditions. Monitoring rapid changes in leaf carbohydrate levels is a sensitive method for assessing the effects of environmental treatments on photosynthetic metabolism.     

Relationship between probable dominant phosphate compound in soil and phosphorus availability to plants

Summary Surface soil materials from the 0- to 15 cm depth of 12 sites that were suspected to contain high levels of P, as a result of years of repeated applications of either inorganic or organic P fertilizers, were cropped with wheat and alfalfa in the greenhouse for about one year. The total P removed in plant materials provided an estimate of the plant available P in the soils. The probable dominant phosphate compound controlling the release of P in the soil solution during cropping was determined using the GEOCHEM program and an activity diagram. The data show that P availability is partly dependent on the stability of the phosphate compound present, although the relative positions of the points on the activity diagram show no quantitative relationship with either the total plant P uptake or the phosphate buffering capacity of the soils. The positions of the points, however, indicate that with time the formation of more stable P compounds during cropping could be attributed to reactions in the soil as well as to crop removal. The more soluble compounds could have recrystallized or were transformed into compounds of lower solubility. There is also the possibility that the more soluble P compounds were exhausted by crop removal leaving behind the less soluble compounds.     

Effect of Insulin-Induced Hypoglycemia on the Concentrations of Glutamate and Related Amino Acids and Energy Metabolites in the Intact and Decorticated Rat Neostriatum

Abstract The glutamate (Glu) terminals in rat neostriatum were removed by a unilateral frontal decortication. One to two weeks later the effects of insulin-induced hypoglycemia on the steady-state levels of amino acids [Glu, glutamine (Gin), aspartate (Asp), γ-aminobutyric acid (GABA), tau-rine] and energy metabolites (glucose, glycogen, α-ketoglu-tarate, pyruvate, lactate, ATP, ADP, AMP, phosphocre-atine) were examined in the intact and decorticated neostriatum from brains frozen in situ. The changes in the metabolite levels were examined during normoglycemia, hypoglycemia with burst-suppression (BS) EEG, after 5 and 30 min of hypoglycemic coma with isoelectric EEG, and 1 h of recovery following 30 min of isoelectric EEG. In normoglycemia Glu decreased and Gin and glycogen increased significantly on the decorticated side. During the BS period no significant differences in the measured compounds were noted between the two sides. After 5 min of isoelectric EEG Glu, Gin, GABA, and ATP levels were significantly lower and Asp higher on the intact than on the decorticated side. No differences between the two sides were found after 30 min of isoelectric EEG. After 1 h of recovery from 30 min of isoelectric EEG Glu, Gin, and glycogen had not reached their control levels. Glu was significantly lower, and Gin and glycogen higher on the decorticated side. The Asp and GABA levels were not significantly different from control levels. The results indicate that the turnover of Glu is higher in the intact than in decorticated neostriatum during profound hypoglycemia.