The regulation of activity in populations of the terrestrial slugLimax maximus (Gastropoda; Limacidae)

The activity of the slug Limax maximus was studied in relation to weather. Three hundred-and-fifty-eight hourly observations of activity and weather were made on 21 nights from May until October, 1976. Factors causally important to molluscan activity were included in a step-down correlation-regression analysis of daily and seasonal behavior. The analysis was also performed using weather data from the previous hourly observation. Models using lag-weather did not explain as much variability as did concurrent weather. The regression models explained about 73% to 87% of the observed variation in activity. The most important factors included in the regression models were time of day (circadian rhythm), light intensity, changes in light intensity and surface temperature. Shelter temperature, temperature gradients, length of the night, and time of sunset were also included in some models. Age and hydration were shown to be key factors in other experiments. A model incorporating weather thresholds estimated from field data explained 83.06% of the variability in the activity of L. maximus over the season. The values predicted from the model did not differ significantly from those actually observed in the field (Kolmogorov-Smirnov test, p>0.50).     

Analysis of associative learning in the terrestrial mollusc Limax maximus. II. Appetitive learning

Summary The odor and taste processing systems of the terrestrial mollusc Limax maximus have been shown capable of a number of complex computations. Most of the complex higher-order features of Limax learning have been demonstrated using differential aversive conditioning. The present experiments probe the appetitive learning ability of Limax. In the first experiment a differential appetitive classical conditioning procedure was used. An aversive CS⁺ odor was paired with an attractive taste while a CS^– odor was explicitly unpaired with the attractive taste. This appetitive conditioning procedure dramatically increased the preference for the CS⁺ odor. Further experiments determined the time course of acquisition, the effect of an extinction procedure and long-term retention of the appetitive conditioning. Now that Limax has been shown capable of appetitive conditioning, the neural network simulation of Limax learning, called LIMAX, can be examined for its ability to display appetitive conditioning.Abbreviations AA amyl acetate - CS conditioned stimulus - ISI interstimulus interval - ITI intertrial interval - MCH methylcyclohexanol - US unconditioned stimulus     

Feeding and arginine deficient diets differentially alter free amino acid concentrations of hindlimb muscle in young rats

Summary The objective of these experiments was to examine short- and long-term (7 d) effects of arginine-deficient diets on free amino acid concentrations in hindlimb muscle of rats. In rats fed the control diet containing arginine (+Arg), muscle alanine and methionine concentrations were higher 1 and 2h after feeding compared to food-deprived rats, whereas branched-chain amino acids, arginine and asparagine concentrations were lower postprandially. In Experiment 1, rats were fed an arginine-deficient (–Arg) diet with glutamate (+Glu) substituted for arginine; alanine (+Ala), ornithine (+Orn) or citrulline (+Cit) were substituted for arginine in Experiment 2. In Experiment 1, arginine concentrations decreased in blood but not in muscle. This contrasts with rats fed –Arg/+Ala or –Arg/+Orn diets which had muscle arginine concentrations less than half the concentrations in controls or in rats fed the –Arg/+Cit diet. Muscle essential amino acids in Experiment 2 did not differ by diet, but muscle branched-chain amino acids were elevated relative to controls in the rats fed –Arg/+Ala or –Arg/+Orn diets; however, rats fed the –Arg/+Cit diet had levels similar to the controls. Also, muscle branched-chain amino acids were correlated with glutamine concentrations in both blood and muscle. The measurements in the post-meal period suggest that muscle amino acid concentrations may more closely reflect dietary amino acid patterns than do blood amino concentrations.Abbreviations BCAA branched-chain amino acids - BCKADH branched-chain ketoacid dehydrogenase - EAA essential amino acids - LNAA large neutral amino acids - NEAA nonessential amino acids - PDV portal-drained viscera - SELSM standard error of least squares means - SSA 5-sulfosalicylic acid - TAA total amino acids Mention of a trade name, proprietary product or specific equipment does not constitute a guarantee by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable.     

Non-essential amino acid sources in crystalline amino acid diets for trout (Oncorhynchus mykiss)

A study was conducted over a 84-day period to evaluate glycine, L-glutamic acid and L-glutamine as sources of non-essential amino acids (NEAA) in dietary 'protein' consisting of crystalline amino acids only. The study was performed with a total of 1200 rainbow trout fingerlings ( Oncorhynchus mykiss ) of 48 g mean body mass. The addition of non-essential amino acids (NEAA) to essential amino acids (EAA) evidently improved growth and feed efficiency: glutamine was superior to glycine and glycine superior to glutamic acid. However, the best results in growth were obtained by adding a mixture of all three NEAA. The improvement of trout performance by glutamine may hypothetically be traced back to a better amino acid absorption capacity by a less acidic intestinal milieu. In consequence, the optimal EAA to NEAA ratio may have to be redefined.     

The amino acid nutrition of respiration deficient and respiration competentSaccharomyces

Respiration deficient variants and normal, respiration competent strains ofSaccharomyces require an exogenous supply of arginine, glutamic acid, leucine, lysine and valine to attain optimal growth. The growth of variant cells, however, is stimulated by these compounds to a far greater proportionate extent than that of normal cells. The petite condition, therefore, exaggerates the limitations in amino acid biosyntheses existent in normal yeasts but does not create new ones. The relative respiratory limitations characteristic of petite and normal cells during growth will account for the qualitative and quantitative aspects of their amino acid requirements.     

Different diets and amino acid supplementation do not affect the voluntary consumption of ethanol by rats

The effects of four different diets (control diet: 19.5% protein, 60.5% carbohydrate, 10% fat; diet I: 65% protein, 10% carbohydrate, 10% fat; diet II: 5% protein, 76% carbohydrate, 10% fat; diet III: 20% protein, 69% carbohydrate, 1% fat; diet IV: 69% protein, 15% carbohydrate, 1% fat) and supplementation with 3 amino acids (tryptophan: 150 mg/kg/d; arginine: 400 mg/kg/d; taurine: 380 mg/kg/d) on the voluntary consumption of ethanol were investigated in rats using the 2 bottle method. First, rats received the control diet and diets I, II, III and IV for 20 days with a choice of ethanol for the last 6 days only. Ethanol consumption was similar in all dietary groups. Second, rats received the control diet for 8 days followed by diets I, II and IV for another 8 days. Ethanol was offered throughout both periods. The switch to the special diets did not affect ethanol consumption. Third, rats received a control diet with arginine, tryptophan or taurine added to the drinking fluids for 16 days with a choice of ethanol for the last 5 days; thereafter supplementation stopped but the ethanol choice remained. No difference in the voluntary intake of ethanol was noted but ethanol consumption fell after cessation of arginine supplementation. In conclusion, diets differing greatly in their composition or supplementation with these 3 amino acids did not affect the voluntary choice of ethanol by rats in a significant manner.     

Modification of cardiac activity in response to dehydration in the terrestrial slug, Limax maximus

The level of body hydration in the terrestrial slug Limax maximus modifies several aspects of behavior such as pneumostome activity, feeding responsiveness, huddling, and contact-rehydration. The relationship between water balance and pneumostome activity and respiratory function suggested that cardiac activity might also be affected. To pursue this possibility, intact slugs and isolated heart-central nervous system (CNS) preparations were used to investigate cardiac responses to the increase in hemolymph osmolality which occurs during dehydration. In intact animals, heart rate increased in response to progressive air-dehydration and to increases in hemolymph osmolality resulting from injections of hyperosmotic solutions of mannitol or NaCl. In isolated preparations, the heart or CNS were separately exposed to hyperosmotic saline. Exposure of the heart alone to hyperosmotic saline resulted in decreased heart rate while exposure of only the CNS resulted in an increase in heart rate. These observations suggest that the increase in heart rate that is observed in intact air-dehydrated slugs is primarily mediated by the CNS.     

Escherichia coli mutants deficient in the aspartate and aromatic amino acid aminotransferases.

Two new mutations are described which, together, eliminate essentially all the aminotransferase activity required for de novo biosynthesis of tyrosine, phenylalanine, and aspartic acid in a K-12 strain of Escherichia coli. One mutation, designated tyrB, lies at about 80 min on the E. coli map and inactivates the "tyrosine-repressible" tyrosine/phenylalanine aminotransferase. The second mutation, aspC, maps at about 20 min and inactivates a nonrespressible aspartate aminotransferase that also has activity on the aromatic amino acids. In ilvE- strains, which lack the branched-chain amino acid aminotransferase, the presence of either the tyrosine-repressible aminotransferase or the aspartate aminotransferase is sufficient for growth in the absence of exogenous tyrosine, phenylalanine, or aspartate; the tyrosine-repressible enzyme is also active in leucine biosynthesis. The ilvE gene product alone can reverse a phenylalanine requirement. Biochemical studies on extracts of strains carrying combinations of these aminotransferase mutations confirm the existence of two distinct enzymes with overlapping specificities for the alpha-keto acid analogues of tyrosine, phenylalanine, and aspartate. These enzymes can be distinguished by electrophoretic mobilities, by kinetic parameters using various substrates, and by a difference in tyrosine repressibility. In extracts of an ilvE- tyrB- aspC- triple mutant, no aminotransferase activity for the alpha-keto acids of tyrosine, phenylalanine, or aspartate could be detected.     

The amino acid sequence of elephant (Elephas maximus) myoglobin and the phylogeny of Proboscidea

The complete amino acid sequence of skeletal myoglobin from the Asian elephant (Elephas maximus) is reported. The functional significance of variations seen when this sequence is compared with that of sperm whale myoglobin is explored in the light of the crystallographic model available for the latter molecule. The phylogenetic implications of the elephant myoglobin amino acid sequence are evaluated by using the maximum parsimony technique. A similar analysis is also presented which incorporates all of the proteins sequenced from the elephant. These results are discussed with respect to current views on proboscidean phylogeny.     

Proteomic analyses of retina of excitatory amino acid carrier 1 deficient mice

Background  

Excitatory amino acid carrier 1 (EAAC1) is a glutamate transporter found in neuronal tissues and is extensively expressed in the retina. EAAC1 plays a role in a variety of neural functions, but its biological functions in the retina has not been fully determined. The purpose of this study was to identify proteins regulated by EAAC1 in the retina of mice. To accomplish this, we used a proteomics-based approach to identify proteins that are up- or down-regulated in EAAC1-deficient (EAAC1^-/-) mice.     

Modulation of amino acid metabolism in transformed tobacco plants deficient in Fd-GOGAT

Tobacco (Nicotiana tabacum) plants expressing a partial ferredoxin-dependent glutamine-2-oxoglutarate aminotransferase (Fd-GOGAT) cDNA in the antisense orientation under the control of the 35S promoter, were used to study the metabolism of amino acids, 2-oxoglutarate and ammonium following the transition from CO₂ enrichment (where photorespiration is inhibited) to air (where photorespiration is a major process of ammonium production in leaves). The leaves of the lowest Fd-GOGAT expressors accumulated more foliar glutamine (Gln) and α-ketoglutarate (α-KG) than the untransformed controls in both growth conditions. Photorespiration-dependent increases in foliar ammonium, glutamine, α-KG and total amino acids were proportional to the decreases in foliar Fd-GOGAT activity. No change in endoprotease activity was observed following transfer to air in the Fd-GOGAT transformants or the untransformed controls which has similar activities over a broad range of pH values. We conclude that several pathways of amino acid biosynthesis are modified when NH₃ ⁺ and Gln accumulate in leaves. This revised version was published online in June 2006 with corrections to the Cover Date.