Effects of essential amino acid deficiency: down‐regulation of KCC2 and the GABAA receptor; disinhibition in the anterior piriform cortex

The anterior piriform cortex (APC) is activated by, and is the brain area most sensitive to, essential (indispensable) amino acid (IAA) deficiency. The APC is required for the rapid (20 min) behavioral rejection of IAA deficient diets and increased foraging, both crucial adaptive functions supporting IAA homeostasis in omnivores. The biochemical mechanisms signaling IAA deficiency in the APC block initiation of translation in protein synthesis via uncharged tRNA and the general amino acid control kinase, general control nonderepressing kinase 2. Yet, how inhibition of protein synthesis activates the APC is unknown. The neuronal K⁺Cl^? cotransporter, neural potassium chloride co‐transporter (KCC2), and GABA_A receptors are essential inhibitory elements in the APC with short plasmalemmal half‐lives that maintain control in this highly excitable circuitry. After a single IAA deficient meal both proteins were reduced (vs. basal diet controls) in western blots of APC (but not neocortex or cerebellum) and in immunohistochemistry of APC. Furthermore, electrophysiological analyses support loss of inhibitory elements such as the GABA_A receptor in this model. As the crucial inhibitory function of the GABA_A receptor depends on KCC2 and the Cl^? transmembrane gradient it establishes, these results suggest that loss of such inhibitory elements contributes to disinhibition of the APC in IAA deficiency.

     

Postnatal protein deprivation in rhesus monkeys

We studied the growth of 97 rhesus monkeys (M. mulatta) that from birth until 120 days of age were fed a diet containing 13.4%, 6.7%, 3.35% protein or a commercial simulated human-milk formula (SMA) affording 9% protein. After 120 days, all animals were fed SMA. Females fed the diet lowest in protein, but not the other diets, were moderately affected, gaining less weight than their well-fed counterparts did, but they recovered their deficit during the repletion period, so that at 240 days no group differences remained. Males fed the two lowest-protein diets were severely and profoundly affected, in keeping with the depth of their protein deficiency. Moreover, unlike the females, they recovered none of their weight deficit during the repletion period. Food intake during deprivation was lower in the animals eating the low-protein diets. During SMA repletion, intakes followed no simple rule, but they did not converge. Except for the males fed the 3.35% protein diet, relative food intake (ml formula/kg body weight) did not differ substantially between diets or sexes at any time during the deprivation and diminished as the animals got older. Those males' relative intakes did not decline. During repletion, the SMA females ate the most in proportion to weight and the 13.4% group the least. The lowest-protein males, in contrast, ate the most in proportion to their weight during both deprivation and repletion. Males fed the lowest-protein diet gained little for what they ate; those fed the highest-protein diet gained much. Females were more efficient than males were when eating the low-protein diet and less efficient when eating the high-protein diet. When fed SMA during repletion, males' food efficiencies (grams gained/liter of diet) were nearly equal; females still differed: the SMA group was the least efficient and the low-protein group most efficient. Its counterpart, protein efficiency, was greatest (during deprivation) for females eating the low-protein diet and least (among females) for those eating the high-protein diet. Males were least protein efficient if eating the low-protein diet. Evidently, a 4 month bout of protein deprivation had prolonged effects on the amount of food the animals needed to produce a given gain in weight.     

Contribution of Indole-3-Acetic Acid Production to the Epiphytic Fitness of Erwinia herbicola

Erwinia herbicola 299R produces large quantities of indole-3-acetic acid (IAA) in culture media supplemented with l-tryptophan. To assess the contribution of IAA production to epiphytic fitness, the population dynamics of the wild-type strain and an IAA-deficient mutant of this strain on leaves were studied. Strain 299XYLE, an isogenic IAA-deficient mutant of strain 299R, was constructed by insertional interruption of the indolepyruvate decarboxylase gene of strain 299R with the xylE gene, which encodes a 2,3-catechol dioxygenase from Pseudomonas putida mt-2. The xylE gene provided a useful marker for monitoring populations of the IAA-deficient mutant strain in mixed populations with the parental strain in ecological studies. A root bioassay for IAA, in which strain 299XYLE inhibited significantly less root elongation than strain 299R, provided evidence that E. herbicola produces IAA on plant surfaces in amounts sufficient to affect the physiology of its host and that IAA production in strain 299R is not solely an in vitro phenomenon. The epiphytic fitness of strains 299R and 299XYLE was evaluated in greenhouse and field studies by analysis of changes in the ratio of the population sizes of these two strains after inoculation as mixtures onto plants. Populations of the parental strain increased to approximately twice those of the IAA-deficient mutant strain after coinoculation in a proportion of 1:1 onto bean plants in the greenhouse and onto pear flowers in field studies. In all experiments, the ratio of the population sizes of strain 299R and 299XYLE increased during periods of active growth on plant tissue but not when population sizes were not increasing with time.

Many plant-associated bacteria have the ability to produce the plant growth regulator indole-3-acetic acid (IAA) (5, 9, 25, 33). IAA is involved in diseases caused by gall- and knot-forming bacterial species (33); however, its role in other bacteria remains undefined. It is unclear whether these bacteria produce IAA during colonization of plant surfaces and whether this metabolite is beneficial to the bacteria during their growth and survival in the phyllosphere. The production of IAA may enable bacteria to detoxify tryptophan analogues present on plant surfaces (15), to downregulate genes involved in plant defense responses (33), or to inhibit the development of the hypersensitive response by plants (26). We recently demonstrated that the ipdC gene, which encodes the indolepyruvate decarboxylase of Erwinia herbicola (Pantoea agglomerans) 299R and which is involved in the indolepyruvate pathway for IAA synthesis in this epiphytic strain (2), is osmoresponsive and plant inducible (3). We hypothesized that the secretion of IAA may modify the microhabitat of epiphytic bacteria by increasing nutrient leakage from plant cells; enhanced nutrient availability may better enable IAA-producing bacteria to colonize the phyllosphere and may contribute to their epiphytic fitness (1).Few studies have attempted to determine the ecological significance of IAA production in pathogenic bacteria. Varvaro and Martella (31) showed that IAA-deficient mutants of Pseudomonas syringae pv. savastanoi, obtained by selection for resistance to α-methyltryptophan, were reduced in their ability to colonize and survive on olive leaf surfaces. The survival of an α-methyltryptophan-resistant IAA-deficient mutant of P. syringae pv. savastanoi in knots also was affected, its population declining more rapidly than that of the parental strain when inoculated alone into oleander leaf tissue (28). The importance of IAA production in bacterial colonization of bean leaves was also tested with the brown spot pathogen P. syringae pv. syringae and an IAA-deficient mutant derived by insertional mutagenesis (21). Although no difference in the survival of the parental and mutant strains on bean leaves was observed in the greenhouse, a small difference in their behavior was apparent in experiments conducted in a mist chamber (21). There have been no studies of the role of IAA production in plant-associated bacteria that do not cause disease.IAA biosynthesis is not essential for bacterial growth and survival, since IAA-deficient mutants grow as well as their IAA-producing parental strain in vitro (2, 29). Large differences in the epiphytic behaviors of IAA-producing bacteria and isogenic IAA-deficient mutants consequently would not be expected. Even small contributions of IAA production to epiphytic fitness could account for the common presence of this phenotype in epiphytic bacteria (19). Measurements of changes in the ratio of two strains following coinoculation, a common approach in ecological studies, can allow the detection of even small differences in the competitive behaviors of two organisms. This approach can detect much smaller differences in behavior between closely related species than comparison of populations of these species when present singly in separate habitats (16). In this study, we tested the role of IAA in the epiphytic fitness of E. herbicola by comparing the relative changes in the population sizes of the parental and IAA-deficient mutant strains with time after their inoculation onto plants in both controlled and field environments.     

Myofibrillar protein turnover and urinary N-tau-methylhistidine output. Response to dietary supply of protein and energy.

The urinary excretion of total N-tau-methylhistidine by the growing rat was measured to evaluate the effects of dietary protein and energy restriction on muscle protein turnover in vivo. 2. Young male rats (about 100 g initial wt.) were fed on one of three diets. Group I (controls) received an adequate 18% lactalbumin diet for 28 days, on which they sustained maximum growth. Group II (protein-depleted) was fed for 14 days on 0.5 lactalbumin diet, which caused loss of weight; this was followed by repletion for 14 days with the control diet. Group III (protein-energy restricted) received a 1% lactalbumin diet at one-half the food intake of group II for 14 days, and this was also followed by 14 days of repletion with the control diet. 3. The controls showed a progressive rise in the daily urinary output of N-tau-methylhistidine, which was proportionally slightly less rapid than the body-weight increase. 4. The protein-depleted group II showed a marked and progressive decrease in N-tau-methylhistidine excretion, which was proportionally greater than the fall in body weight; during repletion, N-tau-methylhistidine output rose in parallel with body-weight increase, but it did not reach the value attained by the control group. 5. Group III, restricted in both dietary protein and energy, showed an initial small increase in daily N-tau-methylhistidine output, which contrasted with the sharp loss of body weight during this period. After 11 days on this restricted diet, group III then underwent a decrease in N-tau-methylhistidine output, which persisted into the first 4 days of the repletion period, after which output of the methylated amino acid became the same as for group II. 6. Creatinine output, used as an additional metabolic measure of muscle metabolism, showed a fairly constant relationship to body weight in groups I and II during depletion and repletion. However, rats with protein-energy deficiency (group III) underwent a marked increase in output of creatinine per unit of body weight, which also persisited into the repletion period before it fell to more normal values relative to body weight. 7. Analysis of the N-tau-methylhistidine content of actin isolated from a group of protein-depleted rats revealed a small (5%) but significance (P less than 0.02) decrease relative to well-nourished controls. 8. Hence, the rate of muscle protein degradation, as indicated by changes in urinary N-tau-methylhistidine output, appears to respond sensitively and in opposite directions to insufficiency of protein of energy in the diet.     

Role of Pseudomonas putida indoleacetic acid in development of the host plant root system

Many plant-associated bacteria synthesize the phytohormone indoleacetic acid (IAA). While IAA produced by phytopathogenic bacteria, mainly by the indoleacetamide pathway, has been implicated in the induction of plant tumors, it is not clear whether IAA synthesized by beneficial bacteria, usually via the indolepyruvic acid pathway, is involved in plant growth promotion. To determine whether bacterial IAA enhances root development in host plants, the ipdc gene that encodes indolepyruvate decarboxylase, a key enzyme in the indolepyruvic acid pathway, was isolated from the plant growth-promoting bacterium Pseudomonas putida GR12-2 and an IAA-deficient mutant constructed by insertional mutagenesis. The canola seedling primary roots from seeds treated with wild-type P. putida GR12-2 were on average 35 to 50% longer than the roots from seeds treated with the IAA-deficient mutant and the roots from uninoculated seeds. In addition, exposing mung bean cuttings to high levels of IAA by soaking them in a suspension of the wild-type strain stimulated the formation of many, very small, adventitious roots. Formation of fewer roots was stimulated by treatment with the IAA-deficient mutant. These results suggest that bacterial IAA plays a major role in the development of the host plant root system.     

Role of Pseudomonas putida Indoleacetic Acid in Development of the Host Plant Root System

Many plant-associated bacteria synthesize the phytohormone indoleacetic acid (IAA). While IAA produced by phytopathogenic bacteria, mainly by the indoleacetamide pathway, has been implicated in the induction of plant tumors, it is not clear whether IAA synthesized by beneficial bacteria, usually via the indolepyruvic acid pathway, is involved in plant growth promotion. To determine whether bacterial IAA enhances root development in host plants, the ipdc gene that encodes indolepyruvate decarboxylase, a key enzyme in the indolepyruvic acid pathway, was isolated from the plant growth-promoting bacterium Pseudomonas putida GR12-2 and an IAA-deficient mutant constructed by insertional mutagenesis. The canola seedling primary roots from seeds treated with wild-type P. putida GR12-2 were on average 35 to 50% longer than the roots from seeds treated with the IAA-deficient mutant and the roots from uninoculated seeds. In addition, exposing mung bean cuttings to high levels of IAA by soaking them in a suspension of the wild-type strain stimulated the formation of many, very small, adventitious roots. Formation of fewer roots was stimulated by treatment with the IAA-deficient mutant. These results suggest that bacterial IAA plays a major role in the development of the host plant root system.     

The effect of exposure to oestrous ewes on rams' sexual behaviour, plasma testosterone concentration and ability to stimulate ovulation in seasonally anoestrous ewes

Ruminants eat a variety of foods from different locations in the environment. While water, cover, social interactions, and predators are all likely to influence choice of foraging location, differences in macronutrient content among forages may also cause ruminants to forage in different locations even during a meal. We hypothesized that lambs forage at locations containing foods that complement their basal diet and meet their nutritional needs. Based on this hypothesis, we predicted that lambs (n=12) fed a basal diet low in protein and high in energy would forage where a high-protein food (Food P) was located, and that lambs (n=12) fed a basal diet low in energy and high in protein would forage where a high-energy food (Food E) was located. Food P was a ground mixture of blood meal (50%), grape pomace (30%), and alfalfa (20%) that contained 47% crude protein (CP) and 2.211 Mcal/kg digestible energy (DE). Food E was a ground mixture of cornstarch (50%), grape pomace (30%), and rolled barley (20%) that contained 6% CP and 3.07 Mcal/kg DE. Food P provided 212 g CP/Mcal DE, whereas Food E provided 20 g CP/Mcal DE. Lambs growing at a moderate rate require 179 g CP and 3.95 Mcal DE. During Trial 1, we determined if lambs foraged to correct a nutrient imbalance, and if they preferred a variety of foods (Foods P and E) to only one food at a location (Food P or E). During Trial 2, we determined if nutrient-imbalanced lambs foraged in the location with the food that corrected the imbalance when the location of the foods changed daily. During Trial 3, lambs were offered familiar foods (Foods P and E) at the location furthest - and novel foods (wheat and soybean meal) at the location nearest - the shelter of their pen. During all three trials, lambs foraged most at the location with the food that contained the highest concentration of the macronutrient lacking in their basal diet, but they always ate some of both foods. Lambs did not feed exclusively at the location with a variety of foods (P and E). Rather, they fed at the location nearest the shelter that contained the macronutrient lacking in their diet. As availability of the food with the needed macronutrient declined in one location, lambs moved to the nearest location that had food with the needed macronutrient. When food that complemented their basal diet was moved to a different location, lambs foraged in the new location. Collectively, these results show that lambs challenged by imbalances in energy or protein selected foods and foraging locations that complemented the nutrient content of their macronutrient imbalanced basal diets.     

Compensatory dietary selection occurs in larval Locusta migratoria but not Spodoptera littoralis after a single deficient meal during ad libitum feeding

ABSTRACT Final instar nymphs of Locusta migratoria (L.) and larvae of Spodoptera littoralis (Boisduval) were given an artificial diet deficient in either protein or digestible carbohydrate for a single meal during ad libitum feeding, after which they were provided with a choice of two diets, one containing protein but no digestible carbohydrate and the other containing carbohydrate but no protein. Detailed analyses of feeding behaviour showed that locusts exhibited a degree of compensatory dietary selection following the single deficient meal. No such response was evident for the caterpillars, although previous work (Simpson et al. , 1988) has demonstrated that compensatory selection behaviour is marked in this species after periods of 4 h or more on the same deficient diets. These results show that locusts are able to respond extremely rapidly to the nutritional quality of their food by utilizing nutritional feedbacks. This capability may have important implications for the study of foraging strategies in other herbivorous insects.     

Rapid depletion of serum tryptophan, brain tryptophan, serotonin and 5-hydroxyindoleacetic acid by a tryptophan-free diet

Rats were trained for 20 days to eat their normal daily meal in a period of 2 hours. On the twentyfirst day they received a diet in which tryptophan was omitted instead of the usual balanced diet. The ingestion of the tryptophan-free diet produced a marked depletion of free serum tryptophan (90%), brain tryptophan (85%), brain 5-HT (58%) and brain 5-HIAA (76%). These changes were almost maximal within 2 hours after food presentation and persisted for more than 24 hours. The mechanism of these changes is discussed.     

Induction of hepatocytes in the pancreas of copper-depleted rats following copper repletion

Pancreatic hepatocytes are induced in rats maintained on copper-deficient diet containing 0.6% D-penicillamine for 8-10 weeks, followed by copper repletion. These induced hepatocytes are morphologically and functionally very similar to parenchymal cells of the liver. Immunofluorescence stains demonstrated the presence of albumin and catalase in these cells. Stains for pancreatic enzymes and hormones were negative. As expected, the hypolipidemic compound, ciprofibrate, induced peroxisome proliferation in these cells. These results indicate that a simple depletion and repletion of copper can trigger transdifferentiation in the pancreas of adult rats.     

Food deprivation and the regulation of meal size in larvae of Chrysopa carnea

ABSTRACT. The course of repletion and the effects of food deprivation on meal size were explored in three experiments on larvae of Chrysopa carnea (Neuroptera). Feeding to repletion was found to occur within the first 30 min of exposure to food. Meal size increased as an ogival function of deprivation, up to the limit of gut capacity. Behavioural components involved in the initiation of feeding were little affected by deprivation and did not appear to be inhibited by distention of the gut. Termination of a meal may be mediated by the stimulation of prey-release behaviour, rather than by inhibition of feeding.     

Response of blood serum constituents to production of and recovery from a kwashiorkor-like syndrome in the young pig.

Twenty-six 3-week-old genetically obese pigs were fed in two experiments to determine the serum chemistry profile during severe protein malnutrition and repletion. Severe protein deficiency was produced in pigs fed the high-fat, low-protein diet (growth failure, rough hair, low serum total protein and albumin). In Experiment 1, blood was sampled from the anterior vena cava of each pig five times during depletion and three times during repletion to determine serum total cholesterol, high density lipoprotein (HDL)-cholesterol, triglycerides, total protein, albumin, glucose, Ca, inorganic P, Mg, Na, K, Cl, total bilirubin, urea N, creatinine, alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, and gamma-glutamyltransferase. In Experiment 2, blood was sampled weekly for 8 weeks for serum total cholesterol, HDL-cholesterol, triglycerides, albumin, glucose, Ca, P, Mg and alkaline phosphatase. HDL-cholesterol was increased (P less than 0.01) and albumin was decreased (P less than 0.01) in protein-deficient pigs in both experiments. Creatinine, total bilirubin, gamma-glutamyltransferase, alanine aminotransferase, and aspartate aminotransferase were elevated in protein-deficient pigs compared with controls after 7 weeks of depletion. Inorganic P (P less than 0.01), Ca (P less than 0.01), and Mg (P less than 0.05) concentrations were depressed in protein-depleted pigs compared with controls in both experiments. After 8 weeks of repletion in Experiment 1, all elements except inorganic P were similar in the two groups. Short-term, severe, protein malnutrition affected lipid, electrolyte, and structural mineral metabolism and indices of liver function in the absence of parasites, diarrhea, and infection. The effects were reversed after 8 weeks of repletion. We conclude that the elevated serum cholesterol in protein deficiency is related primarily to an increase in the HDL fraction.     

Development of bone mineralization and body composition of replacement gilts fed a calcium and phosphorus depletion and repletion strategy

This study investigated the ability of replacement gilts to adapt their calcium and phosphorus utilization and their kinetics in bone mineralization to compensate for modified intake of these nutrients by applying a novel Ca and P depletion and repletion strategy. A total of 24 gilts were fed according to a two-phase feeding program. In the first phase, gilts (60–95 kg BW) were fed ad libitum a depletion diet providing either 60% (D60; 1.2 g digestible P/kg) or 100% (D100; 2.1 g digestible P/kg) of the estimated P requirement. In the second phase, gilts (95–140 kg BW) were fed restrictively (aim: 700–750 g/d BW gain) a repletion diet. Half of the gilts from each depletion diet were randomly assigned to either a control diet or a high-P diet (R100 and R160; with 2.1 and 3.5 g digestible P/kg, respectively) according to a 2 × 2 factorial design, resulting in four treatments: D60-R100, D60-R160, D100-R100 and D100-R160. Dual-energy X-ray absorptiometry was used to measure whole-body bone mineral content (BMC), bone mineral density (BMD) and lean and fat tissue mass on each gilt at 2-week intervals. The depletion and repletion diets, fed for 5 and 8 weeks, respectively, did not influence growth performance. The D60 gilts had a reduced BMC and BMD from the second week onwards and ended (95 kg BW) with 9% lower values than D100 gilts (P < 0.001). During repletion, D60 gilts completely recovered the deficit in bone mineralization from the second and fourth week onwards, when fed R160 (D60-R160 vs D100-R160) or R100 (D60-R100 vs D100-R100) diets, respectively (treatment × time interaction, P < 0.001); thus, the depletion diets did not affect these values at 140 kg BW. These results illustrate the rapid homeostatic counter-regulation capacity of dietary Ca and P, and they show the high potential to limit dietary digestible P concentration by completely excluding the use of mineral phosphates during the depletion phase, representative of the fattening period, without causing any detrimental effects to gilts at mating. The gilts were able to recover their BMC deficit between their selection at 95 kg BW and first mating at 140 kg BW by increasing their dietary Ca and P efficiency. Finally, excess dietary digestible P, requiring increased amounts of mineral phosphates, further increased the gilts’ BMC.     

Zinc‐Induced Hyperleptinemia Relates to the Amelioration of Sucrose‐Induced Obesity with Zinc Repletion

Objective: Dietary zinc repletion can ameliorate sucrose‐induced obesity. A positive correlation between zinc and leptin has been recently noted, and both are known as important mediators in appetite control. In this study, we examined whether the reported amelioration of sucrose‐induced obesity by zinc repletion was consequent on the changes in circulating leptin levels. Research Methods and Procedures: Mice with obesity that was induced by giving a 32% sucrose solution in addition to a semipurified diet were divided into two groups based on whether they had 20 mg/liter zinc supplementation in their drinking water. Results: As expected, the mice with sucrose‐induced obesity had hyperglycemia, hyperinsulinemia, hypertriglyceridemia, hyperleptinemia, and hypozincemia when compared with the mice given the diet alone. Body weight gain, body fat content, and food and sucrose intake tended to decrease but not with statistical significance in sucrose‐fed obese mice with zinc supplementation. Nevertheless, some serum variables (glucose, insulin, triglycerides, and zinc) in sucrose‐fed obese mice with zinc treatment were approximate to those values of the mice given the diet alone. Moreover, sucrose‐fed obese mice with zinc supplementation had the highest serum values of leptin. Discussion: This study indicates that the amelioration of sucrose‐induced obesity by zinc repletion may be partly attributable to the hyperleptinemia induced by the mineral.     

Queuosine‐modified tRNAs confer nutritional control of protein translation

Global protein translation as well as translation at the codon level can be regulated by tRNA modifications. In eukaryotes, levels of tRNA queuosinylation reflect the bioavailability of the precursor queuine, which is salvaged from the diet and gut microbiota. We show here that nutritionally determined Q‐tRNA levels promote Dnmt2‐mediated methylation of tRNA Asp and control translational speed of Q‐decoded codons as well as at near‐cognate codons. Deregulation of translation upon queuine depletion results in unfolded proteins that trigger endoplasmic reticulum stress and activation of the unfolded protein response, both in cultured human cell lines and in germ‐free mice fed with a queuosine‐deficient diet. Taken together, our findings comprehensively resolve the role of this anticodon tRNA modification in the context of native protein translation and describe a novel mechanism that links nutritionally determined modification levels to effective polypeptide synthesis and cellular homeostasis.     

Dietary self-selection in fish: a new approach to studying fish nutrition and feeding behavior

The principles of modern aquaculture encourage the development of fish feeds containing low fish meal content and several types of plant ingredients plus nutrients to avoid depleting global fish stocks and to reduce costs. However, food constituents can affect animal nutrition and feeding behavior, so the effect of different diets on fish behavior and growth needs to be understood to optimize the use of nutrients and to improve fish welfare. The development of multiple-choice self-feeding systems led to a new perspective for investigating these issues in aquaculture species. Our purpose with this review is to summarize the information that has been published to date on this topic and to identify gaps in knowledge where research is needed. Key subjects are assessed under the following major headings: How do we study dietary selection in fish? What food signals do fish use to choose the right diet? and How do fish respond to food challenges? The present review will provide a picture of the main results obtained to date in these studies in aquaculture fish species, as well as perspectives for future research in the field.     

Increased short-term food satiation and sensitivity to cholecystokinin in neurotrophin-4 knock-in mice

Neurotrophin-4 (NT-4) knockout mice exhibited decreased innervation of the small intestine by vagal intraganglionic laminar endings (IGLEs) and reduced food satiation. Recent findings suggested this innervation was increased in NT-4 knock-in (NT-4KI) mice. Therefore, to further investigate the relationship between intestinal IGLEs and satiation, meal patterns were characterized using solid and liquid diets, and cholecystokinin (CCK) effects on 30-min solid diet intake were examined in NT-4KI and wild-type mice. NT-4KI mice consuming the solid diet exhibited reduced meal size, suggesting increased satiation. However, compensation occurred through increased meal frequency, maintaining daily food intake and body weight gain similar to controls. Mutants fed the liquid diet displayed a decrease in intake rate, again implying increased satiation, but meal duration increased, which led to an increase in meal size. This was compensated for by decreased meal frequency, resulting in similar daily food intake and weight gain as controls. Importantly, these alterations in NT-4KI mice were opposite, or different, from those of NT-4 knockout mice, further supporting the hypothesis that they are specific to vagal afferent signaling. CCK suppressed short-term intake in mutants and controls, but the mutants exhibited larger suppressions at lower doses, implying they were more sensitive to CCK. Moreover, devazepide prevented this suppression, indicating this increased sensitivity was mediated by CCK-1 receptors. These results suggest that the NT-4 gene knock-in, probably involving increased intestinal IGLE innervation, altered short-term feeding, in particular by enhancing satiation and sensitivity to CCK, whereas long-term control of daily intake and body weight was unaffected.     

Dietary zinc depletion and repletion affects plasma proteins: an analysis of the plasma proteome

Zinc (Zn) deficiency is a problem world-wide. Current methods for assessing Zn status are limited to measuring plasma or serum Zn within populations suspected of deficiency. Despite the high prevalence of Zn deficiency in the human population there are no methods currently available for sensitively assessing Zn status among individuals. The purpose of this research was to utilize a proteomic approach using two-dimensional gel electrophoresis (2DE) and mass spectrometry to identify protein biomarkers that were sensitive to changes in dietary Zn levels in humans. Proteomic analysis was performed in human plasma samples (n = 6) obtained from healthy adult male subjects that completed a dietary Zn depletion/repletion protocol, current dietary zinc intake has a greater effect on fractional zinc absorption than does longer term zinc consumption in healthy adult men. Chung et al. (Am J Clin Nutr 87 (5):1224–1229, 2008). After a 13 day Zn acclimatization period where subjects consumed a Zn-adequate diet, the male subjects consumed a marginal Zn-depleted diet for 42 days followed by consumption of a Zn-repleted diet for 28 days. The samples at baseline, end of depletion and end of repletion were pre-fractionated through immuno-affinity columns to remove 14 highly abundant proteins, and each fraction separated by 2DE. Following staining by colloidal Coomassie blue and densitometric analysis, three proteins were identified by mass spectrometry as affected by changes in dietary Zn. Fibrin β and chain E, fragment double D were observed in the plasma protein fraction that remained bound to the immunoaffinity column. An unnamed protein that was related to immunoglobulins was observed in the immunodepleted plasma fraction. Fibrin β increased two-fold following the Zn depletion period and decreased to baseline values following the Zn repletion period; this protein may serve as a viable biomarker for Zn status in the future.     

Auxin biosynthesis in maize

For the biosynthesis of the phytohormone indole-3-acetic acid (IAA), a number of tryptophan-dependent and -independent pathways have been discussed. Maize is an appropriate model system to analyze IAA biosynthesis particularly because high quantities of IAA conjugates are stored in the endosperm. This allowed precursor feeding experiments in a kernel culture system followed by retrobiosynthetic NMR analysis, which strongly suggested that tryptophan-dependent IAA synthesis is the predominant route for auxin biosynthesis in the maize kernel. Two nitrilases ZmNIT1 and ZmNIT2 are expressed in seeds. ZmNIT2 efficiently hydrolyzes indole-3-acetonitrile (IAN) to IAA and thus could be involved in auxin biosynthesis. Redundant pathways, e.g., via indole-3-acetaldehyde could imply that multiple mutants will be necessary to obtain IAA-deficient plants and to conclusively identify relevant genes for IAA biosynthesis.     

Nutritional geometry: gorillas prioritize non-protein energy while consuming surplus protein

It is widely assumed that terrestrial food webs are built on a nitrogen-limited base and consequently herbivores must compensate through selection of high-protein foods and efficient nitrogen retention. Like many folivorous primates, gorillas' diet selection supports this assumption, as they apparently prefer protein-rich foods. Our study of mountain gorillas (Gorilla beringei) in Uganda revealed that, in some periods, carbohydrate-rich fruits displace a large portion of protein-rich leaves in their diet. We show that non-protein energy (NPE) intake was invariant throughout the year, whereas protein intake was substantially higher when leaves were the major portion of the diet. This pattern of macronutrient intake suggests that gorillas prioritize NPE and, to achieve this when leaves are the major dietary item, they over-eat protein. The concentrations of protein consumed in relation to energy when leaves were the major portion of the diet were close to the maximum recommended for humans and similar to high-protein human weight-loss diets. By contrast, the concentrations of protein in relation to energy when gorillas ate fruit-dominated diets were similar to those recommended for humans. Our results question the generality of nitrogen limitation in terrestrial herbivores and provide a fascinating contrast with human macronutrient intake.