Intracerebroventricular administration of GABA-A and GABA-B receptor antagonists attenuate feeding and sleeping-like behavior induced by L-pipecolic acid in neonatal chicks

Metabolic Engineering of Saccharomyces cerevisiae for High-Level Production of l-Pipecolic Acid from Glucose

l-Pipecolic acid (L-PA), an essential chiral cyclic nonprotein amino acid, is gaining prominence in the food and pharmaceutical sectors due to its wide-ranging biological and pharmacological properties. Historically, L-PA has been synthesized chemically for commercial purposes. This study introduces a novel and efficient microbial production method for L-PA using engineered strain Saccharomyces cerevisiae BY4743. Initially, an optimized biosynthetic pathway was constructed within S. cerevisiae, converting glucose to L-PA with a yield of 0.60 g/L in a 250 mL shake flask in vivo. Subsequently, a multifaceted engineering strategy was implemented to enhance L-PA production: substrate-enzyme affinity modification, global transcription machinery engineering modification, and Kozak sequence optimization for enhanced L-PA production. Approaches above led to an impressive 8.6-fold increase in L-PA yield, reaching 5.47 g/L in shake flask cultures. Further scaling up in a 5 L fed-batch fermenter achieved a remarkable L-PA concentration of 74.54 g/L. This research offers innovative insights into the industrial-scale production of L-PA.

Mapping GABAergic projections that mediate feeding

Neuroscience offers important insights into the pathogenesis and treatment of obesity by investigating neural circuits underpinning appetite and feeding. Gamma-aminobutyric acid (GABA), one of the most abundant neurotransmitters in the brain, and its associated receptors represent an array of pharmacologically targetable mediators of appetite signalling. Targeting the GABAergic system is therefore an increasingly investigated approach to obesity treatment. However, the many GABAergic projections that control feeding have yet to be collectively analysed. This review provides a comprehensive analysis of the relationship between GABAergic signalling and appetite by examining both foundational studies and the results of newly emerging chemogenetic/optogenetic experiments. A current snapshot of these efforts to map GABAergic projections influencing appetite is provided, and potential avenues for further investigation are provided.

Bifidobacterium breve M-16V regulates the autonomic nervous system via the intestinal environment: A double-blind, placebo-controlled study

We conducted a randomized controlled trial to investigate the potential of Bifidobacterium breve M-16 V to improve mood in humans. In this evaluation, we incorporated the use of near-infrared spectroscopy (NIRS), which has been used to evaluate mood states in studies with small sample sizes. Participants were given B. breve M-16 V (20 billion cells/day) for 6 weeks, and their mood state was assessed before and after ingestion. NIRS data were collected at rest and during a mental arithmetic task (under stress). Intake of B. breve M-16 V decreased the heart rate under stress and increased levels of the GABA-like substance pipecolic acid in stool samples. In addition, B. breve M-16 V improved mood and sleep scores in participants with high anxiety levels. These results suggest that B. breve M-16 V affects the metabolites of the gut microbiota and has the potential to modulate the autonomic nervous system and to improve mood and sleep.

Central effects of the serotoninergic, GABAergic, and cholecystokinin systems on neuropeptide VF (NPVF)-induced hypophagia and feeding behavior in neonatal broiler chicken

The study was performed to evaluate the role of central serotoninergic, GABAergic, and cholecystokinin systems in neuropeptide VF (NPVF)-induced hypophagia in broiler chickens. In this study, 9 experiments were designed, each with one control and three treatment groups (n = 44 in each experiment). Control chicks of all groups were subjected to normal saline + Evans blue 0.1 % Intracerebroventricular (ICV) injection. In the first experiment, 3 groups of chicks received NPVF (4, 8, and 16 nmol). In experiment 2-9, one group of chicks received NPVF (16 nmol), another received 10 µg fluoxetine (serotonin reuptake inhibitor) (experiment 2), 1.25 µg PCPA (serotonin synthesis inhibitor) (experiment 3), 1.5 µg SB-242,084 (5-HT2C receptor antagonist) (experiment 4), 15.25 nmol 8-OH-DPAT (5-HT1A receptor antagonist) (experiment 5), 0.5 µg picrotoxin (GABAA receptor antagonist) (experiment 6), 20 ng CGP54626 (GABAB receptor antagonist) (experiment 7), 1 nmol devazepide (CCKA receptor antagonist) (experiment 8), and 1 nmol/L-365(-|-),260 (CCKB receptor antagonist) (experiment 9), and another final group received combination of specific neurotransmitter + NPVF Then, the cumulative food intake was measured until 120 min post-injection. ICV injection of NPVF (8 and 16 nmol) significantly decreased food intake (P < 0.05). Simultaneous injection of fluoxetine + NPVF and also picrotoxin + NPVF significantly increased hypophagia caused by NPVF (P < 0.05). However, co-administration of PCPA + NPVF and also SB242084 + NPVF significantly decreased NPVF-induced hypophagia (P < 0.05). Finally, 8-OH-DPAT, CGP54626, devazepide, and L-365,260 had no effect on the hypophagia brought on by NPVF (P > 0.05). Count-type behaviors were dose-dependent and decreased in groups that received NPVF compared to the control group (P < 0.05). Our finding recommended an interconnection between central NPVF and serotoninergic, GABAergic, and cholecystokinin systems in neonatal chickens.

Effect of Agaricus bisporus Polysaccharides on Human Gut Microbiota during In Vitro Fermentation: An Integrative Analysis of Microbiome and Metabolome

Agaricus bisporus polysaccharide (ABP) is an important active component in edible mushrooms, but its interaction with gut microbiota is unclear. Therefore, this study evaluated the effect of ABP on the composition and metabolites of human gut microbiota by in vitro batch fermentation. The main degrading bacteria for ABP were Bacteroides, Streptococcus, Enterococcus, Paraprevotella, Bifidobacterium, Lactococcus, Megamonas, and Eubacterium, whose relative abundances increased during 24 h of in vitro fermentation. The short-chain fatty acids (SCFAs) content also increased more than 15-fold, accordingly. Moreover, the effects of ABP on the relative abundance of Bacteroides (Ba.) and Bifidobacterium (Bi.) at the species level were further determined. ABP can enrich Ba. thetaiotaomicron, Ba. intestinalis, Ba. uniformis, and Bi. longum. PICRUSt analysis revealed that the catabolism of ABP was accompanied by changes in the metabolism of carbohydrates, nucleotides, lipids and amino acids, which were also supported by metabonomic results. It is worth mentioning that, after 24 h fermentation, the relative amounts of gamma-aminobutyric acid (GABA), nicotinamide and nicotinamide adenine dinucleotide (NAD+) had 14.43-, 11.34- and 15.36-fold increases, respectively, which were positively related to Bacteroides (Ba. thetaiotaomicron, Ba. intestinalis), Streptococcus, and Bi. longum (|r| > 0.98). These results laid the research foundation for exploring ABP as a potential prebiotic or dietary supplement for the targeted regulation of gut microbiota or metabolites.

Central Interaction Between L-Ornithine and Neuropeptide Y in the Regulation of Feeding Behavior of Neonatal Chicks

Ornithine has been identified as a potential satiety signal in the brains of neonatal chicks. We hypothesized that brain nutrient signals such as amino acids and appetite-related neuropeptides synergistically regulate food intake. To test this hypothesis, we investigated the interaction between neuropeptide Y (NPY) and ornithine in the control of feeding behavior in chicks and the associated central and peripheral amino acid metabolic processes. Five-day-old chicks were intracerebroventricularly injected with saline, NPY (375 pmol), or NPY plus ornithine (2 or 4 μmol) at 10 μl per chick, and then subjected to ad libitum feeding conditions; food intake was monitored for 30 min after injection. Brain and plasma samples were collected after the experiment to determine free amino acid concentrations. Co-injection of NPY and ornithine significantly attenuated the orexigenic effect induced by NPY in a dose-dependent manner. Central NPY significantly decreased amino adipic acid, asparagine, γ-aminobutyric acid, leucine, phenylalanine, tyrosine, and isoleucine levels, but significantly increased lysine levels in the brain. Co-injection of NPY and ornithine significantly increased ornithine and proline levels in all examined brain regions, but decreased diencephalic tryptophan and glycine levels compared with those of the control and NPY-alone groups. Co-injection of NPY and high-dose ornithine significantly decreased methionine levels in all brain regions. Central NPY significantly suppressed the plasma concentrations of amino acids, including proline, asparagine, methionine, phenylalanine, tyrosine, leucine, isoleucine, glycine, glutamine, alanine, arginine, and valine, and this reduction was greater when NPY was co-injected with ornithine. These results suggest that brain ornithine interacts with NPY to regulate food intake in neonatal chicks. Furthermore, central NPY may induce an anabolic effect that is modified by co-injection with ornithine.

Crystal structure analysis of N-acetylated proline and ring size analogs

Crystal structures of N-acetylated proline and homologs with four- and six-membered rings (azetidine carboxylic acid and piperidine carboxylic acid) were obtained and compared. The distinctly different conformations of the four-, five-, and six-membered rings reflect Bayer strain, n → π* interaction, and allylic strain, and result in crystal lattices with a zigzag structure.

Assessment of components related to flavor and taste in Tan-lamb meat under different silage-feeding regimens using integrative metabolomics

Two untargeted metabolomics approaches based on gas chromatography mass spectrometry and ultra-high-performance liquid chromatography quadrupole time-of-flight mass spectrometry were used to identify the effects of different feeding regimes (concentrate, corn silage, alfalfa silage, mulberry leaf silage) on the potential meat flavor and taste components of Tan-lamb. Among 31 identified volatiles, hexanal was affected by the alfalfa silage diet, and 3-hydroxydodecanoic acid was changed by the mulberry leaf silage diet. l-Pipecolic acid (area under the curve = 1, fold change = 0.18-0.48) and trimethylamine N-oxide (area under the curve = 1, fold change = 5.26-22.84) was the potential best discriminant biomarker under alfalfa silage and concentrate feeding, respectively. The hydrophilic components were more readily changed by feeding regimes than volatile flavor compounds. Our findings are helpful for the illustration of Tan-lamb meat chemistry and producing high-quality lamb meat with improved flavor and taste by corn silage, alfalfa silage, or mulberry leaf silage.

Depression and anxiety in patients with active ulcerative colitis: crosstalk of gut microbiota, metabolomics and proteomics

Patients with ulcerative colitis (UC) have a high prevalence of mental disorders, such as depression and anxiety. Gut microbiota imbalance and disturbed metabolism have been suggested to play an important role in either UC or mental disorders. However, little is known about their detailed multi-omics characteristics in patients with UC and depression/anxiety. In this prospective observational study, 240 Chinese patients were enrolled, including 129 patients with active UC (69 in Phase 1 and 60 in Phase 2; divided into depression/non-depression or anxiety/non-anxiety groups), 49 patients with depression and anxiety (non-UC), and 62 healthy people. The gut microbiota of all subjects was analyzed using 16S rRNA sequencing. The serum metabolome and proteome of patients with UC in Phase 2 were analyzed using liquid chromatography/mass spectrometry. Associations between multi-omics were evaluated by correlation analysis. The prophylactic effect of candidate metabolites on the depressive-like behavior of mice with colitis was investigated. In total, 58% of patients with active UC had depression, while 50% had anxiety. Compared to patients with UC without depression/anxiety, patients with UC and depression/anxiety had lower fecal microbial community richness and diversity, with more Lactobacillales, Sellimonas, Streptococcus, and Enterococcus but less Prevotella_9 and Lachnospira. Most metabolites (e.g., glycochenodeoxycholate) were increased in the serum, while few metabolites, including 2'-deoxy-D-ribose and L-pipecolic acid, were decreased, accompanied by a general reduction in immunoglobulin proteins. These related bacteria, metabolites, and proteins were highly connected. A prophylactic administration of 2'-deoxy-D-ribose and L-pipecolic acid significantly reduced the depressive-like behaviors in mice with colitis and alleviated the inflammatory cytokine levels in their colon, blood and brain. This study has identified a comprehensive multi-omics network related to depression and anxiety in active UC. It is composed of a certain set of gut microbiota, metabolites, and proteins, which are potential targets for clinical intervention for patients with UC and depression/anxiety.

Chiral secondary amino acids, their importance, and methods of analysis

Naturally occurring secondary amino acids, with proline as the main representative, contain an alpha-imino group in a cycle that is typically four-, five-, and six-membered. The unique ring structure exhibits exceptional properties-conformational rigidity, chemical stability, and specific roles in protein structure and folding. Many proline analogues have been used as valuable compounds for the study of metabolism of both prokaryotic and eukaryotic cells and for the synthesis of compounds with desired biological, pharmaceutical, or industrial properties. The D-forms of secondary amino acids play different roles in living organisms than the L-forms. They have different metabolic pathways, biological, physiological, and pharmacological effects, they can be indicators of changes and also serve as biomarkers of diseases. In the scientific literature, the number of articles examining D-amino acids in biological samples is increasing. The review summarises information on the occurrence and importance of D- and L-secondary amino acids-azetidic acid, proline, hydroxyprolines, pipecolic, nipecotic, hydroxypipecolic acids and related peptides containing these D-AAs, as well as the main analytical methods (mostly chromatographic) used for their enantiomeric determination in different matrices (biological samples, plants, food, water, and soil).

919 Syrup Alleviates Postpartum Depression by Modulating the Structure and Metabolism of Gut Microbes and Affecting the Function of the Hippocampal GABA/Glutamate System

Postpartum depression (PPD) is a mental disorder that affects pregnant women around the world, with serious consequences for mothers, families, and children. Its pathogenesis remains unclear, and medications for treating PPD that can be used during lactation remain to be identified. 919 syrup (919 TJ) is a Chinese herbal medicine that has been shown to be beneficial in the treatment of postpartum depression in both clinical and experimental studies. The mechanism of action of 919 TJ is unclear. 919 syrup is ingested orally, making the potential interaction between the drug and the gut microbiome impossible to ignore. We therefore hypothesized that 919 syrup could improve the symptoms of postpartum depression by affecting the structure and function of the intestinal flora, thereby altering hippocampal metabolism. We compared changes in hippocampal metabolism, fecal metabolism, and intestinal microflora of control BALB/c mice, mice with induced untreated PPD, and mice with induced PPD treated with 919 TJ, and found that 4-aminobutyric acid (GABA) in the hippocampus corresponded with PPD behaviors. Based on changes in GABA levels, multiple key gut bacterial species (Mucispirillum schaedleri, Bifidobacterium pseudolongum, Desulfovibrio piger, Alloprevotella tannerae, Bacteroides sp.2.1.33B and Prevotella sp. CAG:755) were associated with PPD. Metabolic markers that may represent the function of the intestinal microbiota in mice with PPD were identified (Met-Arg, urocanic acid, thioetheramide-PC, L-pipecolic acid, and linoleoyl ethanolamide). The relationship between these factors is not a simple one-to-one correspondence, but more likely a network of staggered functions. We therefore believe that the composition and function of the entire intestinal flora should be emphasized in research studying the gut and PPD, rather than changes in the abundance of individual bacterial species. The introduction of this concept of “GutBalance” may help clarify the relationship between gut bacteria and systemic disease.

Age-Related Neurometabolomic Signature of Mouse Brain

Neurometabolites are the ultimate gene products in the brain and the most precise biomolecular indicators of brain endophenotypes. Metabolomics is the only "omics" that provides a moment-to-moment "snapshot" of brain circuits' biochemical activities in response to external stimuli within the context of specific genetic variations. Although the expression levels of neurometabolites are highly dynamic, the underlying metabolic processes are tightly regulated during brain development, maturation, and aging. Therefore, this study aimed to identify mouse brain metabolic profiles in neonatal and adult stages and reconstruct both the active metabolic network and the metabolic pathway functioning. Using high-throughput metabolomics and bioinformatics analyses, we show that the neonatal mouse brain has its distinct metabolomic signature, which differs from the adult brain. Furthermore, lipid metabolites showed the most profound changes between the neonatal and adult brain, with some lipid species reaching 1000-fold changes. There were trends of age-dependent increases and decreases among lipids and non-lipid metabolites, respectively. A few lipid metabolites such as HexCers and SHexCers were almost absent in neonatal brains, whereas other non-lipid metabolites such as homoarginine were absent in the adult brains. Several molecules that act as neurotransmitters/neuromodulators showed age-dependent levels, with adenosine and GABA exhibiting around 100- and 10-fold increases in the adult compared with the neonatal brain. Of particular interest is the observation that purine and pyrimidines nucleobases exhibited opposite age-dependent changes. Bioinformatics analysis revealed an enrichment of lipid biosynthesis pathways in metabolites, whose levels increased in adult brains. In contrast, pathways involved in the metabolism of amino acids, nucleobases, glucose (glycolysis), tricarboxylic acid cycle (TCA) were enriched in metabolites whose levels were higher in the neonatal brains. Many of these pathways are associated with pathological conditions, which can be predicted as early as the neonatal stage. Our study provides an initial age-related biochemical directory of the mouse brain and warrants further studies to identify temporal brain metabolome across the lifespan, particularly during adolescence and aging. Such neurometabolomic data may provide important insight about the onset and progression of neurological/psychiatric disorders and may ultimately lead to the development of precise diagnostic biomarkers and more effective preventive/therapeutic strategies.

Intracerebroventricular Injection of L-Pipecolic Acid Exerts Hypnotic Effects Without Activating NMDA Receptors in Neonatal Chicks under Social Isolation-induced Stress

L-Pipecolic acid is an intermediate of L-lysine catabolism. Its central injection exerted a hypnotic effect on the brain, which was partially mediated by the activation of γ-aminobutyric acid-A and γ-aminobutyric acid-B receptors. L-Proline has also been shown to exert a similar effect on N-methyl-D-aspartate receptors. Furthermore, L-pipecolic acid is known as L-homoproline, and both L-pipecolic acid and L-proline belong to the imino acid group; therefore, it is plausible that they share certain commonalities, including similar functions. However, the role of N-methyl-D-aspartate receptors with respect to the effects of L-pipecolic acid has not been examined yet. In the present study, the relationship between N-methyl-D-aspartate receptors and the central function of L-pipecolic acid was investigated in neonatal chicks. The behavioral postures for active wakefulness and standing/sitting motionless with eyes opened were significantly affected after intracerebroventricular injection of L-pipecolic acid; whereas, sitting motionless with head drooped (sleeping posture) was significantly enhanced. However, the N-methyl-D-aspartate receptor antagonist, MK-801, did not affect these changes. In conclusion, the central administration of L-pipecolic acid did not exert hypnotic effects through the activation of N-methyl-D-aspartate receptors in neonatal chicks. These results suggest that the imino group is not a determinant for activating N-methyl-D-aspartate receptors.

Nutritional Characteristics and Functions of D-Amino Acids in the Chicken

D-Amino acids occur in modest amounts in bacterial proteins and the bacterial cell wall, as well as in peptide antibiotics. Therefore, D-amino acids present in terrestrial vertebrates were believed to be derived from bacteria present in the gastrointestinal tract or fermented food. However, both exogenous and endogenous origins of D-amino acids have been confirmed. Terrestrial vertebrates possess an enzyme for converting certain L-isomers to D-isomers. D-Amino acids have nutritional aspects and functions, some are similar to, and others are different from those of L-isomers. Here, we describe the nutritional characteristics and functions of D-amino acids and also discuss the future perspectives of D-amino acid nutrition in the chicken.

Influence of leptin and GABAB-receptor agonist and antagonist on neurons of the hypothalamic infundibular nucleus in the chicken

In birds and mammals, the neuroendocrine regulation of energy balance is conserved in many aspects. Despite significant similarities between the two groups, differences in the regulatory mechanisms were detected. The present study was performed to carry out investigations of the influence of human leptin and GABA_B-receptor agonist and antagonist on the firing rate of neurons of the Nucleus infundibuli hypothalami in brain slices from juvenile chickens. For the first time, we demonstrated a clear, dose-related change in the firing rate of hypothalamic neurons in juvenile chickens after the acute application of recombinant human leptin (1, 10, and 100 nM). All investigated neurons increased their subsequent firing rate. Application of GABA_B-receptor agonist baclofen (1 µM) blocked, while antagonist CGP 35348 (10 µM) increased the spontaneous neuronal activity. Simultaneous application of baclofen and leptin reduced the effect observed from single leptin application. This was not found after simultaneously application of leptin and CGP. Altogether, our results indicate that in bird brain slices, and exemplarily in those of the chicken, hypothalamic neurons show mammalian-like responsiveness after acute leptin and GABA application. GABA_B-mechanisms involved in GABA release play a likely important role in the leptin-mediated effects on NI neurons via functional leptin receptors.

Current knowledge for pyridoxine-dependent epilepsy: a 2016 update

Pyridoxine-dependent epilepsy (PDE) is a rare genetic condition characterized by intractable and recurrent neonatal seizures that are uniquely alleviated by high doses of pyridoxine (vitamin B6). This recessive disease is caused by mutations in ALDH7A1, a gene encoding Antiquitin, an enzyme central to lysine degradation. This results in the pathogenic accumulation of the lysine intermediates Aminoadipate Semialdehyde (AASA) and its cyclic equilibrium form Piperideine-6-carboxylate (P6C) in body fluids; P6C reacts with pyridoxal-5'-phosphate (PLP, the active form of vitamin B6) causing its inactivation and leading to pyridoxine-dependent seizures. While PDE is responsive to pharmacological dosages of pyridoxine, despite lifelong supplementation, neurodevelopment delays are observed in >75% of PDE cases. Thus, adjunct treatment strategies are emerging to both improve seizure control and moderate the delays in cognition. These adjunctive therapies, lysine restriction and arginine supplementation, separately or in combination (with pyridoxine thus termed 'triple therapy'), have shown promising results and are recommended in all PDE patients. Other new therapeutic strategies currently in preclinical phase of study include antisense therapy and substrate reduction therapy. We present here a comprehensive review of current treatment options as well as PDE phenotype, differential diagnosis, current management and views upon the future of PDE research.

Stress and eating: a dual role for bombesin-like peptides

The current obesity “epidemic” in the developed world is a major health concern; over half of adult Canadians are now classified as overweight or obese. Although the reasons for high obesity rates remain unknown, an important factor appears to be the role stressors play in overconsumption of food and weight gain. In this context, increased stressor exposure and/or perceived stress may influence eating behavior and food choices. Stress-induced anorexia is often noted in rats exposed to chronic stress (e.g., repeated restraint) and access to standard Chow diet; associated reduced consumption and weight loss. However, if a similar stressor exposure takes place in the presence of palatable, calorie dense food, rats often consume an increase proportion of palatable food relative to Chow, leading to weight gain and obesity. In humans, a similar desire to eat palatable or “comfort” foods has been noted under stressful situations; it is thought that this response may potentially be attributable to stress-buffering properties and/or through activation of reward pathways. The complex interplay between stress-induced anorexia and stress-induced obesity is discussed in terms of the overlapping circuitry and neurochemicals that mediate feeding, stress and reward pathways. In particular, this paper draws attention to the bombesin family of peptides (BBs) initially shown to regulate food intake and subsequently shown to mediate stress response as well. Evidence is presented to support the hypothesis that BBs may be involved in stress-induced anorexia under certain conditions, but that the same peptides could also be involved in stress-induced obesity. This hypothesis is based on the unique distribution of BBs in key cortico-limbic brain regions involved in food regulation, reward, incentive salience and motivationally driven behavior.

Congenital feeding and swallowing disorders

Although poorly recognized and studied, congenital sucking, swallowing, and/or feeding disorders are common. They can be the symptoms that reveal a neuromuscular disease, or that complicate a neuromuscular disease. It is essential to know feeding physiology during fetal and infant development in order to understand the variety of its disorders and to direct correctly diagnostic and therapeutic processes. A good semiological analysis will identify the symptoms. Several investigations help to determine the mechanism of the trouble (fiber endoscopy, videofluoroscopy, facial and swallowing electromyography, esophageal manometry, etc.). Other investigations, in addition to clinical assessments, help to identify the cause of the whole picture (peripheral electromyography, brain MRI, genetic or metabolic investigations, etc.). The main causes of sucking, swallowing, and feeding disorders are lesions of the brainstem (malformations of the posterior fossa, neonatal brainstem tumors, agenesis of cranial nerves, clastic lesion of the posterior brain, craniovertebral anomalies, syndromes that involve the rhombencephalic development such as Pierre Robin sequence, CHARGE syndrome, etc.). Suprabulbar lesions, neuromuscular disorders, peripheral esophageal, digestive, and laryngeal anomalies and dysfunctions can also be involved. The main principles of the management of congenital sucking, swallowing, and feeding disorders are the following: cure the cause if possible, facilitate the sucking reflex, preventing deleterious consequences of aspiration, preventing malnutrition, and preventing posttraumatic anorexia. Advice can be given to caregivers and physiotherapists who take charge of these children.

Neuropeptide Y-induced feeding is dependent on GABAA receptors in neonatal chicks

In mammals and birds, neuropeptide Y (NPY) and gamma-aminobutyric acid (GABA) are found in brain areas known to be involved in the control of ingestive behavior and act to increase voluntary food intake. In rats, significant evidence suggest a functional and behavioral interaction between NPY and GABA mediated transmission in various brain regions, including the arcuate and paraventricular nuclei of the hypothalamus which can be important in the regulation of feeding behavior. In the present study, the effect of intracerebroventricular (ICV) administration of NPY and GABA receptor antagonists on food intake was examined in neonatal chicks. The ICV injection of NPY strongly stimulated food intake while co-administration of NPY and picrotoxin, a GABA(A) antagonist, (but not CGP54626, a GABA(B) antagonist) weakened food intake induced by NPY. These results suggest that central NPY stimulates food intake in neonatal chicks by interaction with the GABAergic system via GABA(A) receptors.

LKR/SDH plays important roles throughout the tick life cycle including a long starvation period

BACKGROUND

Lysine-ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH) is a bifunctional enzyme catalyzing the first two steps of lysine catabolism in plants and mammals. However, to date, the properties of the lysine degradation pathway and biological functions of LKR/SDH have been very little described in arthropods such as ticks.

METHODOLOGY/PRINCIPAL FINDINGS

We isolated and characterized the gene encoding lysine-ketoglutarate reductase (LKR, EC 1.5.1.8) and saccharopine dehydrogenase (SDH, EC 1.5.1.9) from a tick, Haemaphysalis longicornis, cDNA library that encodes a bifunctional polypeptide bearing domains similar to the plant and mammalian LKR/SDH enzymes. Expression of LKR/SDH was detected in all developmental stages, indicating an important role throughout the tick life cycle, including a long period of starvation after detachment from the host. The LKR/SDH mRNA transcripts were more abundant in unfed and starved ticks than in fed and engorged ticks, suggesting that tick LKR/SDH are important for the starved tick. Gene silencing of LKR/SDH by RNAi indicated that the tick LKR/SDH plays an integral role in the osmotic regulation of water balance and development of eggs in ovary of engorged females.

CONCLUSIONS/SIGNIFICANCE

Transcription analysis and gene silencing of LKR/SDH indicated that tick LKR/SDH enzyme plays not only important roles in egg production, reproduction and development of the tick, but also in carbon, nitrogen and water balance, crucial physiological processes for the survival of ticks. This is the first report on the role of LKR/SDH in osmotic regulation in animals including vertebrate and arthropods.

Conformational Preferences of Proline Analogues with Different Ring Size

The conformational study on L-azetidine-2-carboxylic acid (Ac-Aze-NHMe, the Aze dipeptide) and (S)-piperidine-2-carboxylic acid (Ac-Pip-NHMe, the Pip dipeptide) is carried out using ab initio HF and density functional methods with the self-consistent reaction field method to explore the differences in conformational preferences and cis-trans isomerization for proline residue and its analogues with different ring size in the gas phase and in solution (chloroform and water). The change of ring size by deleting a CH2 group from or adding a CH2 group to the prolyl ring results the remarkable changes in backbone and ring structures compared with those of the Pro dipeptide, especially in the C'-N imide bond length and the bond angles around the N-C(alpha) bond. The four-membered azetidine ring can have either puckered structure depending on the backbone structure because of the less puckered structure. The six-membered piperidine ring can adopt chair and boat conformations, but the chair conformation is more preferred than the boat conformation. These calculated preferences for puckering are consistent with experimental results from analysis of X-ray structures of Aze- and Pip-containing peptides. On going from Pro to Aze to Pip, the axiality (i.e., a tendency to adopt the axial orientation) of the NHMe group becomes stronger, which can be ascribed to reduce the steric hindrances between 1,2-substituted Ac and NHMe groups. As the solvent polarity increases, the polyproline II-like conformation becomes more populated and the relative stability of conformation tC with a C7 hydrogen bond between C'=O of the amino group and N-H of the carboxyl group decreases for both the Aze and Pip dipeptides, as seen for the Pro dipeptide. The cis population and rotational barriers for the imide bond increase with the increase of solvent polarity for both the Aze and Pip dipeptides, as seen for the Pro dipeptide. In particular, the cis-trans isomerization proceeds in common through only the clockwise rotation with omega' approximately +120 degrees about azetyl and piperidyl peptide bonds in the gas phase and in solution, as seen for alanyl and prolyl peptide bonds. The pertinent distance d(N...H-N(NHMe)) and the pyramidality of imide nitrogen can describe the role of this hydrogen bond in stabilizing the transition state structure, but the lower rotational barriers for the Aze and Pip dipeptides than those for the Pro dipeptide, which is observed from experiments, cannot be rationalized.

The melanocortin circuit in obese and lean strains of chicks

Agonists of membranal melanocortin 3 and 4 receptors (MC3/4Rs) are known to take part in the complex control mechanism of energy balance. In this study, we compared the physiological response to an exogenous MC3/4R agonist and the hypothalamic expression of proopic melanocortin (POMC) gene, encoding few MC3/4R ligands, between broiler and layer chicken strains. These strains, representing the two most prominent commercial strains of chickens grown for meat (broilers) and egg production (layers), differ in their food intake, fat accumulation, and reproductive performance and, therefore, form a good model of obese and lean phenotypes, respectively. A single i.v. injection of the synthetic peptide melanotan-II (MT-II; 1 mg/kg body weight) into the wing vein of feed-restricted birds led to attenuation of food intake upon exposure to feeding ad libitum in both broiler and layer chickens. A study of the POMC mRNA encoding the two prominent natural MC3/4R agonists, alpha-MSH and ACTH, also revealed a general similarity between the strains. Under feeding conditions ad libitum, POMC mRNA levels were highly similar in chicks of both strains and this level was significantly reduced upon feed restriction. However, POMC mRNA down-regulation upon feed restriction was more pronounced in layers than in broilers. These results suggest: (i) a role for MC3/4R agonists in the control of appetite; (ii) that the physiological differences between broilers and layers are not related to unresponsiveness of broiler chickens to the satiety signal of MC3/4R ligands. Therefore, these findings suggest that artificial activation of this circuit in broiler chicks could help to accommodate with their agricultural shortcomings of overeating, fattening, and impaired reproduction.

Effects of various mu- and delta-opioid ligands on food intake in the meat-type chick

The present study was designed to examine the effects of mu- and delta-opioid receptor ligands on feeding behavior in meat-type chicks. Intracerebroventricular (ICV) injection of naltrexone (mu- and delta-antagonist), beta-funaltrexamine (beta-FNA; mu-antagonist), ICI-174,864 (ICI; delta-antagonist), or naloxonazine (NAL; mu1-antagonist) significantly decreased deprivation-induced feeding at 30 min postinjection. Co-injection of beta-FNA, but not NAL, significantly blocked the depressive effect of [D-Ala2, N-MePhe4, Gly5-ol]-enkephalin (mu-opioid agonist) under ad libitum conditions. Central injection of ICI attenuated significant effects of [D-Pen(2,5)]-enkephalin (delta-opioid agonist) on feeding behavior in ad libitum fed chicks. Co-injection of beta-FNA, but not ICI, significantly attenuated the orexigenic effect of [D-Ala2, D-Leu3]-enkephalin (mu- and delta-opioid agonist). These results suggest that the endogenous opioid peptides, which act on the mu- and/or delta-opioid receptor, have an important role in feeding behavior in the central nervous system of meat-type chicks.

Brain creatine functions to attenuate acute stress responses through GABAnergic system in chicks

The involvement of brain creatine in the adaptation to acute stress responses was investigated in chicks. In experiment 1, brain creatine content of chicks exposed to social separation stress was significantly increased compared with control chicks. The effects of i.c.v. injection of creatine (2 mug) on vocalizations, spontaneous activity and plasma corticosterone concentration in chicks under social separation stress were investigated in experiment 2. All measurements were attenuated by the i.c.v. injection of creatine compared with the controls under separation stress. Creatine also significantly decreased the active posture, but increased the motionless eye-opened posture, compared with the control. To clarify the relationship between creatine function and GABA receptors, the i.c.v. co-injection of creatine with picrotoxin, a GABA-A receptor antagonist, or CGP54626, a GABA-B receptor antagonist, was investigated in experiments 3 and 4. The effects of creatine on vocalizations and spontaneous activity were attenuated by co-injection of picrotoxin. In this case, active postures decreased by creatine were recovered by co-injection with picrotoxin. However, these effects were not obtained with CGP54626. The results suggest that central creatine functions within the CNS to attenuate the acute stress response by acting through GABA-A receptors in chicks.

Intracerebroventricular injection of muscimol, baclofen or nipecotic acid stimulates food intake in layer-type, but not meat-type, chicks

This study was designed to compare the effects of muscimol (GABA(A) agonist), baclofen (GABA(B) agonist) and nipecotic acid (GABA uptake inhibitor) on food intake in two chicken strains (meat-type and layer-type chicks). The intracerebroventricular (ICV) injection of all GABA agents induced hyperphagia in layer-type chicks. However, in broiler chicks, there were similar tendencies with muscimol and nipecotic acid but not significantly different. Conversely, ICV injection of baclofen depressed feeding of broiler chicks. These results suggest that there are some differences in central GABAergic systems between these strains of chicks, but GABAergic systems have an important role in the regulation of food intake in neonatal chicks.

Central pipecolic acid increases food intake under ad libitum feeding conditions in the neonatal chick

It has been demonstrated that L-pipecolic acid (L-PA) is a major metabolic intermediate of L-lysine in the mammalian and chicken brain. A previous study showed that intracerebroventricular (i.c.v.) injection of L-PA suppressed feeding in neonatal chicks, and the actions were associated with gamma-aminobutyric acid (GABA)-B receptor activation. It has been reported that endogenous L-PA in the brain fluctuated under different feeding conditions. In the present study, we investigated the effect of i.c.v. injection of L-PA on food intake in the neonatal chick under ad libitum feeding conditions. The food intake was increased by 0.5 or 1.0 mg L-PA under ad libitum feeding conditions contrary to previous studies using fasted birds. A hyperphagic effect of L-PA (0.5 mg) was attenuated by both GABA-A receptor antagonist (picrotoxin, 0.5 microg) and GABA-B receptor antagonist (CGP54626, 21.0 ng). These results indicate that a hyperphagic effect of L-PA is mediated by both GABA-A and GABA-B receptors and L-PA differentially affects food intake under different feeding conditions in the neonatal chick.