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L-Ornithine is a potential acute satiety signal in the brain of neonatal chicks
Abstract
Recently, we observed that neonatal chicks exhibit feeding behavior characterized by frequent food intake and short resting intervals, with changes detected in the brain amino acid and monoamine concentrations. In this study, we aimed to clarify further the relationship between the appetite of neonatal chicks and brain amino acid metabolism. In Experiment 1, changes were investigated in free amino acids in the brain under conditions of regulated appetite induced by fasting and subsequent short-term re-feeding. Chicks (5days old) were distributed into four treatment groups - namely, fasting for 3h, and fasting for 3h followed by re-feeding for 10, 20 or 30min. Brain samples were collected after treatment to analyze free amino acid concentrations. Amino adipic acid and proline in all brain parts as well as arginine and ornithine in all brain parts - except mesencephalic arginine and cerebellar ornithine - were increased in a time-dependent manner following re-feeding. In Experiment 2, we further examined the effect of exogenous administration of some amino acids altered in association with feeding behavior in Experiment 1. We chose L-arginine and its functional metabolite, L-ornithine, to analyze their effects on food intake in chicks. Intracerebroventricular injection (2μmol) of L-ornithine, but not L-arginine, significantly inhibited food intake in neonatal chicks. In Experiment 3, we found that central injection of L-ornithine (2, 4, and 6μmol) dose-dependently suppressed food intake in chicks. These results suggested that L-ornithine may have an important role in the control of food intake as an acute satiety signal in the neonatal chick brain.
... Tran et al. [13] demonstrated the frequent feeding behavior of neonatal chicks and initially observed differences in concentrations of amino acids and monoamines in the brain of chicks, who either attempted to obtain food (hungry group) or turned it down (satiety group). This sparked extensive investigation of the relationship between appetite regulation induced by fasting, subsequent short-term refeeding, and central amino acid metabolism [20]. The chicks were divided into four treatment groups: (i) fasting for 3 h and (ii-iv) fasting for 3 h, followed by refeeding for 10, 20, or 30 min. ...
... In terms of food intake regulation, L-arginine and L-ornithine increased in a time-dependent manner in all parts of the brain following refeeding after fasting except for mesencephalic Larginine and cerebellar L-ornithine [20]. Their central exogenous administration resulted in a dose-dependent feeding inhibitory effect only in chicks injected with L-ornithine [20]. ...
... In terms of food intake regulation, L-arginine and L-ornithine increased in a time-dependent manner in all parts of the brain following refeeding after fasting except for mesencephalic Larginine and cerebellar L-ornithine [20]. Their central exogenous administration resulted in a dose-dependent feeding inhibitory effect only in chicks injected with L-ornithine [20]. This implies 3 Tran: Central regulation of feeding in chicks that endogenous L-ornithine may act as a satiety signal in neonatal chicks. ...
Regulation of food intake, especially during the neonatal period, is important to ensure optimal nutrition and meet the metabolic requirements of growing and healthy animals. However, many problems associated with neonatal chicks remain unsolved. Feeding behavior during the neonatal stage is characterized by short resting periods between very brief times spent taking up food. Accordingly, neuropeptides, which take time to synthesize and release, as well as nutrients that are taken up via feeding, may be involved in feeding regulation. The present review summarizes current knowledge about the role of amino acids and their interaction with neuropeptides on the regulation of food intake in neonatal chicks with special emphasis on L-arginine metabolism and neuropeptide Y. Fasting and subsequent short-term refeeding influence amino acid metabolism in the brain. Short-term refeeding induces a rapid increase in the concentrations of several amino acids, which may contribute to satiety signals in the neonatal chick brain. The function of L-arginine is related to its metabolite, L-ornithine, which acts as an innate satiety signal in the control of food intake. Co-injection with L-ornithine attenuates the orexigenic effect of neuropeptide Y in a dose-dependent manner. This implies a potent interaction in the brain between the regulation of food intake by neuropeptide Y and acute satiety signals by L-ornithine. The roles of other amino acids in feeding and their relationship with the stress response are also discussed in this review. In conclusion, endogenous neuropeptides and endogenous and/or exogenous nutrients such as amino acids are believed to coordinate the feeding behavior of neonatal chicks.
... Ornithine itself has also been proposed to play an important role in the induction of sedative and hypnotic effects, but not through polyamine metabolites (Kurauchi et al., 2010). Moreover, ICV injection of ornithine, but not arginine, significantly inhibited food intake in a dose-dependent manner in neonatal chicks (Tran et al., 2016). l-ornithine was shown to exert attenuation effects on the stress response, which is different from its actions on neural circuits in controlling food intake behavior due to the non-responsiveness of stress-related receptors (Tran et al., 2016). ...
... Moreover, ICV injection of ornithine, but not arginine, significantly inhibited food intake in a dose-dependent manner in neonatal chicks (Tran et al., 2016). l-ornithine was shown to exert attenuation effects on the stress response, which is different from its actions on neural circuits in controlling food intake behavior due to the non-responsiveness of stress-related receptors (Tran et al., 2016). More importantly, a time-dependent increase in endogenous ornithine levels in the brain was observed following refeeding after fasting in chicks maintained in an acute satiety state (Tran et al., 2016). ...
... l-ornithine was shown to exert attenuation effects on the stress response, which is different from its actions on neural circuits in controlling food intake behavior due to the non-responsiveness of stress-related receptors (Tran et al., 2016). More importantly, a time-dependent increase in endogenous ornithine levels in the brain was observed following refeeding after fasting in chicks maintained in an acute satiety state (Tran et al., 2016). This implies that endogenous ornithine may physiologically inhibit feeding behavior in 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.
... Several free amino acids in different brain sites were linearly correlated with plasma free amino acids. On the other hand, Tran et al. (2016) determined changes in the free amino acids in the brain under conditions of regulated appetite induced by fasting and subsequent short-term refeeding. Chicks were distributed into four treatment groups, i.e., fasting for 3 h, and fasting for 3 h followed by refeeding for 10, 20, or 30 min. ...
... Therefore, the l-PA pathway may be particularly important in the brain. Tran et al. (2016) demonstrated that amino adipic acid, the end product of l-Lys metabolism (Fig. 3), increased in several brain regions of neonatal chicks shortly after refeeding, suggesting that l-PA is quickly produced from l-Lys in the brain as reported by Chang (1978). ...
... This is the case for the regulation of food intake. Tran et al. (2016) reported that ICV injection of l-Orn, but not l-Arg, significantly inhibited food intake in neonatal chicks. Furthermore, ICV injection of l-Orn suppressed food intake in a dose-dependent manner in chicks. ...
Animals at the neonatal stage have to eat more to support better growth and health. However, it is difficult to understand the mechanism of feeding during an early stage of life in the brain of the rodent model. Chickens are precocial and they can look for their food by themselves right after hatching. Neonatal chicks have a relatively large-sized brain; therefore, the drugs are easy to administer centrally and changes in food intake can be clearly monitored. Sleeping status, which affects food intake, can be estimated from the posture. The closest vertebrate outgroup to mammals is birds, but it was reported that the organization of the human genome is closer to that of the chicken than the mouse. Thus, it is important to understand the central mechanism of feeding regulation in the neonatal chicks. In neuropeptides, the number of candidates as the orexigenic factor was less than those as the anorexigenic factor, even at an early growth stage. Some of the neuropeptides have reverse effects, e.g., ghrelin and prolactin releasing peptides, or no effects compared to the effects confirmed in mammals. Some of the genetic differences between meat-type (broiler) and layer-type chickens would explain the difference in food intake. On the other hand, it was difficult to explain the feeding mechanism by neuropeptides alone, as neonatal chicks have a repeated feeding, sleeping, and resting behavior within a short period. Some of the amino acids and their metabolites act centrally to regulate feeding with sedative and hypnotic effects. In conclusion, endogenous neuropeptides and endogenous and/or exogenous nutrients like amino acids collaborate to regulate feeding behavior in neonatal chicks.
... Moreover, amino acid metabolism is involved in the control of food intake regulation, with feeding behavior affected by the abundance of amino acids and in response to administration of amino acids. For instance, lysine deficiency suppressed food intake in chickens (Latshaw 1993), and central injection of ornithine (Tran et al. 2016), β-alanine and histidine (Tomonaga et al. 2004), suppressed food intake, while leucine increased food consumption in chicks (Izumi et al. 2004). Thus, it is crucial to understand the regulatory mechanisms associated with amino acid profiles in the CNS. ...
... Brain arginine and ornithine were reported to induce sedative and hypnotic effects (Suenaga et al. 2008;Kurauchi et al. 2010). Central injection of ornithine inhibited feeding behavior in neonatal chicks (Tran et al. 2016). Thus, reduced brain arginine and ornithine may contribute to anorexia and sedation induced by taurine. ...
Brain amino acid metabolism has been reported to regulate body temperature, feeding behavior and stress response. Central injection of taurine induced hypothermic and anorexigenic effects in chicks. However, it is still unknown how the amino acid metabolism is influenced by the central injection of taurine. Therefore, the objective of this study was to investigate the changes in brain and plasma free amino acids following central injection of taurine. Five-day-old male Julia layer chicks (n = 10) were subjected to intracerebroventricular (ICV) injection with saline or taurine (5 µmol/10 µL). Central taurine increased tryptophan concentrations in the diencephalon, and decreased tyrosine in the diencephalon, brainstem, cerebellum, telencephalon and plasma at 30 min post-injection. Taurine was increased in all the brain parts after ICV taurine. Although histidine and cystathionine concentrations were increased in the diencephalon and brainstem, several amino acids such as isoleucine, arginine, methionine, phenylalanine, glutamic acid, asparagine, proline, and alanine were reduced following central injection of taurine. All amino acid concentrations were decreased in the plasma after ICV taurine. In conclusion, central taurine quickly changes free amino acid concentrations in the brain and plasma, which may have a role in thermoregulation, food intake and stress response in chicks.
... FI in livestock and poultry is largely influenced by the hypothalamus (Tran et al., 2016). The hypothalamus plays a crucial role in modulating feed conversion efficiency by regulating foraging behavior and the expression of relevant genes. ...
... Amino acids have been extensively studied in nutritional regulation, as they play central roles in protein synthesis and energy production. There is also significant interest in the physiological role of amino acids in the central nervous system, with the intake of feed in mammals and poultry being regulated by the hypothalamus (Tran et al., 2016). Khan et al. (1979) suggested that the control of amino acids in the hypothalamus could be relevant to feeding regulation. ...
Background: There is a current lack of research on the molecular pathways by which lysine regulates feed intake in chicks. Regulation is controlled by the hypothalamus and lysine metabolism links the availability of amino acids and nutritional perception with food intake. The mechanism underlying this phenomenon remains unclear. To investigate the regulatory mechanism of lysine on feed intake in chicks, this study used Yao chickens as a research model. The levels of lysine in the feed of chicks were adjusted to determine the effect on feed intake. The hypothalamus tissue of the chicks was analyzed using RNA-seq and metabolomics to identify the relevant genes. We employed Gene Ontology and identification of signaling pathways to characterize the molecular regulatory biological pathways of lysine in poultry feeding. Methods: This study used RNA-seq technology to investigate the genes and marker metabolites involved in lysine regulation of feed intake in chickens. The study explored the molecular mechanism by which dietary lysine regulates feed intake in chickens via the hypothalamus. Four hundred healthy 1-day-old chicks (Yao chickens) were randomly divided into four groups, with five replicates in each group (n = 20). Result: There was a significant difference in feed intake among chicks fed with diets containing 0.65% (abbreviated as MGO), 0.85% (FIH), 1.0% (MGS) and 1.2% (FIL) lysine levels. The group with the highest feed intake was FIH, while the group with the lowest feed intake was FIL. By conducting RNA-seq of the hypothalamic tissue of chickens in both the highest and lowest feed intake groups, we obtained 2006 differentially expressed genes, comprising 1275 upregulated genes and 731 downregulated genes. Fourteen genes were related to food intake, including growth hormone, recombinant glutamate receptor, metabotropic 1 (GRM1) and recombinant glutamate receptor, metabotropic 3 (GRM3). Using liquid chromatograph mass spectrometer (LC-MS) metabolomics, we identified 25 differential metabolites. Nine metabolites, including C3H5NO4, C10H15NO2 and C13H14N203, were downregulated, while 16 metabolites, including C2H8NO3P, C3H7NO3 and C7H7NO2, were upregulated. Marker metabolites included 5-hydroxytryptophan and L-valine. A KEGG enrichment analysis revealed that the differential metabolites between the FIH and FIL groups were enriched in 26 pathways, with the significantly enriched pathway being the ABC transporter protein pathway (ID: map02010). RNA-seq and LC-MS analyses revealed that in chicks, the expression of the neuropeptides cocaine- and Amphetamine-Regulated Transcript Protein (CARTPT) and neuropeptide Y (NPY)/agouti-related protein (AGRP), along with genes such as sucrose synthase (SS 2), recombinant cholecystokinin A receptor (CCKAR) and recombinant cholecystokinin B receptor (CCKBR), was regulated by the hypothalamic feeding regulation center that senses the level of lysine in the feed. These molecules bind to specific receptors and initiate a signaling cascade in specific hypothalamic neuronal groups, thereby regulating chick feed intake and in turn affecting growth, development and production performance.
... (1) ICV injection of L-leucine increased the food intake of neonatal chicks, while the other two BCAAs or α-ketoisocaproate had no effect (Izumi et al. 2004); (2) ICV injection of L-ornithine, carnosine, L-His, β-Ala, and histamine to neonatal chicks decrease their food intake (Tran et al. 2016;Tomonaga et al. 2004;Kawakami et al. 2000); these AAs are potential acute satiety signals in the brain of neonatal chicks; (3) the effect of L-Pro on food intake by neonatal chicks varied with feeding status, with ICV injection of L-Pro stimulating food intake under free access conditions but decreasing food intake in the fasting state (Haraguchi et al. 2007). To translate these discoveries into feeding, studies involving dietary supplementation of one or more AAs should be conducted with poultry. ...
Both poultry meat and eggs provide high-quality animal protein [containing sufficient amounts and proper ratios of amino acids (AAs)] for human consumption and, therefore, play an important role in the growth, development, and health of all individuals. Because there are growing concerns about the suboptimal efficiencies of poultry production and its impact on environmental sustainability, much attention has been paid to the formulation of low-protein diets and precision nutrition through the addition of low-cost crystalline AAs or alternative sources of animal-protein feedstuffs. This necessitates a better understanding of AA nutrition and metabolism in chickens. Although historic nutrition research has focused on nutritionally essential amino acids (EAAs) that are not synthesized or are inadequately synthesized in the body, increasing evidence shows that the traditionally classified nutritionally nonessential amino acids (NEAAs), such as glutamine and glutamate, have physiological and regulatory roles other than protein synthesis in chicken growth and egg production. In addition, like other avian species, chickens do not synthesize adequately glycine or proline (the most abundant AAs in the body but present in plant-source feedstuffs at low content) relative to their nutritional and physiological needs. Therefore, these two AAs must be sufficient in poultry diets. Animal proteins (including ruminant meat & bone meal and hydrolyzed feather meal) are abundant sources of both glycine and proline in chicken nutrition. Clearly, chickens (including broilers and laying hens) have dietary requirements for all proteinogenic AAs to achieve their maximum productivity and maintain optimum health particularly under adverse conditions such as heat stress and disease. This is a paradigm shift in poultry nutrition from the 70-year-old “ideal protein” concept that concerned only about EAAs to the focus of functional AAs that include both EAAs and NEAAs.
... Amino acids play important roles in growth and could also play critical roles in controlling body temperature Chowdhury et al., 2015), food intake Erwan et al., 2013;Tran et al., 2016) and behavior (Kabuki et al., 2011;Erwan et al., 2013;Ikeda et al., 2014;Tran et al., 2015). Several free amino acids were significantly increased in the blood, brain and muscle of chicks within 15 or 30 min of exposure to high ambient temperature (HT; 35°C; Ito et al., 2014); however, most of those free amino acids declined in the brain and plasma when chicks were exposed to HT (35°C) for a long timethat is, for either 24 or 48 h . ...
Thermal manipulation (TM) of incubation temperature causes metabolic alterations and contributes to improving thermotolerance in chicks post hatching. However, there has been no report on amino acid metabolism during TM and the part it plays in thermotolerance. In this study, we therefore first analyzed free amino acid concentrations in the embryonic brain and liver during TM (38.6 °C, 6 h/d during embryonic day (ED) 10 to ED 18). It was found that leucine (Leu), phenylalanine and lysine were significantly decreased in the embryonic brain and liver. We then chose l-Leu and other branched-chain amino acids (l-isoleucine (l-Ileu) and l-valine (l-Val)) for in ovo injection on ED 7 to reveal their roles in thermoregulation, growth, food intake and thermotolerance in chicks. It was found that in ovo injection of l-Leu, but not of l-Ileu or l-Val, caused a significant decline in body temperature at hatching and increased food intake and body weight gain in broiler chicks. Interestingly, in ovo injection of l-Leu resulted in the acquisition of thermotolerance under high ambient temperature (35 ± 1 °C for 180 min) in comparison with the control thermoneutral temperature (28 ± 1 °C for 180 min). These results indicate that the free amino acid concentrations during embryogenesis were altered by TM. l-Leu administration in eggs caused a reduction in body temperature at hatching, and afforded thermotolerance in heat-exposed young chicks, further suggesting that l-Leu may be one of the key metabolic factors involved in controlling body temperature in embryos, as well as in producing thermotolerance after hatching.
Background:
Exposure to a high ambient temperature (HT) can cause heat stress, which has a negative impact on physiological functions. L-tryptophan (L-Trp) as a precursor of serotonergic and kynurenine (Kyn) pathways, has a calmative effect during different stress statuses.
Aims:
This study was carried out to determine the influence of intraperitoneal injection of Trp on feeding behavior, rectal temperature, and some blood parameters in the heat stress condition.
Methods:
L-tryptophan (25 and 50 mg/kg body weight, BW) was administered intraperitoneally during either HT (39°C) or control temperature (CT; 31°C) for 5 h whilst fed or fasted in 7-day-old chicks.
Results:
L-tryptophan caused elevation in decreased food intake and significantly decreased rectal temperature during acute heat stress at the dose of 50 mg/kg BW. Rectal temperature reduced in the fasted state at the dose of 50 mg/kg BW, and at the dose of 25 mg/kg BW Trp in the fed state in comparison with the other experimental groups. Reduction of serum glucose, triglyceride, and corticosterone levels was seen during the fed state. L-tryptophan had a significant reducing effect on the serum corticosterone level in the fasted state in comparison with the fed state, and also revealed a significant decline at the dose of 25 mg/kg BW on the elevated serum corticosterone under heat stress.
Conclusion:
Administration of L-tryptophan leads to increase cumulative food intake and decrease rectal temperature during heat stress. Also, L-Trp causes to decline increased serum corticosterone level under heat stress and fasted state. These findings indicated the potential regulator role of Trp to modulate stress response in heat-exposed chicks.
With global warming, heat stress is becoming a pressing concern worldwide. In chickens, heat stress reduces food intake and growth, and increases body temperature and stress responses. Although it is believed that young chicks do not experience heat stress as they need a higher ambient temperature to survive, our series of studies in young chicks showed that they are sensitive to heat stress. This review summarizes current knowledge on amino acid metabolisms during heat stress, with special emphasis on the hypothermic functions of L-citrulline (L-Cit) and L-leucine (L-Leu), and the functions of neuropeptide Y (NPY) in terms of body temperature and heat stress regulation in chicks. Amino acid metabolism is severely affected by heat stress. For example, prolonged heat stress reduces plasma L-Cit in chicks and L-Leu in the brain and liver of embryos. L-Cit and L-Leu supplementation affords thermotolerance in young chicks. NPY expression is increased in the brains of heat-exposed chicks. NPY has a hypothermic action under control thermoneutral temperature and heat stress in chicks. The NPY-sub-receptor Y5 is a partial mediator of the hypothermic action of NPY. Further, NPY stimulates brain dopamine concentrations and acts as an anti-stress agent in heat-exposed fasted, but not fed chicks. In conclusion, young chicks can serve as a model animal for the study of heat stress in chickens. L-Cit, L-Leu, and NPY were identified as biomarkers of heat stress, with the potential to afford thermotolerance in chicks.
Neurotrophin 3 (NT3) is a potent neurotrophic factor for promoting remyelination and recovery of neuronal function; upregulation of its expression in the central nervous system (CNS) is thus of major therapeutic importance for neurological deficits. Matrine (MAT), a quinolizidine alkaloid derived from the herb Radix Sophorae Flavescent, has been recently reported to effectively ameliorate clinical signs in experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), by secreting antiinflammatory cytokines. In the present study, our goal was to investigate whether MAT could affect NT3 expression of glial cells in the CNS, the major cell populations in the CNS foci of MS/EAE. We found that MAT markedly upregulated NT3 expression in the CNS not only by microglia/macrophages and astrocytes, but also by oligodendrocyte precursor cells, indicative of both paracrine and autocrine effects on myelinating cells. While MAT treatment reduced the numbers of iNOS(+) M1, but increased Arg1(+) M2 microglia/macrophage phenotypes, NT3 expression was upregulated in both phenotypes. These results indicate that MAT therapy for EAE acts, at least in part, by stimulating local production of NT3 by glial cells in the CNS, which protects neural cells from CNS inflammation-induced tissue damage.
Domesticated chicks are precocial and therefore have relatively well-developed feeding behavior. The role of hypothalamic neuropeptides in food-intake regulation in chicks has been reported for decades. However, we hypothesized that nutrients and their metabolites in the brain may be involved in food intake in chicks because these animals exhibit a very frequent feeding pattern. Therefore, the purpose of this study was to examine the feeding behavior of chicks as well as the associated changes in free amino acid and monoamine concentrations in the chick brain. The feeding behavior of chicks was recorded continuously for 6 h. The next day, brain and blood samples were collected when the chicks either attempted to have food (hungry group) or turned food down (satiated group), in order to analyze the concentrations of the free amino acids and monoamines. We confirmed that the feeding behavior of neonatal chicks was characterized by short resting periods between very brief times spent on food intake. Several free amino acids in the mesencephalon were significantly lower in the satiated group than in the hungry group, while l-histidine and l-glutamine were significantly higher. Notably, there was no change in the free amino acid concentrations in other brain regions or plasma. As for monoamines, serotonin and norepinephrine were significantly lower in the mesencephalon of the hungry group compared with the satiated group, but 5 hydroxyindolacetic acid (5-HIAA) was higher. In addition, serotonin and norepinephrine levels were significantly higher in the brain stem of the hungry chicks compared with the satiated group, but levels of 5-HIAA and homovanillic acid were lower. Levels of both dopamine and its metabolite, 3,4-dihydroxyphenylacetic acid, were significantly higher in the diencephalon and telencephalon of the chicks in the hungry group. In conclusion, the changes in the free amino acids and monoamines in the brain may have some role in the feeding behavior of neonatal chicks.
In this study we examined fasted and refed cfos activation in cortical, brainstem and hypothalamic brain regions associated with appetite regulation. We examined a number of time points during refeeding to gain insight into the temporal pattern of neuronal activation and changes in endocrine parameters associated with fasting and refeeding. In response to refeeding, blood glucose and plasma insulin returned to basal levels within 30 mins, whereas plasma NEFA and leptin returned to basal levels after 1 and 2 hours, respectively. Within the hypothalamic arcuate nucleus (ARC), fasting increased cfos activation in ∼25% of NPY neurons, which was terminated 1 hour after refeeding. Fasting had no effect on cfos activation in POMC neurons, however 1 and 2 hours refeeding significantly activated ∼20% of ARC POMC neurons. Acute refeeding (30, 60 and 120 minutes) but not fasting, increased cfos activation in the nucleus accumbens, the cingulate cortex (but not the insular cortex), the medial and lateral parabrachial nucleus, the nucleus of the solitary tract, the area postrema, the dorsal raphe and the ventromedial nucleus of the hypothalamus. After 6 hours refeeding, cfos activity was reduced in the majority of these regions compared to earlier time points. Our data indicates that acute refeeding, rather than long-term fasting activates cortical, brainstem and hypothalamic neural circuits associated with appetite regulation and reward processing. While the hypothalamic ARC remains a critical sensory node detecting changes in metabolic state and feedback during fasting and acute refeeding, our results also reveal the temporal pattern in cfos activation in cortical and brainstem areas implicated in the control of appetite and body weight regulation.
The effects of intracerebroventricular injection of L-tryptophan on feeding behavior and the levels of brain neurotransmitters (amino acids or monoamines) were investigated in ad libitum chicks. The tryptophan treatment (3 or 6μmol) significantly inhibited food intake in chicks at 30 min postinjection. The levels of serotonin (5-HT) and its metabolite, 5-dihydroxyindolacetic acid, in chicks treated with tryptophan were significantly higher than those with saline at 15 min postinjection. However, there were no differences in the levels of catecholamines (adrenaline, noradrenaline and dopamine) and amino acid neurotransmitters (e.g., γ-aminobutyric acid, glycine and glutamic acid). The tryptophan-induced anorexia tended to be attenuated by the 5-HT2A receptor antagonist ketanserin (10μg). These results suggest that the administration of tryptophan into the chick brain produces the anorexic effect, and that the change in brain 5-HT content may be involved in this anorexia.
Background:
The brain levels of glutamate (Glu) and glutamine (Gln) are partially regulated through the Glu-Gln cycle. Astrocytes play a role in regulating the Glu-Gln cycle, and loss of astrocytes has been associated with depressive disorders. We hypothesized that levels of Glu and Gln would be affected by astrocyte loss and dysregulation of the Glu-Gln cycle and that depressive-like behaviours would be closely related to the level of changes in Glu and Gln.
Methods:
We used liquid chromatography to measure Glu and Gln concentrations in the prefrontal cortex of male mice infused with L-α aminoadipic acid (L-AAA), a specific astrocyte toxin, in the prelimbic cortex. Methionine sulfoximine, a Gln synthetase inhibitor, and α-methyl-amino-isobutyric acid, a blocker of neuronal Gln transporters, were used to disturb the Glu-Gln cycle. We assessed the behavioural change by drug infusion using the forced swim test (FST) and sucrose preference test.
Results:
The Glu and Gln levels were decreased on the fifth day after L-AAA infusion, and the infused mice showed longer durations of immobility in the FST and lower sucrose preference, indicative of depressive-like behaviour. Mice in which Gln synthetase or Gln transport were inhibited also exhibited increased immobility in the FST. Direct infusion of L-Gln reversed the increased immobility induced by astrocyte ablation and Glu-Gln cycle impairments.
Limitations:
Genetically modified animal models and diverse behavioural assessments would have been helpful to solidify our conclusions.
Conclusion:
Neuronal Gln deficiency in the prefrontal cortex may cause depressive behaviours.
By the 1990s a convergence of evidence had accumulated to suggest that neurons within the lateral hypothalamus (LH) play important roles in the stimulation of feeding behavior. However, there was little direct evidence demonstrating that neurotransmitters in the LH could, like electrical stimulation, elicit feeding in satiated animals. The present paper is a brief review in honor of Bartley Hoebel's scientific contributions, emphasizing the evidence from my lab that the excitatory neurotransmitter glutamate and the inhibitory neurotransmitter gamma aminobutyric acid (GABA) in the LH mediate feeding stimulation and feeding inhibition respectively. Specifically, we summarize evidence that LH injection of glutamate, or agonists of its N-methyl-D-aspartate (NMDA) and non-NMDA receptors, elicits feeding in satiated rats, that NMDA receptor antagonists block the eating elicited by NMDA and, more importantly, that NMDA blockade suppresses natural feeding and can reduce body weight. Conversely, GABA(A) agonists injected into the LH suppress feeding and can also reduce body weight, while GABA(A) receptor antagonists actually elicit eating when injected into the LH of satiated rats. It is suggested that natural feeding may reflect the moment-to-moment balance in the activity of glutamate and GABA within the LH.
Several different neuronal populations are involved in regulating energy homeostasis. Among these, agouti-related protein (AgRP) neurons are thought to promote feeding and weight gain; however, the evidence supporting this view is incomplete. Using designer receptors exclusively activated by designer drugs (DREADD) technology to provide specific and reversible regulation of neuronal activity in mice, we have demonstrated that acute activation of AgRP neurons rapidly and dramatically induces feeding, reduces energy expenditure, and ultimately increases fat stores. All these effects returned to baseline after stimulation was withdrawn. In contrast, inhibiting AgRP neuronal activity in hungry mice reduced food intake. Together, these findings demonstrate that AgRP neuron activity is both necessary and sufficient for feeding. Of interest, activating AgRP neurons potently increased motivation for feeding and also drove intense food-seeking behavior, demonstrating that AgRP neurons engage brain sites controlling multiple levels of feeding behavior. Due to its ease of use and suitability for both acute and chronic regulation, DREADD technology is ideally suited for investigating the neural circuits hypothesized to regulate energy balance.
In mammals, L-arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health status of the individual. It can be derived from proline or glutamate, with the ultimate synthetic step catalyzed by argininosuccinate lyase. L-arginine is catabolized by arginases, nitric oxide synthases, arginine:glycine amidinotransferase, and possibly also by arginine decarboxylase, resulting ultimately in the production of urea, proline, glutamate, polyamines, nitric oxide, creatine, or agmatine. There is considerable diversity in tissue-specific and stimulus-dependent regulation of expression within this group of enzymes, and the expression of several of them can be regulated at transcriptional and translational levels by changes in the concentration of L-arginine itself. Consequently, the interplay among these enzymes in the regulation of specific aspects of arginine metabolism can be quite complex. For example, nitric oxide production can be affected by the interplay between nitric oxide synthases, arginases, and argininosuccinate synthetase. This metabolic complexity can pose challenges for analyses of arginine metabolism not only because L-arginine is a substrate for several different enzymes but also because ornithine and citrulline, key products of arginine metabolism, can each be produced by multiple enzymes. This overview highlights key features of the arginine metabolic enzymes and their interactions.
Recently, we observed that central administration of L-arginine attenuated the stress responses of neonatal chicks by inducing a sedative and hypnotic effect. In addition, L-ornithine, which is produced from L-arginine in the brain, appeared to interact with L-arginine during a stress response. Several putative metabolites from L-ornithine, including L-citrullme and D-ornithine, were therefore investigated in the present study. The effects of intracerebroventricular injection of L-ornithine, L-citrulline and D-ornithine were compared in chicks under an isolation-induced stress. L-ornithine greatly attenuated the stress response and induced sedative and hypnotic effects. D-ornithine weakly attenuated the stress responses, while L-citrulline had no effect.
Heat stress causes an increase in body temperature and reduced food intake in chickens. Several neuropeptides and amino acids play a vital role in the regulation of food intake. However, the responses of neuropeptides and amino acids to heat-stress-induced food-intake regulation are poorly understood. In the current study, the hypothalamic mRNA expression of some neuropeptides related to food intake and the content of free amino acids in the brain and plasma was examined in 14-day-old chicks exposed to a high ambient temperature (HT; 40±1°C for 2 or 5h) or to a control thermoneutral temperature (CT; 30±1°C). HT significantly increased rectal temperature and plasma corticosterone level and suppressed food intake. HT also increased the expression of neuropeptide Y (NPY) and agouti-signaling protein (ASIP) precursor mRNA, while no change was observed in pro-opiomelanocortin, cholecystokinin, ghrelin, or corticotropin-releasing hormone precursor mRNA. It was further found that the diencephalic content of free amino acids - namely, tryptophan, leucine, isoleucine, valine and serine - was significantly higher in HT chicks with some alterations in their plasma amino acids in comparison with CT chicks. The induction of NPY and ASIP expression and the alteration of some free amino acids during HT suggest that these changes can be the results or causes the suppression of food intake.
Copyright © 2015. Published by Elsevier Inc.
1. An experiment was conducted to analyse the changes in free amino acid concentrations in the blood, brain and muscle of chicks in response to 15 or 30 min exposure to high ambient temperature (HT).
2. Food intake and body weight were not affected, while rectal temperature was significantly increased by short-term HT exposure.
3. Several free amino acid concentrations increased in the blood, brain and muscle even with short-term HT, whereas levels of a few amino acids declined significantly. As well as the nonessential amino acids, essential amino acids also significantly increased with exposure to HT.
4. 3-Methylhistidine, a marker of proteolysis, significantly declined in the muscle of HT chicks, implying a reduction of protein breakdown under HT.
5. These results indicate that alteration of protein metabolism may occur in chicks even with short-term heat exposure.
High ambient temperatures (HT) reduce food intake and body weight in young chickens, and HT can cause increased expression of hypothalamic neuropeptides. The mechanisms by which HT act, and the effects of HT on cellular homeostasis in the brain, are however not well understood. In the current study lipid peroxidation and amino acid metabolism were measured in the brains of 14 d old chicks exposed to HT (35 °C for 24 or 48 h) or to control thermoneutral temperature (CT; 30 °C). Malondialdehyde (MDA) was measured in the brain to determine the degree of oxidative damage. HT increased body temperature and reduced food intake and body weight gain. HT also increased diencephalic oxidative damage after 48 h, and altered some free amino acid concentrations in the diencephalon. Diencephalic MDA concentrations were increased by HT and time, with the effect of HT more prominent with increasing time. HT altered cystathionine, serine, tyrosine and isoleucine concentrations. Cystathionine was lower in HT birds compared with CT birds at 24 h, whilst serine, tyrosine and isoleucine were higher at 48 h in HT birds. An increase in oxidative damage and alterations in amino acid concentrations in the diencephalon may contribute to the physiological, behavioral and thermoregulatory responses of heat-exposed chicks.
Key points
Proteins are more satiating than fats or lipids. Proteins are built by the 20 proteogenic amino acids.
Here, we identified l ‐arginine, l ‐lysine and l ‐glutamic acid as the most potent anorectic amino acids in rats.
l ‐Arginine and l ‐glutamic acid require intact neurons in the area postrema to inhibit food intake, whereas l ‐lysine requires intact afferent fibres of the vagus nerve. All three mediate their effect by the blood stream.
All three amino acids induce gastric distension by delaying gastric emptying and inducing secretion. However, the gastric phenotype does not mediate the anorectic response.
These results unravel amino acid‐specific mechanisms regulating digestion and eating behaviour and thereby contribute to the understanding of nutrient sensing in vivo .
Abstract To maintain nutrient homeostasis the central nervous system integrates signals that promote or inhibit eating. The supply of vital amino acids is tuned by adjusting food intake according to its dietary protein content. We hypothesized that this effect is based on the sensing of individual amino acids as a signal to control food intake. Here, we show that food intake was most potently reduced by oral l ‐arginine (Arg), l ‐lysine (Lys) and l ‐glutamic acid (Glu) compared to all other 17 proteogenic amino acids in rats. These three amino acids induced neuronal activity in the area postrema and the nucleus of the solitary tract. Surgical lesion of the area postrema abolished the anorectic response to Arg and Glu, whereas vagal afferent lesion prevented the response to Lys. These three amino acids also provoked gastric distension by differentially altering gastric secretion and/or emptying. Importantly, these peripheral mechanical vagal stimuli were dissociated from the amino acids’ effect on food intake. Thus, Arg, Lys and Glu had a selective impact on food processing and intake suggesting them as direct sensory input to assess dietary protein content and quality in vivo . Overall, this study reveals novel amino acid‐specific mechanisms for the control of food intake and of gastrointestinal function.
Pyruvate can be synthesized from amino acids such as L-alanine, L-serine and L-cysteine. Recently, we reported that intracerebroventricular (i.c.v.) injection of L-serine and L-cysteine attenuated acute stress in chicks. This fact implies that amino acid substrates for pyruvate play a sedative role in the brain. However, no information was available for L-alanine. To elucidate the central effect of L-alanine on stress responses, L-alanine (0.8μmol) or saline was administered i.c.v. just before exposure to social separation stress. The social separation stress increased spontaneous activity and vocalization of chicks, but these responses were attenuated by the i.c.v. injection of L-alanine. In conclusion, in addition to L-serine and L-cysteine, centrally administered L-alanine may be effective in attenuating anxiety induced by a psychological stressor.
Kyotorphin (KTP), first isolated in the bovine brain and now having been identified in a variety of species, is known most extensively for its analgesic-like properties. KTP indirectly stimulates opioid receptors by releasing methionine enkephalin (met-enkephalin). Stimulation of opioid receptors is linked to hunger perception. In the present study, we sought to elucidate the effect of KTP on food intake in the neonatal chick. Intracerebroventricular injection of 0.6, 3.0 and 12nmol KTP increased feeding up to 60min post-injection. KTP treated chicks increased pecking efficiency and decreased time spent in deep rest, 20 and 30min following injection, respectively. Gastrointestinal transit rate was not affected by KTP. Blocking mu, delta, and kappa opioid receptors suppressed orexigenic effects of KTP, suggesting that all three types are involved in KTP's stimulatory effect. The lateral hypothalamus (LH) and arcuate nucleus (ARC) of the hypothalamus and the nucleus of the solitary tract (NTS), within the brainstem had increased numbers of c-Fos immunoreactive cells following KTP treatment. In conclusion, KTP caused increased feeding in broiler-type chicks, likely through activation of the LH, ARC, and NTS.
Intracerebral injection of C14-labeled L-proline resulted in its distribution in periventricular tissue (including septum, hippocampus, and hypothalamus) in neonatal chicks decapitated 1 min after injection. Delay of decapitation for 3, 9 or 45 min resulted only in an increased spread of label into the fourth ventricle. A simple, effective chick head-holder is also described.
Lateral hypothalamic (LH) injections of the excitatory neurotransmitter glutamate, or its excitatory amino acid (EAA) agonists, kainic acid (KA), d,l-α-amino-3-hydroxy-5-methyl-isoxazole propionic acid (AMPA), or N-methyl-d-aspartic acid (NMDA), can rapidly elicit an intense feeding response in satiated rats. To determine whether the LH is the actual locus of this effect, we compared these compounds' ability to stimulate feeding when injected into the LH, versus when injected into sites bracketing this region. Food intake in groups of adult male rats was measured 1 h after injection of glutamate (30–900 nmol), KA (0.1–1.0 nmol), AMPA (0.33–3.3 nmol), NMDA (0.33–33.3 nmol) or vehicle, through chronically implanted guide cannulas, into one of seven brain sites. These sites were: the LH, the anterior and posterior tips of the LH, the thalamus immediately dorsal to the LH, the amygdala just lateral to the LH, or the paraventricular and perifornical areas medial to the LH. The results show that across doses and agonists the eating-stimulatory effects were largest with injections into the LH. In the LH, glutamate between 300 and 900 nmol elicited a dose-dependent eating response of up to 5 g within 1 h (P <0.01). Each of the other agonists at doses of 3.3 nmol or less elicited eating responses of at least 10 g with injections into this site. Injections into the other brain sites produced either no eating, or occasionally smaller and less consistent eating responses. These results, demonstrating that glutamate and several of its agonists can act within the LH to elicit eating, suggest that glutamate and several of its receptor subtypes may participate in LH regulation of eating behavior.
I.c.v. injection of L-ornithine has been shown to have sedative and hypnotic effects on neonatal chicks exposed to acute stressful conditions. To clarify the mechanism, we conducted three experiments under strengthened stressful conditions with corticotropin-releasing factor (CRF). In Experiment 1, the effect of i.c.v. injection of CRF, L-ornithine (0.5 μmol) or CRF with L-ornithine on the stressful response of chicks was investigated. Compared with the vehicle control, CRF increased distress vocalizations and the time spent in active wakefulness. L-ornithine increased the time spent in sleeping posture, even following stimulation with CRF. In Experiment 2, dose-dependent effects of L-ornithine were investigated using i.c.v. administration with vehicle, CRF alone or CRF plus L-ornithine (0.125, 0.25 or 0.5 μmol). L-ornithine decreased the CRF-stimulated distress vocalizations in a dose-dependent manner. In Experiment 3, the chicks were injected i.c.v. with either CRF, CRF plus L-ornithine (0.5 μmol), CRF plus the γ-aminobutyric acid (GABA)A receptor antagonist picrotoxin or L-ornithine with picrotoxin. The sedative and hypnotic effects induced by L-ornithine were blocked with co-administration of picrotoxin. These results suggest that L-ornithine could attenuate CRF-stimulated stress behaviors acting at GABAA receptors.
To clarify whether L-ornithine and/or its metabolite involves sedative and hypnotic effects under social separation stress, the effects of intracerebroventricular (i.c.v.) injection of L-ornithine and polyamines (putrescine, spermidine and spermine) were compared in chicks. Birds were injected i.c.v. with 0.5 mumol of L-ornithine, putrescine, spermidine, spermine or saline (control). After injection, chicks were immediately separated from the flock and monitored for the number of distress vocalizations and various postures. L-Ornithine greatly attenuated the stress response and caused sedative and hypnotic effects. Among the polyamines, only putrescine attenuated distress vocalizations but did not induce sleep. In conclusion, the sedative and hypnotic effect of L-ornithine was mainly induced by L-ornithine itself, while the polyamines contributed to the sedative, but not hypnotic, effect under social separation stress.
Although, the central function of amino acids on food intake has been investigated, little information is available on the role of the amino acid L-proline. To clarify the central effect, several doses (0, 0.25, 0.5 and 1.0 mg) of L-proline were intracerebroventricularly (i.c.v.) injected into chicks under fasting (3 h) or ad libitum feeding conditions. Food intake was determined through 60 min post injection. Under fasting conditions, the following regression equation was obtained: food intake (g) = 3.047 + 3.496x - 5.332 x2 (x in mg of L-proline, R2 = 0.466, RMS = 1.056). Similarly, the regression equation was obtained under ad libitum conditions as follows: food intake (g) = 0.479 (SE 0.164) + 2.130 (SE 0.815)x - 2.452 (0.747)x2 (R2 = 0.313, RMS = 0.487). These results indicated that food intake was mildly stimulated by low levels of L-proline, but was suppressed by high levels in chicks. It is suggested that L-proline may act in the central nervous system to differentially regulate food intake, depending upon dose.
The purpose of the present study was to clarify the central nervous system function of amino acids during acute stress. In Experiment 1, changes in free amino acid pattern were investigated in the brain of neonatal chicks exposed to either restraint with isolation-induced or fasting stress. L-proline and L-arginine were decreased in the telencephalon and diencephalon under any stress. Since the central nervous system functions of L-arginine during the stress response has recently been reported, in Experiment 2, the effect of intracerebroventricular injection of L-proline (0.5, 1.0, 2.0 micromol) during isolation-induced stress was investigated. L-proline induced sedative and hypnotic effects in a dose-dependent manner. It is suggested that L: -proline may have an important role to attenuate the stress response in the central nervous system of chicks.
The purpose of this study was to clarify further the site of action in the amygdala as well as functional characteristics of feeding in response to two GABA receptor agonists. Guide cannulae for microinjection were implanted stereotaxically in the rat just above the central nucleus of the amygdala (CNA). Microinjections of 0.05, 0.25, 0.5 or 1.0 nmol muscimol, a GABAA-selective receptor agonist, produced a dose- and time-dependent decrease of food intake in both the satiated and fasted rat. The bilateral injection of muscimol into the amygdala was more effective than a unilateral injection during the first 2 h, although the overall effects were similar. Microinjection of 0.1 nmol bicuculline methiodide, a GABAA receptor antagonist, into the CNA significantly blocked this inhibitory effect of 0.05 and 0.5 nmol muscimol again in both the satiated and fasted rat. Doses of 0.05, 0.5, 5.0 and 10.0 nmol of the selective GABAB agonist, baclofen, injected into homologous sites in the CNA did not alter food intake. These findings support the viewpoint that the amygdala and its central nucleus comprise a pivotal region involved in the mechanisms underlying the control of feeding behavior. Further, it is envisaged that hypophagic or anorexic responses are induced through the activation of GABAA receptors by the presynaptic release of GABA from neurons which form a component of the anatomical system for hunger and satiety.
Neutral amino acid (NAA) transport across the blood-brain barrier was examined in pentobarbital-anesthetized rats with an in situ brain perfusion technique. Fourteen of 16 plasma NAAs showed measurable affinity for the cerebrovascular NAA transport system. Values of the transport constants (Vmax, Km, KD) were determined for seven large NAAs from saturation studies, whereas Km values for five small NAAs were estimated from inhibition studies. These data, together with our previous work, provide a complete set of constants for prediction of NAA influx from plasma. Among the NAAs, Vmax varied at least fivefold and Km varied approximately 700 fold. The apparent affinity (1/Km) of each NAA was related linearly (r = 0.910) to the octanol/water partition coefficient, a measure of NAA side-chain hydrophobicity. Predicted influx values from transport constants and average plasma concentrations agree well with values measured using plasma perfusate. These results provide accurate new estimates of the kinetic constants that determine NAA transport across the blood-brain barrier. Furthermore, they suggest that affinity of a L-alpha-amino acid for the transport system is determined primarily by side-chain hydrophobicity.
The ability of human tissues to convert lysine and α-ketoglutarate to saccharopine [] has been investigated vitro. Liver is the most effective organ, though some activity could be demonstrated in several other tissues. The responsible enzyme lysine-ketoglutarate reductase (lysine:α-ketoglutarate: TPNH oxidoreductase ()) has been partially purified from human liver and optimal conditions for its assay determined. There is a specific requirement for TPNH that cannot be satisfied by DPNH. A pH optimum near neutrality and inhibition by ammonium sulfate were observed. The enzyme is stable at −25°, both in tissues obtained at post-mortem and in its purified form. The assay for lysine-ketoglutarate reductase is sufficiently sensitive to be used on the limited amount of tissue obtainable by needle biopsy of the liver.
BUT for two exceptions1,2, attempts to inhibit feeding behaviour by direct intrahypothalamic administration of glucose have been unsuccessful3-6. The effects of other nutrients have yet to be assessed. We have found that microinjections of balanced amino-acid solutions into dorsolateral perifornical hypothalamic tissue, where consummatory behaviours are obtained with electrical stimulation, inhibit feeding in rats.
1. Recently, 2 novel neuropeptides were discovered, both derived from the same precursor by proteolytic processing, which bind and activate 2 closely related orphan G protein-coupled receptors, Named orexin-A and -B (Sakurai et al., 1998). Both stimulate food intake when administered centrally to rats. 2. Our aim was to elucidate whether central injection of mammalian orexin-A or -B stimulates food intake in the chick. 3. Under conditions of free access to food, orexin-A did not alter the food intake of chicks, but cumulative food intake was significantly suppressed by orexin-B. 4. The orexin-B was then administered to chicks deprived of food for 3 h to confirm its suppressive effect. No significant effect of orexin-B on food intake was detected. 5. Central injection of orexin-B did not modify food intake when appetite was stimulated by fasting. 6. Neither of these orexins appears to stimulate feeding in chicks.
It has been demonstrated that L-pipecolic acid (L-PA), a major metabolic intermediate of L-Lysine (L-Lys) in the brain, is involved in the functioning of Gamma-aminobutyric acid. In the present work the effect of intracerebroventricular (i.c.v.) administration of L-PA, and its relatives, on food intake and behavior in neonatal chicks was investigated. The i.c.v. injection of 1 mg of L-PA and D-PA significantly inhibited food intake during the 2 h following injection, whereas greater than 2 mg of L-Lys was required to inhibit food intake. In behavioral tests, the i.c.v. injection of L-PA reduced active wakefulness and feeding behavior while inducing sleeping-like behavior in chicks. These results suggest that L-PA has an important role for the regulation of behaviors in the neonatal chick after conversion from L-Lys in the brain.
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.
Ornithine transcarbamylase, argininosuccinate synthetase, argininosuccinate cleavage enzyme, and arginase, but not carbamyl phosphate synthetase, have been found in the chick kidney in moderate amounts. None of these, except traces of arginase, have been found in chick liver. Relatively small amounts of the cleavage enzyme have also been found in pancreas, spleen, and intestinal tract. The distribution of these enzymes is consistent with the ability of the chick to utilize citrulline in the diet in place of arginine and the inability to utilize ornithine in place of arginine. The significance of the findings is discussed in relation to arginine and nitrogen metabolism in the growing chick and in the developing embryo.
Branched-chain amino acids (BCAAs) are essential amino acids that play a major role in brain energy metabolism. This study was done to elucidate whether central injection of BCAAs influences feeding behavior in chicks. We found that the intracerebroventricular injection of leucine (200 microg) significantly stimulated food intake in neonatal chicks during 30 min postinjection. Additionally, the starting time of feeding and pecking rhythm after injection were significantly accelerated by leucine. In contrast, isoleucine and valine had no effect on ingestive response during experiment periods. Moreover, a metabolite of leucine (alpha-ketoisocaproic acid) at an equimolar concentration of leucine also did not increase food intake in chicks. These results suggest that leucine induces hyperphagia of neonatal chicks and it may be due to the synthesized glutamate by exogenous leucine.
Even though their contents in the brain are high, the function of brain carnosine and its constituents has not been clarified. Both carnosine and anserine inhibited food intake in a dose dependent fashion when injected intracerebroventricularly. The constituents of carnosine, beta-alanine (beta-Ala) and l-histidine (His), also inhibited food intake, but their effects were weaker than carnosine itself. Co-administration with beta-Ala and His inhibited food intake similar to carnosine, but also altered other behaviors. Injection of carnosine induced hyperactivity and increased plasma corticosterone level, whereas beta-Ala plus His induced hypoactivity manifested as sleep-like behavior. This later effect seemed to be derived from beta-Ala, not His. These results suggest that central carnosine may act in the brain of chicks to regulate brain function and/or behavior in a manner different from its constituents.
The present study investigated whether centrally administered phosphatidylserine (PS) could modify the behavior of chicks under isolation-induced stress. Isolation stress-induced vocalization and spontaneous activity for 10 min, which were attenuated by intracerebroventricular (i.c.v.) injection of PS. The effect of PS was compared with other phospholipids or L-serine, a constituent of PS. Phosphatidylcholine (PC) had no effect on these behavior, but phosphatidylethanolamine (PE) significantly increased vocalizations and spontaneous activity compared with PS. L-Serine similarly decreased isolation-induced vocalizations and spontaneous activity. To clarify the mechanism by which central PS attenuates isolation-induced stress behavior, the contribution of the acetylcholine (ACh) receptor (AChR) was also investigated. PS was co-injected i.c.v. with the muscarinic AChR (M-AChR) antagonist scopolamine or the nicotinic AChR (N-AChR) antagonist hexamethonium. The suppression of vocalizations and spontaneous activity by PS was partially attenuated by scopolamine, but not hexamethonium. These findings indicate that isolation-induced stress behavior are attenuated by PS, acting partially through the M-AChR.
The mammalian Target of Rapamycin (mTOR) protein is a serine-threonine kinase that regulates cell-cycle progression and growth
by sensing changes in energy status. We demonstrated that mTOR signaling plays a role in the brain mechanisms that respond
to nutrient availability, regulating energy balance. In the rat, mTOR signaling is controlled by energy status in specific
regions of the hypothalamus and colocalizes with neuropeptide Y and proopiomelanocortin neurons in the arcuate nucleus. Central
administration of leucine increases hypothalamic mTOR signaling and decreases food intake and body weight. The hormone leptin
increases hypothalamic mTOR activity, and the inhibition of mTOR signaling blunts leptin's anorectic effect. Thus, mTOR is
a cellular fuel sensor whose hypothalamic activity is directly tied to the regulation of energy intake.
In the present study, the changeover from the Pico.Tag HPLC method to the AccQ.Tag(ultra) UPLC method for the analysis of amino acids in casein and bovine serum albumine hydrolysates is described. The total chromatographic run time of the AccQ.Tag(ultra) UPLC method was only 40% of the time required for the Pico.Tag HPLC method. Quantitative results of both methods for casein and bovine serum albumine hydrolysates compared fairly well. The derivatisation protocol for the formation of AQC derivatives of amino acids was automated using a Gilson Model 215 liquid handler. Comparison of the manual derivatisation protocol with the automated protocol showed lower coefficients of variation for the latter. Combination of the AccQ.Tag(ultra) UPLC method and automated derivatisation resulted in improved throughput compared to the Pico.Tag HPLC method.
L-arginine participates in many important and diverse biochemical reactions associated with the normal physiology of the organism. In the present study, we investigated the effect of central administration of L-arginine on the stress response and its mechanism in neonatal chicks. Intracerebroventricular (i.c.v.) injection of L-arginine clearly attenuated the stress response in a dose-dependent manner, and induced sleep-like behavior during 10 min. To clarify the mechanism by which L-arginine induces sedative and hypnotic effects in chicks, we investigated the effects of nitric oxide (NO) synthase (NOS) inhibitors on L-arginine-induced sedative and hypnotic effects, and as well as the effects of a NO donor. L-Arginine-induced (1.9 micromol) sedative and hypnotic effects were attenuated by i.c.v. co-injection with a non-selective NOS inhibitor N(G)-nitro-L-arginine methyl ester HCl (400 nmol). In addition, the effects of L-arginine were slightly attenuated by the inactive isomer of the NOS inhibitor N(G)-nitro-D-arginine methyl ester HCl (400 nmol). The i.c.v. injection of 3-morpholinosylnomine hydrochloride, a spontaneous NO donor, had little effect on postures. The i.c.v. injection of L-arginine had no effect on NOx concentration at various brain sites. These results suggested that the contribution of NO generation via NOS may be low in the sedative and hypnotic actions of L-arginine. Therefore, L-arginine and/or its metabolites, excluding NO, may be necessary for these actions.
Recently, we observed that central administration of L-arginine attenuated stress responses in neonatal chicks, but the contribution of nitric oxide (NO) to this response was minimal. The sedative and hypnotic effects of L-arginine may be due to L-arginine itself and/or its metabolites, excluding NO. To clarify the mechanism, the effect of intracerebroventricular (i.c.v.) injection of L-arginine metabolites on behavior under social separation stress was investigated. The i.c.v. injection of agmatine, a guanidino metabolite of L-arginine, had no effect during a 10 min behavioral test. In contrast, the i.c.v. injection of L-ornithine clearly attenuated the stress response in a dose-dependent manner, and induced sleep-like behavior. The L-ornithine concentration in the telencephalon and diencephalon increased following the i.c.v. injection of L-arginine. In addition, several free amino acids including L-alanine, glycine, L-proline and L-glutamic acid concentrations increased in the telencephalon. In conclusion, it appears that L-ornithine, produced by arginase from L-arginine in the brain, plays an important role in the sedative and hypnotic effects of L-arginine observed during a stress response. In addition, several other amino acids having a sedative effect might partly participate in the sedative and hypnotic effects of L-arginine.
Cherkin A, autoradio-graphic distribution of L-proline in chicks after intracerebral injection
- J L Davis
- D T Masuoka
- L K Gerbrandt
J.L. Davis, D.T. Masuoka, L.K. Gerbrandt, Cherkin A, autoradio-graphic distribution of
L-proline in chicks after intracerebral injection, Physiol. Behav. 22 (1979) 693-695,
http://dx.doi.org/10.1016/0031-9384(79)90233-6.