Dietary tyrosine suppresses the rise in plasma corticosterone following acute stress in rats

Effects of Photoperiod Regime on Meat Quality, Oxidative Stability, and Metabolites of Postmortem Broiler Fillet (M. Pectoralis major) Muscles

The objective of this study was to evaluate the effects of photoperiod on meat quality, oxidative stability, and metabolites of broiler fillet (M. Pectoralis major) muscles. A total of 432 broilers was split among 4 photoperiod treatments [hours light(L):dark(D)]: 20L:4D, 18L:6D, 16L:8D, and 12L:12D. At 42 days, a total of 48 broilers (12 broilers/treatment) was randomly selected and harvested. At 1 day postmortem, fillet muscles were dissected and displayed for 7 days. No considerable impacts of photoperiods on general carcass and meat quality attributes, such as carcass weight, yield, pH, water-holding capacity, and shear force, were found (p > 0.05). However, color and oxidative stability were influenced by the photoperiod, where muscles from 20L:4D appeared lighter and more discolored, coupled with higher lipid oxidation (p < 0.05) and protein denaturation (p = 0.058) compared to 12L:12D. The UPLC-MS metabolomics identified that 20 metabolites were different between the 20L:4D and 12L:12D groups, and 15 were tentatively identified. In general, lower aromatic amino acids/dipeptides, and higher oxidized glutathione and guanine/methylated guanosine were observed in 20L:4D. These results suggest that a photoperiod would result in no considerable impact on initial meat quality, but extended photoperiods might negatively impact oxidative stability through an alteration of the muscle metabolites.

pH-Responsive Polypeptide-Based Smart Nano-Carriers for Theranostic Applications

Smart nano-carriers have attained great significance in the biomedical field due to their versatile and interesting designs with different functionalities. The initial stages of the development of nanocarriers mainly focused on the guest loading efficiency, biocompatibility of the host and the circulation time. Later the requirements of less side effects with more efficacy arose by attributing targetability and stimuli-responsive characteristics to nano-carriers along with their bio- compatibility. Researchers are utilizing many stimuli-responsive polymers for the better release of the guest molecules at the targeted sites. Among these, pH-triggered release achieves increasing importance because of the pH variation in different organ and cancer cells of acidic pH. This specific feature is utilized to release the guest molecules more precisely in the targeted site by designing polymers having specific functionality with the pH dependent morphology change characteristics. In this review, we mainly concert on the pH-responsive polypeptides and some interesting nano-carrier designs for the effective theranostic applications. Also, emphasis is made on pharmaceutical application of the different nano-carriers with respect to the organ, tissue and cellular level pH environment.

Metabolomics reveals distinct neurochemical profiles associated with stress resilience

Acute social defeat represents a naturalistic form of conditioned fear and is an excellent model in which to investigate the biological basis of stress resilience. While there is growing interest in identifying biomarkers of stress resilience, until recently, it has not been feasible to associate levels of large numbers of neurochemicals and metabolites to stress-related phenotypes. The objective of the present study was to use an untargeted metabolomics approach to identify known and unknown neurochemicals in select brain regions that distinguish susceptible and resistant individuals in two rodent models of acute social defeat. In the first experiment, male mice were first phenotyped as resistant or susceptible. Then, mice were subjected to acute social defeat, and tissues were immediately collected from the ventromedial prefrontal cortex (vmPFC), basolateral/central amygdala (BLA/CeA), nucleus accumbens (NAc), and dorsal hippocampus (dHPC). Ultra-high performance liquid chromatography coupled with high resolution mass spectrometry (UPLC-HRMS) was used for the detection of water-soluble neurochemicals. In the second experiment, male Syrian hamsters were paired in daily agonistic encounters for 2 weeks, during which they formed stable dominant-subordinate relationships. Then, 24 h after the last dominance encounter, animals were exposed to acute social defeat stress. Immediately after social defeat, tissue was collected from the vmPFC, BLA/CeA, NAc, and dHPC for analysis using UPLC-HRMS. Although no single biomarker characterized stress-related phenotypes in both species, commonalities were found. For instance, in both model systems, animals resistant to social defeat stress also show increased concentration of molecules to protect against oxidative stress in the NAc and vmPFC. Additionally, in both mice and hamsters, unidentified spectral features were preliminarily annotated as potential targets for future experiments. Overall, these findings suggest that a metabolomics approach can identify functional groups of neurochemicals that may serve as novel targets for the diagnosis, treatment, or prevention of stress-related mental illness.

Effects in dogs with behavioural disorders of a commercial nutraceutical diet on stress and neuroendocrine parameters

The well-being of dogs can be affected by changes in human lifestyle, eating habits and increased stressors that lead to behavioural disorders including fear, hyperactivity and anxiety, followed by negative affective moods and poor welfare. This randomised, controlled clinical evaluation involved 69 dogs, 38 males and 31 females, of different breeds, with behavioural disorders related to anxiety and chronic stress. They were fed a control diet or a nutraceutical diet (ND group) for 45 days. Neuroendocrine (serotonin, dopamine, β-endorphins, noradrenaline and cortisol) and stress (derivatives of reactive oxygen metabolites (dROMs) and biological antioxidant potential (BAP)) parameters related to behavioural disorders were evaluated at the beginning and end of the study period. Results showed a significant increase in serotonin, dopamine and β-endorphins plasma concentrations (*P<0.05, *P<0.05 and **P<0.01, respectively) and a significant decrease in noradrenaline and cortisol plasma concentrations in the ND group (*P<0.05). dROMs significantly decreased in the ND group (*P<0.05) while BAP was not affected. This study demonstrated for the first time that a specific diet significantly and positively affected neuroendocrine parameters and dROMs. These results open significant perspectives concerning the use of diet and nutraceuticals in the treatment of behavioural disorders.

Elevation of rat brain tyrosine levels by phenelzine is mediated by its active metabolite β-phenylethylidenehydrazine

Phenelzine, a non-selective irreversible inhibitor of monoamine oxidase (MAO), has been used in the treatment of depression and anxiety disorders for several decades. It is a unique inhibitor of MAO as it is also a substrate for MAO, with one of the metabolites being β-phenylethylidenehydrazine (PEH), and it also inhibits several transaminases (e.g. GABA transaminase) in the brain when administered i.p. to rats. Administration of either phenelzine or PEH to rats has been reported to produce dramatic increases in rat brain levels of GABA and alanine while reducing levels of glutamine; these effects are abolished for phenelzine, but not for PEH, when the animals are pre-treated with another MAO inhibitor, suggesting that they are mediated by the MAO-catalyzed formation of PEH from phenelzine. In the present report, we have found that phenelzine and E- and Z-geometric isomers of PEH significantly increased rat whole brain concentrations of L-tyrosine. In a time-response study, acute administration of phenelzine, E-PEH and Z-PEH (30 mg/kg i.p.) elevated rat whole brain L-tyrosine levels at 3 and 6h following injection, reaching approximately 265-305% of vehicle-treated controls at 3h. To determine whether the effect on L-tyrosine is MAO-dependent, animals were pre-treated with the non-selective MAO inhibitor tranylcypromine (1mg/kg i.p.) prior to administration of phenelzine, racemic PEH or vehicle controls. This pre-treatment reversed the effects of phenelzine, but not of PEH, on brain L-tyrosine levels, suggesting that the tyrosine-elevating property of phenelzine is largely the result of its active metabolite PEH. These results are discussed in relation to possible therapeutic applications of these drugs.

Dietary l-tyrosine alleviates the behavioral alterations induced by social isolation stress in mice

Chronic stress induces abnormal mental state and behavior, and can be a risk factor for mental disorders. Although it is reported that l-tyrosine, an amino acid that is a precursor of catecholamine synthesis, alleviated the change of cognition and behavior induced by acute stress, knowledge about its effects on chronic stress is limited. In the present study, the effects of dietary l-tyrosine on behavioral alteration induced by chronic stress were investigated by employing a social isolation stress model in mice. Social isolation stress increased locomotor activity in both the home cage and open field. These increases of locomotor activity were suppressed by dietary l-tyrosine. Moreover, l-tyrosine increased both the concentration and turnover rate of norepinephrine metabolites. These findings partly suggest the availability of dietary l-tyrosine for psychic dysfunctions induced by chronic stress.

Impact of nutrition on canine behaviour: current status and possible mechanisms

Each year, millions of dogs worldwide are abandoned by their owners, relinquished to animal shelters, and euthanised because of behaviour problems. Nutrition is rarely considered as one of the possible contributing factors of problem behaviour. This contribution presents an overview of current knowledge on the influence of nutrition on canine behaviour and explores the underlying mechanisms by which diet may affect behaviour in animals. Behaviour is regulated by neurotransmitters and hormones, and changes in the availability of their precursors may influence behaviour. Tryptophan, the precursor of serotonin, may affect the incidence of aggression, self-mutilation and stress resistance. The latter may also be influenced by dietary tyrosine, a precursor to catecholamines. As diet composition, nutrient availability and nutrient interactions affect the availability of these precursors in the brain, behaviour or stress resistance may be affected. PUFA, especially DHA, have an important role as structural constituents in brain development, and dietary supply of n-3 and n-6 PUFA could modify aspects of the dopaminergic and serotonergic system and, consequently, cognitive performance and behaviour. Finally, persistent feeding motivation between meals can increase stereotyped behaviour and aggression and decrease resting time. This feeding motivation may be altered by dietary fibre content and source. At present, few studies have been conducted to evaluate the role of nutrition in canine (problem) behaviour through the above mentioned mechanisms. Studies that explore this relationship may help to improve the welfare of dogs and their owners.

Tyrosine ameliorates some of the clinical, biochemical and haematological effects of acute stress associated with transportation of desert sheep

We studied some clinical, biochemical and haematological variables in Desert (Najdi) sheep acutely stressed in the course of individual road transportation, and the influence thereon of pretreatment with tyrosine. Transportation for 30 min resulted in variable but statistically insignificant increases in heart, pulse and respiratory rates. It also caused significant increases in the plasma concentration of cortisol (from 43.5 to 101.7 mmol/L) and glucose (from 3.1 to 4.5 mmol/L), and a decrease in that of magnesium (from 0.85 to 0.72 mmol/L). The endogenous thiocyanate level was unaffected. The transportation stress also decreased the haematocrit (PCV) and the number of lymphocytes, and increased the concentration of haemoglobin. Pretreatment of sheep with tyrosine at a dose of 100 mg/kg by the intravenous route significantly ameliorated the stress-induced clinical, biochemical and haematological changes. The treatment caused no overt adverse effects.

Tyrosine improves behavioral and neurochemical deficits caused by cold exposure

The effects of acute cold stress were assessed behaviorally and neurochemically. The norepinephrine (NE) precursor, tyrosine (TYR), the catecholamine-releasing compound, amphetamine (AMPH), and the adrenoceptor agonist, phenylpropanolamine (PPA), were administered systemically either alone or in conjunction with TYR 30 min prior to cold exposure. All three sympathomimetic treatments dose-dependently improved performance in a forced swim test following hypothermia (T(c)=30 degrees C). AMPH/TYR or PPA/TYR combinations further improved performance vs. either agent given alone. Microdialysis showed elevated hippocampal NE concentrations in response to hypothermia. TYR further elevated NE concentration in cold/restrained rats vs. saline (SAL)-treated controls. These results suggest that sympathomimetic agents, including the nutrient TYR, which enhance noradrenergic function, improve performance in animals acutely stressed by hypothermia.

Amino Acid Effects on Post-Stress Ulcers: Relationship to Brain Serotonin, 5-HIAA and Norepinephrine

To replicate and extend results of earlier studies on amino acid effects on post-stress ulcers, rats were subjected to i.p. injections of (a) saline, (b) tryptophan, (c) tyrosine + valine or(d) tryptophan + tyrosine + valine, either 30 minutes before or immediately after one hour of water restraint stress. Gastric lesions, brain norepinephrine, serotonin and 5-hydroxyindoleacetic acid (5-HIAA) were examined after one hour of poststress rest. We hypothesised that post-stress lesions could be aggravated by central noradrenergic hypoactivity and serotonergic hyperactivity during the post-stress period. Other studies have indicated that tyrosine + valine reduces central serotonergic activity, while additional tryptophan blocks this effect. We therefore expected post-stress lesions to be reduced in tyrosine + valine but not in tryptophan + tyrosine + valine treated animals. Although these expectations were met tentatively in animals injected prior to stress, thus replicating tyrosine + valine effects we had observed earlier, opposite results were found in animals treated post-stress. The brain analyses indicate that the data cannot be explained by a norepinephrine/serotonin imbalance hypothesis. The time dependency of the effects underlines the need for caution in clinical applications of these amino acid treatments.

Tyrosine enhances behavioral and mesocorticolimbic dopaminergic responses to aversive conditioning

Tyrosine is a precursor in the biosynthesis of catecholamines and, when administered systemically, has been shown to enhance the in vivo rate of tyrosine hydroxylation in the medial prefrontal cortex. Additionally, exogenous tyrosine has been demonstrated to enhance the pharmacologically-induced increase in dopamine metabolism seen following administration of haloperidol or the anxiogenic B-carboline, FG-7142. In this report, we examine the effect of a physiologically relevant dose of tyrosine (25 mg/kg) on biochemical and behavioral consequences of aversive conditioning. Rats were conditioned to fear a tone by pairing it with footshock, so that when challenged with the tone alone, rats responded with immobility, defecation, and elevated dopamine metabolism in the medial prefrontal cortex and nucleus accumbens. When tyrosine was administered on the test day (tones alone), the rats displayed an even greater elevation of dopamine metabolism in the nucleus accumbens and prolonged immobility to the tone, compared to the saline/conditioned controls. Tyrosine did not alter mobility or dopamine utilization in the nucleus accumbens in nonconditioned controls. However, dopamine metabolism in the medial prefrontal cortex of nonconditioned rats treated with tyrosine was increased to levels similar to those in the conditioned groups. This may be accounted for by handling and by exposure to an unfamiliar environment necessary for nonconditioned controls. We conclude that exogenous tyrosine is able to 1) elevate stress-induced dopamine metabolism in the nucleus accumbens, 2) alter dopamine utilization in the medial prefrontal cortex of handled, nonconditioned controls, and 3) enhance fear-induced immobilization. These data suggest a role for dietary tyrosine in biochemical and behavioral responses to aversive stimuli.

L-tyrosine ameliorates some effects of lower body negative pressure stress

Tyrosine, a large neutral amino acid normally present in protein foods, is the precursor of the catecholamine neurotransmitters dopamine, norepinephrine, and epinephrine. Animal studies indicate that systemic administration of tyrosine in pharmacological quantities can reduce physiological and behavioral decrements induced by highly stressful conditions. The current study was designed to test the effects of tyrosine (100 mg/kg of body weight) on humans exposed to cardiovascular stress. Twenty participants were exposed to two Lower Body Negative Pressure (LBNP) sessions (-50 mm Hg for a maximum of 30 min) during each of two testing sessions of a repeated measure double-blind placebo-controlled study. The detected effects of tyrosine include an overall increase in pulse pressure (LBNP typically reduces pulse pressure) and an increase in auditory event related potential amplitude (P300-N300), an electro-physiological correlate of attention which may indicate enhanced cognitive activation.

Restraint stress in biomedical research: an update

Since the publication of our initial review of restraint stress in 1986, much work has continued with this technique, either as a tool for the investigation of other pharmacological, physiological, or pathologic phenomena or with restraint stress itself serving as the object of the study. As we noted in 1986, the major use of restraint has been for the induction of stress responses in animals and, more specifically, for the investigation of drug effects, particularly as they affect typical stress-related pathology--gastrointestinal, neuroendocrine, and immunological agents have been extensively studied. In compiling this update on restraint stress and its effects, we noted an increasing emphasis on central nervous system mechanisms in peripheral disease, especially gastrointestinal disease. In particular, many CNS-active agents have been tested for their effects on gastric and duodenal lesion formation and gastric secretion, including antidepressants, antipsychotics, anxiolytics, noradrenergic, serotonergic, dopaminergic, and peptidergic compounds. Some of these agents are especially active in the gastrointestinal tract even when administered centrally, further solidifying the concept of a brain-gut axis. The present update includes studies of: methods and procedures, pre-restraint manipulations, post-restraint/healing effects, and drug effects. In addition, a current bibliography of reports that have employed restraint is included.

Simultaneous changes in hypothalamic catecholamine levels and plasma corticosterone concentration in the rat after acute morphine and during tolerance

The effects of morphine on plasma corticosterone and hypothalamic noradrenaline (NA) and dopamine (DA) content were studied in naive and in morphine-tolerant rats. Acutely administered morphine (30 mg/kg i.p.) significantly increased the plasma levels of corticosterone and significantly reduced the hypothalamic NA and DA content. In chronically morphine-treated rats (subcutaneously implanted with pellets for 7 days), a challenge dose of morphine (30 mg/kg intraperitoneally (i.p.)) did not modify the plasma corticosterone levels and inhibited the morphine-induced decreases in hypothalamic NA and DA content. These results suggest that: (1) In naive rats, the morphine-induced activation of hypothalamus-pituitary-adrenocortical (HPA) axis is mediated by catecholaminergic neurons in the hypothalamus; (2) In tolerant rats morphine did not modify the plasma corticosterone concentrations, presumably by attenuating hypothalamic noradrenergic and dopaminergic activity. (3) Hypothalamic catecholamines have a role in regulating the HPA axis during morphine tolerance.

Pavlovian conditioning of corticotropin-releasing factor-induced increase of blood pressure and corticosterone secretion in the rat

Corticotropin-releasing factor (CRF) is clearly involved in the central regulation of the pituitary-adrenal axis and, moreover, of autonomic nervous system functions. Enhanced sympathetic activity with subsequent increases in blood pressure and heart rate and attenuation of the baroreceptor reflex results from the intracerebroventricular (i.c.v.) administration of CRF. Additionally, the peptide has a variety of potent effects on behavioural responses in animals similar to those observed after an experimentally evoked stress. It was therefore of obvious interest to examine whether CRF is a possible mediator of the learning processes associated with physiological stress reaction patterns. This report clearly demonstrates a classical conditioning of the endocrine (i.e. corticosterone secretion) and haemodynamic (i.e. blood pressure) sequelae following central CRF application and thus indicates that this mechanism is of physiological significance for learned stress responses.

Exogenous tyrosine potentiates the methylphenidate-induced increase in extracellular dopamine in the nucleus accumbens: a microdialysis study

Previous work has shown that the synthesis and release of dopamine may, under certain conditions, be influenced by an increase in the availability of its amino acid precursor, tyrosine. To examine whether exogenous tyrosine could potentiate the methylphenidate-induced increase in extracellular dopamine, male rats were implanted with microdialysis probes aimed at the right nucleus accumbens. Samples were collected from awake animals beginning 22 h after surgery. A repeated measures design was used involving the continuous collection of 20-min samples for a 4-h period once a day for 3 consecutive days. On a given day, an animal was infused with methylphenidate, tyrosine, or methylphenidate plus tyrosine. Periods of infusion with the active compounds were preceded and followed by baseline conditions, and treatments were counterbalanced to control for possible order effects. Methylphenidate plus tyrosine significantly increased extracellular levels of dopamine in comparison to drug alone. This effect was long-lasting, persisting into the post-treatment sampling period and peaking 40 min after the peak induced by methylphenidate alone. Tyrosine alone induced a small but significant increase in extracellular dopamine in the absence of any treatment to accelerate the firing of dopamine cells. These findings may have implications for the treatment of attention deficit hyperactivity disorder.

Modulation of the actions of tyrosine by alpha 2-adrenoceptor blockade

1. Eight normal subjects were given, in double-blind, random order L-tyrosine 50, 250 and 500 mg kg-1 and placebo orally. Plasma tyrosine concentrations rose in a dose-dependent manner, without affecting the concentrations of the other large neutral amino acids. Tyrosine stimulated the secretion of prolactin and thyrotrophin (TSH) but had no effect on the plasma concentrations of adrenocorticotrophic hormone (ACTH), cortisol, growth hormone or the gonadotrophins. 2. The lack of a stimulant effect of tyrosine on ACTH secretion was presumed to be due to activation of one of the negative feedback mechanisms that control the rate of synthesis and release of the catecholamines, and this hypothesis was tested by examining the effects of the alpha 2-adrenoceptor antagonist idazoxan on the actions of tyrosine. 3. Seven normal males were given on 6 separate occasions tyrosine 250 and 500 mg kg-1 and placebo orally following pretreatment with saline and idazoxan (0.1 mg kg-1 i.v.). Following pretreatment with idazoxan, tyrosine stimulated the secretion of ACTH and noradrenaline in a dose-dependent manner, although neither tyrosine nor idazoxan on their own had any effect on the secretion of either substance. 4. The lack of effect of tyrosine when given on its own appears to be due, to partly, to activation of alpha 2-adrenoceptors, which inhibit the release of noradrenaline. Idazoxan caused a small increase in systolic blood pressure, both when given on its own and in combination with tyrosine. Neither tyrosine nor idazoxan had any significant effect on the state of behavioural arousal, as measured by visual analogue scales, or on the secretion of growth hormone or the gonadotrophins.

Restraint stress in biomedical research: a review

The use of restraint or immobilization for investigations of animal physiology, pathology and pharmacology has an extensive history. The major use of this technique has been as a "stressor" for the induction of stress response syndromes in animals. Many such syndromes have been characterized from the behavioral level to the neurochemical concomitants of stress. As a consequence of this particular use of the restraint procedure, much information concerning drug effects on stress response syndromes has been obtained. Indeed, many researchers in the area of gastrointestinal drugs routinely screen their new compounds in a restraint model of gastric stress ulcer. The purpose of this review is to present for researchers, a summary of the methods for, the parameters of, and known drug effects on, restraint-induced pathology. In our experience, this technique has proven to be a very useful one for the examination of both central and peripheral mechanisms of stress-related disorders, as well as for studying drug effects upon these disorders.