Haruka Yamane

Intracerebroventricular injection of L-arginine induces sedative and hypnotic effects under an acute stress in neonatal chicks.

Summary.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 µmol) sedative and hypnotic effects were attenuated by i.c.v. co-injection with a non-selective NOS inhibitor NG-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 NG-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.

Carnosine-induced antidepressant-like activity in rats

Depression is a pathological state of mood and is considered as one of the major causes of disabilities. Thus, the prevention of depression and care for individuals with depression is important. In the present study, we examined whether a single oral dose of CBEX (chicken breast extract), or carnosine (one of the major components of CBEX) affects immobility time, an index of depressive-like behavior, in the forced swimming test in male Wistar rats. CBEX tended to (P=0.09) and carnosine significantly (P<0.05) decreased immobility time in the forced swimming test. In the hippocampus, both CBEX and carnosine significantly decreased 3-methoxy-4-hydroxyphenylglycol, a major metabolite of norepinephrine, indicating that CBEX and carnosine could reduce NE activity in the hippocampus in the forced swimming test. CBEX and carnosine did not affect total locomotive distance or rearing in the open field test, suggesting that the reductions of immobility time by both treatments in the forced swimming test were not merely due to the stimulation of general motor activity. Taken together, these results suggest that CBEX has an antidepressant-like effect, which may be due, in part, to the effect of carnosine.

Central l-arginine reduced stress responses are mediated by l-ornithine in neonatal chicks

Summary.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.

Intracerebroventricular injection of L-proline and D-proline induces sedative and hypnotic effects by different mechanisms under an acute stressful condition in chicks

The central effects of L-proline, D-proline and trans-4-hydroxy-L-proline were investigated by using the acute stressful model with neonatal chicks in Experiment 1. Sedative and hypnotic effects were induced by all compounds, while plasma corticosterone release under isolation stress was only attenuated by L-proline. To clarify the mechanism by which L-proline and D-proline induce sedative and hypnotic effects, the contribution of the strychnine-sensitive glycine receptor (glycine receptor) and N-methyl-D-aspartate glutamate receptor (NMDA receptor) were further investigated. In Experiments 2–3, the glycine receptor antagonist strychnine was co-injected intracerebroventricular (i.c.v.) with L-proline or D-proline. The suppression of isolation-induced stress behavior by D-proline was attenuated by strychnine. However, the suppression of stress behavior by L-proline was not attenuated. In Experiment 4, the NMDA receptor antagonist (+)-MK-801 was co-injected i.c.v. with L-proline. The suppression of stress behavior by L-proline was attenuated by (+)-MK-801. These results indicate that L-proline and D-proline differentially induce sedative and hypnotic effects through NMDA and glycine receptors, respectively.

Forced swimming and imipramine modify plasma and brain amino acid concentrations in mice.

The relationships between monoamine metabolism and forced swimming or antidepressants have been well studied, however information is lacking regarding amino acid metabolism under these conditions. Therefore, the aim of the present study was to investigate the effects of forced swimming and imipramine on amino acid concentrations in plasma, the cerebral cortex and the hypothalamus in mice. Forced swimming caused cerebral cortex concentrations of L-glutamine, L-alanine, and taurine to be increased, while imipramine treatment caused decreased concentrations of L-glutamate, L-alanine, L-tyrosine, L-methionine, and L-ornithine. In the hypothalamus, forced swimming decreased the concentration of L-serine while imipramine treatment caused increased concentration of beta-alanine. Forced swimming caused increased plasma concentration of taurine, while concentrations of L-serine, L-asparagine, L-glutamine and beta-alanine were decreased. Imipramine treatment caused increased plasma concentration of all amino acid, except for L-aspartate and taurine. In conclusion, forced swimming and imipramine treatment modify central and peripheral amino acid metabolism. These results may aid in the identification of amino acids that have antidepressant-like effects, or may help to refine the dosages of antidepressant drugs.

N-Methyl-d-aspartate and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptors involved in the induction of sedative effects under an acute stress in neonatal chicks

Glutamate, an excitatory amino acid, acts at several glutamate receptor subtypes. Recently, we reported that central administration of glutathione induced hypnosis under stressful conditions in neonatal chicks. Glutathione appears to bind to the N-methyl-d-aspartate (NMDA) receptor. To clarify the involvement of each glutamate receptor subtype during stressful conditions, intracerebroventricular (i.c.v.) injection of several glutamate receptor agonists was given to chicks under social separation stress. Glutamate dose-dependently induced a hypnotic effect. NMDA, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and kainate are characterized as ionotropic glutamate receptors (iGluRs). Although NMDA also induced sleep-like behavior or sedative effects, the potency of NMDA was less than that of glutamate. AMPA tended to decrease distress vocalizations induced by acute stress and brought about a sedative effect. Kainate and (S)-3, 5-dehydroxyphenylglycine, which is a metabotropic glutamate receptor agonist, had no influence on chick behavior. Thus, it is suggested that the iGluRs, NMDA and AMPA, are important in inducing hypnosis and sedation under acute stress in chicks.

Relationships between the sedative and hypnotic effects of intracerebroventricular administration of L-serine and its metabolites, pyruvate and the derivative amino acids contents in the neonatal chicks under acute stressful conditions

Summary.Intracerebroventricular (i.c.v.) injection of L-serine was shown to have sedative and hypnotic effects on neonatal chicks under acute stressful conditions. To clarify the central mechanism of these effects of L-serine, two experiments were done. First, we focused on the glycogenic pathway in which L-serine is converted into pyruvate and finally glucose. I.c.v. administration of pyruvate (0.84 µmol) did not induce any behavioral and endocrinological changes, while L-serine and glucose triggered sedative and hypnotic effects. Secondly, the relationship between the sedation by L-serine and the metabolism into other amino acids which have sedative effects was investigated in the telencephalon and diencephalon. In both brain areas, a dose-dependent increase was seen in L-serine, although other amino acids were not changed. In the present study, it was concluded that the sedative action of L-serine was not due to the action of its metabolite pyruvate, or to the action of other amino acids.

Oral administration of chicken breast extract increases brain carnosine and anserine concentrations in rats

Abstract Carnosine (β-alanyl-L-histidine) and its derivative anserine (β-alanyl-1-methyl-L-histidine) are antioxidants and putative neurotransmitters in the brain. These dipeptides are rich in the commercially available supplement chicken breast extract (CBEX). To clarify the effects of CBEX on the brain, we examined whether single oral administration of CBEX (20 ml/kg) affects brain dipeptide and free amino acid concentrations in male Wistar rats. CBEX significantly and time-dependently increased carnosine and anserine levels in the plasma (at 120 min after injection, increase rates were 2976 and 4142%, respectively), hippocampus (64 and 78%), and hypothalamus (188 and 120%), but not in cerebral cortex. Significant and time-dependent increases in citrulline in the hippocampus (49%) and hypothalamus (41%) demonstrated generation of nitric oxide due to the increased carnosine and/or anserine levels in these brain regions. These findings suggest that CBEX modifies brain functions by increasing levels of these dipeptides.

Intracerebroventricular injection of glutathione and its derivative induces sedative and hypnotic effects under an acute stress in neonatal chicks

Glutathione-related enzymes glyoxalase 1 and glutathione reductase 1 regulates anxiety in mice. To clarify the central function of glutathione as a neurotransmitter in the stress reaction, the effect of intracerebroventricular (i.c.v.) injection of reduced (GSH) (0.5, 1, 2 micromol) and oxidized (GSSG) glutathione (0.25, 0.5, 1 micromol) were investigated under an isolation-induced stress in the neonatal chick. Both GSH and GSSG dose-dependently decreased distress vocalizations and induced sleep-like behavior in chicks under acute stressful conditions. However, which glutathione is actually responsible for inducing sleep was unclear since glutathione cycles between GSH and GSSG in which two tripeptides are linked by a disulfide bond. Therefore, the behavior of chicks was monitored following the i.c.v. injection of S-methylglutathione (SMG) (0.0625, 0.25, 1 micromol). SMG does not form a disulfide bond due to the methylation of the SH group of the cysteine moiety. SMG had similar effects as observed in GSH and GSSG. In conclusion, glutathione and its derivative have sedative and hypnotic effects, and might be effective in improving psychic stress such as anxiety.

Intracerebroventricular injection of L-aspartic acid and L-asparagine induces sedative effects under an acute stressful condition in neonatal chicks.

The present study was conducted to clarify the central functions of L-aspartic acid (Asp) and L-asparagine (Asn) during an acute stressful condition in chicks. Intracerebroventricular (i.c.v.) injection of Asp and Asn (0.84 micromol) attenuated the vocalization that normally occurs during social separation stress. Asp decreased the time spent in active wakefulness and induced sedation. Asn had a similar effect to Asp, although somewhat weaker. However, i.c.v. injection of Asp and Asn further enhanced plasma corticosterone release under social separation stress. Taken together, the i.c.v. injection of Asp and Asn has sedative effects under an acute stressful condition, which does not involve the hypothalamic-pituitary-adrenal axis.