Kazutaka Shigemi

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.

L-Serine induces sedative and hypnotic effects acting at GABAA receptors in neonatal chicks

Intracerebroventricular injection of l-serine has been shown to have sedative and hypnotic effects on neonatal chicks exposed to acute stressful conditions. However, the mechanism by which l-serine induces these effects is unclear. The present study was conducted to clarify the mechanism by l-serine. The involvement of gamma-aminobutyric acid (GABA)(A) receptors on the effect of l-serine was investigated using the GABA(A) receptor antagonist picrotoxin. Co-administration of picrotoxin attenuated the sedative and hypnotic effect of l-serine. Further, we also investigated the involvement of glycine receptors since l-serine is suggested to act as the alpha-homomeric glycine receptor agonist. Glycine similarly induced sedative and hypnotic effects in chicks, but its effect was attenuated by the glycine receptor antagonist strychnine. Therefore, whether the effect of l-serine was mediated through the glycine receptor was investigated using l-serine and strychnine. The effect of l-serine was inhibited by picrotoxin, but not strychnine. It appears that l-serine induces sedative and hypnotic effects by enhancing inhibitory neurotransmission via GABA(A) receptors.

L-ornithine attenuates corticotropin-releasing factor-induced stress responses acting at GABAA receptors in neonatal chicks.

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.

Oral administration of l-serine reduces the locomotor activity of socially isolated rats

L-Serine is considered a functional amino acid in the central nervous system, since intracerebroventricular injection of L-serine induced sedative and hypnotic effects in neonatal chicks exposed to acute stressful conditions. Accordingly, L-serine is a candidate anti-stress factor, but the effect of daily intake of L-serine on behavior of animals exposed to chronic stress has not been investigated. In the present study, we exposed rats to social isolation stress for 4 weeks, and home cage test and open field test were concluded to evaluate the effect of L-serine on behavior. To investigate L-serine supplementation modifies the brain L-serine and its metabolite contents, free amino acid contents were measured by a high performance liquid chromatography. L-Serine in the drinking water increased L-serine levels in some brain areas, but changes in its metabolites were almost negligible. L-Serine decreased locomotor activity in rats exposed to a familiar environment. In addition, L-serine decreased exploratory behavior of isolated rats, even in a novel environment. Our results could suggest that daily intake of L-serine can attenuate symptoms induced by chronic stress.

Intracerebroventricular injection of orexin-A, but not orexin-B, induces arousal of layer-type neonatal chicks.

In order to determine if orexins affect arousal in neonatal chicks, we intracerebroventricularly (ICV) injected either orexin-A or orexin-B to layer and broiler type chicks (Gallus gallus) and measured their behaviors and food intake following injection. Layer chicks treated with orexin-A at 0.2 and 2.0 nmol had increased arousal but their food intake was not affected. However, arousal was not affected in broiler chicks treated with orexin-A, but they spent less time feeding. When orexin-B was administered to layer and broiler chicks, neither had altered arousal and their food intake was not affected. Therefore, the orexin peptides may differentially affect arousal in the two stocks tested; orexin-A causes a stock dependant increase whereas orexin-B does not affect either.

Central L-ornithine, but not polyamines, induces a hypnotic effect in neonatal chicks under acute stress

Abstract 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 μmol 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.

Intracerebroventricular injection of orexin-A stimulates monoamine metabolism but not HPA axis in neonatal chicks

We investigated the effects of intracerebroventricular (ICV) injection of orexin-A on plasma corticosterone (CORT) concentration and brain monoamine metabolism to clarify the mechanism by which ICV orexin-A induced arousal in chicks. In Experiment 1, plasma CORT concentrations were measured as an indicator of hypothalamic-pituitary-adrenal (HPA) axis activity. There was no significant difference in CORT concentration between the control and orexin-A administered groups. In Experiment 2, the concentrations of monoamines (norepinephrine, dopamine and serotonin), their metabolites, and their metabolic turnover rates in the telencephalon, mesencephalon, and diencephalon were investigated. All metabolic turnover rates studied were increased at all brain sites after ICV orexin-A injection. In conclusion, the HPA axis does not appear to be involved in arousal-inducing mechanisms of orexin-A in neonatal chicks; however, several monoaminergic systems do.

L-DOPA attenuates hyperactivity of Roborovskii hamsters.

The Roborovskii hamster (Phodopus roborovskii) has been shown to have high locomotor activity (hyperactivity) and low dopamine concentrations in the brain. We hypothesized that low brain dopamine concentrations play a role in the pathogenesis of hyperactivity. In this study, therefore, we investigated the effects of L-DOPA (L-3,4-dihydroxyphenylalanine), the precursor of dopamine, on the locomotor activity of Roborovskii hamster to verify the above hypothesis. An open field test was employed to measure the locomotor activity. Administration of L-DOPA dose-dependently decreased locomotor activity including distance of path and time spent moving. L-DOPA increased the brain concentration of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid. Concurrently, L-DOPA caused increase of norepinephrine, decrease of serotonin, and atypical alteration of their metabolite concentrations. These findings mainly suggest that in Roborovskii hamsters, a low level of brain dopamine neurotransmission is one of the reasons for hyperactivity, and hyperactivity can be attenuated by L-DOPA.

Central l-proline attenuates stress-induced dopamine and serotonin metabolism in the chick forebrain

Using microdialysis, we investigated the effect of l-proline on monoamine release in the medio-rostral neostriatum/hyperstriatum ventrale (MNH) of freely moving and restricted chicks. A 30 min handling-stress resulted in a significant increase in extracellular homovallinic acid (HVA), a dopamine metabolite, and 5-hydroxyindoleacetic acid (5-HIAA), a serotonin metabolite, in the MNH. l-Proline, perfused through the microdialysis probe into the MNH during the stressed condition, significantly attenuated the average dialysate concentration of HVA produced by handling-stress. Handling-stress resulted in a significant increase in 5-HIAA levels in the control group, which were attenuated by profusion with l-proline. l-Proline did not significantly modify basal concentrations of HVA or 5-HIAA in the MNH during control conditions. These results show that perfusion of l-proline modified the turnover/metabolism of dopamine and serotonin in the MNH caused by handling-stress.

Chronic l-tyrosine alters the locomotor activity and brain monoamine levels in Roborovskii hamsters

The Roborovskii hamster (Phodopus roborovskii) has high locomotor activity (hyperactivity) and low dopamine levels in the brain compared with the congeneric Djungarian hamster (Phodopus sungorus). To clarify the efficacy of dietary l-tyrosine in ameliorating signs of hyperactivity, we investigated the effects of chronic administration of l-tyrosine, the primary precursor of dopamine, on locomotor activity and brain monoamine levels in Roborovskii hamsters. Chronic supplementation of l-tyrosine had no effect on locomotor activity in the open field, but did decrease locomotor activity in the home cage. Tyrosine increased dopamine and norepinephrine turnover rates and decreased in serotonin turnover rate in the brain. These findings suggest that long-term feeding of l-tyrosine may be effective in ameliorating signs of hyperactivity.