Central Injection of Glucose Modifies Behavior, Amino Acid and Monoamine Metabolism in Neonatal Chicks under Acute Stressful Conditions.

The effect of intracerebroventricular (i.c.v.) injection of a wide range of glucose concentrations on the behavioral response, central amino acid and monoamine contents was investigated in chicks exposed to a social isolation stressful condition. The chicks were given an i.c.v. injection of 0.21, 0.42, 0.84, and 1.68 µmol of D-glucose, and then behavioral changes were observed over 10 min. The behavioral stress response was dose-dependently decreased and calm behavior was increased by i.c.v. administration of glucose. In the diencephalon, glutamine was positively correlated, whereas glycine was negatively correlated with the dose of glucose. In the telencephalon, the dopamine metabolite and dopamine turnover rates were positively correlated, whereas dopamine was negatively correlated with doses of glucose. In the plasma, isoleucine and hydroxyproline were positively correlated with the dose of glucose, and several amino acids were also influenced by glucose levels. These results suggest that the possible pathways of the sedative effect of glucose include: (1) amino acids synthesized from injected glucose, which can induce the sedative and/or hypnotic effects; (2) amino acids modified by injected glucose transported in the brain from the peripheral tissues; and (3) injected glucose-induced decreases in brain dopamine levels. In conclusion, these changes induced by central glucose interact and induce the sedative effect in neonatal chicks.

Comparison of centrally injected tryptophan-related substances inducing sedation in acute isolation stress-induced neonatal chicks.

In the present study, we first focused on the function of l-tryptophan (TRP) metabolites which are synthesized in different metabolic pathways, namely, the kynurenine (KYN) pathway and serotonin (5-HT) pathway during an acute isolation stress. When l-TRP metabolites were intracerebroventricularly injected on an equimolar basis (100 nmol), 5-HT induced a sedative effect in neonatal chicks. Additionally, plasma corticosterone, dopamine, 5-HT, and its metabolite 5-hydroxyindoleacetic acid concentrations were increased in the diencephalon of the 5-HT treated group compared with other groups. Second, the two doses (400 or 800 nmol) of l- and d-TRP were compared under a corticotrophin-releasing hormone-augmented social isolation stress. When comparing the efficacy between l- and d-TRP against stress behavior, both amino acids had a similar effect and quickly suppressed distress vocalizations. Finally, d-amino acid levels in the diencephalon and telencephalon were measured but d-TRP was not found. These results indicate that l- and d-TRP induce the same effect in attenuating stress but the mode of action of TRP derivatives, namely 5-HT differs during an acute isolation stress in neonatal chick. The absence of d-TRP in the diencephalon further suggests that instead of being an endogenous factor it may play role as a pharmacological factor.

Orally administered whole egg demonstrates antidepressant-like effects in the forced swimming test on rats.

OBJECTIVE: Several studies have reported that vegetarian diets are associated with a higher prevalence of major depression. Therefore, we hypothesised that the consumption of animal products, especially eggs, may have positive effects on mental health, especially on major depression, because a previous study reported that egg consumption produces numerous beneficial effects in humans. The purpose of the present study was to evaluate the effects of chronic whole-egg treatment on depression-like behaviours in Wistar rats, a control strain, and Wistar Kyoto rats, an animal model of depression. METHODS: In both the rats, either whole-egg solution (5 ml/kg) or distilled water (5 ml/kg) was orally administrated for 35 days. During these periods, the open-field test (OFT) was conducted on the 21st day, and a forced swimming test (FST) was enforced on the 27th and 28th days. On the 36th day, the plasma and brain were collected. RESULTS: Chronic whole-egg treatment did not affect line crossing in the OFT, whereas it reduced the total duration of immobility in the FST on both strains. Furthermore, interestingly, the results indicated the possibility that whole-egg treatment elevated the incorporation of tryptophan into the brain, and the tryptophan concentration in the prefrontal cortex was actually increased by the treatment. CONCLUSION: This study demonstrated that whole-egg treatment exerts an antidepressant-like effect in the FST. It is suggested that whole egg may be an excellent food for preventing and alleviating the conditions of major depression.

Central administration of L- and D-aspartate attenuates stress behaviors by social isolation and CRF in neonatal chicks.

Intracerebroventricular (i.c.v.) administration of L-aspartate (L-Asp) attenuates stress responses in neonatal chicks, but the mechanism has not been clarified. In the present study, three behavioral experiments were carried out under socially isolated stressful conditions exacerbated by the use of corticotrophin-releasing factor (CRF). In Experiment 1, i.c.v. injection of L-Asp attenuated behavioral stress responses (distress vocalization and active wakefulness) in a dose-dependent manner. Furthermore, L-Asp increased time spent standing/sitting motionless with eyes open and sitting motionless with head dropped (sleeping posture) in comparison with the group receiving CRF alone. In Experiment 2, i.c.v. injection of D-Asp dose-dependently decreased the number of distress vocalizations and the amount of time spent in active wakefulness. D-Asp increased the time spent standing/sitting motionless with eyes open compared with the group receiving CRF alone. In Experiment 3, we directly compared the effect of L-Asp with that of D-Asp. Both L- and D-Asp induced sedative effects under an acutely stressful condition. However, L-Asp, but not D-Asp, increased the time spent in a sleeping posture. These results indicate that both L- and D-Asp, when present in the brain, could induce a sedative effect, while the mechanism for hypnosis in neonatal chicks may be different for L-Asp in comparison with D-Asp.

Hypothesis with abnormal amino acid metabolism in depression and stress vulnerability in Wistar Kyoto rats.

While abnormalities in monoamine metabolism have been investigated heavily per potential roles in the mechanisms of depression, the contribution of amino acid metabolism in the brain remains not well understood. In additional, roles of the hypothalamus-pituitary-adrenal axis in stress-regulation mechanisms have been of much focus, while the contribution of central amino acid metabolism to these mechanisms has not been well appreciated. Therefore, whether depression-like states affect amino acid metabolism and their potential roles on stress-regulatory mechanisms were investigated by comparing Wistar Kyoto rats, which display depression-like behaviors and stress vulnerability, to control Wistar rats. Brain amino acid metabolism in Wistar Kyoto rats was greatly different from normal Wistar rats, with special reference to lower cystathionine and serine levels. In addition, Wistar Kyoto rats demonstrated abnormality in dopamine metabolism compared with Wistar rats. In the case of stress response, amino acid levels having a sedative and/or hypnotic effect were constant in the brain of Wistar Kyoto rats, though these amino acid levels were reduced in Wistar rats under a stressful condition. These results suggest that the abnormal amino acid metabolism may induce depression-like behaviors and stress vulnerability in Wistar Kyoto rats. Therefore, we hypothesized that abnormalities in amino acid and monoamine metabolism may induce depression, and amino acid metabolism in the brain may be related to stress vulnerability.