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.

LPLRFamide causes anorexigenic effects in broiler chicks and Bobwhite quail

Although LPLRFamide was the first member of the RFamide family to be isolated from a vertebrate species, its effects on hunger and satiety-related processes are poorly documented. Thus, we intracerebroventricularly administered LPLRFamide (3.0-15.0 nmol) to both Cobb-500 (a broiler type of Gallus gallus) and Bobwhite quail (Colinus virginianus) chicks and measured their food intake. The threshold of anorexigenic response was 7.0 nmol in Cobb-500 chicks and the effect had diminished by 30 min post-injection. In Bobwhite quail all doses of LPLRFamide tested caused anorexia that remained throughout the 60 min observation period. A comprehensive behavior analysis was conducted and Cobb-500 chicks had increased food pecks early in the observation period and spent a greater amount of time in deep rest. Although food pecks were increased pecking efficiency was decreased. In Bobwhite quail, feeding pecks and the number of jumps were reduced after LPLRFamide treatment. We judged that these behaviors in both species were likely not competitive with ingestion and thus did not secondarily contribute to anorexia. These results demonstrate that LPLRFamide is associated with satiety-related processes in Cobb-500 chicks and Bobwhite quail, while threshold of responses are different.

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.

High concentrations of HGF inhibit skeletal muscle satellite cell proliferation in vitro by inducing expression of myostatin: a possible mechanism for reestablishing satellite cell quiescence in vivo

Skeletal muscle regeneration and work-induced hypertrophy rely on molecular events responsible for activation and quiescence of resident myogenic stem cells, satellite cells. Recent studies demonstrated that hepatocyte growth factor (HGF) triggers activation and entry into the cell cycle in response to mechanical perturbation, and that subsequent expression of myostatin may signal a return to cell quiescence. However, mechanisms responsible for coordinating expression of myostatin after an appropriate time lag following activation and proliferation are not clear. Here we address the possible role of HGF in quiescence through its concentration-dependent negative-feedback mechanism following satellite cell activation and proliferation. When activated/proliferating satellite cell cultures were treated for 24 h beginning 48-h postplating with 10-500 ng/ml HGF, the percentage of bromodeoxyuridine-incorporating cells decreased down to a baseline level comparable to 24-h control cultures in a HGF dose-dependent manner. The high level HGF treatment did not impair the cell viability and differentiation levels, and cells could be reactivated by lowering HGF concentrations to 2.5 ng/ml, a concentration that has been shown to optimally stimulate activation of satellite cells in culture. Coaddition of antimyostatin neutralizing antibody could prevent deactivation and abolish upregulation of cyclin-dependent kinase (Cdk) inhibitor p21. Myostatin mRNA expression was upregulated with high concentrations of HGF, as demonstrated by RT-PCR, and enhanced myostatin protein expression and secretion were revealed by Western blots of the cell lysates and conditioned media. These results indicate that HGF could induce satellite cell quiescence by stimulating myostatin expression. The HGF concentration required (over 10-50 ng/ml), however, is much higher than that for activation, which is initiated by rapid release of HGF from its extracellular association. Considering that HGF is produced by satellite cells and spleen and liver cells in response to muscle damage, local concentrations of HGF bathing satellite cells may reach a threshold sufficient to induce myostatin expression. This time lag may delay action of the quiescence signaling program in proliferating satellite cells during initial phases of muscle regeneration followed by induction of quiescence in a subset of cells during later phases.

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.

Dietary conjugated linoleic acid modifies the brain endocannabinoid system in mice

Conjugated linoleic acid (CLA) has a role of biogenic regulation through modifying prostaglandin production. However, its effects on related metabolites of arachidonate remain unclear. Therefore, the effects of CLA on brain endocannabinoid content as well as its analogs were investigated. Mice (3-week-old), provided with diets containing 3% linoleic acid or 3% CLA for 4 weeks, were sacrificed and lipids were extracted from their cerebral cortex and hypothalamus. The amounts of N-arachidonoyl-ethanolamide, 2-arachidonoyl-glycerol (2-AG), oleoyl-ethanolamide and palmitoyl-ethanolamide were determined quantitatively by LC-MS. The 2-AG level in the cerebral cortex was significantly decreased by CLA treatment, but the other compounds were unaffected in the cerebral cortex and hypothalamus. The present study indicated that dietary CLA site-selectively decreases 2-AG in the cerebral cortex.

Current knowledge of the roles of ghrelin in regulating food intake and energy balance in birds

A decade has passed since the peptide hormone ghrelin was first discovered in rat stomach. During this period, ghrelin has been identified not only in other mammals but also in fish, amphibians, reptiles and birds, and its physiological functions have been widely investigated. Avian ghrelin was first identified in chickens in 2002 and to date, the amino acid sequences of six different avian ghrelin peptides have been reported. In mammals, ghrelin is the only known gut-derived hormone to stimulate food intake when administered centrally or peripherally. In studies on chickens and quail, however, ghrelin inhibits food intake when injected centrally, while the effects on feeding behavior elicited by ghrelin injected peripherally are equivocal. This review summarizes what is currently known about the regulation of food intake and energy balance by ghrelin in birds.

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.

Oral administration of Excitin-1 (beta-alanyl-L-leucine) alters behavior and brain monoamine and amino acid concentrations in rats

We previously demonstrated that beta-alanyl-branched chain amino acids have excitatory effects. Therefore, we named beta-alanyl-L-leucine, beta-alanyl-L-isoleucine and beta-alanyl-L-valine as Excitin-1, -2, and -3 , respectively. Since there is little known about the effects of Excitins, we clarified whether oral administration of Excitin-1 affects behavior in rats, alters the monoamine and amino acid levels in the central nervous system, whether Excitin-1 is incorporated into the brain, and how long it remains in the blood. Excitin-1 increased motor behavior, increasing the distance of path and number of rearings in the open field. Excitin-1 influenced some monoamine and amino acid levels in the cerebral cortex and hypothalamus. Following oral administration, Excitin-1 was detected in the cerebral cortex, hypothalamus, hippocampus and olfactory bulb. In the plasma, Excitin-1 and its metabolites beta-alanine and L-leucine were recorded. The present study demonstrated that Excitin-1 was incorporated in the brain and promoted behavioral changes in rats.

Behavioral responses of neonatal chicks exposed to low environmental temperature

Research has shown that on exposure to low environmental temperature, neonatal chicks (Gallus gallus) show hypothermia and absence of gene transcript enhancement of putative thermogenic proteins, mitochondrial fatty acid transport, and oxidation enzymes. Various behavioral abnormalities may also decrease the thermogenic capacity of low-temperature-exposed neonatal chicks. Therefore, to investigate behavioral irregularities in low-temperature-exposed (20 degrees C) neonatal chicks, we studied behavioral responses when compared with the control kept at thermoneutral temperature (30 degrees C). Two-day-old chicks (n = 5) were exposed to either low or thermoneutral temperature for 3 h and were then immediately placed in an acrylic monitoring cage (40 x 30 x 20 cm). The monitoring cage was fitted with a 3-dimensional mirror (to prevent isolation-induced stress) and maintained either at 20 or 30 degrees C. Behavioral responses were monitored for 10 min. Behavioral observations revealed that low-temperature exposure decreased distress vocalizations and spontaneous activity. Low-temperature exposure induced sleep-like behavior in neonatal chicks; active wakefulness was decreased while standing or sitting motionless with eyes closed or open and sleeping posture was significantly increased. In conclusion, there is evidence that on exposure to low-temperature, neonatal chicks decrease behavioral activity. Increased sleep-like behavior and decreased activity may reduce heat production in low-temperature-exposed neonatal chicks and could potentiate the sensitivity to cold exposure.