Disparities in activity levels and learning ability between Djungarian hamster (Phodopus sungorus) and Roborovskii hamster (Phodopus roborovskii).

The Djungarian hamster and the Roborovskii hamster belong to the same genus of Phodopus. However, the Djungarian hamster is tame and shows sedative behavior, while Roborovskii hamster is not tame and shows high levels of locomotor activity. Hyperactivity occurs in animals with tameless behavior.

Antidepressant-like effect of bright light is potentiated by L-serine administration in a mouse model of seasonal affective disorder.

Bright light therapy is used as the primary treatment for seasonal affective disorder; however, the mechanisms underlying its antidepressant effect are not fully understood. Previously, we found that C57BL/6J mice exhibit increased depression-like behavior during a short-day condition (SD) and have lowered brain serotonin (5-HT) content. This study analyzed the effect of bright light on depression-like behaviors and the brain serotonergic system using the C57BL/6J mice.

Serotonin levels in the dorsal raphe nuclei of both chipmunks and mice are enhanced by long photoperiod, but brain dopamine level response to photoperiod is species-specific.

Seasonal affective disorder (SAD) is a subtype of major depressive or bipolar disorders associated with the shortened photoperiod in winter. This depressive disorder is integrally tied to the seasonal regulation of the brain's serotonergic system. Recently, we found that C57BL/6J mice subjected to a forced-swim test exhibited immobility, a photoperiod-dependent depression-associated behavior, and suppression of brain serotonin levels.

Melatonin adjusts the expression pattern of clock genes in the suprachiasmatic nucleus and induces antidepressant-like effect in a mouse model of seasonal affective disorder.

Recently, we have shown that C57BL/6J mice exhibit depression-like behavior under short photoperiod and suggested them as an animal model for investigating seasonal affective disorder (SAD). In this study, we tested if manipulations of the circadian clock with melatonin treatment could effectively modify depression-like and anxiety-like behaviors and brain serotonergic system in C57BL/6J mice. Under short photoperiods (8-h light/16-h dark), daily melatonin treatments 2 h before light offset have significantly altered the 24-h patterns of mRNA expression of circadian clock genes (per1, per2, bmal1 and clock) within the suprachiasmatic nuclei (SCN) mostly by increasing amplitude in their expressional rhythms without inducing robust phase shifts in them.

Oral administration of D-aspartate, but not L-aspartate, depresses rectal temperature and alters plasma metabolites in chicks.

Aims: L-Aspartate (L-Asp) and D-aspartate (D-Asp) are physiologically important amino acids in mammals and birds. However, the functions of these amino acids have not yet been fully understood. In this study, we therefore examined the effects of L-Asp and D-Asp in terms of regulating body temperature, plasma metabolites and catecholamines in chicks.

Central injection of L- and D-aspartate attenuates isolation-induced stress behavior in chicks possibly through different mechanisms.

Intracerebroventricular (i.c.v.

Photoperiodic responses of depression-like behavior, the brain serotonergic system, and peripheral metabolism in laboratory mice.

Seasonal affective disorder (SAD) is characterized by depression during specific seasons, generally winter. The pathophysiological mechanisms underlying SAD remain elusive due to a limited number of animal models with high availability and validity. Here we show that laboratory C57BL/6J mice display photoperiodic changes in depression-like behavior and brain serotonin content.