The automatic hole-board test is an experimental method that can serve as a useful tool for objectively evaluating the changes in various emotional states of mice. Previously, we found that pretreatment of mice with 5-HT_1A receptor agonists 24 hr before testing resulted in the development of stress resistance, i.e. the decrease in head-dipping behaviors in the hole-board test induced by exposure to acute restraint stress is suppressed. In addition, we also created stress-adaptive and -maladaptive models in mice based on the diversity of changes in head-dipping behavior in the hole-board test induced by repeated exposure to different levels of restraint stress. Biochemical studies investigating the role of the brain 5-HT nervous system in the development of stress adaptation found an increase in the tryptophan hydroxylase, an enzyme of 5-HT synthesis, in stress-adaptive mice. Furthermore, pharmacological activation of 5-HT_1A receptors by selective agonist promoted the development of stress adaptation in stress-maladapted mice. These findings suggest that the brain 5-HT nervous system could play an important role in the stress resilience. In this symposium, we would like to introduce and discuss the recent findings from studies using these animal models, which were created on the basis of the hole-board test.