Changes in head-dipping behavior in the hole-board test reflect the anxiogenic and/or anxiolytic state in mice

Abstract

The effects of treatment with anxiogenic or anxiolytic agents and exposure to acute restraint stress on emotional behavior in mice were examined using an automatic hole-board apparatus. Changes in the emotional state of mice were evaluated in terms of changes in exploratory activity, i.e., total locomotor activity, numbers and duration of rearing and head-dipping, and latency to the first head-dipping. The typical benzodiazepine anxiolytics diazepam (0.05–0.5 mg/kg, i.p.) and chlordiazepoxide (0.5–4 mg/kg, i.p.) dose-dependently increased the number and duration of head-dips at doses that did not produce sedation. In contrast with these anxiolytics, the typical anxiogenic drugs N-methyl- β-carboline-3-carboxamide (FG7142, 0.125–10 mg/kg, i.p.) and methyl- β-carboline-3-carboxylate ( β-CCM, 0.1–2 mg/kg, i.p.) decreased both the number and duration of head-dips, and increased the latency to head-dipping. Moreover, decreases in the number and duration of head-dips, and an increase in the latency to head-dipping, were also observed in animals that were exposed to acute restraint stress. These effects of acute restraint stress were suppressed by treatment with diazepam at a dose that alone did not produce significant behavioral effects (0.1 mg/kg, i.p.). In addition, non-benzodiazepine anxiolytic flesinoxan (0.1 mg/kg, i.p.), a 5-HT 1A receptor agonist, also had an effect on the restraint stress-induced decrease in head-dipping behavior. The present study shows that the changes in several exploratory behaviors could be objectively measured using our automatic hole-board apparatus. Therefore, this system can serve as a useful tool for evaluating the changes in various emotional states of animals. Moreover, we also found that treatment with anxiolytics or anxiogenics and exposure to acute restraint stress affected head-dipping behavior. These results suggest that changes in head-dipping behavior in the hole-board test may reflect the anxiogenic and/or anxiolytic state of animals.