A method for investigating the effects of drugs on the exploratory behaviour of mice.

1. Exploratory behaviour in mice was observed when they were put on a wooden board to which twelve tunnels were fixed. The number of different tunnels entered (indicating exploration) and the total entries into tunnels were recorded over 5 min on 2 successive days.2. Untreated mice entered more different tunnels in the first minute on the second day on the tunnel board, and this difference in behaviour was taken as an indication that exploration had occurred on the first day. When the behaviour of the treated mice on the second day was similar to that of inexperienced mice on the first day it was inferred that drug treatment had adversely affected exploration.3. Haloperidol 4 mg/kg, chlorpromazine 8 mg/kg and thioridazine 16 mg/kg adversely affected exploration at doses which almost immobilized the mice.4. Amphetamine at 8 mg/kg disrupted exploratory behaviour in the mice, although the mice were observed to move round the board very quickly.5. With tranylcypromine 2 mg and nialamide 100 mg, increased exploratory behaviour by comparison with controls was recorded in the mice when they were tested 24 h after drug treatment.6. Imipramine at 20 mg/kg reduced the total number of tunnels entered by the mice on the first day, but on the second day the mice behaved in a similar way to mice treated with monoamine oxidase inhibitors.