Acute and chronic caffeine exposure effects on play fighting in the juvenile rat

Effects of acute and chronic exposure to caffeine on the behavior of juvenile rats were assessed in three experiments. In Experiment 1, two indices of play fighting--pin frequency and duration--were decreased and locomotor activity was increased in dose dependent fashions by caffeine. Social investigation of another juvenile was not affected by the drug. In Experiment 2, juvenile rats were isolated and given caffeine in their drinking fluid for 10-11 days. Play fighting was increased by all except the highest caffeine dose. In Experiment 3, juveniles were housed in groups of four and received either tap water or caffeine in their drinking fluid. Pin frequency of caffeine treated subjects was lower than controls on days 2-4, and higher than controls on days 9-11 after caffeine treatment was initiated. Evidently, caffeine has inhibitory and facilitatory effects on juvenile play fighting behavior, contingent on duration of exposure to the drug.