Caffeine: effects on the behaviors of juvenile rats.

Caffeine, a central nervous system stimulant, was found to alter the expression of 3 behaviors in the juvenile rat. After caffeine administration, locomotor activity was increased in rats of all ages studied (24-84 days old). Pinning, a behavior characteristic of the juvenile period and used as an index of play-fighting, was suppressed following caffeine exposure, but only in rats 24-54 days old. Social investigation was not affected by caffeine in 24- and 34-day-old rats. However, in animals 44-84 days of age caffeine increased both the frequency and duration of investigation of a novel juvenile. Although caffeine influenced all the behaviors we observed, the developmental time course of caffeine's effects was different for each behavior.