Sex and housing conditions modify the effects of adolescent caffeine exposure on anxiety-like and depressive-like behavior in the rat.

Previously observed antidepressant-like effects of caffeine in adolescent rats have been shown in individually housed (IH) rats. Because IH presents a social stressor that may create depressant-like effects in control animals, this study sought to compare the effects of chronic caffeine in IH and pair-housed (PH) adolescent male and female rats. Housing conditions began on postnatal day 24 (P24) and half of the rats were provided caffeine (0.25 g/l) in their drinking water beginning on P28. Open-field behavior was assessed on P42, a light/dark test was conducted on P43, and a forced swim test was conducted on P44-P45. PH and caffeine separately increased behavior in the open-field test and females reared more than males. In the light/dark test, IH animals and males showed greater anxiety-like behavior than PH animals and females, respectively. In the forced swim test, PH animals showed less overall immobility and caffeine decreased immobility in IH rats and PH females but increased immobility in PH males. Swimming behavior was higher in PH rats overall and caffeine increased swimming in IH rats but decreased swimming in PH rats. Climbing behavior was increased by caffeine in all groups except PH males with the greatest increase in PH females. We conclude that the effects of caffeine on depressive-like and anxiety-like behavior in adolescents are dependent on sex and housing conditions.