Abstract 306

Synthetic glucocorticoids (GC) are widely used for the prevention of chronic lung disease after severe respiratory distress syndrome in premature infants. This treatment may interfere with the development of the immature brain and little is known about the long-term consequences on behavior of these infants. The present study investigated the effects of neonatal treatment with clinically relevant doses of GC on a naturally occurring behavior in juvenile rats, i.e. social play behavior. This behavior is the first non-mother directed form of social behavior. Moreover, the effects of neonatal treatment with GC on novelty-induced locomotion activity in juvenile rats were investigated. Rat pups were treated (i.p.) with dexamethasone-phosphate (DEX-group) on postnatal day (PD) 1 (0.5 µg/g), day 2 (0.3 µg/g) and day 3 (0.1 µg/g). Control pups were treated with equivalent doses of saline (SAL-group), or left untreated (UNTR-group). Social play behavior of rats placed in a test arena for 15 minutes was registered on PD 25, 30 and 35. Pinning, as a measure of social play behavior, was significantly (p=0.03) elevated in rats of the DEX-group (34.2±5.2) compared with the SAL-group (17.9± 2.6) and UNTR-group (16.3±6.1) at PD 25. No significant differences in play behavior were found at PD 30 (p=0.8) and 35 (p=0.9). Novelty-induced locomotion activity was registered for 4 consecutive days for 4 minutes at PD 50-53. No differences in locomotion activity (p=0.8) or exploring strategy (p=0.5) of the novel environment were found. In conclusion, early neonatal DEX treatment affects social play behavior, but not novelty-induced activity in juvenile life. The question remains if early neonatal GC treatment also may affect social behavior in adult rats. Our data suggest that GC treatment of premature infants may have consequences for the development of social behavior in juvenile life.