Neonatal testosterone augmentation increases juvenile play fighting but does not influence the adult dominance relationships of male rats

Neonatal male rats were either injected subcutaneously with testosterone propionate (TP) or oil vehicle. When weaned, each treated pup was paired with an untreated male sibling. The play fighting of TP?and oil?treated rats were compared at the juvenile phase (30-36 days), and in adulthood (84-90 days). In the juvenile phase, the rate of initiating playful attacks was significantly greater for TP?treated rats. Playful defense in response to such attacks did not differ between TP? and oil?treated rats. At the completion of the study, cortical thickness was measured for all the groups of rats. Oil treatment decreased overall cortical thickness relative to untreated pairmates, whereas TP treatment did not. Both oil and TP treatment abolished the asymmetry in hemispheric thickness, which was present in the untreated pairmates. The reversal of at least one of these injectioninduced changes in the cortex by TP provided independent evidence for the effectiveness of the TP treatment. As adults, neither the TP treatment nor the oil treatment influenced which pairmate became dominant. Dominance was judged by which pairmate initiated less playful attacks. Therefore, it is concluded that the early neonatal testosterone surge is not likely to be a factor in influencing the behaviors that lead to adult dominance. In contrast, play fighting is influenced by hormonal events in this early neonatal phase. It thus appears that play fighting and the aggressive systems subserving dominance relationships are differentially controlled. © 1992 Wiley?Liss, Inc. Copyright © 1992 Wiley?Liss, Inc., A Wiley Company

Neonatal male rats were either injected subcutaneously with testosterone propionate (TP) or oil vehicle. When weaned, each treated pup was paired with an untreated male sibling. The play fighting of TP?and oil?treated rats were compared at the juvenile phase (30-36 days), and in adulthood (84-90 days). In the juvenile phase, the rate of initiating playful attacks was significantly greater for TP?treated rats. Playful defense in response to such attacks did not differ between TP? and oil?treated rats. At the completion of the study, cortical thickness was measured for all the groups of rats. Oil treatment decreased overall cortical thickness relative to untreated pairmates, whereas TP treatment did not. Both oil and TP treatment abolished the asymmetry in hemispheric thickness, which was present in the untreated pairmates. The reversal of at least one of these injectioninduced changes in the cortex by TP provided independent evidence for the effectiveness of the TP treatment. As adults, neither the TP treatment nor the oil treatment influenced which pairmate became dominant. Dominance was judged by which pairmate initiated less playful attacks. Therefore, it is concluded that the early neonatal testosterone surge is not likely to be a factor in influencing the behaviors that lead to adult dominance. In contrast, play fighting is influenced by hormonal events in this early neonatal phase. It thus appears that play fighting and the aggressive systems subserving dominance relationships are differentially controlled. © 1992 Wiley?Liss, Inc. Copyright © 1992 Wiley?Liss, Inc., A Wiley Company

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