Effects of 6-hydroxydopamine on shock-elicited aggression, emotionality and maternal behavior in female rats

Tests of emotionality and shock-elicited aggression, which have revealed consistent changes in behavior in male rats given 6-hydroxydopamine (6-OHDA), were administered to female rats intraventricularly injected with 250 mug of 6-OHDA to determine whether aspects of the 6-OHDA syndrome are shared by female and male rats. The results confirmed that female rats become hyperemotional as well as hyperaggressive after 6-OHDA, as do males. Using the hypothesis that the behavioral effects of 6-OHDA lesions of catecholamine neurons result from a general reduction in threshold to aversive stimuli, it was predicted that arbitrarily selected stimuli having aversive components should enhance the behavior normally elicited by these stimuli. Stimuli selected for testing were those that normally elicit maternal defensive aggression and maternal retrieval. Both of these behaviors were found to be enhanced in 6-OHDA treated female rats, thus supporting the prediction. These findings were interpreted as inconsistent with the hypothesis that norepinephrine chemically codes specific behaviors, particularly aggressive behavior.