Decrement of dominant rat aggression level induced by an unpredictable stimulus

ANDRÉS P. LEMOINE; LORENA RELA; ENRIQUE T. SEGURA

Ciudad del Cabo, Sudáfrica

Congreso; IX Biennial Meeting of the International Society for Comparative Psychology; 1998

International Society for Comparative Psychology

Learned helplessness (LH), a syndrome originally attributed to the lack of control, was found to be elicited by unpredictable stimuli (Overmeier & Seligman, 1967; Lemoine et al, 1994). It has been previously shown that both individual behaviour, central noradrenergic neurotransmission and adrenocortical catecholaminergic secretion are modified by uncontrollable and unpredictable stressors, but remained within the basal range when the animals received the same amount of uncontrollable but predictable stimuli. The behavioural literature showed that predictability, through relief and relaxation elicited by safety cues (in our case, constant ITIs) can reduce the aversiveness of inescapable shocks. On the other hand, unpredictable stimuli (in this case, variable ITIs) result in a state of chronic fear, which accounts for the observed behavioural impairment. According to Williams (1987), this occurs through the displacement of several behaviours, such as freezing (the stress-coping-fear-defense hypothesis). Due to the potential relevance of LH in the study of human depression (Gray, 1987), we decided to investigate the possible effects of these two treatments on the social status of randomly formed pairs of experimental animals. Again, a transient change in the hierarchical status of dominants rats was observed. This poster focuses on further evidence concerning the phenomenon of transient dominance reversion in rats, assessing aggression between the dominant and submissive subjects of each dyad. Pairs of naive Sprague-Dawley rats (adult males) were randomly formed 1 month before testing. Dominance was assessed pre- and post-treatment of dominant animals with variable or constant ITIs. Dominance was assessed by scoring priority to access to a time-limited water source, displacement from the source, time in contact with the source (available for 10 s every minute during the 30 min. test), agonistic behaviours (boxing, stepping, etc) and individual behaviour as indicators of distress(such as autogrooming). The amount of time spent near the limited source of water was also measured. Accessory data are also shown, such as context preference and behavioural impairment in a simple task acquisition. The reported data supports our previous observations, showing that unpredictable treatment of dominants with inescapable shocks leads to a transient but significative reduction of its social status, due mainly to a reduction of its aggressive display.