Opponent strain effect on eliciting attacks in NZB mice: physiological correlates.

In agonistic encounters between male mice, the characteristics of the opponent may influence the attacking behavior of its partner. The present study shows that the opponent's ability to elicit attacking behavior in NZB males is strain dependent. BALB/c opponents elicit attacks more frequently, earlier and more intensively than C57BL/6 males. Plasma testosterone concentration was found to be higher in BALB/c than in C57BL/6 intact males. The weight of seminal vesicles in castrated males of both strains increased with injections of either 10- or 250-micrograms testosterone propionate (TP). This response was greater in BALB/c with the higher TP dose. The submandibular glands reacted to TP only in castrated BALB/c males with the higher dose. Furthermore, BALB/c males produced more marking secretions than C57BL/6 males. These results suggest that for these two strains, a higher testosterone sensitivity and a greater production of secretions are associated with a higher probability of opponents to elicit attacks. Genetic hypotheses on the underlying mechanisms are discussed.