Figure 3.

Lack of aggressive behavior in trp2−/− males and lactating females. (A) trp2−/− males are not aggressive in a resident–intruder assay. Trp2 (n = 23, blue bars) and control (n = 25, red bars) male mice were observed for behaviors elicited by the addition of a male to their home cage for 15 min prior to and after mating experience with females. Trp2 males were significantly different from control males by all measures of aggressive behavior (latency to attack, attack frequency and attack duration, P < 0.0001, Mann–Whitney U test). There was also a significant increase in all parameters of aggressive behavior after sexual experience in the control group (P < 0.05, Wilcoxon signed rank test), but sexual experience did not stimulate aggression in the trp2−/− group. (B) trp2−/− lactating females are not aggressive in a maternal aggression assay. Lactating trp2 (n = 11) and control (n = 11) mothers were tested for aggression toward intruder males in a 15-min test. Trp2 females were significantly different from control females by all measures of aggressive behavior (P < 0.05). Forty-five percent of control females responded aggressively toward intruder males on at least one of the test sessions, whereas trp2 females never initiated attacks.