Low Contact Strategy to Measure Flutamide’s Effects on Territorial Aggression in C57BL/6J Male Mice

Abstract

While numerous factors contribute to mouse behavior, biological drivers are paramount to many regulatory processes that undergird behavior. In particular, the sex hormone testosterone plays a key role in the regulation of aggression, physical activity, mating, and other behaviors known to be influenced by the presence of an experimenter. Due to this experimenter bias, strategies that minimize direct and frequent contact with research animals are needed to reduce any undesirable effects. The purpose of this research was to explore the effects of an androgen receptor antagonist (Flutamide) on territorial aggression in male C57BL/6J mice utilizing a low contact technique for chemical delivery. It was hypothesized that the introduction of an androgen receptor inhibiting substance under a low contact delivery strategy would result in effective reduction of the territorial aggression response in mice introduced to an unknown male mouse in the home cage environment, mimicking similar blunting responses characterized in previous work evaluating aggression in rodents. Silastic (Dow Corning, Midland, MI) implants were used as the lower contact delivery strategy for drug administration. This strategy allowed minimal contact with the experimental technician and eliminated the need for daily contact required for the commonly used injection strategies employed elsewhere. A series of aggression trials before, 24, 96, and 192 hours after Flutamide implantation were conducted in three groups of mice. Control mice (n=4) received 100% Cholesterol-containing implants, low exposure mice (n=5) received 80% Cholesterol/20% Flutamide-containing implants, and high exposure mice (n=5) received 100% Flutamide-containing implants. Each aggression trial consisted of introducing a foreign mouse to an experimental mouse’s home cage for an 8-minute period. The time to initial aggression and the total number of aggressions over the 8 minutes was quantified. The time to initial aggression was unaffected by flutamide administration throughout the study [F(26,91) =0.37, p=0.864]. The total number of aggressions were significantly affected by flutamide exposure [F(28,82) = 2.90, p=0.029]. Follow-up post hoc testing indicated a significant reduction in aggression in both the low and high dose groups 24 (low: p = 0.001; high = 0.001) and 96 (low: p = 0.009; high = 0.012) hours after implantation compared to the control at the same time points. The use of Silastic implants to deliver the anti-androgenic compound was a valuable technique that reduced research animal contact with experimental technicians. This technique can be modified for prolonged exposure by lengthening the implant or increasing the diameter of the Silastic tubing. This anti-androgen exposure methodology requiring less interaction reduces the confounding variables that impact mouse behavior and could prove beneficial to observe and study other androgen-related behaviors including physical activity and mating. All funding for this research was provided by the Union University Department of Biology. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.