Testosterone enhances risk tolerance without altering motor impulsivity in male rats

Abstract

Summary Anabolic-androgenic steroids (AAS) increase impulsive and uncontrolled aggressive (‘roid rage) in humans and enhance agonistic behavior in animals. However, the underlying mechanisms for AAS-induced aggression remain unclear. Potential contributing elements include an increase risk-taking and/or motor impulsivity due to AAS. This study addressed the effects of chronic high-dose testosterone on risk tolerance using a risky decision-making task (RDT) and motor impulsivity with a go/no-go task in operant chambers. Male Long-Evans rats were treated for at least 4 weeks with testosterone (7.5mg/kg) or vehicle beginning in late adolescence. Testosterone was used because it is popular among human AAS users. In RDT testing, one lever was paired with delivery of a small “safe” food reward, while the other was paired with a large “risky” reward associated with an increasing risk of footshock (0, 25, 50, 75, 100%) in successive test blocks. Three shock intensities were used: 1.0, 1.2, and 1.4 mA/kg. As shock intensity and risk of shock increased, preference for the lever signifying a large reward significantly declined for both vehicle- and testosterone-treated rats (p<0.05). There was also a significant effect of drug (p<0.05), where testosterone-treated rats showed greater preference for the large reward, compared to vehicle- treated controls. Increased preference for the large reward, despite risk of footshock, is consistent with increased risk tolerance. In go/no-go testing, rats were trained to press a single lever if the go cue was presented (stimulus light) or to refrain from pressing during the no-go cue (tone). There was no effect of testosterone on pre-cue responses, or performance in go and no-go trials. These results suggest that AAS may increase risk-tolerance without altering motor impulsivity.

Sex differences in a rat model of risky decision making.

“…The fact that there was no significant correlation between body weight and mean percent choice of the large, risky reward (controlling for sex, r = 0.18, p = 0.35) argues against this possibility [see also (Mitchell et al, 2014)]. To address this issue more directly, however, shock intensities were adjusted as a function of body weight (1.0 mA/kg) every other day in the second cohort of rats (Cooper, Goings, Kim, & Wood, 2014). Rats were tested in the RDT using these procedures until stable behavior emerged (18 sessions; Fig 3).…”

Neural mechanisms regulating different forms of risk-related decision-making: Insights from animal models

“…3B, rats tested in this task prefer the large reward when the probability of punishment is low, but shift their preference away from the large reward (and toward the small, safe reward) as the probability of punishment increases. The degree of preference for the large, "risky" reward is strongly dependent on shock intensity, with higher intensities resulting in decreased choice of the large reward (Simon et al, 2009;Cooper et al, 2014;Shimp et al, 2015). Somewhat surprisingly, the magnitude of the large reward appears to play less of a role in directing choice behavior in this task.…”

Cooperation in rats playing the iterated Prisoner's Dilemma game

“…200 g body weight at the start of the study; Charles River Laboratories, Wilmington, MA, U.S.A.) were pair-housed with a same-sex conspecific under a reversed 14:10 h light:dark cycle. To facilitate operant responding, male rats were maintained on a slow rate of growth (3–4 g/day) during training, as in Cooper, Goings, Kim, and Wood (2014). To eliminate cyclic fluctuations in ovarian steroid hormones and maintain chronic physiologic levels of oestrogen, female rats were ovariectomized via bilateral dorsal flank incision, and received a subcutaneous 4 mm Silastic oestradiol implant (inner diameter: 1.98 mm, outer diameter: 3.18 mm; Dow Corning, Midland, MI, U.S.A.; Bridges, 1984).…”