Using a dependent schedule to measure risky choice in male rats: Effects of d-amphetamine, methylphenidate, and methamphetamine.

Abstract

Risky choice is the tendency to choose a large, uncertain reward over a small, certain reward, and is typically measured with probability discounting, in which the probability of obtaining the large reinforcer decreases across blocks of trials. One caveat to traditional procedures is that independent schedules are used, in which subjects can show exclusive preference for one alternative relative to the other. For example, some rats show exclusive preference for the small, certain reinforcer as soon as delivery of the large reinforcer becomes probabilistic. Therefore, determining if a drug increases risk aversion (i.e., decreases responding for the probabilistic alternative) is difficult (due to floor effects). The overall goal of this experiment was to use a concurrent-chains procedure that incorporated a dependent schedule during the initial link, thus preventing animals from showing exclusive preference for one alternative relative to the other. To determine how pharmacological manipulations alter performance in this task, male Sprague Dawley rats (n = 8) received injections of amphetamine (0, 0.25, 0.5, 1.0 mg/kg), methylphenidate (0, 0.3, 1.0, 3.0 mg/kg), and methamphetamine (0, 0.5, 1.0, 2.0 mg/kg). Amphetamine (0.25 mg/kg) and methylphenidate (3.0 mg/kg) selectively increased risky choice, whereas higher doses of amphetamine (0.5 and 1.0 kg/mg) and each dose of methamphetamine impaired stimulus control (i.e., flattened the discounting function). These results show that dependent schedules can be used to measure risk-taking behavior and that psychostimulants promote suboptimal choice when this schedule is used.

A method for studying reinforcement factors controlling impulsive choice for use in behavioral neuroscience

“…Thus, a conjunctive schedule, with an FR component, was used in the initial links to require a minimum sample of responses per cycle while still controlling for entry rate into the terminal links as much as possible. Although dependent FR initial links have been used to investigate neurobiological manipulations in rodents within the context of concurrent chains (e.g., Pope et al, 2015; Yates et al, 2020), the rate of entry into the terminal links is directly related to response rates on the assigned lever in a dependently scheduled component with only an FR schedule. Thus, a strong preference for one lever could result in substantially differential rates of entry into the respective terminal link.…”

“…The delay component was included in the magnitude procedures to control the terminal‐link duration, such that a greater amount of time was spent in the terminal link relative to the initial links; this has also been reported to be associated with a greater control of choice (Grace, 1994). The FR 1 schedule was included after the delay to ensure that the rat was near the opening when the dipper was presented (also see Yates et al, 2020).…”

“…Indeed, numerous studies indicate that response allocation in the initial links by pigeons is exquisitely controlled by the reinforcement parameters arranged in the terminal links. Although concurrent-chains procedures have been used with rodents (e.g., Aparicio et al, 2013Aparicio et al, , 2016Aparicio et al, , 2019Ito & Asaki, 1982;Johnson et al, 2013;Orduña et al, 2013;Yates et al, 2018Yates et al, , 2020, this literature is much less extensive than with pigeons. Furthermore, there is lab lore suggesting that choice in rodents does not come under control of within-session changes in reinforcement parameters as readily as choice does in pigeons (e.g., Kyonka, personal communication; we have not been as successful with rats as we have been with pigeons).…”

“…This approach permits evaluation of a relatively large sample of behavior (i.e., more responses are made) and calculation of response ratios. Further, dependent scheduling (e.g., Stubbs & Pliskoff, 1969; Yates et al, 2020) ensures equal exposure to the arranged contingencies, which has two advantages. First, it reduces the impact of differential exposure to response outcomes that necessarily occurs as a function of preference under nondependent scheduling.…”

“…First, it reduces the impact of differential exposure to response outcomes that necessarily occurs as a function of preference under nondependent scheduling. Second, it reduces the need for forced trials that typically are used in discrete‐trial procedures (e.g., see Yates et al, 2020).…”