A Comparison of Responding Maintained Under Second‐order Schedules of Intramuscular Cocaine Injection or Food Presentation in Squirrel Monkeys

Abstract

Key pressing by squirrel monkeys was maintained under second-order schedules of either intramuscular cocaine injection or food presentation. Under one schedule, each completion of a 10-response fixed-ratio unit produced a brief visual stimulus; the first fixed-ratio unit completed after 30 minutes elapsed produced the stimulus paired with either cocaine injection or food presentation. Generally, short pauses followed by high rates of responding were maintained within the fixed-ratio units, and responding was positively accelerated over the 30-minute interval. Under another schedule, each completion of a 3-minute fixed-interval unit produced the brief stimulus; completion of the 10th fixed-interval unit produced the stimulus paired with either cocaine injection or food presentation. Rates of responding increased within the fixed-interval units, and to a greater extent over the entire 10 fixed-interval units. Patterns of responding depended more on the schedule of reinforcement than on whether cocaine or food maintained responding. Omitting the brief stimuli following all but the last fixed-ratio or fixed-interval units decreased average rates and altered the patterns of responding. Substituting a visual stimulus that was never paired with cocaine or food following all but the last fixed-ratio or fixed-interval units decreased response rates to a lesser extent and did not substantially alter patterns of responding. When the duration of the paired stimulus was varied from .3 to 30.0 seconds, the highest response rates occurred at intermediate durations (1.0 to 10.0 seconds). The manner in which the stimulus changes affected performances depended more on the schedule of reinforcement than on whether cocaine injection or food presentation maintained responding.

A comparison of drug-seeking behavior maintained by d-amphetamine, l-deprenyl (selegiline), and d-deprenyl under a second-order schedule in squirrel monkeys

“…The present finding, that d-amphetamine was clearly and significantly self-administered above saline-vehicle levels by squirrel monkeys under a second-order schedule with drug injection at the end of each session, is similar to previous findings with cocaine (Goldberg et al 1976;Goldberg et al 1981;Katz, 1979) and morphine (Goldberg et al 1976;Goldberg and Tang 1977) under this type of second-order schedule in squirrel and rhesus monkeys. Response rates were very low at the start of the single 30-min fixed interval, but increased to a high rate by the end of the fixed interval.…”

“…They have been shown to be particularly useful in demonstrating reinforcing effects of drugs under conditions where the onset of drug effect might be delayed (e.g., intramuscular injection; Goldberg et al 1976;Katz 1979) or where repeated injections within a session might have cumulative effects that depress responding (Goldberg 1973;Goldberg et al 1990;Schindler et al 2002). On a second-order schedule, animals respond on one schedule for the presentation of a brief stimulus (e.g., a light), and the brief stimulus is then intermittently paired with a primary reinforcer (e.g., amphetamine) according to a second schedule.…”

Randomized trial of prize-based reinforcement density for simultaneous abstinence from cocaine and heroin.

“…In preclinical studies, second-order schedules of reinforcement have been shown to support robust and persistent operant responding for both natural and drug reinforcers (Alderson, Robbins, & Everitt, 2000;Goldberg, Kelleher, & Goldberg, 1981;Goldberg & Tang, 1977;Katz, 1979Katz, , 1980Mello et al, 1995). In addition, laboratory studies suggest that humans will learn to respond to a variety of reinforcers under second-order schedules (Lamb et al, 1991;Mello, Mendelson, Palmieri, Lex, & Teoh, 1990;Panlilio et al, 2005).…”

Human Cocaine-Seeking Behavior and its Control by Drug-Associated Stimuli in the Laboratory

“…This distinction emphasizes the importance of analyzing responding that occurs prior to the delivery of the drug, either by focusing on responding during the first component of the session (eg Arroyo et al, 1998;Pilla et al, 1999), or by arranging the schedule parameters so that the drug is only delivered at the end of the session (eg Goldberg et al, 1976Goldberg et al, , 1981Goldberg and Tang, 1977;Heishman et al, 2000, Katz, 1979Kelleher and Goldberg, 1977). The results of the present study suggest that responding is more dependent on the brief stimulus during periods in which the drug is available than during periods when the drug is not available.…”

“…After a certain interval of time has passed (eg 1 h), the next time the subject fulfills the response requirement, the stimulus is presented along with an injection of cocaine. Studies with non-human primates and rats have shown that the brief stimulus can become a powerful conditioned reinforcer, maintaining responding during long periods when the drug is unavailable (Di Ciano and Everitt, 2003;Kelleher and Goldberg, 1977;Goldberg et al, 1979Goldberg et al, , 1981Katz, 1979). Thus, second-order schedules provide a laboratory model of the drug abuse environment, where stimuli guide and maintain the complex sequences of behavior required to obtain, prepare, and ingest the drug.…”