Ross, L., & Schaal, D. W. (2002).
Time of supplemental feeding alters the effects of cocaine on lever pressing of rats.
Journal of the Experimental Analysis of Behavior,
77, 199-208.
The present experiment assessed the effects of cocaine on the
lever pressing of 4 rats maintained during 15-min sessions by a
fixed-ratio 50 schedule of food reinforcement. Across phases,
supplemental food was provided either immediately or 2 hr after
sessions. Two rats began the experiment in the delayed-feeding
condition, and 2 began the experiment in the immediate-feeding
condition. Rates of lever pressing of 2 rats sometimes decreased
to low levels near the ends of sessions when supplemental feeding
was provided immediately, but were consistently high throughout
sessions when supplemental feeding was delayed. Cocaine (1.0 to
17.0 or 30.0 mg/kg) was administered intraperitoneally 15 min
prior to test sessions. In most cases, cocaine suppressed
response rates at lower doses under immediate-feeding conditions.
Decreases in overall response rates were correlated with
dose-dependent increases in the time rats spent not responding.
It is suggested that delaying the time of postsession feeding
increased response strength, as indicated by greater resistance
to the rate-suppressive effects of cocaine.
Key words: cocaine, fixed-ratio schedule, response strength,
supplemental feeding, rats