Belke, T. W., & Dunbar, M. J. (2001).
Effects of cocaine on fixed interval responding reinforced by the opportunity to run.
Journal of the Experimental Analysis of Behavior,
75, 77-91.
Rate dependent drug effects have been observed for operant
responding maintained by food, water, heat, light onset,
electrical brain stimulation, shock-stimulus termination, and
shock presentation. The present study sought to determine if the
effects of cocaine on lever pressing maintained by the
opportunity to run could also be described as rate dependent.
Seven male Wistar rats were trained to respond on levers for the
opportunity to run in a wheel. The schedule of reinforcement was
fixed interval 60 s, and the reinforcing consequence was the
opportunity to run for 60s. On this schedule, overall rates of
responding were low, usually below six presses per minute, and
pauses frequently exceeded the 60s interval. Despite these
differences, an overall scalloped pattern of lever pressing was
evident for each rat. Doses of 1, 2, 4, 8, and 16 mg/kg cocaine
were administered 10 min prior to a session. Only at the 16 mg/kg
dose did the responding of the majority of rats change in a
manner suggestive of a rate dependent drug effect. Specifically,
lower response rates at the beginning of the intervals increased
and higher rates at the end of the intervals decreased, as
indicated by the fact that slopes from the regression of drug
rates on control rates decreased. These data provide tentative
support for the generalization of rate dependent effects to
operant responding maintained by wheel running. Differences in
the baseline performance maintained by wheel running compared to
those for food and water point to the need for further
experimentation before this effect can be firmly established.
Key words: wheel-running reinforcement, fixed-interval schedule,
rate dependency, cocaine, lever press, rats