Effects of diazepam on responding suppressed by response-dependent and independent electric-shock delivery

While the effects of benzodiazepines on punished responding (response-dependent shock) are straightforward and unambiguous, their effects on behavior suppressed by response-independent shock are conflicting and inconsistent. Some investigators reported that benzodiazepines either have no effect on, or suppress further, responding during response-independent shock, while others reported that benzodiazepines enhance response rates during independent shock delivery in the same manner as during dependent shock. The present study compared the effects of diazepam on rates of lever pressing maintained by a variable-interval 35-sec schedule of food delivery in rats exposed alternately to fixed-interval 180 sec (response-dependent) and fixed-time 180 sec (response-independent) schedules of shock delivery. Diazepam increased punished responding in a dose-dependent manner for each animal. "Rate-dependency," degree of suppression and presence of external stimuli influenced rate-enhancement by the drug. Effects of diazepam on responding suppressed by response-independent shock were inconsistent, with two animals revealing rate enhancement comparable to punished responding, and two others revealing further increases in response suppression. Reasons for the differential effects of diazepam on response-rates suppressed by the two forms of shock delivery remain obscure, although the basic phenomenon seems to be real and not merely an artifact of "rate-dependency."