Abstract

Ephedrine and d-amphetamine increased the rate of key pecking by pigeons during the fixed-interval component of a multiple fixed-ratio, fixed-interval schedule of food presentation, but decreased the rate of key pecking during the fixed-ratio component. Tetrabenazine (TBZ) and phenylephrine decreased rates of responding during both schedule components. Ephedrine and d-amphetamine partially counteracted the rate-decreasing effects of TBZ during both schedule components, but phenylephrine only added to the rate-decreasing effects of TBZ. Analysis of the rates of responding during the fixed-ratio component and during local segments of the fixed-interval component suggested that the ability of ephedrine and d-amphetamine to partially reverse the effects of TBZ was related to the rate-increasing effect that these drugs have on low rates of responding, even when the low rates have resulted from injections of TBZ. The rate-decreasing effects of TBZ could also be reversed in the pigeon by caffeine, whereas d-amphetamine could also increase low rates after TBZ in the squirrel monkey and after NSD 1034 in the pigeon. Although certain dosages of both TBZ and NSD 1034 reduced the brain levels of norepinephrine in the pigeon, the dosages at which the brain levels of norepinephrine were lowered did not correlate well with the dosages at which behavioral changes occurred.