RESPONSE SUPPRESSION DURING CUMULATIVE DOSING - A ROLE FOR PAVLOVIAN CONDITIONING

Key pecking by pigeons was maintained by a fixed-ratio 15 or a fixed-i nterval 15 s schedule off food presentation. Sessions consisted of six blocks that included a 4 min blackout then 2 min of schedule time or six food presentations, Cumulative dose-response curves were assessed by injecting saline at the start of the second block and increasing co caine doses at the onset of subsequent blocks, Repeated cumulative dos ing often shifted dose-response curves to the left, and these effects appeared to be due to the reliable correlation between smaller and lar ger doses administered early and later in the session. When saline was substituted for the larger doses later in the session, dose-response curves initially remained shifted to the left, and continued substitut ion eventually resulted in curves shifting to the right. Cumulative do sing was compared with two noncumulative dosing procedures: (a) pre-se ssion dosing and (b) one cocaine injection at the block in which the s ame cumulative dose would be tested, with saline injections at the oth er blocks (except the first). Noncumulative dosing tended to produce m ore reliable (repeatable) results than did cumulative dosing, and at l east one interpretation is the possibility of conditioning factors tha t may be present in cumulative-dosing but not in noncumulative-dosing procedures. Behav Pharmacol 1998; 9:255-271 (C) 1998 Lippincott-Raven Publishers.