CONDITIONED SUPPRESSION OF OPERANT RESPONDING IN RESPONSE TO A STIMULUS PAIRED WITH PENTOBARBITAL INJECTIONS

Conditioned suppression of ongoing behavior in response to a stimulus paired with barbiturate treatment was investigated in rats leverpressi ng for food pellets by presenting an audiovisual stimulus (conditioned stimulus [CS]) 3 min before injection of 15 mg/kg sodium pentobarbita l (experimental group, la = 9) or water (control group, n = 8). The ex perimental rats completely stopped responding during the 20-min postin jection period. During 12 conditioning days, the experimental group de veloped conditioned suppression to the preinjection CS as indicated by decreases in response rate to 35% of baseline, significantly differen t from the 70% control group mean. The preinjection conditioned respon se lowered response rate, as did the actual drug treatment. Visual obs ervation revealed that the CS elicited locomotor activity that interfe red with leverpressing, indicating that although the conditioned respo nse rate change was ''isodirectional'' to the drug effect (uncondition ed response), an opposite-direction conditioned locomotor conditioned response was elicited by preinjection stimuli. The ability of the inje ction procedure to elicit conditioned responses was determined after 1 2 conditioning days in an extinction-test session in which water only was injected in both groups. Neither significant conditioned suppressi on nor conditioned motor activity was elicited by the injection proced ure.