Anticipatory responding, exclusive drug-context pairing and conditioned effects in sensitization to apomorphine-induced climbing in mice

1. The conditioning aspects of contextual sensitization were examined in th e case of apomorphine-induced wall-climbing in mice, measuring onset latenc ies of the pharmacological response and controlling differential habituatio n to the test context during drug treatment. 2. Sensitization was generated in male out-bred mice which received intermi ttent i.p. injections of 0.4 mg/kg apomorphine over 9 daily sessions. On da y 10, they were tested for contextual sensitization (all mice under apomorp hine). On day 14, after 3 sessions of reinstatement, mice were tested for c onditioned climbing (all mice under saline). 3. It was found that simultaneous exposure to both apomorphine and the test context facilitated the expression of a full-blown contextual sensitizatio n (some non-contextual sensitization emerging too); importantly, sensitizat ion was accompanied by a progressive shortening of the latencies to climb ( before injections); conditioned climbing appeared only in mice pairing the drug with the test context, that response being absent in mice treated outs ide the context or never exposed to the context. 4. It is likely that contextual sensitization to apomorphine-induced climbi ng relies on Pavlovian conditioning processes rather than on habituation-re lated processes.