ORIGINAL INVESTIGATION Transfer of the discriminative stimulus effects of Δ 9 -THC and nicotine from one operant response to another in rats Joseph R. Troisi II & Brian J. LeMay & Torbjörn U. C. Järbe Received: 13 November 2009 / Accepted: 24 June 2010 / Published online: 14 July 2010 # Springer-Verlag 2010 Abstract Objective Transfer of the discriminative stimulus effects of two drugs from one operant (original-response) to a topographically different response (transfer-response) that was spared drug discrimination training was investigated. Materials Eight rats were trained in a counterbalanced one manipulandum (lever press and nose poke) drug discrimi- nation procedure. Counterbalanced IP administered nicotine (0.3 mg/kg) or Δ 9 -tetrahydrocannabinol (3.0 mg/kg) functioned as discriminative stimuli. S D drugs occasioned sessions of food-reinforcement (variable-interval 30-s schedule); S Δ drugs occasioned non-reinforcement. The original-response (lever-pressing or nose-poking) was ini- tially reinforced during 30-min S D drug sessions, and non- reinforced on the other alternating S Δ -drug sessions. Results Two separate 5-min non-reinforcement tests, coun- terbalanced by drug order, revealed stimulus control over the original-response by both drugs, which transferred to the transfer-response. Subsequent extinction training of the transfer-response attenuated the original-response response rates with the S D drug conditions but had little impact on discriminative control. Discriminative control was reversed for the transfer-response but had little impact on the original-response but, again, reduced response rate. Conclusion These data demonstrate that (a) discriminative control by two distinct drug states can transfer and modulate a topographically different free-operant response and, (b) as is true for exteroceptive stimuli, drug states that function as antecedents embedded within the operant three-term contin- gency have differing relationships with the response and the primary reinforcer. Keywords Drug discrimination . Δ 9 -Tetrahydrocannabinol . Nicotine . Extinction . Modulation . Occasion-setting . Reversal learning . Rats Introduction Drugs can function as operant discriminative stimuli (S D s) embedded within the three-term contingency (i.e., S D : R→S r+ ). A growing literature has explicated remarkable functional similarities between interoceptive (drug states) and exteroceptive (audio-visual and contextual cues) stim- ulus control phenomena, as reported in the Pavlovian and operant conditioning literatures (c.f., Troisi 2003a,b, 2006 for recent reviews). Exteroceptive operant S D s establish two relationships, one with the response they occasion (S D :R) and another with the primary reinforcer (S D :→S r+ ) contingent on the R; as such, they functionally transfer stimulus control across operant responses that share the same primary reinforcer (Colwill and Rescorla 1990; DeGrandpre et al. 1992; Rescorla 1990, 1992). Conversely, the operant S Δ occa- sions non-reinforcement of responding and has no relation- ship with the reinforcer. S D s modulate Pavlovian conditional responding (CR) elicited by a conditional stimulus (CS+) (Davidson et al. 1988). Drug states can function similarly. For instance, nicotine and ethanol, after first functioning as either CS+ (predicted food) or a CS- (predicted no food) in a Pavlovian drug discrimination J. R. Troisi II (*) Department of Psychology, Saint Anselm College, 100 St. Anselm Dr., Manchester, NH 03102, USA e-mail: jtroisi@anselm.edu B. J. LeMay : T. U. C. Järbe Center for Drug Discovery, Department of Pharmaceutical Sciences, Northeastern University, Boston, MA, USA Psychopharmacology (2010) 212:171–179 DOI 10.1007/s00213-010-1940-6