SCHEDULE INDUCTION CONDITIONS NOT ONLY EXAGGERATE INTAKE BUT ALSO ENHANCE DRUG SOLUTION CHOICE

In previous research, rats exposed to daily, 3 h sessions of schedule induced polydipsia (SIP) self-administered high doses of cocaine orall y. However, a strong and durable preference for cocaine solution to wa ter requires training in addition to mere oral self-administration exp osure. If cocaine is dissolved in a preferred vehicle solution, and th e vehicle is subsequently faded to water, then a strong preference for cocaine remains. A similar preference can be instituted for lidocaine solution. Such preferences may develop because the gustatory property of a drug becomes associated with the preferred vehicle and remains t o function as a durable conditioned reinforcer after vehicle fading. T o determine if drug preference is solely a function of this posited co nditioning mechanism, or whether it also depends upon the STP conditio n, rats were exposed to daily, 3 h sessions of single-ration feeding, rather than the SIP condition. A preferred vehicle (glucose/saccharin solution) was slowly faded from a 0.19 mg/ml lidocaine solution, which was presented concurrently with a choice for water. Although a prefer ence for lidocaine solution to water could be generated, it occurred f or only 5 out of 9 rats, and the preference was relatively unstable. B y contrast, in two previous studies using SIP, 26 out of 27 rats maint ained a preference for lidocaine solution. Thus, SIP nor only exaggera tes the amount of drug solution ingested but also contributes to the f ixation of the associative drug solution choice. (C) 1997 Elsevier Sci ence Inc.