m^ 



tion of saline for nicotine, systematic changes in dose, and, the addi- 

 tion of programred response indepeident nicotine infusions at intervals 

 of 30, 45, 60 and 9C min. The rate of control lever respcndirg wjs 

 recorded throughout experimental ranipulaticrs and was coirpared to f'e 

 rate of responding recorded from tt"e lever resulting in nicotine in-'u- 

 sions. All rats were tested with the saline substitution procedure and 

 3 rats were given prcgramrred infusions. In the 7 rats not receiving 

 P'-og'-an"jred infusicns the effect of infusion dose was (ieterp.inec oi tha 

 nuriier of infusions delivered and the total nicotine intake 

 (mg/kg/24 h) under an PR 1 schedule. Infusion dcses f64, 32, 16 srd s 

 -g/kg/in-fusion) were presented in descending ordej* *or ; iriniwjr of 7 

 day; each, fit each infusion dose, lever pressing was al''owPd to stabil- 

 ize before char.ges were made. !n the 3 rats that had received pro- 

 grarred infusions the effects of Fr s^ze (1-8 responses/32 -^g/kg/^rfj- 

 sion) on the ""orber of lever presses ard the number of infusicrs were 

 studied. Fixed-ratios wei-e oresented in ascending order and the rats 

 were "^airtained u'der each ratio for a mir.inur of 7 to IC sessions. 



'■ • ■ ■ ■,- ■ M^ ., '■. .. .- ■ 



Effects of mecairyl amine, hexairethon''un ana naloxone on nicotine- 

 maintained responding under a FR I Scnedule . ''espcnding by S other 

 rats was established and maintained unopr a FP, 1 schedule of iv nico- 

 tine infusions (32 -^g/kg) in experimental sessions that lasted 24 h. 

 After -espcnding developed and stabilized {3-5 days wit*- no increasing 

 or drc-easing trends in the nunber of nicotine infusions) saline was 

 substituted for nicotine. 



