64 



Apparatus . Nine identical operant conditioning chambers (Lehigh Valley 

 Electronics, LVE No. 193-25), each contained in a sound-attenuated cubi- 

 cle (LVE No. 132-02) were used. Located at one end of the chairber were 

 two levers, six cue lights {lever lights), a house light and water 

 spout. Presses on the right lever were programmed to activate the infu- 

 sion pump (Harvard Apparatus Peristaltic Puup No. 1201) for 4s, deliver- 

 ing an infusion of 137 yl of solution into the blood stream of the 

 rat. The pattern of responses was recorded on strip chart recorders. 

 Responses on the left lever (control lever) were recorded but had no 

 programmed consequences. The house light (4.5 watts) provided general 

 illumination and blinked at a rate of 10 Hz when the infusion pump was 

 activated. White noise was continuously present and an exhaust fan pro- 

 vided ventilation. During all experimental sessions (20-30 g) Purina 

 Pat Chow and unlimited water were available. Experimental events were 

 scheduled and responses recorded by equipment located in an adjacent 

 room. 



Lever pressing maintained by nicotine Infusions . Responding by 10 rats 

 was established and maintained by an FR 1 schedule of 1v nicotine infu- 

 sions (32 wg/kg). Experimental sessions lasted 24 h. After responding 

 developed and stabilized (3-5 days with no increasing or decreasing 

 trends in the number of nicotine infusions per day) changes were made 

 in the nicotine delivery procedure to determine if lever pressing was 

 being maintained by the contingency established between lever pressing 

 and nicotine delivery (Pickens et al. 1978). Changes Included substitu- 



