84 



figure 1. Number of infusions (32 ug/kg/infusion) as i function of 

 the number of days of access to r.icc:ine for two individual 

 rats. The solid line shows the rat with the longest accuisi- 

 fion time and the dashed line shows the rat with the short- 

 est acquisition time. Tre open circle shows the ave'-aqe 

 acquisition time for all 18 rats ± standard error. 



Figure 2. Number o' irfusiors ('eft oareM ard the session intake 

 (right panel, ng/kg/ sess ion) as a 'unction of varying the 

 dose of nicotire under an FP 1 schedule, f'icotine doses 

 we-e presented in a descend:ng order. Each point is a r.ein 

 of 21 sessions (7 rats / 3 sessions) and tne ve-tical 'ines 

 show the stanco'-d error. 



Figure 3. "he average noT.be- of self-admi':istered (solid 'ire) infu- 

 sions (32 „g/'cg/infus''C'rs !' and the total nu:T'be'" c' 'nfusicns 

 (prog'ar'-ed ^ response continge-t, dashed lire) as a furc- 

 ticn of the interval between response independent nicotine 

 Infusions. Each point is the average of 3 rats and the ver- 

 tical lines show the standard error. Points above control 

 show the average numberof infusions with no prcgra.Timed infu- 

 sions. 



27 



