INS£?T FIG. 2 



68 



Fffect of Saline Substitution. Nicotine Dose and Prograinned 

 Nicotine Infusions en Nicotire Maintained Responding . Substi'tiiticn of 

 saline for nicotine solution failed to maintain leve pressinc. Sa'ine 

 substitution produced a temporary (4 to 8 h) increase in lever Dress- 

 ing, wh'ch rapid'y declined to less than 1? infusions {- 2 %J.y.) liurirg 

 the following Z4 h session. Periodic observation o' the rats when nico- 

 tine was available ard during the saline sucstitution failed to revpa^ 

 ary signs of physical deoerdence (anorexia, pilo-erection, inpeired 

 irotor activity or convulsions). When nicotire v,a5 reirtrodjcrd (32 

 -.g/kg) tne number of infusions increased to previous levels within i-B h 

 (T4 t 6 SEK). The average r StH daily nicotine intake during this con- 

 dition was 2.5 : O.ce mg/kg. W^'en nicotine was available leve* press- 

 ing occurred almost entirely on the lever delivering nicotine infusions 

 a.id control lever responses were less then ".0% of the total number of 

 responses for all rats. 



The effect of varying nicotine dose on the number o' infusions 

 under a FP 1 schedule is shown in the left panel of Fig. 2. As the 

 dose of nicotine was decreased the number c' infusions first ''ncreased, 

 then dec-eased. In contrast, session intake (mg/kg of body weight) 

 increased directly as a function of nicotine dose (Fig. 2 right per- 

 el). The 8 'jg/kg,'' infusion dose maintained lever p-essirg Just above 

 saline levels. A retest of the 32 i-g/kc dose was not different from 

 the original values (x t £EM = 74 t 3 infusicns/24 h). 



10 



