71 



fror cont'-ol values. In contrast, injections of heyamethoriut? (Fig. 5) 

 or naloxone did not alter the total number of infusions 5) or change 

 the witt-.in session pattern. 



DISCUSSION 



Leve' pressing b> rats was initiated and maintained under an FR 

 sc'"ed'jle ty iv infusions of nicotine. These results derronstrate that 

 iv delivered "icotine can ircrease end maintain lever pressing that 

 results in its delivery. The changes in the nicotine delivery prc- 

 cedure shc-.ved that lever pressing was maintained by the nicotine cmtin- 

 gency. T^-ere were four indications of the positive reinforcing effects 

 Q-f nicotine: 1; a c'eate-- nunber of lever presses when nicotine was 

 respcnse-ccnt ingent than v;hen saline was resporse-contircent ; 2) a 

 greater n'^rber of responses on the nicotine lever tnan on the control 

 lever; 3) a systeratic decrease in the number of contingent infusions 

 when nicot'ne was delivered ncncontirgently; ^1 systematic changes in 

 lever pressing as a function of the nicotine dose. '" ' • ' '' 



Several previous repcts have examined the maintenance of respond- 

 ing by iv infusions of nicotine under an FR 1 schedule in rats (Clarke 

 1969; Lang et al. 1979; Singer et al . 1976; Hanson et al. 1979; Latiff 

 et al. 1980). Although self-administration of nicotine was de«>on- 

 strated in irost of these studies the 'ates of responding were gere'ally 

 ■"ower than those maintained by othe-- rein'orcers jnder similar condi- 

 tions (-ickens et al. 197£). In adcition, several previous studies 



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