72 



_.../ under conditions of reduced body weight and/or con- 

 current fixed-time food presentations win nicotine maintain rates of 

 responding above those maintained by saline (Lang et a1. 1977; Latiff 

 et a1. 1S80). In the present study, however, several doses of nicotine 

 maintained lever pressing above saline levels in the absence of weight 

 reduction procedures or fixed-time 'ood presentations. One poss<ble 

 explanation for the different effects of nicotine in the present stucjy 

 is that nicotine's reinforcing effects were not associated wi*h deliv- 

 ery of another reinforcer (food). L'nder conditions of fixed-time food 

 delivery, self-administration of nicotine iriay be controlled only in 

 part by the pharmacological consequences of nicotine and the inducing 

 schedule tray be required :c maintain tre self-ad.nlnlstration behavior 

 (Falk and Sairson 1975) . 



In most previous studies with rats only one response was required 

 to produce a nicotine infusion (Clark 1S£9; Lang et al . 1977; Hanso" et 

 al. 1979; Latiff et al. 1980). However, in the p'-esent study when the 

 ratio size was increased the number of lever presses increased across 

 several ratios such that a relatively stable level of dally Infusions 

 was obtained. Although in the present study iv delivered nicotine sain- 

 tained ratio performance, the overall rates of responding under the var- 

 ious ratio sizes were low compared to other iv delivered reinforcers 

 (Pickens et al. 1978). While this is in general agreement with the 

 findings of Hansen et al. (1379; there are several differences between 

 the results of the two studies. Hansor et al. (1979) reported that 



14 



