63 



granmed nicotine Infusions for several days (Hanson et a1. 1979) the 

 levels of responding maintained by iv nicotine following the programned 

 infusions have been reported to be low. The present study demonstrates 

 that iv delivered nicotine functions as a positive reinforcer in rats 

 in the absence of food inducement or programmed infusion conditions. 

 Nicotine self-administration was studied under different FR values and 

 across a range of infusion doses. In addition, the effects of mecamyl- 

 amine, hexarrethonium and naloxone on nicotine maintained lever pressing 

 were evaluated. 



METHODS 

 Subjects. Eighteen experimentally naive male Long Evans hooded rats 

 (Blue Spruce Farms) weighing 350 to 400 g were used. Pats were anesthe- 

 tized with ketamine (70 mg/kg/im) and sodium pentobarbital (18 

 mg/kg/ip) and implanted with a venous catheter under aseptic condi- 

 tions. One end of the catheter (inside diameter, 0.30 nw; outside diam- 

 eter 0.61 mm) was passed by way of the external jugular vein into the 

 superior vena cava at the level of the right atrium. The distal end of 

 the catheter was passed subcutaneously and out through the skin in the 

 middle of the rat's back. This end of the catheter was connected to a 

 stainless steel back plate and via protective tubing and swivel joints 

 it was connected to a remote infusion pump. Each rat was allowed seven 

 days recovery In its hone cage before being placed in the test cham- 

 ber. The general catheterization procedure has been described in 

 detail elsewhere (Weeks 1972). 



