If-.S£PT FIG. 



67 



Drugs . Nicotine hydrogen (+)-tartrate (Chemical Procurement Labora- 

 tories, NY), mecamylamine HCl , hexan-ethcnium and naloxone were dis- 

 solved in C.9" saline solution. Solutions were diluted so that all 

 presesslon ''njections were of equal volumes of 1 ml/kg. Nicotine infu- 

 sion dose is expressed as the free base and p'-esession antagonist injec- 

 tions as the salt. ' 



RESULTS 



Acouisitiop and Maintenance c* Pespondinq Under the FR 1 Schedule 

 of N-cctine Infusion . Pespordino under the FR 1 schedule was initiated 

 and maintained by 22 ug/kc ifusions of nicotine ir all rats {72 in^'u- 

 sion per 2^ h session t 6 SEV) . The nu"iber o*' Infusions stabilized in 

 all rats within 2^ dayi. The average i SZ^ runber of days for acouisi- 

 tion c' stable behavior to be acouired was 1£ days (r 2). Tne range 



and the cenerai patterr of acquisition is shewn in Fig. ! for the rat 

 with the shortest acquisition t^ne fdashed Mnes) and the 'at with t^e 

 longest acquisition time (solid lines). Most rats neintalned acquisi- 

 t^:on patterns similar to those shewn in Fig. 1 with the major character- 

 istic being ? to 5 days of low --esoonding (4 to 30 infusion/24 h) fol- 

 lowed by a gradual (3 to 5 days) inc-ease to near stable response 

 rates. The within session pattern of nicotine in'usions under the FR 1 

 schedule was typically a series of closely spaced infusions {2 *o 4 per 

 trin), followed by a pause (30 tc SC min} during wfhic*- tire little or r.o 

 infusions were talren. "^ 



