doses of nicotine after chronic dosing. Attenuated rate decreases were greater 

 in the before group than in the after group; the+r difference was most pro- 

 nounced at the .8 mg/'<g dose for rates during minutes 0-6 of the session. Two 

 additional higher doses of nicotine (1.2 and 1.6 mg/kg) decreased overall 

 response rates to a lesser degree in the before group than in the after group. 

 In the before group, 1.6 mgAg reduced overall response rates to a similar 

 degree as .8 rng/kg initially. In the after group, 1.2 rtg/kg reduced overall 



response rates to a similar degree as .8 mg/kg initially, and 1.6 mg/kg reduced 



^fe 



response rates to a greater^ degree. - Redetermination of the effe<^s of the 



lower doses of nicotine (.2 and .4 mg/kg) revealed that response rates were now 

 increased beyond control levels to a small degree in the before group but not 

 in the after group following chronic dosing. Substituting saline for the usual 

 presession administration of .8 mg/kg of nicotine in the before group produced 

 no observable changes in response rates. These results indicate that there was 

 a greater shift to the right in the dose-effect functions of the before group 

 than of the after group, further suggesting that the development of tolerance 

 to nicotine was enhanced by presession administration. 



Nicotine increased the latency to complete the first ratio as a function 

 of dose in bctn groups of rats (Table 1). Tolerance developed with chronic 

 dosing in the before group such that the latency to complete the fiTst ratio 

 gradually decreased over sessions I to 30; latenci es we re stilr somewhat 

 lengthened compared to control on day 30 (Table ^. Chronic nicotine did not 

 alter latencies in the after group over sessions 1 to 30. On day 31 the pre- 

 session administration of .8 mg/kg of nicotine produced a markedly longer 

 latency in the after group than in the before group; due to intersubject vari- 

 ability this difference just failed to achieve statistical significance 



>.05- 

 (p tO.O ). Redetermination of the dose-effect functions revealed shorter 



