108 



Data Analysis 



Performance measures included overall session response rates and the time 

 to complete the first FR. Response frequencies were also collected in five 

 successive six minute bins to examine the within-session time course of (-)- 

 nicotine's action. 



RESULTS 

 " All rats had characteristic FR rates and patterns of responding {Ferster 

 and Skinner, 1957). Food pellet__d£llvery was followed by a sh&t pause in 

 lever pressing and then by a high response rate that was sustained until the 

 ratio was completed and the next reinforcer was delivered. 



Figure 1 shows the initial dose-effect functions for the effects of 

 {-)-nicotine on response rates (filled circles). The overall session baseline 

 response rates (mean ± SE) were 2.43 ± 0.30 responses/sec for the before group 

 and 2.39 ± 0.24 responses/sec for the after group. Nicotine produced small 

 decreases in overall response rates at the lower doses (.05, .1 and .2 mg/kg) 

 and more pronounced dose-dependent decreases at the .4 and .8 mg/kg doses 

 (Figure 1, top). The dose effect functions for the before and after groups 

 were similar. 



The typical pattern in the cumilative records following nicotine adminis- 



0- 



tration was a suppression of lever pressing early in the session foFowed by 

 recovery of control-like rates after the completion of several ratios. 

 Occasionally, rates of responding following recovery exceeded control rates. 

 The time of maximal rate reduction, therefore, occurred during the first six 

 minute segment of the session. Response rates during minutes 0-6 were reduced 

 in a dose-dependent manner and to a similar degree in both groups of rats 

 "(Figure 1, botton, filled circles). Rates were decreased by 50 - 60% by .4 

 mg/kg of (-)-nicotine and were almost totally suppressed by .8 mg/kg. 



