Quantifying nicotine's value-enhancement effect using a behavioral economic approach

Nicotine increases the value of some reinforcing stimuli, and this effect may contribute to nicotine's widespread abuse. We aimed to quantify this effect using a behavioral economic analysis. Six Long- Evans rats were exposed to a modified observing response procedure. In this procedure, presses to one lever resulted either in food according to a variable-interval 15 s schedule or extinction; presses to a second, observing lever illuminated stimuli correlated with the schedule in effect on the food/extinction lever (i.e., conditioned reinforcers). The FR requirement on the observing lever increased across sessions. The number of presentations of the conditioned reinforcers was plotted as a function of FR value to generate a demand curve. Nicotine was then administered at a dose of 0.3 mg/kg. All demand curves were fitted to the exponential demand equation and a parameter reflecting reinforcer value was evaluated. Nicotine increased the value of the conditioned reinforcers as measured by this equation; nicotine also increased responding on the food/extinction lever. This analysis demonstrates that nicotine increases the value of conditioned reinforcers under certain conditions. The current procedure allows for a novel method of analyzing demand for conditioned reinforcers.