The effect of nicotine pre-exposure on demand for cocaine and sucrose in male rats

Abstract

The aim of the present study was to determine how nicotine pre-exposure affects the elasticity of demand for intravenous cocaine and for sucrose pellets in adult male rats. In Experiment 1, demand for cocaine was assessed in rats that had nicotine in their drinking water. Nicotine pre-exposure significantly decreased rats' willingness to defend cocaine consumption as the price (measured as the number of responses per cocaine infusion) increased compared with a control group with no nicotine pre-exposure. That is, nicotine increased the elasticity of demand for cocaine infusions. Experiment 2 repeated the first experiment, but with rats working for sucrose pellets instead of cocaine. Nicotine pre-exposure had no effect on the elasticity of demand for sucrose. This pattern of results suggests that nicotine pre-exposure can reduce the reinforcing effects of cocaine, but not sucrose, in adult male rats.

Figure 1

(A) Group mean (± SEM) percent change in body weight over the duration of Experiment 1. (B) Group mean (± SEM) ml of liquid consumed over the duration of Experiment 1. (C) Nicotine group mean (± SEM) dose of nicotine over the duration of Experiment 1.

Figure 2

(A) Group mean demand for cocaine in the nicotine and control groups in Experiment 1: numbers of cocaine infusions earned at each FR plus demand curves fit by Equation 1. (B) Normalized consumption as a function of normalized price as well normalized demand curves fit by Equation 1. Consumption is normalized by expressing the numbers of reinforcers earned as a percentage of Q₀. Normalized price is the number of responses required at a particular FR to obtain 1% of Q₀.

Figure 3

(A) Mean (+ SEM) essential value of cocaine for the N and C groups. (B) Mean (+ SEM) essential value of food for the N and C groups.

Figure 4

(A) Group mean (± SEM) percent change in body weight over the duration of Experiment 2. (B) Group mean (± SEM) ml of liquid consumed over the duration of Experiment 2. (C) Nicotine group mean (± SEM) dose of nicotine over the duration of Experiment 2.

Figure 5

(A) Group mean (+ SEM) demand for food in the nicotine and control groups in Experiment 2: numbers of food reinforcers earned at each FR plus demand curves fit by Equation 1. (B) Normalized consumption as a function of normalized price as well normalized demand curves fit by Equation 1. Consumption is normalized by expressing the numbers of reinforcers earned as a percentage of Q₀. Normalized price is the number of responses required at a particular FR to obtain 1% of Q₀.