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. 2017 Sep 1:178:87-93.
doi: 10.1016/j.drugalcdep.2017.04.031. Epub 2017 Jun 13.

Heroin and saccharin demand and preference in rats

Lindsay P Schwartz  1 , Jung S Kim  1 , Alan Silberberg  1 , David N Kearns  2
Affiliations

Heroin and saccharin demand and preference in rats

Lindsay P Schwartz et al. Drug Alcohol Depend. .

Abstract

Background: Several recent studies have investigated the choice between heroin and a non-drug alternative reinforcer in rats. A common finding in these studies is that there are large individual differences in preference, with some rats preferring heroin and some preferring the non-drug alternative. The primary goal of the present study was to determine whether individual differences in how heroin or saccharin is valued, based on demand analysis, predicts choice.

Methods: Rats lever-pressed for heroin infusions and saccharin reinforcers on fixed-ratio schedules. The essential value of each reinforcer was obtained from resulting demand curves. Rats were then trained on a mutually exclusive choice procedure where pressing one lever resulted in heroin and pressing another resulted in saccharin. After seven sessions of increased access to heroin or saccharin, rats were reexposed to the demand and choice procedures.

Results: Demand for heroin was more elastic than demand for saccharin (i.e., heroin had lower essential value than saccharin). When allowed to choose, most rats preferred saccharin. The essential value of heroin, but not saccharin, predicted preference. The essential value of both heroin and saccharin increased following a week of increased access to heroin, but similar saccharin exposure had no effect on essential value. Preference was unchanged after increased access to either reinforcer.

Conclusion: Heroin-preferring rats differed from saccharin-preferring rats in how they valued heroin, but not saccharin. To the extent that choice models addiction-related behavior, these results suggest that overvaluation of opioids specifically, rather than undervaluation of non-drug alternatives, could identify susceptible individuals.

Keywords: Choice; Demand; Essential value; Heroin self-administration; Rats; Saccharin.

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Conflict of interest statement

Conflict of Interest

All authors declare that they have no conflicts of interest.

Figures

Figure 1
Figure 1
Schematic diagram of sequence of phases.
Figure 2
Figure 2
a: Group mean numbers of heroin infusions (filled circles) and saccharin reinforcers (open squares) earned at each FR plus demand curves fit by the exponential model. b: Normalized consumption as a function of normalized price as well as normalized demand curves fit by the model. c: Mean (± SEM) essential value of heroin (black bar) and saccharin (white bar). ** indicates p < 0.01.
Figure 3
Figure 3
a: Percent choice of heroin averaged over criterion sessions for individual subjects. The horizontal line represents group mean preference. b: Mean (± SEM) percent choice of heroin at each saccharin FR. The FR for heroin was always 1. c: Scatter plot and best-fit line showing relationship between heroin’s essential value and percent choice of heroin. d: Scatter plot and best-fit line showing relationship between saccharin’s essential value and percent choice of heroin. * indicates p < 0.05. ** indicates p < 0.01
Figure 4
Figure 4
Mean (± SEM) essential value of heroin and saccharin for heroin preferers (black bars) and saccharin preferers (white bars). * indicates p < 0.05
Figure 5
Figure 5
Mean (± SEM) essential value of heroin (black bars) and saccharin (white bars) before and after the increased-access phase for the Heroin group (left of dashed line) and the Saccharin group (right of dashed line). ** indicates p < 0.01
See this image and copyright information in PMC

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