The effect of economy type on heroin and saccharin essential value

Abstract

According to behavioral economics, reinforcer value should be lower in an open economy than in a closed economy. An animal model was used to determine how economy type affected the value of heroin and saccharin. In a first phase, separate groups of rats worked for heroin or saccharin. The price of these reinforcers increased over sessions. For rats in the open heroin or open saccharin economies, the work period of each session was followed by a postwork period where a cheaper source of heroin or saccharin was available for three hours. For rats in the closed economies, the work period was their only opportunity to obtain the reinforcer. Rats in the open saccharin economy worked less hard to defend consumption of saccharin as price increased than rats in the closed saccharin economy. That is, opening the saccharin economy reduced its essential value. In contrast, economy type had no effect on heroin's essential value. In a second phase, rats were allowed to choose between heroin and saccharin. The majority of rats strongly preferred saccharin over heroin regardless of economy type. The finding that economy type changed the essential value of saccharin, but not heroin, adds to previous findings suggesting that the value of drug reinforcers is unaffected by future drug availability. The difference in effect of economy type on drug versus nondrug reinforcers could be relevant to addiction. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

1.

Schematic diagram of procedures used in Phase 1 and Phase 2. In the second phase, all groups were trained on the same discrete-trials choice procedure.

2.

The top panels present group mean consumption of heroin (left) and saccharin (right) for rats in the open (circles) and closed (triangles) economies plus fits of the exponential demand model. Note that the scale of the Y-axes differ for heroin and saccharin. The inset tables provide mean (± SEM) essential value (EV), Q₀, and R² for the fits of the model to individual subjects’ data. The bottom panels show normalized consumption as a function of normalized price as well the exponential demand model fits. Consumption was 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. Note that the scale of the X-axes differ for heroin and saccharin.

3.

Mean (± SEM) essential value (top panel) and Q₀ (bottom panels) for heroin (left) and saccharin (right) based on fits of the exponential model to individual subjects’ data for the rats in the open (white bars) and closed (black bars) economies. * indicates p < 0.05. *** indicates p < 0.001.

4.

Mean (± SEM) number of reinforcers obtained during the post-work period (circles) and mean (± SEM) combined number of reinforcers (squares) obtained during the work and post-work periods for the Heroin Open group (top panel) and the Saccharin Open group (bottom panel). Triangles represent mean (± SEM) total number of reinforcers obtained for rats in the closed economy groups, which only had access to the reinforcer during work periods. Note the difference in Y-axis scales across panels.

5.

Mean (± SEM) and individual subjects’ percent choice of heroin averaged over the final 3 choice sessions for the Heroin Open (circles), Heroin Closed (squares), Saccharin Open (upward-pointing triangles), and Saccharin Closed groups (downward-pointing triangles). The dashed line represents indifference (50% preference).