Effects of experimental Unemployment, Employment and Punishment analogs on opioid seeking and consumption in heroin-dependent volunteers

Abstract

This study investigated the extent to which hydromorphone (HYD) choice and behavioral economic demand differed during experimental analogs of Unemployment ( Drug Only: HYD and no money alternative), Employment ( Drug or Money: HYD and $4 alternative), and Punishment ( Drug Only + Money Loss: HYD only and $4 subtracted for each HYD choice), in the context of anticipated high vs. low post-session drug availability (HYD 24 mg vs. placebo). Eleven heroin-dependent, buprenorphine-stabilized (8 mg/day) volunteers first sampled two HYD doses (0 and 24 mg IM in randomized, counterbalanced order, labeled Drug A [session 1] and Drug B [session 2]). In each of the final six sessions, volunteers were given access to a 12-trial choice progressive ratio (PR) task and could work to receive HYD unit doses (2 mg each); cumulative dose units earned were administered in a bolus injection after the work session. Before the PR task, volunteers were told which HYD dose (Drug A or B) would be available 3 h after the PR-contingent injection. Relative to Unemployment ( Drug Only), Employment ( Drug or Money) and Punishment ( Drug Only + Money Loss) each significantly suppressed HYD seeking (e.g., breakpoints). Employment and Punishment also reduced HYD behavioral economic demand, but via different mechanisms: Employment increased HYD price-elasticity, whereas Punishment decreased HYD demand intensity. Adjusting for the initial level difference (i.e., normalized demand), Employment significantly decreased P max (i.e., lower “essential value” of HYD) and O max (maximum HYD responding) compared to Punishment or Unemployment. These effects were not significantly altered by post-session drug availability.