Persistent effects of the orexin-1 receptor antagonist SB-334867 on motivation for the fast acting opioid remifentanil

The orexin (hypocretin) system is important for reward-seeking behavior. The orexin-1 receptor (Ox1R) antagonist SB334867 (SB) reduces seeking of food and drug reward under conditions of high motivation. There is some evidence that the effects of systemic SB on reward seeking persist beyond the pharmacological availability of the drug, however the time course of these effects is not well characterized, nor is it known whether similar persistent effects are observed following intraparenchymal injections. Here, we used a behavioral economics paradigm, which allows for repeated testing of drug motivation across consecutive days, to examine the persistent effects of acute systemic and local treatment with SB on motivation for the short-acting opioid remifentanil. Systemic injections of SB immediately prior to behavioral testing reduced motivation for remifentanil; this effect was sustained on a subsequent test at 24h, but not on a third test at 48h. When injected locally into caudal ventral pallidum (cVP) the effects of SB were more persistent, with reduced motivation observed for up to 48h. We next made SB injections into cVP 24h prior to behavioral testing; this produced persistent effects that persisted for at least 72h post-treatment. Cued reinstatement of extinguished remifentanil seeking was also attenuated by pretreatment with SB 24h prior. These data indicate that the effects of SB on opioid seeking behavior persist beyond the bioavailability of the compound. These observations might have important ramifications for the future clinical use of orexin receptor antagonists for the treatment of addiction.