Theberge, F.Li, X.Kambhampati, S.Pickens, C.St Laurent, R.Bossert, J.Baumann, M.Hutchinson, M.Rice, K.Watkins, L.Shaham, Y.2013-11-052013-11-052013Biological Psychiatry, 2013; 73(8):729-7370006-32231873-2402http://hdl.handle.net/2440/80705BACKGROUND Recent evidence implicates toll-like receptor 4 (TLR4) in opioid analgesia, tolerance, conditioned place preference, and self-administration. Here, we determined the effect of the TLR4 antagonist (+)-naltrexone (a μ-opioid receptor inactive isomer) on the time-dependent increases in cue-induced heroin seeking after withdrawal (incubation of heroin craving). METHODS In an initial experiment, we trained rats for 9 hours per day to self-administer heroin (.1 mg/kg/infusion) for 9 days; lever presses were paired with a 5-second tone-light cue. We then assessed cue-induced heroin seeking in 30-minute extinction sessions on withdrawal day 1; immediately after testing, we surgically implanted rats with Alzet minipumps delivering (+)-naltrexone (0, 7.5, 15, 30 mg/kg/day, subcutaneous) for 14 days. We then tested the rats for incubated cue-induced heroin seeking in 3-hour extinction tests on withdrawal day 13. RESULTS We found that chronic delivery of (+)-naltrexone via minipumps during the withdrawal phase decreased incubated cue-induced heroin seeking. In follow-up experiments, we found that acute injections of (+)-naltrexone immediately before withdrawal day 13 extinction tests had no effect on incubated cue-induced heroin seeking. Furthermore, chronic delivery of (+)-naltrexone (15 or 30 mg/kg/day) or acute systemic injections (15 or 30 mg/kg) had no effect on ongoing extended access heroin self-administration. Finally, in rats trained to self-administer methamphetamine (.1 mg/kg/infusion, 9 hours/day, 9 days), chronic delivery of (+)-naltrexone (30 mg/kg/day) during the withdrawal phase had no effect on incubated cue-induced methamphetamine seeking. CONCLUSIONS The present results suggest a critical role of TLR4 in the development of incubation of heroin, but not methamphetamine, craving.enCopyright status unknownCravingextinctiongliaheroin self-administrationopioid drugsreinstatementrelapseTLR4Journal article002012474910.1016/j.biopsych.2012.12.0190003171595000072-s2.0-8487569668321657Hutchinson, M. [0000-0003-2154-5950]