Damgo

A role for the mu-opioid receptor (MOPr) in binge-like, compulsive eating has been identified (Colantuoni et al., 2002 ; Cooper and Turkish, 1989 ; Cottone et al., 2008 (link); Doyle et al., 1993 ; Drewnowski et al., 1992 (link); Ferraro et al., 2002 (link); Katsuura and Taha, 2010 (link); Kirkham and Cooper, 1988 (link)). Experiments in rodents demonstrate that the DMS and DLS subregions of the dorsal striatum contribute to goal-directed and habitual food seeking, respectively (Yin et al., 2004 (link)). Therefore, MOPr function in dorsal striatum is likely an important factor in various food consumption phenotypes. Similar to our previous work (Atwood et al., 2014 (link)), we examined MOPr-mediated long term synaptic plasticity in DMS and DLS MSNs. In order to do this, EPSCs (at −60 mV) were electrically evoked every 20 s as described above. After a stable 10-min baseline, the selective MOPr agonist [D-Ala2, NMe-Phe4, Gly-ol5]-enkephalin (DAMGO; Bachem, Bubendorf, Switzerland) was washed on to the slice for a 5-min period at a concentration of 0.3 μM. EPSCs continued to be recorded following DAMGO application for a total of 40 minutes of recording. Plasticity was assessed by comparing the average EPSC peak amplitude for the final 10 min of recording to the average for the 10 min baseline (Atwood et al., 2014 (link)).

Oxycodone hydrochloride (Sigma Aldrich, St. Louis, MO) was dissolved in saline (0.9% w/v) for in vivo injections and in reverse-osmosis water for drinking studies. DAMGO was purchased from Bachem (Torrance, CA). All other chemicals and reagents were purchased from Sigma-Aldrich (St. Louis, MO) or ThermoFisher (Waltham, MA).