50 ¼M Picrotoxin and 20 ¼M CNQX. Evoked synaptic currents were elicited using an extracellular concentric bipolar stimulating electrode positioned approximately 100 ¼m away from the cell soma. All recordings in cultured human neurons were performed at room temperature because recordings made at higher temperature in cultured neurons resulted in poor recording quality and short time period of recordings. Cells were excluded from analysis if access resistance changed by more than 20% along the duration of the recording. In addition, any iNs whose access resistance was greater than 35 MΩ was also excluded from analysis. The following MOR agonists/antagonist were used for the recordings: DAMGO (Hellobio): 0.1-10 ¼M; Naltrexone hydrochloride (Tocris): 5 ¼M; Morphine sulphate: 10 ¼M; Data presentation: All data are presented as mean ± S.E.M. Student’s t-test or 2-way ANOVAs were used to assess statistical significance.
