There was no significant difference between saline (n=male: 5 rats, 18 cells; females: 7 rats, 26 cells) and oxycodone (n=male: 8 rats, 36 cells; females: 6 rats, 20 cells) groups. (D) Left, the magnitude of the paired-pulse ratio decreases in the oxycodone groups (n=males: 7 rats, 33 cells; females: 6 rats, 22 cells) compared to saline control groups (n=males: 5 rats, 23 cells; females: 7 rats, 23 cells). Saline (n=males: 5 rats, 11 cells; females: 7 rats, 14 cells) and oxycodone (n=males: 7 rats, 16 cells; females: 5 rats, 14 cells). In analogously designed experiments, we assayed the effects of prolonged abstinence on synaptic transmission in PVT-NAcSh projections. This relative shift in the excitation–inhibition balance may facilitate MSN output within relapse-related circuitry and contribute to the behavioral effects observed following prolonged abstinence.