Whole-cell patch-clamp recordings were obtained in the medial shell of the NAc (NAcSh). Data were collected with a Multiclamp 700B amplifier, Digidata 1550B (Molecular Devices, US), and using Clampex 11 (pClamp; Molecular Devices, US). All recordings were acquired in voltage clamp at 34° Celsius and were digitized at 10 kHz and low pass filtered at 2 kHz. Patch pipette was filled with internal solution containing (in mM): 143 CsCl, 10 HEPES, 0.25 EGTA, 5 Phosphocreatine, 4 MgATP, 0.3 NaGTP (295–305 mOsm, pH 7.4 with CsOH) and 1 mg/ml Neurobiotin (cat # SP-1120, Vector Labs, US). CNQX (50 μM, cat # 0190, Tocris Biosciences, UK) and AP5 (10 µM, cat # 0106, Tocris Biosciences, UK) were added to aCSF to block glutamate receptors. All pipettes (3–4 MΩ) were pulled from borosilicate glass (cat # PC-100, Narishige, US). Series resistance (Rs) was monitored throughout the recording for patch sealing. Once whole-cell configuration was obtained, holding potential was set at −70 mV and a 1 ms, 5 mW light pulse was delivered every 10 s (0.1 Hz) through a 40× objective. Once current response was obtained, picrotoxin (100 µM, cat # P1675, Sigma-Aldrich, US) was washed in the recording chamber to verify that optically evoked inhibitory postsynaptic current (oIPSC) was mediated by GABAa receptor activation. Once recording was complete slices were transferred to 4% PFA overnight at 4° Celsius then to 0.1 M PB for post hoc processing of Neurobiotin (cat # SP-1120, Vector Labs, US)51 (link).
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