Excitatory postsynaptic currents were recorded from cell bodies identified at 80 × on an AxioExaminer D1 Differential Interference Contrast (DIC) microscope (Zeiss, Thornwood, New York, USA). CA1 neurons were identified by triangular appearance and large apical dendrite. Striatal medium spiny neurons (MSNs) were identified by their oval shape, multiple dendrites, and hyperpolarized resting membrane potential (approximately −85mV) measured after break-in. Stimulating electrode was placed just below the corpus callosum (Fig. 10A) ~150–200µm from the recorded MSN as described [Jaramillo et al., 2016 (link)]. Borosilicate glass electrodes (4–6MX) were filled with internal solution containing (in mM): 110 CsMethanesulfonate, 15 CsCl, 8 NaCl, 10 TEA-Cl, 2 EGTA, 10 HEPES, 3 QX 314, 2 ATP, 0.3 GTP. Observed junction potential was ~10 mV and was compensated. Cells with > 25% change in access resistance (15–25 MΩ) or holding current were not included. Stimulation was controlled via a Model 2200 stimulus isolator (A-M Systems, Sequim, WA, USA) though a monopolar tungsten microelectrode (FHC, Bowdoin, ME) with a 0.1 msec biphasic pulse. 100 µM picrotoxin was in bath for all experiments. Sample size (n) indicates number of cells with no more than five cells per mouse and five or more mice per genotype.