2 mm ventral to the pial surface). In a subset of animals (n = 14), the second stimulating electrode was placed into the right thalamus (2.8 mm posterior to bregma, 3.0 mm lateral to midline, and 4.2 mm ventral to the pial surface) instead of the fimbria. Current pulses through the stimulating electrodes were generated by ISO-Flex stimulus isolation units (AMPI, Jerusalem, Israel) driven by a Master 8 Stimulator (AMPI). Intracellular microelectrodes were pulled from borosilicate glass tubing (1 mm outer diameter; World Precision Instruments, Sarasota,

FL, USA) to a resistance of 40–110 MΩ using a P-97 Flaming-Brown microelectrode puller (Sutter Instruments, Novato, CA, USA). Recording electrodes were filled with 2% Neurobiotin (Vector Laboratories, Burlingame, CA, USA) in 2 M potassium acetate and lowered into the right limbic striatum (1.2–1.8 mm anterior to bregma, 1.2–1.4 mm

lateral to midline, CX-5461 order and 3.5–6.5 mm below the pial surface) using a model 2662 Direct Drive Micropositioner (David Kopf). In 15 animals, 200 μM picrotoxin (Sigma-Aldrich, St. Louis), the GABAA open-channel blocker, was included in the intracellular solution contained in the recording electrode. Electrical signals from impaled cell membranes passed through a chloride-coated silver selleck compound wire housed inside the glass microelectrode via a headstage to an intracellular amplifier (IR-283, NeuroData, Delaware Water Gap, PA, USA). Intracellular signals were low-pass filtered at 2 kHz

(FLA-01, Cygnus Technologies, Delaware Water Gap, PA, USA), digitized (Digidata 1322A, Axon Instruments, Union City, CA, USA), sampled at 10 kHz using Axoscope (Axon Instruments), and stored on a PC. Once impaled, neurons were recorded in current-clamp mode at baseline for at least 5 min to ensure stability of membrane properties. Only cells exhibiting a resting membrane potential of at least −65 mV and action potential amplitude of at least 40 mV from threshold were used in this study. A series of positive and negative current steps delivered through the recording electrode (0.1– 0.5 nA, 100 ms) were used to assess the input resistance of recorded cells. Subsequent to baseline recordings, the responses of stable cells to medial PFC and fimbria TCL stimulation were assessed using the following protocol once every 15 s for 8–15 repetitions. A single-pulse stimulation of the fimbria (1.0 mA; 0.5 ms; F1) was delivered 500 ms before train stimulation of the mPFC (50 Hz train of ten pulses; 0.4–1.0 mA; 0.5 ms). A second fimbria pulse (1.0 mA; 0.5 ms; F2) was then delivered either 50 ms or 500 ms after the last pulse in the train stimulation of the PFC. This protocol was intended to test the effect of burst-like PFC stimulation on MSN responses to hippocampal inputs in the limbic striatum.