The cells were voltage clamped at −70 mV holding potential. Pipette offset potential, series resistance (Rs), and capacitance were compensated before recording. Only cells with low holding current (<50 pA) and stable baseline were used. Input resistance (Rin), Rs, and membrane capacity (Cm) were also measured before each recording by using 5-mV hyperpolarizing pulses. To ensure consistent recording qualities, only cells with Rs < 20 MΩ, Rin > 500 MΩ, and Cm > 10 pF were accepted. Further, if these values changed by more than 20% during measurements, the recordings were discarded (35 ). The pipette solution contained (in mm): HEPES 10, KCl 140, EGTA 5, CaCl2 0.1, Mg-ATP 4, and Na-GTP 0.4 (pH 7.3 with NaOH). The resistance of the patch electrodes was 2–3 MΩ. Spike-mediated transmitter release was blocked in all experiments by adding the voltage-sensitive Na-channel inhibitor tetrodotoxin (TTX) (750 nm; Tocris) to the aCSF 10 min before control miniature postsynaptic currents (mPSCs) were recorded. Picrotoxin (100 μm; Sigma, St. Louis, MO) was used in the aCSF to verify that mPSCs were related to GABAA-R activation. In subsequent experiments, modulation of mPSCs by CB1 was addressed by treating slices with the CB1 agonist WIN55,212 (1 μm; Tocris) for 10 min. In other experiments, slices were incubated with the CB1 antagonist AM251 (1 μm; Tocris) for 10 min and recorded. Then WIN55,212 (1 μm) was added and recording repeated after 10 min. Finally, the source of endogenous cannabinoids that regulate GABAergic afferents to GnRH neurons was investigated: the diacylglycerol (DAG) lipase inhibitor tetrahydrolipstatin (THL) was added to the intracellular solution at 10 μm to block 2-AG synthesis. To minimize THL spill, the GnRH cells were approached rapidly (<1 min), and the flow rate of aCSF was increased from 5–6 to 8–9 ml/min. Just before release of the positive pressure in the pipette, the flow rate was restored to 5–6 ml/min to avoid any mechanical movement of the slice. The pipette solution containing THL was allowed to equilibrate with the intracellular milieu of the cell for 25 min before control recording. Then AM251 was added for 10 min and recording repeated.