Seven days after cannulation, the rat was subjected to the hot-plate test (50C) as explained previously (H.-T. and activates neurons in the rostroventral medulla (RVM), which send inhibitory projections to the dorsal horn of the spinal cord. Increasing evidence suggests that activation of postsynaptic GqPCRs, such as group I metabotropic glutamate or M1/M3 muscarinic receptors (Kano et al., 2009), results in hydrolysis of the plasma membrane lipid, phosphatidylinositol 4,5-bisphosphate, by phospholipase C (PLC), yielding diacylglycerol (DAG), which Adrafinil is definitely deacylated by DAG lipase (DAGL) to 2-arachidonoylglycerol (2-AG), an endocannabinoid. 2-AG then diffuses retrogradely to activate the type 1 cannabinoid (CB1) receptors located on presynaptic nerve terminals, reducing neurotransmitter launch. 2-AG can also be degraded by monoacylglycerol lipase (MGL), which is located in nerve terminals or nearby glia (Kano et al., 2009; Uchigashima et al., 2011). This GqPCRCPLCCDAGLC2-AG retrograde inhibitory signaling module is present in several brain regions, including Adrafinil the PAG (Drew et al., 2008; Lau and Vaughan, 2008; H.-T. Liao Adrafinil et al., 2011). We, consequently, hypothesized that activation of orexin receptors, which are also GqPCRs, could initiate this GqPCRCPLCCDAGLC2-AG retrograde inhibition onto the tonic GABAergic transmission in the vlPAG, leading to antinociception. In this study, we have validated this hypothesis using a combination of electrophysiological, anatomical, and behavioral methods. Materials and Methods All experiments abide by the guidelines authorized by the Institutional Animal Care and Use Committee of College of Medicine, National Taiwan University or college. Electrophysiology Brain slice preparation. Coronal midbrain slices (400 m) comprising the PAG were dissected from 9- to 18-d-old Wistar rats as explained previously (H.-T. Liao et al., 2011; Y.-Y. Liao et al., 2011). After dissection, the slices were equilibrated in artificial CSF (aCSF) at space temp for at least 1 h before recording. The aCSF contained the following (in mm): 117 NaCl, 4.5 KCl, 2.5 CaCl2, 1.2 MgCl2, 1.2 NaH2PO4, 25 NaHCO3, and 11.4 dextrose, and was oxygenated with 95% O2/5% CO2, pH 7.4. During recordings, one slice was mounted on a submerged recording chamber and continually perfused with oxygenated aCSF at a rate of 3C4 ml/min. Blind patch-clamp recordings. All electrophysiological recordings, except the data in Number 10, were performed by blind patch-clamp whole-cell recordings in vlPAG slices using 4C7 M microelectrodes as explained previously (Y.-Y. Liao et al., 2011). A K+-centered internal solution comprising the following (in mm): 125 K+ gluconate, 5 KCl, 0.5 CaCl2, 5 BAPTA, 10 HEPES, 5 MgATP, and 0.33 GTP-Tris, pH 7.3, 280 mOsm/L (liquid junction potential, 11.4 mV), was utilized for recording membrane potentials and evoked postsynaptic potentials (PSPs) in the current-clamp mode. When evoked EPSCs, IPSCs, and miniature IPSCs (mIPSCs) were recorded, a Cs+-centered internal remedy was used, which contained the following (in mm): 110 Cs+ gluconate, 5 TEA (tetraethylammonium), 5 QX314, 0.5 CaCl2, 5 BAPTA, 10 HEPES, 5 MgATP, and 0.33 GTP-Tris (liquid junction potential, 14.6 mV). In one set of experiments, the Ca2+-buffering capacity of the internal solution was improved by elevating the BAPTA concentration to 25 mm. In all cases, liquid junction potentials have been corrected. Electrophysiological signals were acquired and analyzed using an Axon setup (Molecular Products). Signals were sampled at 5C10 kHz by pClamp 8 via an Axopatch 200B amplifier and Digidata 1200A AD converter and analyzed by Clampfit 8. FUT3 Open in a separate window Number 10. Orexin A induced a CB1 receptor-dependent major depression of IPSCs in vlPAG neurons projecting to the rostral ventromedulla (RVM-vlPAG neurons). RVM-vlPAG neurons were retrogradely labeled by injecting reddish fluorescent RetroBeads into the RVM of rats 3 d before preparing brain slices for recordings. 0.01 versus control (one-sample.