Complexes of GPR81 receptor components and ligand components, such as L-lactate or GHB, may be used as an assay reagent for screening for modulators of GPR81 receptor activity. The transparent substrate has gate lines, source lines, gate pads and source pads, a light-curable low-k protection layer, and pixel electrodes located on the light-curable low-k protection layer. An articulating member is rotatably coupled to a bottom of the body. The inserting holes correspond to boss parts of a pole core which correspond to coil parts of the form coil.