[3H]A-585539 [(1S,4S)-2,2-Dimethyl-5-(6-phenylpyridazin-3-yl)-5-aza-2-azoniabicyclo[2.2.1]heptane], a Novel High-Affinity α7 Neuronal Nicotinic Receptor Agonist: Radioligand Binding Characterization to Rat and Human Brain