Disclosed is a probe for measuring the dynamic state of cyclic-AMP response element binding protein (CREB) or actin, which is a substance closely associated with brain functions (e.g., memory formation) in living animals, in real time. Specifically disclosed is a probe which contains luciferase in a form split into an N-terminal-side part and a C-terminal-side part and comprises at least one probe selected from the following probes (1) to (3): (1) a probe containing, in the molecule, a KID domain of CREB, a KIX domain of CREB-binding protein (CBP), the N-terminal-side part of luciferase (LucN) and the C-terminal-side part of luciferase (LucC); (2) (a) a probe composed of two molecules, i.e., a molecule containing the LucN and the KID domain and a molecule containing the LucC and the KIX domain or (b) a probe composed of two molecules, i.e., a molecule containing the LucN and the KIX domain and a molecule containing the LucC and the KID domain; and (3) a probe composed of two molecules, i.e., a molecule containing actin and the LucN and a molecule containing actin and the LucN.
PROBE FOR VISUALIZING NERVE ACTIVITY