Cyclic AMP (cAMP) is the "second messenger" within cells, playing a core role in cell signal transduction. When cells receive external signals (such as hormones), cAMP acts as an intermediary molecule, transmitting these signals to the cell interior, regulating energy metabolism and physiological functions. The discovery of cAMP dates back to the mid-20th century. American scientist Earl W. Sutherland Jr. discovered cAMP while studying hormone action mechanisms. His research drove the establishment of the "Second Messenger" theory and earned him the 1971 Nobel Prize in Physiology or Medicine. Subsequently, cAMP's critical role in neural signal transduction and memory formation was again associated with Nobel Prize-winning achievements, further confirming that cAMP is not only a regulator of cell metabolism but also the molecular foundation of higher brain functions such as learning and memory.