In the 1950s, neurochemistry became a recognized scientific research discipline. The founding of neurochemistry as a discipline traces it origins to a series of "International Neurochemical Symposia", of which the first symposium volume published in 1954 was titled Biochemistry of the Developing Nervous System. These meetings led to the formation of the International Society for Neurochemistry and the American Society for Neurochemistry. These early gatherings discussed the tentative nature of possible neurotransmitter substances such as acetylcholine, histamine, substance P, and serotonin. By 1972, ideas were more concrete. Neurochemicals such as norepinephrine, dopamine, and serotonin were classified as "putative neurotransmitters in certain neuronal tracts in the brain."