Before 1989, All Sorts of Research on Cannabinoids Was Conducted Because No One Knew How they Worked on the Brain:

"Until recently, very little was known about the cellular mechanisms through which cannabinoids act . . . Without evidence that cannabinoids act through a specific receptor coupled to a functional effector system, researchers were prone to study the effects of cannabinoids on membrane properties, membrane-boundenzymes, eicosanoid production, metabolism, and other neurotransmitter systems in vitro."

Herkenham, M. (1992), "Cannabinoid Receptor Localization in Brain: Relationship to Motor and Reward Systems," P.W.Kalivas and H.H. Samson (eds.), The Neurobiology of Drug and Alcohol Addiction, Annals of the American Academy of Sciences. 654:19-32,1992. pg. 19.