ABSTRACT
Receptors are the functional units of action for neurotransmitters, hormones, and drugs. Brain cells are well-protected, self-contained units. The plasma membrane separates the intracellular space from the extracellular space, isolating the cellular machinery from environmental (extracellular) events. For a drug to influence the activity of a cell, it must have access to the intracellular signaling mechanisms, and, for the majority of drugs, the receptor is the point of access. It is logical that the investigations of drug actions in the brain begin with the search for, and identification of, drug-specific receptors. The study of hormone actions in the brain is no exception.
