Drugs as Tools in Neurotransmitter Research : Humana Press : 9780896031227 : 0896031225 : 18 Apr 1989 : Serendipitous discovery has played an important role m the identification of physiological mechanisms in central and peri- eral neurotransmission. In many cases, the subsequent followup of these discoveries has been substantially aided by previouslyiden- fied natural substances that interfered with these mechanisms. The site of neuromuscular blockade produced by curare extracts, for example, was shown in the 1850s by Claude Bernard, and Sir Henry H. Dale m 1906 discovered the reversal of the pressor effects of adrenal extracts by ergot alkaloids. These findings were the first clues that led eventually to the definition of mcotinic cholinergic receptors and the present classification of adrenergic receptors. In the 1950s many discoveries, including the identification of the catecholamines and 5-hydroxytryptamine in the central n- vous system, followed by the development of specific se