Catecholamines and Endorphins as Neurotransmitters and Neuromodulators

  • George R. Siggins


In a meeting devoted to the discussion of synaptic regulation, it seems instructive first to address the issue of what kinds of synaptic messages may be transmitted and what criteria may be developed to define the different types. This task seems particularly timely now because of the burgeoning number of substances found in brain which seem not to strictly fit our preconceived notions of a neurotransmitter. After counting all the peptides, monoamines, amino acids, nucleotides, prostaglandins and steroids that have been advanced as transmitter candidates, I come up with a number exceeding 60. It seems unlikely that such a wide variety of substances would provide only a few chemical messages. Therefore, after developing criteria for neurotransmitters, neuromediators, and modulators, I will provide examples of substances that could satisfy the criteria for these classifications, with special emphasis on norepinephrine (NE), cyclic AMP and the opioid peptides.


Purkinje Cell Locus Coeruleus Dorsal Root Ganglion Neuron Cyclic Nucleotide Opioid Peptide 
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© Plenum Press, New York 1981

Authors and Affiliations

  • George R. Siggins
    • 1
  1. 1.Arthur V. Davis Center for Behavioral NeurobiologyThe Salk InstituteLa JollaUSA

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