Pharmacologically important neurotransmitters and their receptors

Chapter 7. Some aspects of neurophysiology relevant to pharmacology 

While both dopamine and norepinephrine are derived from tyrosine, serotonin (5-hydroxytryptamine, 5-HT) is derived from tryptophan. All three transmitters are very important 

GABA (y-aminobutyric acid) is derived from glutamate by decarboxylation. It occurs predominantly in inhibitory synapses in the central nervous system, as does glycine. Tetanus toxin acts on glycinergic neurons in the spinal cord, which exert inhibitory regulation on the a-motoneurons.  

P-Endorphin is but one of an ever-increasing number of peptide neurotransmitters, and one of the rare cases in which there actually are specific agonists and antagonists - the name endorphin stands for endogenous morphine . 

Morphine and other opioids act on reeeptors for p-endor-phin and the related enkephalins. P-Endorphin was found earlier than the other peptide transmitters beeause opioids were made available by nature they eould be used as probes to find the reeeptors, whieh eould then in turn be used to sereen brain extracts for substances that would dis-plaee opioids from their reeeptors. 

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