ABSTRACT
Introduction .................................................................................................................................... 113 Neurotransmitters and Relevant Pharmacological Receptors ........................................................ 114
5-Hydroxytryptamine ................................................................................................................ 114 Catecholamines ......................................................................................................................... 115 Histamine .................................................................................................................................. 117
Neuropeptides and Relevant Pharmacological Receptors.............................................................. 117 Neuropeptide Y ......................................................................................................................... 117 Galanin ...................................................................................................................................... 119 Corticotropin-Releasing Factor ................................................................................................. 119 Orexins ...................................................................................................................................... 120 Melanocortin ............................................................................................................................. 121
α-MSH .................................................................................................................................. 121 β-MSH .................................................................................................................................. 122 ACTH ................................................................................................................................... 122
Other Chemicals and Relevant Pharmacological Receptors .......................................................... 122 Endocannabinoids ..................................................................................................................... 122
Summary and Conclusions ............................................................................................................ 123 Bibliography .................................................................................................................................. 123
In addition to its well-known actions on the gastrointestinal tract and cardiovascular system, 5-HT (serotonin) plays an important role as a neurotransmitter in the central nervous system (CNS). 5-HT is biosynthesized from the essential amino acid tryptophan by two enzymes: tryptophan hydroxylase and aromatic l-amino acid decarboxylase. Dietary tryptophan is converted into 5-hydroxytryptophan (5-HTP) by tryptophan hydroxylase. At the nerve terminal, 5-HTP is rapidly converted into 5-HT by the enzyme l-amino acid decarboxylase. Newly synthesized 5-HT is stored in vesicles at serotonergic neurons and is released by exocytosis following a nerve action potential. In the nervous system, the effect of released 5-HT is terminated by a reuptake process into neurons by a specic transporter. The localization of 5-HT transporters on membranes of serotonergic axon terminals facilitates the reuptake process. It is pertinent to note that the 5-HT transporter plays an important role in the action of this neurotransmitter in the regulation of obesity. Drugs that inhibit the activity of this transporter (such as d-norfenˆuramine and ˆuoxetine) increase the concentration of 5-HT at synaptic sites and have been reported to have a suppressive action on food intake.
