Tryptamine receptors in the rat stomach strip preparation

5-HT (5-hydroxytryptamine, serotonin) has a widespread occurrence in numerous species of plants and animals. It is present for example in several vegetables and edible fruits, in the urticant fluid of the stinging nettle as well as in the intestine, blood platelets and nervous system of all classes of vertebrates. Its occurrence in the central nervous system (CNS) of both vertebrates and invertebrates has attracted particular attention. In the CNS the transmission of impulses from one nerve fibre to another is accomplished by the action of chemical mediators, called neurotransmitters. The junction between two nerve fibres is called synapse. At the arrival of an action-potential the presynaptically stored transmitter is released and subsequently causes the depolarization of the postsynaptic fibre as consequence of the interaction with a specific receptor, which is a molecular system incorporated in the post-synaptic membrane. 5-HT came to be regarded as a possible neurotransmitter. However, direct evidence for its neuronal localization was not presented until 1965 when Dahlstrom and Fuxe actually demonstrated its presence within the perikarya of the brain stem raphe nuclei and its projections in discrete regions of the fore-brain.