Biologically important amines neurotransmitters

The chromaffin cells of the adrenal medulla may be considered to be modified sympathetic neurons that are able to synthesize E from NE by /V-methylation. In this case the amine is Hberated into the circulation, where it exerts effects similar to those of NE in addition, E exhibits effects different from those of NE, such as relaxation of lung muscle (hence its use in asthma). Small amounts of E are also found in the central nervous system, particularly in the brain stem where it may be involved in blood pressure regulation. DA, the precursor of NE, has biological activity in peripheral tissues such as the kidney, and serves as a neurotransmitter in several important pathways in the brain (1,2). 

The aromatic amino acids give rise to many plant substances. The PLP-dependent decarboxylation of some amino acids yields important biological amines, including neurotransmitters. 

Taurine is one of the most abundant and ubiquitous free amino acids in the fluids and tissues of animals (Huxtable an Pasantes-Morales, 1982 Sturman, 1983), and much evidence suggests that it plays an important role as an inhibitory neurotransmitter or neuromodulator in the body (Davidson, 1976 Schaffer et al., 1981). The determination of Tau in biological samples has been carried out by various methods, but analysis by GC has only recently been introduced (Kataoka et al., 1984) The method involves the isocarboxycarbonylation of the amine, followed by conversion of the sulfonic acid moiety to sulfonyl chloride. The sulfonyl chloride is subsequently condensed with a secondary amine to form a sulfonamide (Fig 8) that is analyzed on an OV-17 column. This procedure appears to be sensitive and specific for Tau. 

Colombian poison dart frogs are tiny, beautiful, and deadly. They produce a poison called histrionicotoxin, which is an amine that causes paralysis. Death from histrionicotoxin results by suffocation through paralysis of the victim s respiratory muscles. (A molecular model of histrionicotoxin is shown above.) Curare, the Amazonian arrow poison that is a mixture of compounds from a woody vine, contains another paralytic neurotoxin, called cf-tubocu-rarine. Histrionicotoxin and d-tubocurarine both block the action of acetylcholine, an important neurotransmitter. Amines like these and others have fascinating roles in biological systems, as we shall see in this chapter while studying the properties, reactivity, and synthesis of amines. 

Fluorescence techniques can be applied to all kinds of material. Because fluorescence microscopy requires more complex and expensive instrumentation than conventional transmitted-light microscopy, fluorescence microscopy is usually reserved for those applications in which its high sensitivity is of importance i.e., to examine substances present in low concentrations. Fluorescence microscopy can also be applied to detect particles below the resolution of a light microscope, and in histochemistry to visualize substances which cannot be seen by conventional microscopy - e.g. neurotransmitter amines. Biological material is commonly stained in some manner with a fluorescent stain. 

In vivo, there are a number of important biologically active quaternary amines. The neurotransmitter acetyl choline is biosynthesised as shown in Figure 3.26. 

---