GABA structure

GABA (y-aminobutyric acid) is an amino acid with mostly inhibitory functions in the mammalian central nervous system. Structures involved in releasing or binding GABA as a neurotransmitter constitute the GABAergic system. The GABAergic system is involved... 

Gamma aminobutyric acid (GABA) receptors are located on the postsynaptic membranes of inhibitory synapses of both vertebrates and insects and contain within their membrane-spanning structure a chloride ion channel. They are found in both vertebrate brains and invertebrate cerebral ganglia (sometimes referred to as brains) as well as in insect muscles. Particular attention has been given to one form of this receptor—the GABA-A receptor—as a target for novel insecticides (Eldefrawi and Eldefrawi 1990). It is found both in insect muscle and vertebrate brain. The remainder of this description will be restricted to this form. 

Brooks, G.T. (1992). Progress in structure-activity smdies on cage convnlsants and related GABA receptor chloride ionophore antagonists. In D. Otto and B. Weber (Eds.) Insecticides Mechanism of Action and Resistance. Newcastle npon Tyne, UK Intercept Press, 237-242. 

To achieve their different effects NTs are not only released from different neurons to act on different receptors but their biochemistry is different. While the mechanism of their release may be similar (Chapter 4) their turnover varies. Most NTs are synthesised from precursors in the axon terminals, stored in vesicles and released by arriving action potentials. Some are subsequently broken down extracellularly, e.g. acetylcholine by cholinesterase, but many, like the amino acids, are taken back into the nerve where they are incorporated into biochemical pathways that may modify their structure initially but ultimately ensure a maintained NT level. Such processes are ideally suited to the fast transmission effected by the amino acids and acetylcholine in some cases (nicotinic), and complements the anatomical features of their neurons and the recepter mechanisms they activate. Further, to ensure the maintenance of function in vital pathways, glutamate and GABA are stored in very high concentrations (10 pmol/mg) just as ACh is at the neuromuscular junction. 

Figure 11.4 Blockers of GABA transport.The upper panel shows the structure of several GABA analogues that inhibit GABA transport into neurons or glia (see text). The lower panels show more recently developed compounds that exhibit selectivity for various cloned GABA transporters...

Roberts, E (1986) GABA the road to neurotransmitter status. In BenzodiazepinejGABA receptors and chloride channels structural and functional properties (Eds Olsen, R and Venter, CJ), Alan R. Liss, New York, pp. 1-39. 

Figure 16.7 The structure of some established antiepileptic drugs (AEDs) and some newer ones. Note that while the structures of phenytoin and ethosuximide are similar and also close to that of phenobarbitone, they are effective in different forms of epilepsy. Vigabatrin, progabide and gabapentin are clearly related to GABA. Muscimol is a GABAa agonist but is not an effective antiepileptic drug...

Fig. 2. Agents controlling the opening of Cl -channels. The structural formula, the name, the respeetive Cl -channel, and an appropriate reference are provided. (A) Note the similarity of GABA, taurine, and P-alanine. Note also that DPC and its analogues such as NPPB contain a -alanine backbone. (B) The structure of torasemide comes close to both DPC and furosemide or buraetanide. It blocks the Na ZCPK" -cotransporter with very high affinity and with lesser affinity also the TAL-Cl -channel. Note that IAA-94 is related to phenoxyaeetic acids (e.g., ethacrynic acid). Amidine is related to IAA-94 but it has a positive net charge. Amidine as well as IAA-94 block the ICOR channel at around lO mol/1 [63].

Egebjerg, Schousboe, and Krogsgaard-Larsen, Eds., Glutamate and GABA Receptors and Transporters Structure, Function and Pharmacology, Taylor Francis, London, 2001. 

The 5-HT3 receptor is not coupled to G proteins. It directly activates a 5-HT-gated cation channel, which leads to depolarization of a variety of cells. As a result, there is an increase in the release of DA, NA, GABA, ACh, and 5-HT at central sites (Stanford, 2001). The 5-HT3 receptor is present in cortical and subcortical structures (Table 9.7). 

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