GABA and

Table 10. GABA and GABA Receptor Agonists and Antagonists...

J. Ulrich, Y. IJzoguz, and K. Wangnickiu B. Biscans, N. Gabas, and C. Laguiirie, eds.. Proceedings Cystalli tion Industrielle etPrecipitation, Lavoisier Technique et Documentation, Paris, 1991. 

There are numerous transmitter substances. They include the amino acids glutamate, GABA and glycine acetylcholine the monoamines dopamine, noradrenaline and serotonin the neuropeptides ATP and NO. Many neurones use not a single transmitter but two or even more, a phenomenon called cotransmission. Chemical synaptic transmission hence is diversified. The basic steps, however, are similar across all neurones, irrespective of their transmitter, with the exception of NO transmitter production and vesicular storage transmitter release postsynaptic receptor activation and transmitter inactivation. Figure 1 shows an overview. Nitrergic transmission, i.e. transmission by NO, differs from transmission by other transmitters and is not covered in this essay. 

The exocytotic release of neurotransmitters from synaptic vesicles underlies most information processing by the brain. Since classical neurotransmitters including monoamines, acetylcholine, GABA, and glutamate are synthesized in the cytoplasm, a mechanism is required for their accumulation in synaptic vesicles. Vesicular transporters are multitransmembrane domain proteins that mediate this process by coupling the movement of neurotransmitters to the proton electrochemical gradient across the vesicle membrane. 

Synaptic vesicles isolated from brain exhibit four distinct vesicular neurotransmitter transport activities one for monoamines, a second for acetylcholine, a third for the inhibitory neurotransmitters GABA and glycine, and a fourth for glutamate [1], Unlike Na+-dependent plasma membrane transporters, the vesicular activities couple to a proton electrochemical gradient (A. lh+) across the vesicle membrane generated by the vacuolar H+-ATPase ( vacuolar type proton translocating ATPase). Although all of the vesicular transport systems rely on ApH+, the relative dependence on the chemical and electrical components varies (Fig. 1). The... 

Acamprosate. Acamprosate (calcium acetylhomotaurinate), an amino acid derivative, affects both GABA and excitatory amino acid (i.e., glutamate) neurotransmission (the latter effect most likely being the one that is important for its therapeutic effects in alcoholism). Initially evaluated in a singlecenter trial in France, acamprosate was shown to be twice as effective as placebo in reducing the rate at which alcoholic patients returned to drinking (Lhuin-tre et al. 1985). The safety and efficacy of the medication have been studied most widely in Europe, and three of these studies provided the basis for the recent approval of acamprosate by the FDA for clinical use in the United States. As with naltrexone, there exist a number of meta-analytic studies that provide consistent evidence of the efficacy of the medication in the treatment of alcohol dependence. 

Figure 11.3 Regulation of GAD during the synthesis of GABA. Active GAD (GAD-PLP) combines with glutamate (1) to form a complex (GAD-PLP-GLU). After decarboxylation (2) this yields GABA and GAD-PLP (3). The intermediate product (GAD-INT) can undergo an alternative reaction (4) to produce succinic semialdehyde (SSA) and pyridoxamine-5 -phosphate (PMP). PMP dissociates from GAD (5) leaving inactive enz5mie, which requires additional PLP to be reactivated (6), a process that is affected by ATP and inorganic phosphate...

O Brien, JA and Berger, AJ (1999) Cotransmission of GABA and glycine to brain stem motoneurons. J. Neurophysiol. 82 1638-1641. 

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