Synaptic transmission GABA release

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. 

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At the same time, several other mechanisms may be activated to compensate for some of the excitatory effect, perhaps to keep the system from being hyperreactive. These mechanisms include (1) presynaptic inhibition of glutamate release from the primary afferent terminals, (2) activation of the NKl receptors on the soma/dendrite of GABAergic intemeurons to enhance GABA release, and (3) an enhanced glycine synaptic transmission via an enhanced glycine receptor function through a protein kinase C or a Ca/calmodulin dependent protein kinase 11 pathway (Fig. 2). 

There are inhibitory presynaptic G-protein coupled receptors in mossy fibre synapses for a number of transmitters, such as glutamate, y-aminobutyric acid (GABA), adenosine and dynorphin. The release of glutamate and GABA can therefore have a depressant effect on mossy fibre synaptic transmission. The mossy fibre pathway predominantly synapses onto inhibitory intemeurons, rather than excitatory hilar mossy cells and CA3 pyramidal cells. 

Bradford H F. (1981) GABA release in vivo and m vitro Responses to Physiological and Chemical Stimuli, in Regulatory Mechanisms of Synaptic Transmission (Tapia R and Cotman R. W., eds.) Plenum, New York, pp 103-140... 

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