Excitation vs. Inhibition      

gamma-Aminobutyric acid (Wiki) 
    "γ-Aminobutyric acid or GABA is the chief inhibitory neurotransmitter in the mammalian central nervous system. It plays a role in regulating neuronal excitability throughout the nervous system. ... In humans, GABA is also directly responsible for the regulation of muscle tone.[2]"  

In vertebrates, GABA acts at inhibitory synapses in the brain by binding to specific transmembrane receptors in the plasma membrane of both pre- and postsynaptic neuronal processes. This binding causes the opening of ion channels to allow the flow of either negatively charged chloride ions into the cell or positively charged potassium ions out of the cell. Depending on which ion channels open, the membrane potential is either hyperpolarized or repolarized. This action results in a negative change in the transmembrane potential, usually causing hyperpolarization." 
    Two general classes of GABA receptor are known: GABAA in which the receptor is part of a ligand-gated ion channel complex, and GABAB metabotropic receptors, which are G protein-coupled receptors that open or close ion channels via intermediaries (G proteins).

My comment
I find it interesting that both classes have the end result of opening or closing ion channels.      

The diagram, below, pictures both the ionotropic and the metabotropic functions of GABA."   

The production, release, action, and degradation of GABA at a stereotyped GABAergic synapse. 


Oxytocin Accumbens - PubMed    Sorted by Recently Added   
107<107    also   Oxytocin Accumbens      
Deafferentation studies on the glutamic acid decarboxylase content of the supraoptic nucleus of the rat.
Meyer DK, Oertel WH, Brownstein MJ.
Brain Res. 1980 Oct 27;200(1):165-8.
PMID: 6998543   Related citations  
Thus, the neurons in the supraoptic nucleus seem to receive a large part of their GABAergic afferents from the n. accumbens. In addition to that, GABAergic neurons intrinsic or adjacent to the supraoptic nucleus seem to contribute to the regulation of the release of vasopressin and/or oxytocin."   

GAD65 and GAD67 Isoforms of the Glutamic Acid Decarboxylase Gene Originated Before the Divergence of Cartilaginous Fishes   

Inhibitory influence of GABA on central serotonergic transmission. Raphé nuclei as the neuroanatomical site of the GABAergic inhibition of cerebral serotonergic neurons.

Graded response to GABA by native extrasynaptic GABA receptors.   
GABA is the main inhibitory neurotransmitter in the mammalian CNS. GABA in the brain is commonly associated with a fast, point-to-point form of signalling called synaptic transmission (phasic inhibition), but there is growing evidence that GABA participates in another, slower and more diffuse form of signalling often referred to as tonic inhibition. Unresolved questions regarding tonic neuronal inhibition concern activation and functional properties of extrasynaptic GABAA receptors (GABARex) present on neurones. Extrasynaptic receptors are exposed to submicromolar GABA concentrations and may modulate the overall excitability of neurones and neuronal networks. Here, we examined GABA-activated single-channel currents in dentate gyrus granule neurones in rat hippocampal slices. We activated three types (I, II, III) of GABARex channels by nanomolar GABA concentrations (EC50 I: 27 +/- 12; II: 4 +/- 3; III: 43 +/- 19 nm). The channels opened after a delay and the single-channel conductance was graded (gammamax I: 61 +/- 3; II: 85 +/- 8, III: 40 +/- 3 pS). The channels were differentially modulated by 1 microm diazepam, 200 nm zolpidem, 1 microm flumazenil and 50 nm THDOC (3alpha, 21-dihydroxy-5alpha-pregnan-20-one), consistent with the following minimal subunit composition of GABARex I alpha1betagamma2, GABARex II alpha4betagamma2 and GABARex III alphabetadelta channels."    
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GABA Receptors 
    "The GABA receptors are a class of receptors that respond to the neurotransmitter gamma-aminobutyric acid (GABA), the chief inhibitory compound in the mature vertebrate central nervous system. There are two classes of GABA receptors: GABAA and GABAB. GABAA receptors are ligand-gated ion channels (also known as ionotropic receptors); whereas GABAB receptors are G protein-coupled receptors, also called metabotropic receptors. "