Gq Protein

Cross references:  Receptors in General     G-Protein Coupled Receptors      
Ligands     Glutamate Metabotropic Receptor     GABA Metabotropic Receptor   
Serotonin Metabotropic Receptor
Acetylcholine Metabotropic Receptor   
Neuropeptide Receptor    Melatonin Receptor     Arrestin & Rhodopsin Receptors   

Gq alpha subunit (Wiki)   
    "Gq protein or Gq/11 is a heterotrimeric G protein subunit that activates phospholipase C (PLC). PLC in turn hydrolyzes Phosphatidylinositol 4,5-bisphosphate (PIP2) to diacyl glycerol (DAG) and inositol trisphosphate (IP3) signal transduction pathway. DAG acts as a second messenger that activates Protein Kinase C (PKC) and IP3 helps in phosphorylation of some proteins.
    I thought that if I clicked on some of the active links they'd explain it to me, but what I found was even more complexity.  For example: 

inositol trisphosphate    
Inositol trisphosphate (Wiki)       
Inositol trisphosphate or inositol 1,4,5-trisphosphate (also commonly known as triphosphoinositol; abbreviated InsP3 or Ins3P or IP3), together with diacylglycerol (DAG), is a secondary messenger molecule used in signal transduction and lipid signaling in biological cells. While DAG stays inside the membrane, IP3 is soluble and diffuses through the cell. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the plasma membrane, by phospholipase C (PLC)."                      

The inositol trisphosphate trianion   
(Click on the nested screen symbol on the lower left to enlarge the diagram.)     
  Taking the next step and looking at:   

3. IP3 Signaling Pathway

PLC cleavage of PIP2 to IP3 and DAG initiates intracellular calcium release and PKC activation.   
(Click on the nested screen symbol on the lower left to enlarge the diagram.)     

    Increases in the intracellular Ca2+ concentrations are often a result of IP3 activation. When a ligand binds to a G protein-coupled receptor (GPCR) that is coupled to a Gq heterotrimeric G protein, the α-subunit of Gq can bind to and induce activity in the PLC isozyme PLC-β, which results in the cleavage of PIP2 into IP3 and DAG.[10]

    If a receptor tyrosine kinase (RTK) is involved in activating the pathway, the isozyme PLC-γ has tyrosine residues that can become phosphorylated upon activation of an RTK, and this will activate PLC-γ and allow it to cleave PIP2 into DAG and IP3. This occurs in cells that are capable of responding to growth factors such as insulin, because the growth factors are the ligands responsible for activating the RTK.[11]

    IP3 (also abbreviated Ins3P) is a soluble molecule and is capable of diffusing through the cytoplasm to the ER, or the sarcoplasmic reticulum (SR) in the case of muscle cells, once it has been produced by the action of PLC. Once at the ER, IP3 is able to bind to the Ins3P receptor (Ins3PR) on a ligand-gated Ca2+ channel that is found on the surface of the ER. The binding of IP3 (the ligand in this case) to InsP3R triggers the opening of the Ca2+ channel, and thus release of Ca2+ into the cytoplasm.[11] In heart muscle cells this increase in Ca2+ activates the ryanodine receptor-operated channel on the SR, results in further increases in Ca2+ through a process known as calcium-induced calcium release. IP3 may also activate Ca2+ channels on the cell membrane indirectly, by increasing the intracellular Ca2+ concentration.[10]

4. Function

    4.1 Human

    IP3's main functions are to mobilize Ca2+ from storage organelles and to regulate cell proliferation and other cellular reactions that require free calcium. (In smooth muscle cells, for example, an increase in concentration of cytoplasmic Ca2+ results in the contraction of the muscle cell).[12]

    In the nervous system, IP3 serves as a second messenger, with the cerebellum containing the highest concentration of IP3 receptors.[13] There is evidence that IP3 receptors play an important role in the induction of plasticity in cerebellar Purkinje cells.[14]

    "In neurons, voltage-dependent, calcium-selective ion channels are important for synaptic transmission through the release of neurotransmitters into the synaptic cleft by vesicle fusion of synaptic vesicles."  

Cell type Effect
Various Activation of protein kinase C
Further reading: Function of protein kinase C
T cells Activation in response to antigen presentation to the T cell receptor[7]
secretory cells (mostly) ↑secretion (vesicle fusion)
Parathyroid chief cells ↓secretion[6]
Neurons transmission (vesicle fusion)
juxtaglomerular cell ↓secretion[6]
endothelial cells ↑vasodilation

My comment
    Since what I'm really interested in are:  

Neurons    transmission (vesicle fusion)
secretory cells     (mostly)↑secretion (vesicle fusion)

I guess I'd better look at:  vesicle fusion  

Vesicle fusion (Wiki)   
    "Vesicle fusion is the merging of a vesicle with other vesicles or a part of a cell membrane. In the latter case, it is the end stage of secretion from secretory vesicles, where their contents are expelled from the cell through exocytosis. Vesicles can also fuse with other target cell compartments, such as a lysosome.

Vesicle fusion may depend on SNARE proteins in the presence of increased intracellular calcium (Ca2+) concentration.

My comment
    So it looks like receipt of Oxytocin  by the Gq Proteins of an  Oxytocin Receptor  which is on a neuron would stimulate that neuron to release its neurotransmitter into the synaptic cleft at the end of its axon.