Final answer:
Glycine (option C) is the amino acid neurotransmitter released at inhibitory synapses, where it causes hyperpolarization of the postsynaptic neuron, making it less likely to fire an action potential.
Step-by-step explanation:
The neurotransmitter that is an amino acid released at inhibitory synapses is glycine (C). Glycine, along with GABA (gamma-aminobutyric acid), is considered an inhibitory amino acid. This is because the receptors for glycine and GABA cause hyperpolarization of the postsynaptic cell, which makes it less likely that the neuron will fire an action potential. Glycine and GABA are part of their own systems, known as glycinergic and GABAergic systems, respectively.
They have their own receptors and do not interact with other systems. Amino acid neurotransmitters are cleared from the synapse through a process called reuptake, where they are absorbed by a pump in the presynaptic element or a neighboring glial cell and recycled for future use.